insights winter 15 16

8/18/2019 Insights Winter 15 16

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insightsinsightsWinter 2015-16

A DRESSER-RAND BUSINESS PUBLICATION

NEW HGM ENGINE

HITS THE MARKET

COMBINED RESOURCES

EXPAND OPPORTUNITIES

FOR LNG PROJECTS

TWO BECOME ONE

dresser-rand.com/insights

Visit usonline:


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CONTENTS

06

insightsWINTER 2015-16

This document contains

statements related to

our future business and

financial performance

and future events or

developments involving

Siemens that may

constitute forward-

looking statements.

These statements may

be identified by words

such as “expect,” “look

forward to,” “anticipate,”

“intend,” “plan,” “believe,”

“seek,” “estimate,” “will,”

“project” or words ofsimilar meaning. We may

also make forward-looking

statements in other

reports, in presentations,

in material delivered to

shareholders and in press

releases. In addition,

our representatives may

from time to time make

oral forward-looking

statements. Such

statements are based on

the current expectations

and certain assumptions

of Siemens’ management,

of which many are beyond

Siemens’ control. Theseare subject to a number

of risks, uncertainties and

factors, including, but not

limited to those described

in disclosures, in particular

in the chapter Risks in the

Annual Report. Should

one or more of these

risks or uncertainties

materialize, or should

underlying expectations

not occur or assumptions

prove incorrect, actual

results, performance or

achievements of Siemens

may (negatively or

positively) vary materiallyfrom those described

explicitly or implicitly in the

relevant forward-looking

statement. Siemens

neither intends, nor

assumes any obligation,

to update or revise

these forward-looking

statements in light of

developments which differ

from those anticipated.

engineer’s notebook

VSDs Motor Inverter Design Concept for

Compressor Trains Avoiding Interharmonics

in Operating Speed Range and Verification

Ultimately, a close collaboration between the manufacturer of

the driver and compressor is of vital importance when designing

a variable speed drive system-driven turbo compressor train.

15

02

people power

The Power of Giving Back

Dresser-Rand KG2 turbines provide on-site electrical power for

one of Russia’s largest oil producers.12

The latest HGM engine model offer

a balanced relationship between

efficiency, reliability and price.

14New HGM Engine

Hits the Market

Welcome to Komi

See how the passionate efforts of our employees help make their

communities a better place to live and work.

10

Berenice touts the right tools, good communication skills and

flexibility as keys to success in her key client manager role.

08

Expanded portfolio of compressors

and drivers available for LNG

applications.

Combined Resources

Expand Opportunitie

for LNG Projects

Bruce Bailie, integration program

manager, reinforces importance of

communication and positive spirit.

candid visions

Two Become OneThe First 40 Years Are the Hardest

At 85, Dave Morse is still moving and shaking in the compressor

business.

04

profile

Making Best Use of the Tools at Hand

Dresser-Rand offers a wide variety of product training programs

for 2016.

33 Product Training Programs


3/36

Janet Straub Ofano,

external/internal

communications

specialist & editor,

insights magazine

Collaboration, Communicationand (the right) CombinationIn reviewing this edition, these three concepts cropped up throughout.

While we face a challenging business climate due to low oil prices, both inside and outside

the workplace our employees collaborate, communicate and combine their resources, efforts

and knowledge to achieve personal and professional success. They continue to accomplish

amazing things within the communities where they live and work as highlighted in the

People Power feature.

In an interview with Bruce Bailie, the integration program manager for the Dresser-Rand

business, we learned that a successful integration requires all three attributes. As you’ll see

in the Candid Visions feature, Bruce shared with us some of the highlights and challenges during

the Siemens / Dresser-Rand integration, pre- and post-close.

Our profile feature gives us a glimpse into the life of key client manager, Berenice Flores.

Strong communication skills and a delicate balancing act help ensure a win-win between herclient and Dresser-Rand.

One of my favorite articles, “The First 40 Years are the Hardest,” is a delightful read about the

talented, amicable and highly regarded Dave Morse. Six impressive decades in the business

and his enthusiasm and commitment remain.

We listened to our clients’ demands for a 1 MW power output “sweet spot” and created

the HGM 420 Guascor® gas engine. This efficient, reliable, cost effective engine achieves

approximately 91 percent thermal efficiency.

A Russian oil producer selected Dresser-Rand KG2 turbine generator sets to upgrade its power

generation facilities. The decision was based on a combination of factors: the KG2 turbine

accepts a wide variety of fuels; it boasts a simple, low-maintenance design; it’s highly reliable;

and the turbines operate with a heat recovery system, so they not only produce electric powerbut provide heat energy as well – an important attribute in the frigid Komi climate.

With the combined resources of Siemens, the value proposition for LNG clients from the new

Dresser-Rand business within Siemens Power and Gas division expanded. The addition of

Siemens’ SGT-750 gas turbine driver and Industrial Trent® 60 aero-derivative gas turbine to the

portfolio increases our capabilities for offshore and onshore liquefied natural gas (LNG) projects.

And finally, even the Engineer’s Notebook feature embraces the importance of collaboration

between manufacturers of compressors and drivers to design a suitable variable speed drive

system-driven turbo compressor train.

As you peruse this issue, I’m confident you’ll see these three important themes that underscore

the importance of the human element as we persevere during this downturn in the oil business.It is these practices that will continue to smooth the way for our continued success.

Enjoy – and Happy New Year!.

Janet Straub Ofano

editor, insights magazine


4/36

c a

n d i d

v i s

i o n s

Bruce Bailie

program manager

integration

2 insights

BB: Before the deal closed the effort was all

about strategy and planning. This phase was quite

challenging in an environment where we could not

freely share information because Dresser-Rand

and Siemens were still competitors. Once the deal

closed there was tremendous urgency and the foc

immediately centered on execution. We changed

the structure of the integration team to reflect

the project deployment phase. The integration

managers moved on to the executive staff of thenew business. One of the integration managers,

Chris Rossi, became CEO of the Dresser-Rand

business. The integration project leadership was

transferred to Christian Gerbaulet and me.

insights: What is your role, as program manager,

following closing?

BB: To best serve our clients, we must avoid

disrupting ongoing business and quickly move to

Editor’s Note: Mid-2015, Siemens acquired Dresser-Rand and formed the new Dresser-Rand business, wherein

Dresser-Rand’s business, together with Siemens’ compressor unit and the related service business, formed a new

business within Siemens Power and Gas Division.

We recently interviewed Bruce Bailie, the program manager for the integration of the new Dresser-Rand business.

Two Become One

Iinsights: What were the integration managers’

initial roles?

BB: The integration managers comprised senior

leaders from both companies with the knowledge,

insight and experience to mentor and guide a

team to architect the new business. They defined

a compelling vision of the business that Siemens

wanted to form and then developed a detailed

and robust master plan to achieve that vision.

They assembled an integration team consistingof top functional and business leaders from both

companies. The team developed the integration

master plan to ensure the resultant business was

founded on the “best-of-the-best” from either

company.

insights: What were the differences for the

integration team before and after the deal closed?


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c a n d i d

v i s i on s

our new business model. The program manager is a

bit like a conductor for the integration process and

teams and ensures that all 26 work streams

(or project teams) are coordinated in their activities

and schedules. Managing risk and rapidly identifying

and escalating issues is critical to success. Good

communication is essential, as is ensuring constant,

reliable communication at all levels. It’s also

important to understand how any changes inbusiness decisions, such as consolidating legal

entities, might impact the overall integration

master plan.

insights: How long does an integration team

typically remain in place post-close with an

acquisition of this magnitude?

BB: It really depends on the type of acquisition and

the strategy for the new business. Our integration

work is expected to run two years post-close, but a

number of work streams will complete their work

within the first year. Some functions take longerbecause of the integration complexity, such as

information technology and finance. The bottom

line is to maintain top-notch service to our clients

so as to not interrupt their businesses during the

integration.

That’s one of the primary reasons our executive

vice president of Services Worldwide for the

Dresser-Rand business, Luciano Mozzato, formed

a Client Experience Council. This worldwide team

of carefully selected, cross-functional Dresser-Rand

business personnel provides recommendations anda strategic roadmap that deliver on our vision to

earn client loyalty for life.

insights: What, in your opinion, is the most

important aspect of integration success?

BB: Good communications. We must share what

needs to be done, and why it needs to be done.

Then the teams figure out how to accomplish their

tasks. Understanding the rationale for the plan

helps keep everyone aligned.

insights: What do you feel was the biggest

challenge so far? And what went particularly well?

BB: Prior to final closing, we were not able to share

the level of detailed information needed to make

decisions for the path forward. Dresser-Rand and

Siemens were still competitors and neither of us

could share anything that could give either company

a competitive advantage. Once the transaction

closed, we had to quickly confirm assumptions

made and validate the related decisions.

As far as what went well, we held welcome events

at facilities all over the world that were especially

well received. Employees of the combined business

had the opportunity to meet one another, hear

our leaders’ visions for the new business and ask

questions.

Also, the work stream structure mostly worked to

perfection. Each of the 26 work streams had their

own sub-projects, which allowed them to focus on

their own areas of business. And having smaller

sub-projects enabled the projects to run efficiently.

insights: Have you seen any synergies between the

two organizations?

BB: Realized synergies thus far have exceeded our

expectations.

For example, a Louisiana pipeline company

requested an overhaul of its legacy Siemens

compressor and needed spare parts inspected and

refurbished. Dresser-Rand had an existing masterservice agreement with the client and an excellent

working relationship and rapidly responded. This

relationship, coupled with Siemens’ strong technical

background on the equipment, translated into the

overhaul of four legacy compressors.

In another example, a pulp and paper plant in

Indonesia damaged the inlet valve body of its

Siemens legacy steam turbine. Siemens experts

offered to balance the rotor to prevent potential

issues during start-up; however, the client could

not afford the approximately $1 million inproduction losses if the unit had to be shipped

elsewhere for repair. Dresser-Rand’s Indonesian

repair center field service team in Cilegon

developed a comprehensive service plan and was

able to perform the work on site.

Earlier last year, Siemens signed an 18-year long-

term service agreement with a firm in the United

Arab Emirates. Under the agreement, the new

business will now provide service and maintenance

for nine Trent 60 aero-derivative gas turbines and

nine Dresser-Rand centrifugal compressors.

insights: Are there any last words of wisdom about

the integration to-date?

BB: We all need to have open minds and work

together with a positive spirit to build our future

around the mainstay of our business – earning our

clients’ loyalty for life. •


6/364 insights

T

are the Hardest

Those who know Dave Morse might imagine his

office as an archive of compression history. It’s true.

Dave’s office is full of old technical manuals, text

books, price books, early compressor photographs,

and D-R and its competitors’ history and literature.

However, the most complete collection of

compressor industry information in the officeresides within Dave himself.

Perhaps most commendable though is Dave’s

willingness to patiently share his wealth of

knowledge with others. He has a brilliant mind

with an infallible memory and remains selfless

in teaching, nurturing and supporting others – a

characteristic that shone in Dave from an early age.

Dave, along with his brother and two sisters, was

raised in Cedar Rapids, Iowa, where his father was

a credit and office manager for a large department

store and his mother was a housewife. He spenthis high school summers as a YMCA summer camp

counselor for boys.

Dave attended Iowa State University on a Naval

Reserve Officers Training Corp (NROTC) scholarship

and graduated in June 1952 with a BS degree in

General Engineering. He immediately went on

active duty to fulfill his scholarship commitment. He

served one year on the USS Deuel, APA-160 (attack

transport) and two years on the USS LST-1164

(landing ship tank). Dave was the first ship’s officer

to arrive in Pascagoula, Mississippi, where she wasbeing built.

Dave’s Compressor Career BeginsAfter fulfilling his scholarship commitment, Dave

began his career as an application engineer at

Ingersoll-Rand’s New Orleans, Louisiana sales

office in July 1955 and supported the branch

manager and three sales engineers. At that time,

I-R offices handled a variety of products, including

reciprocating and vane-type air compressors,

reciprocating and centrifugal gas compressors,

reciprocating and centrifugal pumps, steam

condensers, and steam turbines.

“The most challenging part of that job was keeping

up with the three sales engineers!” Dave recalls.

One of the things he enjoyed most was learning

about the equipment and how it works.

A little more than two years later, Dave was

promoted to sales engineer and covered most of

Louisiana and Southern Mississippi. After 11 years

in Louisiana, Dave was transferred to I-R’s gas

engine marketing department at I-R headquarters

in New York, N.Y. One year later, I-R de-centralized

and moved its marketing departments to its

supporting factories and Dave relocated to Painted

Post, N.Y., where he was later promoted to gas

engine marketing manager.

In 1971, the gas engine marketing departmentwas consolidated with I-R’s packaging subsidiary,

Southwest Industries (SWI), and moved to the SWI

facility in Houston, Texas. Here, Dave managed

application engineering and sales coordination

for integral gas engine compressors and gas field

separable compressors. Later, he also served as

manufacturing manager and facility operations

manager.

In 1974, Dave transferred to the I-R Compression

Services (I-RCS) Division in Tulsa, Oklahoma, as

engineering manager, later adding the servicedepartment to his responsibilities. The I-RCS

business was growing rapidly; business doubled

in 1974 and grew at a rate of approximately 33

percent for several years thereafter. By 1977 that

growth required I-RCS to de-centralize into district

Dave became district manager in charge of sales,

service and operations of both the 59-01 Tulsa

District and 59-05 New Orleans District.

In 1980, as a result of another re-organization, Dav

returned to the I-R sales team in Tulsa as district

At 85 years old, Dave Morse is still moving and shaking in the

compressor business.

First 40 YearsThe


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manager of field compression sales, and later as

district manager for turbo and reciprocating sales.

He retained this position following the combination

of Dresser Industries and Ingersoll-Rand in 1987 to

form Dresser-Rand.

Dresser-Rand’s compression sales team was created

in September 1988 and Dave returned to his

position as sales coordination manager. He held this

title until his retirement in December 1997. He later

consulted with D-R Compression Services untilSeptember 2000 and then contracted for

Dresser-Rand’s high-speed reciprocating

compressor (HSRC) business unit – and still does

today.

Sixty Years of

Compression KnowledgeThere is no doubt that Dave has seen a lot of

changes in the compression industry over the last

six decades, from the days of integral gas engine

compressors (often packaged) to the introduction

of the high-speed, balance-opposed separable

compressor by D-R / Clark Brothers in 1957 and D-R

/ I-R in 1958, to the growth of the packaged, high-

speed reciprocating compressor industry.

“My greatest challenge has always been to increase

Dresser-Rand’s business and market share,” says

Dave. “There is always room to improve.” He

participated in many new product developments,

including the TVS-TVR-SVS, KVGR, KVSR, KVR, 5HHE,

5RDH, 5.5RDS, HOS™, VIP®, HOSS™, and MOS™

compressors.

“In addition to learning more each day about the

equipment and the industry, getting to know our

clients and how they apply our compressors in their

business is always interesting and challenging,”

notes Dave.

Dave observes, “There is no greater reward than

watching people you have hired and/or helped train

succeed.” Over the years, Dave has shared his wisdom

via “Morse-grams” or other immediate means. Among

those are: “define the question;” and “working withgood people with a “team” spirit seeking win-win

solutions makes it that way.”

“It’s a Wonderful Life”Dave’s family life has been just as rich. In 1958, Dave

married Pat, a Baton Rouge native. They had two

children. Ed, born in 1960, is a professional musician,

and Karen, born in 1965, is a computer specialist at

St. Francis Hospital in Tulsa, Oklahoma. Pat passed

away in 2005, following an 18-year battle with

Parkinson’s disease.

Dave’s commitment to serving others goes back to

the beginning…as a summer camp counselor in high

school, a naval officer who served his country and

then serving his company and colleagues. He

remains well-known and respected in the

compression industry today.

Being 85 years old and able to contribute to one

company for the last six decades is a blessing few can

enjoy, and an accomplishment not many can claim. •

““The first 40

years are thehardest; work

is (even) more

fun when you

don’t have to.”


8/366 insights

SGT-750 Low-weight

Industrial Gas TurbineThe Siemens SGT-750 low-weight industrial gas

turbine was designed and developed to incorporate

size and weight advantages of the aero-derivative

gas turbine while maintaining the robustness,

flexibility and longevity of the traditional heavy-

duty industrial gas turbine. With a power output

of 37 MW for power generation, or of 38.2 MW

for mechanical drive, the SGT-750 turbine was

specifically designed for long operating times

with extended overhaul intervals. It offers high

reliability resulting from extremely low downtimesfor planned overhaul and maintenance work (only

17 days in 17 years), and achieves the highest

availability in its performance class.

The SGT-750 turbine offers easy access to all the

key components. It is assembled as a unit on a

single-lift frame with a divider between the turbine

and the driven equipment. The SGT-750 turbine

is a two-shaft machine optimized for simple cycle.

It has a single, rigid rotor compressor body that is

electron beam-welded to ensure reliable, stable

and uniform run-up in hot or cold conditions. Axial

blade attachment grooves allow blade replacement

without rotor removal.

Industrial Trent 60

Aero-derivative Gas TurbineThe Siemens Industrial Trent 60 aero-derivative

gas turbine (ADGT) delivers up to 66 MW of

electric power in simple cycle service at 42 percent

efficiency. It meets the higher power and variable

speed demands required by LNG operators

and offers fast delivery and installation times.

Renowned for its fuel economy and cost savings,the Industrial Trent 60 ADGT has already been

selected by clients for an LNG onshore project as

well as two floating LNG (FLNG) offshore projects

since Dresser-Rand and Siemens came together.

LNGo ™ Natural Gas

Liquefaction SystemLNG clients can combine these expanded Siemens

products with Dresser-Rand’s DATUM® compresso

and LNGo™ natural gas liquefaction system, the

latest innovation for the LNG market. The LNGo natural gas liquefaction system uses a combination

of Dresser-Rand technologies, including its MOS™

reciprocating compressor, Guascor® gas engine

and Enginuity® control system in a portable, small

footprint package that can be placed on well pads

gas flares and similar sites. The system allows for

small, portable, stand-alone plants and can be

moved to support changing requirements and

needs.

Boil-off Gas Compressors

Siemens is the technology and market leader forcryogenic temperature boil off gas compressors

for LNG production plants. With operating

temperatures as low as -160 degrees Celsius

(-256 degrees Fahrenheit), Siemens single shaft bo

off gas compressors (STC) are designed to withstan

thermal shock and feature heavy duty dry gas seal

protected in a heated seal carrier, variable inlet

guide vanes for easy start up and best turndown,

and an option for direct online start-up which doe

not require static cooling nor gas needed for flarin

With the combined resources of Siemens, the value proposition for LNG clients

from the new Dresser-Rand business within Siemens Power and Gas divisionhave expanded. Dresser-Rand’s innovations in compression technology, rotor

dynamics, head capacity, and efficiency per compression section all serve to

provide incremental production gains that are important to the operator. The

addition of Siemens’ SGT-750 gas turbine driver and Industrial Trent® 60 aero-

derivative gas turbine to the portfolio increase Dresser-Rand’s capabilities for

offshore and onshore liquefied natural gas (LNG) projects.

Combined Resources ExpandOpportunities for LNG Projects


9/36

The STC boil-off gas compressor takes the

evaporated gas at the storage temperature and

pressure and compresses it. The compressed vapor

is then cooled and expanded to re-liquefy it – or it

is cooled and injected directly into a pressurized

liquid stream for sale of gas.

World Class Test FacilitiesThanks to the combined resources, the Dresser-Rand

business comprises four world class test facilities

(Duisburg, Germany; Hengelo, The Netherlands;Olean, NY, United States and LeHavre, France) that

can full load test a main liquefaction train with both

a driver and a compressor.

Magnolia Project in

Lake Charles, LouisianaLast year, four Siemens SGT-750 gas turbine

drivers for the main refrigerant trains were sold to

Magnolia LNG LLC for the initial two LNG trains. This

scope will then be expanded into the full four-train,

eight million tons per annum (mtpa) facility locatedin Lake Charles, Louisiana USA.

The project for LNG Limited features four mixed

refrigerant Siemens STC-SV barrel-type compressors

which will each be driven by a Siemens SGT-750

industrial gas turbine, while four ammonia

refrigerant STC-SV compressors will each be driven

by a Siemens SST-600 steam turbine. Additionally,

the scope of supply includes two motor-driven

feed gas booster compressors. The subsequent

two LNG trains necessary to achieve the full eight

mtpa for Magnolia will bring the total number of

compressors to 20 at the site.

The SGT-750 industrial gas turbine driving the

compressors was one of the main reasons for

selecting Siemens for the project because the

turbine’s power rating is a good match for the

LNG train design. Its power output is more than

enough for the project’s requirements, providing

about an extra three MW compared to its nearest

competitor, thus providing a solution that reduces

project risk. The SGT-750 turbine also has lower

emissions and lower operating expenditures over

the plant’s lifetime, compared with the competition.

Apart from the performance of the gas turbine,

an important factor in Siemens securing the

contract was its ability to provide the entire LNG

compression train. It enabled Magnolia LNG to

bundle the entire LNG compression train through

a single supplier for better support and project

efficiency. This approach simplifies mechanical

design, reduces interfaces for better project

management, streamlines commissioning, andgenerally lowers overall project risks.

Installation of the LNG trains at Magnolia, expected

to begin in late 2016 or early 2017, comes at an

important time, and not just for the United States.

There has been tremendous interest in the SGT-750

gas turbine across the industry and Magnolia will be

an important demonstration of its suitability to such

applications, especially in this mid-range-sized LNG

facility. •


10/36

p r o f i l e

8 insights

P

Perhaps this phrase helps describe the work

mindset of Berenice Flores, a key client manager

for a major oil company. After all, this Hemingway

classic is her favorite novel. “It’s a tale that includes

many virtues, especially courage and endurance,”

she says.

“I see my role as Dresser-Rand’s representative

to the client and as the client’s representative to

Dresser-Rand. It’s somewhat of a balancing act. I

have to ensure that my client’s needs are met, as

well as those of our company.

In a competitive market like this, being able to

discuss how the Dresser-Rand business can match

its services to a client’s needs is what helps position

us ahead of our competitors,” Berenice continues.Among her responsibilities are providing support

in the sales cycle for all opportunities, fulfilling

quotation requests, maintaining the price book,

and solving any issues that arise with order

execution and delivery, to name only a few. It’s

easy to imagine that working in so many facets

of the business could become stressful, but

Berenice manages her workload with the support

of her coworkers and by continually updating her

communications skills.

“I think it’s important that we all seek to improvehow we communicate,” she maintains. Berenice

also enjoys the collaborative nature of her work,

adding “I like learning different topics, interacting

with different people and solving problems. That’s

why I was always attracted to jobs where I get to

interact with people at various organizational levels

and across cultures – where there is always room

for learning.”

With a degree in Business Administration from

the Instituto Tecnologico y de Estudios Superiores

de Monterrey, Berenice has worked with an

assortment of diverse companies, including Alucap

Group, Panasonic, Mattel, and Amazon.com.

She also worked as a contractor when her twin

daughters were smaller, giving her the flexibility to

work from home.

Berenice grew up in the Mexican city of Cuernavac

the capital of Morelos state, located about an hou

south of Mexico City. Known for its great weather

year round, it is celebrated as “The City of the

Eternal Spring.”

“Cuernavaca is a beautiful place to grow up,” says

Berenice. “It is full of history, culture, traditions,art, and great food.” With its gated haciendas and

sprawling estates, the city has attracted foreign

princes, archdukes and other nobles seeking to

enjoy its warmth, clean air, fresh water springs,

and eye-catching architecture. Central among

these structures is the Cuauhanahuac Museum,

also known as Cortes Palace – home of the Spanis

conqueror, Hernan Cortes – which helps preserve

the region’s history.

Another “can’t miss” site, according to Berenice,

is the Cathedral of Franciscan Order, built in

1522. It was the fifth Franciscan construction in

Mexico, established by the first 12 Franciscan friar

who arrived in the country. “There are so many

fascinating sites in my hometown that I enjoyed

with family and friends. Now, I go back as much as

can with my twin daughters. I want them to collec

great memories as I did when growing up.”

Making Best Use

of the Tools At Hand

BERENICE FLORES

Berenice Flores,

key client manager

In Ernest Hemingway’s, The Old Man and the Sea, the aging fisherman,

Santiago, would say to himself, “Now is no time to think of what you do

not have. Think of what you can do with what there is.”


11/36

pr of i l e

Reminiscing about growing up in Cuernavaca,

Berenice reveals that her mother was her biggest

role model. “She was a teacher. She taught with

passion, dedication, love, and joy. I witnessed many

times how grateful her former and current students

were to her and she was highly respected not only

by her pupils, but by parents as well.” Perhaps

that’s why Berenice has always chosen jobs where

she interacts with people at various organizational

levels.

Outside the office, Berenice is passionate about

doing what’s best for her family and maintaining

a strong connection with them. The focus of her

priorities, she says, is making sure her daughters

have a good education. “I want to teach them

to think critically, to be open-minded and

encourage them to keep the appetite they have

for learning.” Among her pastime activities are

teaching her daughters volleyball, visiting parks and

museums, attending classic concerts, and reading

Brain Pickings, an online assortment of eclectic

information.

When asked about lessons learned on the job at

Dresser-Rand, Berenice reveals that “no matter

what industry you work for, you can adapt and fit in

as long as you are willing to learn and work the best

you can. And it’s important to be flexible, creative

and able to work with the tools provided.”

Just like Hemingway’s fisherman, Santiago. •

“Now is no time to

think of what you

do not have. Think of

what you can do

with what there is.” Santiago - The Old Man and the Sea


12/36

p e o p l e p o w e r

10 insights

We recognize that strong communities are advantageous

for growth and prosperity. Worldwide, our employees

look for ways to give back, strengthen community

programs and support worthwhile causes.

The Power of Giving Back

Duisburg’s Turbo Bikers Conquer

Challenging Circuit to Raise Money

for Local CharitiesFor the last eight years, the Turbo Bikers team

at Siemens Duisburg, Germany location has

participated in Europe’s largest non-stop 24-hour

mountain bike race. Held in Duisburg, this annual

event attracts approximately 2,400 cyclists. The

winner is the team that bikes the most rounds;

each round is 5.3 miles, or 8.5 kilometers.

In August, 450 teams (consisting of one to eight

people) competed on the 262 foot (80 meter)

elevation gain Landschaftspark Nord circuit.

The Landschaftspark public park in Duisburgwas designed in the early 1990s as a tribute

to the area’s industrial past as a coal and steel

production plant.

“You really need a mountain bike to conquer the

track because there is no street and part of this

circuit involves going through the old plant,” says

Peter Bongartz, the Turbo Biker’s lead organizer

responsible for Services Sales and Marketing for

the Americas at Siemens. “And because we bike

24 hours non-stop – as many as 373 miles

(600 km) per team – sleep is an elusive luxuryfor a while,” Bongartz added.

About six weeks prior to the race, the Turbo

Bikers begin soliciting colleagues, friends and

family for either a fixed donation or an agreement

to pay a specific amount for each mile (km) biked

– typically between one USD cent, or 0,01 euro

and USD 1.65, or 1.50 euro per mile / km.

See the peoplebehind our

products and services.

Last year, the Turbo Biker teams (two teams of

eight and six teams of four) biked approximately

373 miles (600 km) in a 24-hour time period andraised nearly USD 15,400 (14,000 euros). Proceeds

including race entry fees, were donated to the

Bunter Kreis organization that supports families

with premature infants, disabled children and

children with chronic illness or disabilities and

the VKM organization that provides consultation,

training and school inclusion services to people

with handicaps.

“Since the team’s inception we have raised

approximately USD 93,000 (85,500 euro) to help

local organizations,” says Bongartz. “We are well

aware that help is needed worldwide, but we

choose to donate to organizations close to home

and ensure that 100 percent of the donations go

directly toward helping these children and their

families.”

Further information and photos can be found at:

www.turbo-biker.de. •

Editor’s Note: People Power is about recognizing our employees for their selfless service and dedication to being

a part of something bigger than themselves by giving back to their communities. We are happy to highlight in this

issue three examples of the passionate efforts of our employees and how they’re playing a role in making their

communities a better place to live and work.


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Camp STEMovation Inspires Students

to Pursue Degrees in Science,

Technology, Engineering, and

MathematicsReynaldo Guerra was failing math classes during

his junior year of high school and was kicked offthe basketball team as a result of his poor grades.

Motivated by his desire to continue to play the

game he loved, Guerra began working on his math

skills just as intensely as he practiced basketball.

Before long, Guerra realized he actually enjoyed

math.

Guerra graduated from the University of Houston’s

(UH) Cullen College of Engineering in 2003 with

a BSME degree. During his time there, Guerra

was part of the Mexican American Engineers and

Scientists (MAES) organization that coordinated fun,hands-on projects with K-12 students at Houston-

area schools to inspire them to pursue degrees in

STEM.

Following college graduation, Guerra and some of

his former class mates formed Camp STEMovation,

a nonprofit organization that brings science,

technology, engineering, art, and mathematics

(STEAM) workshops and activities into Houston-area

schools in low-income neighborhoods.

Employees Ride to Raise Money

for National Multiple Sclerosis (MS)

SocietyIt began as a few D-R business employees from

Houston’s Latin America Services team gathering

informally after work to bike together a few times

a month. By April 2015, this small team grew by

word of mouth into an organized cycling team of17 colleagues who signed up for the BP MS 150 in

April 2015.

The BP MS 150 is a two-day fundraising bike ride

organized by the National MS Society South Central

Region. It is the largest of 100 bike events in the

United States with 13,000 cyclists, 3,500 volunteers

and countless spectators. The 180-mile ride begins

in Houston and finishes in Austin, Texas.

In 2015, the first day of the race was cancelled due

to heavy rain the week prior which flooded the

campground at LaGrange where the teams werestaying. Refusing to let the weather stop them, the

D-R team rode to Fayetteville (close to LaGrange)

on Saturday and then car-pooled back to Houston.

Photo: Nathan Powell; Pablo Enrique Alarcon; Graham

Sherlock; Jennie Orellana; Chris Cowden; Erick Scherzer;

Christopher Petrillo; David Sanchez; Bernardo Alvarez;

Jerome Beguerie; Maribel Socorro; Octavio Primo.

Source: University of Houston Cullen College of Engineering

On Sunday, the team car-pooled back to Fayetteville

at 4:00 am to complete day two of the race.

This year, the MS Society raised approximately

$20 million, of which the Dresser-Rand business

team collected more than $12,000. Six D-R business

employees volunteered their time to help make the

event a success. •

In March 2015, Camp STEMovation held a STEAM

Extravaganza event at Rick Schneider Middle School

where the students participated in hands-on, super

hero-themed STEAM workshops. The workshop

Guerra taught began by teaching students basic

engineering principles. He then challenged the

students to build super hero lairs using just stripsof card stock paper and tape. The lairs were then

subjected to three tests: Guerra dropped the lair to

the floor; he then stood on the lair with one foot;

and finally, he simultaneously dropped two large

college-sized textbooks onto the lair.

Students were awarded points based on how well

the lair survived all three tests, the aesthetics of the

lairs and how many materials were used to build it.

The student awarded the most points won science

kits and a trophy.

“You can see thelightbulbs going off in

their heads,” Guerra

said of the students who

partook in the event.

Suddenly they go from

having never even heard

the word ‘engineering’ to

this becoming an option

for them.” •


14/3612 insights

The climate is often severe, with long, cold winters

and short, cool summers. Average temperatures in

January hover just above zero degrees Fahrenheit

(-18 degrees Celsius).

Welcome to Komi.

One of the northernmost republics of European

Russia, Komi is located approximately 650 miles

(1,046 km) north of Moscow and less than 400

miles (644 km) south of the Arctic Circle. It’s

among the largest oil and gas producing regions in

European Russia and one of the country’s top 10

producers.

One of the area’s oldest fields, Lekkerskoje (Lekker),

is situated near the city of Usinks, founded in 1966

as an oil and gas production center settlement.

Since the Lekker deposit is in a remote location,

there are no external electric power networks.

Because of this, it’s critical to maintain an

uninterrupted power supply.

Initially, diesel power stations were used to provid

power to the local infrastructure. Russia’s second

largest oil producer, Lukoil-Komi (a branch ofLukoil), decided to upgrade its power generation

facilities at Lekker. After careful consideration of t

proposals, company managers opted to purchase

and install four 1.8 MW Dresser-Rand KG2 turbine

generator sets and auxiliary equipment. Zvezda-

Energetika, a key player in the Russian power

generation industry, was selected as the local

packager for the four skid-mounted KG2 turbine

generator sets.

Dresser-Rand KG2 turbines provide on-site electrical power

for one of Russia’s largest oil producers.

Welcome to

Komi


15/361

Sustainable Power StationsDesigned to meet demanding emissions regulations,

the KG2 gas turbine is ideally suited for continuous

power generation on- and offshore, emergency and

stand-by power supply, and as an indirectly-fired

option for CO2-neutral biomass plants. Because of

its simple, low-maintenance design, high reliability,

and operational experience, the KG2 turbine

generator package is a preferred solution for these

types of applications. The wide fuel range also

enables operation on extremely low heating value

fuels, landfill gas and associated gas from crude oil

production.

One of Lukoil-Komi’s key variables in choosing the

KG2 is that it can accept a wide variety of fuels,

ranging from pipeline quality natural gas to low

heating value gas. According to Russian Federationlaw, flaring of gas is subject to heavy fines. The

Dresser-Rand power station solved this problem

by producing electricity on-site from available

resources, which prevented flaring. These types of

power stations are specifically engineered for fuel

flexibility and sustainability, so that the gas can be

used as an energy resource instead of being wasted

through venting or flaring. It’s not only efficient, but

better for the environment, too.

A History of Reliable OperationThe KG2 has proven itself in a variety of

installations, with more than 1,200 units clocking

more than 25 million operating hours with 99

percent availability. Some engines have been

running more than 245,000 continuous hours and

have achieved a lifetime of more than 30 years of

run time.

The unit requires minimal maintenance, important

in a region with limited accessibility. In addition, the

package is suited to the harsh northern conditions

because the container is constructed in such a

way that all maintenance can be performed from

the inside. Some of the competing units have

tight containers and maintenance is possible only

through open doors or hatches.

Cogeneration – an Added BenefitAnother advantage of the versatile KG2 turbine is its

combined heat and power (CHP), or cogeneration

capability. CHP systems facilitate electricity

production and provide useful heat at a very high

efficiency. The turbines at Lekker operate with a

heat recovery system, so they not only produce

electric power but provide heat energy as well. •


16/3614 insights

TThe Guascor HGM 420 model provides 1 MWe of

power and extends the Guascor HGM family of low

emissions, lean burn, spark-ignited gas engines that

employ Miller Cycle technology. The 42-liter, V12

engine (bore 160 x stroke 175 mm) is rated 1,040

kW mechanical and 1,010 kW electrical at 1,500

rpm. The engine achieves greater than 42 percent

mechanical efficiency and its electrical efficiencyexceeds 41 percent.

The Guascor HGM 420 gas engine is normally

connected to an external grid and is suitable for

projects that require approximately 1 MWe of

power. With high thermal demand and continuous

operation, these engines can be supplied as stand-

alone power units, as part of a cogeneration system

on a skid, packaged as a gen-set, or containerized.

In addition to its electrical efficiency, the Guascor

HGM 420 gas engine is able to recover heat from

Clients with high energy efficiency requirements can now take advantage of

the Dresser-Rand business’ new Guascor® HGM 420 gas engine. The newest

model in the Guascor HGM engine family, it offers a balanced relationship

between efficiency, reliability and price.

main and auxiliary water circuits, as well as heat

from exhaust. It achieves approximately 91 percen

thermal efficiency and can run more than 8,000

hours per year with the balance of the year set

aside for routine maintenance.

The Guascor HGM 420 model is also available

at 1,800 rpm, with 1,040 kW mechanical and1,006 kW electrical. The engine achieves greater

than 40 percent mechanical and 39 percent

electrical efficiencies, respectively, as well as

90 percent of total heat efficiency.

The overall power range of the Guascor HGM fam

is 520 to 1,240 kW at rated speeds from 1,500 to

1,800 rpm. These engines can burn a wide variety

of fuels including natural gas, biogas from anaerob

digestion of organic matter, methane from landfill

sites and sewage plants, and most any type of gas

derived from bio digestion processes.

•

Hits the MarketNew HGM Engine


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VSDS Motor Inverter DesignConcept for Compressor Trains Avoiding Interharmonics in

Operating Speed Range and Verification

Volker Hütten

Head of Numerical Design Department

Siemens Energy Sector

Duisburg, Germany

Tim Krause

Mechanical Design Engineer


Duisburg, Germany

Vijay Anantham Ganesan

Medium Voltage Drive System Consultant

Siemens Industry Sector

Nuremberg, German

Christian Beer

Senior E-Drive Expert


Erlangen, Germany

Sven Demmig

Medium Voltage Drive System Consultant

Siemens Industry Sector

Nuremberg, Germany

Editor’s Note: Reproduced with permission of the Turbomachinery Laboratory (http://turbolab.tamu.edu). From

Proceedings of the Forty-Second Turbomachinery Symposium, Turbomachinery Laboratory, Texas A&M University,

College Station, Texas, Copyright 2013.

Volker Hütten has been the head of the

Numerical Design department of Siemens Oil

& Gas Division, in Duisburg, Germany since

2010. During his more than 21 years in this

company he is responsible for the machinery

dynamics of compressors and compressor

trains of order related tasks. He has been

active in correlating analytical results with

field data in numerous troubleshooting and problem

diagnosis situations. Volker Hütten received his Diplomadegree from the University of applied sciences in Krefeld

in 1990.

Christian Beer is a senior e-drive expert at

Siemens Oil & Gas Division in Erlangen,

Germany. Since 1989 he has specialized

in electrical drive systems and has been

responsible for LNG e-drive solutions.

Tim Krause is a mechanical engineer

at Siemens Oil & Gas Division in

Duisburg, Germany, where he is

responsible for engineering and

troubleshooting of compressor trains

in the field of machinery dynamics. He

received his diploma degree from the

University of applied sciences in

Dortmund in 2005.

Vijay Anantham Ganesan is medium

voltage drive system consultant

at Siemens Industry Sector in

Nuremberg, Germany. He received

his M.Sc. degree in electrical power

engineering from RWTH Aachen

University, Germany in 2005. From

2005 to 2010, he was a research

assistant at Leibniz University Hannover, Germany.

Sven Demmig is a medium voltage drive

system consultant at Siemens Industry

Sector in Nuremberg, Germany. After

achieving his PhD in the field of electrical

drive systems, he has been working for

Siemens since 2008.


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A

ABSTRACT

During operation of compressor trains by a variable speed drive system (VSDS),

integer and non-integer harmonic currents are generated in the inverter. Via the

electrical system of the inverter and the motor, an excitation torque is transferred

across the motor air gap into the main mass of the motor rotor. The frequency

of this excitation may cause torsional resonances. Due to the rapid increase in

excitation frequency of integer harmonics, intersections with relevant torsionalnatural frequencies (TNFs) can in general be avoided within the operating speed

range. In contrast, the intersections of the noninteger harmonic excitation

frequencies, also called interharmonics, with TNFs within the operating speed

range may have an essential impact on the vibration behaviour of the rotating

equipment. This aspect has to differentiate between two train configurations. The

first are direct driven trains and the second, trains including an intermediate gear.

For direct driven trains, only fatigue problems have to be considered. In trains with

an intermediate gear, on top of that, interaction of torsional and lateral movement

may have a negative effect on the lateral vibration behaviour of the gear rotors.The main focus of this publication is on a simple but effective method for turbo

compressor applications that allows avoiding main resonances within the operating

speed range caused by intersections of interharmonic excitations with relevant

TNFs. This method is based on detailed knowledge of the inverter behaviour

and possible design options of the motor itself. This in-depth understanding was

developed by correlating numerical and experimental results based on dynamic

torque measurements of real turbo compressor trains. During this investigation the

mechanically relevant torsional excitations were identified. Therefore, the different

types of inverters and their corresponding characteristics had to be analyzed and

understood in detail. This knowledge, in combination with possible motor designs,

with regard to the number of pole pairs and the most common train configurations

(direct driven and/or trains including intermediate gears), is incorporated in this

report.

IntroductionAdvantages of VSDS Driven Trains

Rotating equipment in the turbomachinery industry

traditionally uses mechanical drivers as primemovers. Process and mechanical engineers have

confidence in their equipment and might have

reservations about not yet installed electrical

equipment. Ongoing discussions about energy

efficiency, equipment availability, operability and

avoidance of green house gas emissions (GHG)

has lead to a steadily increasing use of electric

motors, either as fixed speed or as variable speed

drivers. The industry has reacted with an array of

electrical drive systems that can beneficially replac

gas turbines and gas engines as prime movers of

compressors and pumps. In smaller power ratings

the electric motor is unchallenged in all industrial

fields, including the oil & gas industry. Its simplicitrobustness and performance is unmatched by any

other drive in most all applications. In megawatt

power ratings, however, electric motors are

challenged by gas turbines. Detailed driver selectio

studies are the rule when it comes to find the

best suited driver for a given application. With the

introduction of electronic variable speed drives in

the late ‘70s to the industry the benefits of fixed

speed electric motor drives have been significantly


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enhanced and these additional features are most

often the reason for their selection:

• Soft start and fully torque controlled operation

over a wide speed range

• Dynamic and accurate speed control via

electronic variable speed controllers

• Ability to ride through brief power busdisturbances

• Energy efficiency above 95 percent also in part-

load mode and related speed range

• Shaft speeds in excess of the customary 3,000

or 3,600 rpm dictated by the power system

frequency, eliminating step-up gears in many

cases

• Insensitivity to frequent start/stop cycles and

ability to (re)start fully loaded compressors

• Instantaneous starting capability providesprocess flexibility

• Lower GHG and noise emissions

Suppliers of such motors and many engineering

contractors have the experience, know-how and

tools to select and recommend the optimum

variable speed drive system for a given application.

History

After the technology’s potential to realize variable

speed operating envelopes in combination with

high efficient electric drives was discovered, it wasinstalled more frequently. However, it turned out

that the ecologic and economic advantages of all-

electric compression with VSDS driven trains come

along with a technical issue to solve.

For many years occasionally high lateral vibration

in intermediate gears as well as coupling or shaft

end damage occurred and was reported to the

industry (Corcoran, et al., 2010), (Kita, et al.,

2008), (Kocur and Corcoran, 2008), (Naldi, et al.,

2008), (de la Roche and Howes, 2005), (Feese and

Maxfield, 2008). Measurements revealed high

torque oscillation amplitudes, initially caused by

torque oscillations generated in the inverter. These

travelled across the motor air gap towards the

rotating equipment and excited the fundamental

TNF of the entire train.

Variable speed drive systems rectify alternating line

current (AC) of 50 Hz and/or 60 Hz, to direct current

(DC), and invert the DC to a variable frequency AC

current in order to operate the motor at variable

speeds. As illustrated in Figure 1 the electrical

conversion from line side to the motor side, quite

small harmonic distortion of the inverter output

current causes forced torsional vibration. Due to

small amplitudes, this is outside the resonances of

a well endurable load for the train components.

Unfortunately, the vibration is amplified when the

excitation frequency of torque ripples match a TNF

with a suitable mode shape to excite the train.These can then be high enough to either transfer

the torsional vibration energy into lateral pinion

vibration through the gear, or even exceed the

component’s fatigue lifetime capacity.

Figure 1. Electro-mechanical interaction.

The turbocompressor manufacturers historically

dealt mainly with torsionally easy to handle gas

and steam turbine drives and fixed-speed electric

motors. They now had to close the ranks with the

electric drive equipment manufacturers to gainground in bringing the two disciplines, electrical and

mechanical engineering, together.

Technical Impact of Torsional Resonances

Excited by VSDS

In principle, generated harmonic torque oscillations

may have an essential impact on the torsional

vibration behavior of the entire train. Consequently,

the train-responsible party, mostly the compressor

manufacturer, must carry out detailed analyses to

examine the operational condition of the rotating

equipment in order to do a proper engineeringdesign. Therefore, close collaboration of driver

and compressor manufacturer in designing and

engineering of such a VSDS-driven train is essential,

as also stated by Hudson (1992).

First of all, it is an essential task to avoid fatigue

in the torque-transmitting elements. Torsional

excitation may cause fatigue which could eventually

lead to a catastrophic failure of torque transmitting

elements. During the engineering phase of


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any project the occurring peak torque and the

corresponding torque capability of each individual

train component has to be evaluated. Furthermore,

in systems including intermediate gears, elevated

lateral vibration of the pinion and bull-gear rotors

could also occur. Due to the fact that torsional and

lateral vibrations are coupled via the gear mesh,

excitations have to be examined to avoid higher

lateral amplitudes and/or to avoid clattering ingears in addition to fatigue problems.

Based on the authors’ experience, excessive

high lateral vibrations caused by a torsional

excitation were observed in some cases. It is due

to the coupled movement in lateral and torsional

direction, a more or less plausible behaviour.

Nevertheless, the authors have, in some cases, also

observed high torsional vibration amplitudes and,

simultaneously, only few microns of relative shaft

vibration corresponding to the torsional excitation

frequency.

A case of white noise excitation in contrast to the

widely known single frequency excitation has not

yet been encountered by the authors. However,

two cases of VFD compressor trains in the LNG

industry showing such phenomenon were recently

published (Kocur and Muench, 2011).

Ultimately, only a dynamic torque measurement

during string testing and/or during commissioning

would be able to identify the potential risk of a

failure. The alternative is to have a reliable strategy

for the engineering. One specific will be presentedas the main topic of this paper, but also other

options will be discussed which positively influence

the aspects.

Generation of Torque Ripples in VSDSPrinciple of Generation of Torque Ripples

The motor air gap torque is generated by the rotor

flux in combination with the stator current. For a

perfect sinusoidal stator current waveform and

a perfect air gap field, the motor torque would

be constant. Using a VFD, the motor currentwaveform is not perfectly sinusoidal. The AC-DC-AC

conversion adds torsional excitation frequencies to

the system. Integer harmonics and interharmonics

excitation generated in the converter cause torque

oscillations in the motor air-gap. This effect cannot

be disregarded due to the fact that interharmonic

excitations can be of such frequency that they can

generate torsional resonances in the operating

speed range.

The air gap torque ripple generated by the VFD

characteristic can be split in two categories

(Figure 2):

• Integer harmonic torque excitation

• Interharmonic torque excitation

The excitation frequencies are written for the

integer harmonic torque harmonics as f exc-h = C1*f dand for the interharmonics as f exc-i = |(C2*f do-C3*f l)|

The integer harmonics are directly proportional to

the motor stator current frequency and therefore

the motor speed. The characteristics depend on

the converter topology e.g. VSI or LCI and the puls

number of the motor side rectifier. The amplitudeof the air gap torque ripple depends, just to

mention the main factors, on:

• Switching device characteristic

• Motor impedance

• Motor voltage

• Motor cable characteristic

• PWM characteristic for VSI drives

The non-integer harmonics are caused by the not

perfect DC current (LCI drives) or DC-voltage (VSIdrives). This means the characteristic of the line si

inverter is modulated on the motor currents by th

motor side rectifier. Because of this modulation, th

frequency of the interharmonics depends on the

line frequency, the motor frequency and the pulse

number of the motor and the line side rectifier. Th

amplitude is influenced by the same parameters a

the integer harmonics plus additional parameters

Figure 2. Typical VFD Campbell diagram.


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the DC-link and the line side:

• DC-link capacitance / inductance

• Line side characteristic (harmonic pre-load,

frequency-dependant impedance, etc.)

• Transformer impedance

The resulting torque ripple frequency of the

interharmonic air gap torque varies within therange of operation depending on the parameters

explained before. Nevertheless, this may result

in an interaction with the TNF of the mechanical

string even if the amplitude is much lower than the

amplitude of the integer harmonics.

Because of the large number of parameters

influencing the amplitude of the air gap torque

ripple, the prediction of specific amplitude is

complicated and only possible with tolerances. But

knowing the drive and motor type the torque ripple

frequencies over the complete speed range can bepredicted easily even without any simulation.

It has to be pointed out that this kind of behaviour

is inherent to all state-of-the-art inverters in

the entire market. It varies only with regard

to interharmonic frequencies and excitation

magnitude for each particular configuration.

Typical Motor Design and Number of Pole Pairs

Electrical motors can be built in 2, 4, 6, … pole

design (equivalent to number of pole pairs (NPP) of

1, 2, 3, …) and this leads to synchronous speed of:

nsyn = (f l / NPP) *60 (1)

As can be seen in Figure 3, a motor with a number

of pole pairs of 1 runs with supply frequency.

Whereas a motor with a number of pole pairs of 2

at half and with a number of pole pairs of 3 at one-

third of the supply frequency accordingly. This is an

essential fact in order to find resonance-free train

design solutions within this new design concept.

Overview of Relevant Frequency Converter Types

In the turbomachinery industry two frequency

converter types are typically used:

• Voltage source inverter (VSI)

• Load commutated inverter (LCI)

Both types have specific advantages and

disadvantages and the selection is based on power

and voltage range, complexity and the referencesituation. In general, VSI are used for the lower

power ratings up to 25 MW and the LCI is the

preferred solution for the highest power ratings

up to 120 MW. In the range of 15 to 25 MW both

topologies can be used. The VSI can be used with

all motor types and topologies with different pulse

numbers. The VSI will generate motor voltage in

block form. The resulting motor current depends

on the stator inductance, the cable parameter,

the pulse number, and the control characteristic.

Nevertheless, the current total harmonic distortion

(THD) of VSI drives is lower than the current THD ofLCI drives. As explained before, this leads to a lower

torque ripple which may be advantageous for the

overall compressor string design.

The LCI instead can be used for synchronous

motors only. Also for the LCI topologies, different

pulse numbers are available. The motor current is

generated in a block form, results finally in higher

current THD.

Experience With and Consequences

of Interharmonic ExcitationSeveral case studies of vibration issues related to

torque excitation caused by inverter fed motors

have already been published. Here, two of our

own typical examples of case studies are presented

which were used in order to get an in-depth

understanding of the operating behaviour of the

individual inverter types. This information is needed

to realize the new train design concept that is lastly

the main focus of this publication.

Excitation Pattern of a VSI

In the first case, a 1.5 MW 12-pulse VSI inverterfeeds the induction motor of a single-shaft radial

compressor train with intermediate gear. During

run-up with constant acceleration the dynamic

torque measurement at low speed coupling

recorded amplitudes as shown in Figure 4. As the

inverter speed control actively accelerates the train,

the harmonic and interharmonic excitation lead to

Figure 3. Effect of number of pole pairs (N pp ) on

motor speed.


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dynamic torque peaks at speeds where torsional

resonance occurs. The blue line is the torque

measurement and the green line shows the motor

speed, both versus time. Some torque peaks can

be observed: one single major amplitude at about

2,700 rpm and some peaks quite close together

especially in the low speed range.

It is practical to plot these together with the TNFs

and excitation frequencies in a Campbell diagram.

Figure 5 represents this diagram with the first two

TNFs (dashed lines) and torque ripple excitation

frequencies (solid blue lines) versus motor

operating speed. At motor speeds where the first

TNF and excitation frequency intersect, a resonance

is present. The red circles indicate the relevant

resonances.

The diagram reveals that the by far dominating

torque peak at 2,700 rpm is caused by the |3*f do-

6*f l| interharmonic excitation frequency exciting

the first TNF. This excitation should therefore, as

major resonance, not fall within the operating

speed range. Apart from this, secondary amplitude

at about 10 percent peak-to-peak the motor rated

torque are observed. The first natural frequency

is stimulated by the |9*f do-6*f l| interharmonic

excitation frequency and 1*f do at about 900 rpm.

Due to its mode shape, the first natural frequency

for this train configuration commonly leads to

the highest torque amplification for excitation at

the motor air gap. Torque amplitudes at otherspeeds, due to their limited amount, are considere

not relevant for the train design. These results

leveraged the confidence to use the numerically

derived excitation frequencies for this inverter typ

for the later described train design concept.

Excitation Pattern of a LCI

The following example is related to a 16 MW

12-pulse LCI-driven synchronous motor train,

connected to a 50 Hz grid, including intermediate

gear and a single shaft radial compressor. The

train has been designed to operate in a speed

range of 1,260 rpm to 1,890 rpm. In order to get

the required information with regard to relevant

interharmonic excitation the train was equipped

temporarily with strain gauges at the low-speed

coupling for a dynamic torque measurement.

During the measurement program the train was

ramped-up slowly with an acceleration rate of 0.2

up to 0.5 rpm per second. The measured dynamic

torque (blue line) and the motor speed (green

line) are shown versus time in Figure 6. Four main

torsional resonances could be observed. These

resonances correlate with the fundamental TNF an

the expected interharmonic torque excitation of th

6- and 12-order. Based on that result, it means tha

higher orders of interharmonic excitations are not

relevant regarding torsional excitation within this

system.

Figure 4. Trend of motor speed and dynamic torque at

low speed coupling.

Figure 5. Campbell diagram with relevant resonances.

Figure 6. Ramp-up of 16 MW LCI-driven train.


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In the next step it is essential to know what

happens to the torque amplitude by running

in resonance conditions. In order to get an

understanding of the behaviour of the vibration

system, each individually observed resonance was

entered for a period of time. For one example

of these tests see Figure 7. The observed torque

amplitude was generally higher during continuous

operation in contrast to crossing the resonance.However, the maximum torque amplitude achieved

stationary conditions. This information is of

paramount importance with regard to a worst case

operating scenario of the fatigue design of the

train components running in resonance condition

permanently.

For this particular case, the measured torque

amplitudes at torsional resonance condition were

above the expected, based on the state-of-the-art

electro-mechanical simulation. Nevertheless, theapplied service factors considering the simulation

uncertainties ensure that the mechanical train

components are capable of withstanding the

observed dynamic torque amplitudes permanently.

Therefore, the train can be operated without any

operational restrictions.

Comparison of Simulated and Measured Results

Several VSDS driven trains were investigated on

a numerical basis. For some of them, measured

results of dynamic torques are available for

correlation. The analytical investigation is generally

able to identify the relevant interharmonic

excitations. The TNF and the corresponding motor

speed can be determined with satisfactory accuracy.

But nevertheless, based on the authors experience

of correlating results of various simulated and

observed torsional turbomachinery systems, the

peak torque amplitude in the state of resonance

condition cannot be predicted with sufficient

accuracy in order to carry out a fatigue analysis on a

numerical basis only. Therefore, it can be concluded

that further uncertainties exist in the electrical

and also in the mechanical model. To compensate

for these uncertainties the service factors are

conservatively selected. This guarantees safe design

while accepting the drawback of over-engineering.

For an accurate prediction of the occurring dynamic

torque in the train elements, the magnitude of

torque excitations including realistic tolerances areessential. Further investigations and improvements

of the electro-mechanical simulation model are of

course an ongoing task.

Experience with Interaction of Torsional

and Lateral Vibrations

For trains including an intermediate gear and/or for

trains with an integrally geared type compressor,

the torsional and lateral vibration system are

coupled in movement via the gear mesh. In such

a case, the lateral vibration spectrum may also

present frequency components of the torsional

excitation frequency.

Higher lateral vibrations were observed in the field

with trains featuring gears. This kind of observation

is not only reflected by the authors’ experience, but

is also published in other literature sources (Kita, et

al., 2008), (Naldi, et al., 2008).

At a first glance it seems to be plausible that

high torque fluctuation also produces high lateral

vibrations. This is the reason why only concerns

regarding high dynamic torques are raised, when

high lateral gear shaft vibrations are also evident.

In contrast, cases could also be observed where

high torque fluctuations were measured, although

only insignificant lateral vibrations of the gear

pinion and/or the bull gear could be seen. Having

the physical relationships in mind, this issue boils

down to the influence of the dynamic oil film

stiffness of the gear bearings.

Generalized, one can only conclude that if

TNFs can be measured in the lateral vibration

spectrum, dynamic torque oscillation will, with highprobability, be present in the train. However, low

levels of radial vibrations do not necessarily mean

low levels of dynamic torque fluctuation in the train

components.

White noise excitation

Harmonic, inter-harmonic and control loop torque

disturbances form the group of single frequency

excitation mechanisms. These are widely considered

the main issue related to VFDs, but recently two

Figure 7. Stationary operation in resonance of 16 MW

LCI-driven train.


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cases of VFD compressor train torsional vibration

were published, which were connected with white

noise excitation (Kocur and Muench, 2011). This

made it necessary for the involved parties to

rethink the strategy for torsional analysis, including

the system response to banded Gaussian white

noise into the scope. The authors cannot give a

recommendation in this matter, since they have

never experienced a case of torsional vibration

related to white noise, simulated or practical, with

their equipment so far.

Conventional Strategies of Dealing

With Interharmonic ExcitationIf a resonance with an interharmonic excitation is

detected and countermeasures are found to be

necessary, one can today choose from a wide range

of proven alternatives. These can be sorted into one

of the following categories:

• Damping increase

• Excitation reduction

• Torque transmitting component fatiguecapability increase

• Resonance avoidance

What follows, they are presented and discussed

with their inherent advantages and disadvantages

to give an overview.

Inverter Control Setup

Although the basic root cause was not exactly thesame in all of the case study papers mentioned in

the introduction, for all of these cases modifications

of the setup of the inverter control or inverter

control type change finally reduced the excitation

torque amplitudes sufficiently. De la Roche and

Howes (2005) describe the case of a motor-

driven reciprocating compressor with motor shaft

failure on one of two trains. For the first train,

inverter software parameter change was able to

increase, as well as satisfyingly decrease the torque

oscillations. They and Corcoran and Kocur (2008)

as well, mention the speed feedback into theinverter control to be a contributing factor to the

overall vibration. It is considered able to amplify

the oscillation, when the speed control counteracts

the speed fluctuation initiated by the torsional

vibration.

When torsional vibration is present, it is

adequate to first exhaust the remaining room

for improvement in the inverter control for

optimization.

Designing Components Robust Enough to

Withstand Torque Ripples

According to the applicable paragraphs of API617

7th edition, if excitation mechanisms are known

to act in a compressor train, the train responsible

party shall conduct a stress analysis. This shall show

permissible amplitudes compared to high cycle

fatigue capabilities of the train components. Itwould be therefore satisfying to design the relevan

train components in such a way that they can

withstand the occurring dynamic torsional load ov

the train’s lifetime. The benefit for the operator

is that the train can be operated with the whole

speed range specified, although resonances are

present only at certain speeds.

Necessarily, the dynamic torque amplitude must

be known from torque measurement records, or

it must be sufficiently and accurately predicted

by torsional analysis. Independently, whether the

simulation model is a harmonic forced response

simulation or a coupled electrical/mechanical

simulation, both deliver the dynamic torque

response within the train elements of interest at th

detected resonant conditions. These results vitally

depend on the damping assumption made in the

analysis and the accuracy of the expected dynamic

air gap torque excitation magnitude. If uncertainti

regarding the above aspects are present, service

factors need to be conservatively defined. From th

authors’ point of view, there is still some need for

refinement of simulation models. It promises for tfuture service factors to be reduced to appropriate

figures, thus preventing over engineering.

Individual Exclusion Speed Ranges at

Resonance Condition

The torsional resonances described before can

also be avoided by using individual exclusion

ranges. It is practicable to determine resonances

of relevance, i.e. with a dynamic torque amplitude

probable to exceed a component’s high cycle

fatigue capability, by torque measurement at

the manufacturers test bed facilities or duringcommissioning. The countermeasure is then to

implement the identified resonant motor speeds

into the inverter speed control. These speeds,

plus a separation margin including tolerances and

uncertainties, are blocked. It is by this, of course,

not possible to exclude resonances from the speed

range, but it limits the time of operation within to

a minimum. In a variable speed performance map,

blocked speed ranges can be illustrated as the are


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shown in Figure 8. It must be clear that for the plant

operator, a blocked speed range, even if it is small,

always is a limitation of production flexibility.

Using individual exclusion ranges seems to be a

simple and effective solution. However, a lot ofparameters and uncertainties have to be born in

mind by setting the real problem solving exclusion

speed ranges.

For one single train installed, these include the

accuracy of the dynamic torque measurement itself,

changing of material properties over life cycle and/

or due to temperature and local grid frequency

variation, just to name few. The last parameter

can, especially in countries with high grid frequency

fluctuation, become the decisive parameter for the

blocked speed range. It would necessarily increase,unless the grid frequency was considered in a speed

control algorithm as an additional parameter, which

is possible.

In case of multiple identical trains installed, efforts

increase. If a torsional measurement is going to

be done for one train only, it should be critically

discussed, how material property uncertainties

between the train components are reflected in the

determination of the blocked speed range(s).

Damping in Control Loop

Active damping of the load or the process using

the VFD is standard in some industries. Also for

compressor strings there are approaches to use

the VFD for active damping (Naldi, et al., 2008).

The challenge for the compressor trains is the low

frequency of the switching devices and the limits

of the specific topologies. Another challenge is the

identification of the train characteristic. The control

loop needs as input parameter the actual status of

the train. Therefore, additional sensors are most

likely needed.

The conventional multi parameter control system

of an inverter is extended by an additional damping

control loop. This feature should be considered

in detail during engineering and also during the

commissioning process in order to achieve a reliable

operation. As long as additional sensors need tobe installed and are crucial for the functionality,

redundancy is essential.

Damper Coupling using Elastomeric Elements

Occurring torque response in resonance condition

is mainly determined by the magnitude of the

torque excitation and the mechanical amplification.

Therefore, torsional damping is a significant

influence parameter for the overall system.

Couplings consisting of a steel structure combined

with integrated elastomeric elements are used

as common dampening device. The main task ofthese elastomeric elements is to absorb torsional

vibration energy by compressed deformation of

the elements in contrast to solid steel couplings.

It is of utmost importance that this coupling be

located close to the node of the mode shape of the

fundamental TNF to be most effective in increasing

system damping. As a consequence of the material

properties, the rubber elements degrade over time

due to heating up and environmental factors. The

main disadvantage of this kind of coupling is usually

increased maintenance for reliable operation,

in contrast to solid steel couplings. Due to thisfact, elastomeric couplings are principally not

allowed per specification of the operators for some

applications.

The authors are convinced that using such kind of

coupling may help to limit the torque amplitude

during crossing resonances for a short period

of time. However, for VSDS-driven trains it may

happen that the train is running in condition

of a torsional resonance for a longer period.

If amplitudes are excessively high, running in

resonance condition for a longer period mayoverload the elastomeric elements. Coupling

failure in a VSDS-driven train are, in most cases,

not necessarily caused by a poor coupling capability,

but are quite often caused by the train behaviour

itself (Corcoran and Kocur, 2008).

Figure 8. Blocked speed ranges in a performance map.


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New Train Design Concept to

Avoid Interharmonics in Operating

Speed RangeBasis of the New Train Design Concept

In principle, the basis of the new train design

concept to avoid interharmonics within the

operating speed range is an in-depth understanding

of inverter behavior, motor design and finally,the various compressor train configurations and

their corresponding torsional behavior. First of

all, it is essential to work out the details of the

mechanically relevant torsional excitations caused

by the individual inverter types. This task has

been done on a numerical basis by simulating the

electrical and mechanical system. Due to the fact

that the occurring torque amplitude in a state of

resonance condition is connected with tolerances,

although using state-of-the-art coupled electrical

and mechanical simulation models, correlation

with dynamic torque measurements are of vital

importance. This is to separate the relevant

exc

insights winter 15 16

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