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Power equipment center application guideE50001-F710-A394-X-4A00

Definition

A PEC is a prefabricated, modular electrical/instrument enclosure. As a self-contained unit, it is a completely assembled enclosure manufactured entirely at the factory. The most common designs employ self-framing interlocking wall and roof panels attached to a structural steel base.

Equipment enclosed within a PEC can include:

Low- and medium-voltage switchgear

High-voltage gas-insulated switchgear (GIS)

Low- and medium-voltage motor control centers

Protective relay panels

Remote terminal units

Instrument control panels

Distributed control systems

Heat trace panels

Uninterruptible power supply systems

Supervisory control and data systems.

Power equipment center application guide

Introduction

For many years, the petrochemical industry has utilized power equipment centers (PECs) to house electrical equipment. Many utility and industrial customers are now utilizing PECs for their equipment as well. This document explains the benefits of PECs and compares them to conventional site-built technology for housing outdoor electrical equipment.

The Siemens PPS facility has been manufacturing PECs since 1988 with installations across many industries.

Figure 1: Modular

PEC enclosures

Figure 2: Typical wall, roof and ceiling panel

for Siemens interlocking panel

(type SIP) PEC

16” (406 mm)

2.9” (74 mm)

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A PEC is designed and manufactured in accordance with a number of rigorous industry standards. Additionally, a PEC must be built to comply with local building codes.

A partial list of industry standards met by PECs built by Siemens:

ASCE/SEI 7-05 - Minimum Design Loads for Buildings and Other Structures

NFPA 70 - National Electrical Code®

AWS D1.1 - Structural Welding Code

ASTM A-525 - Standard Specification for Sheet Steel with Galvanized Coating to G90 Standards

ASTM A36 - Standard Specification for Carbon Structural Steel

AISC Manual of Steel Construction Allowable Stress Design

IBC - International Building Code.

Standards

Figure 2: Typical Siemens interlocking panel (SIP) PEC construction detail

A

C

D

E

Item Description

A Roof trim

BWeatherproof interlocking

panels

C Polycarbonate viewing window

D Panic bar hardware for safety

E 1/4”(6 mm) floor plate

FStructural steel support; sized

for weight and strength

G C-channel supports

H Perimeter base

I Interior wall liner

J 3” (76 mm) insulating space

KInterior interlocking ceiling

panels

B

B

F

GH

I

J

K

3

Roof system

Roof panels are typically constructed from 18-gauge minimum, powder coated, galvanized steel (G90) that are formed to provide an interlocking system. Roof panels are supplied in a single continuous length from eave line to ridgeline and designed for 30 psf loading. Higher roof loads can be achieved as required.

Roof structures can also be designed for roof mounted HVAC units, entrance bushings and overhead bus supports.

Figure 4: Roof - section view through the top wall cap provides a typical roof and ceiling section view detail.

Wall system

Wall panels are typically constructed from 18-gauge minimum, powder coated, galvanized steel that are formed into an interlocking system. Interlocking 3” (76 mm) exterior wall panels are arranged on 16” (406 mm) centers and provide 90 MPH allowable wind loading. Higher wind load ratings can be provided as required.

Interior wall liners and various insulation levels can also be provided.

Figure 5: Section view through an insulated wall and Figure 6: Typical wall-floor connection on page 5 reveal construction details of the interlocking wall and the connection of these walls to the PEC floor.

Construction

Base structure

The steel supporting skid is fabricated from standard AISC shapes using ASTM A36 steel. Provisions are made for lifting the PEC for shipping and erection. The floor plate is ASTM A36 material and is typically designed for 250 pounds per square foot (psf) loading. All structural framing members are cleaned by metal-bead blasting and then painted with a protective coating. The PEC base is typically structural steel perimeter members rigidly braced with structural steel cross-members for installation on a concrete foundation or piers.

Figure 3: Typical skid construction details depicts such a base design.

Figure 3: Typical skid construction details

A

Item Description

A Appropriately sized and spaced cross members

B Appropriately sized and spaced supports

C Appropriately sized perimeter channel

D 1/4” (6 mm) plate

E Lift point

B

CD

D

E E

Length

Width

Figure 4: Roof - section view through the top wall cap

Item Description Item Description

A Fascia E Sloped roof panels

B Top and bottom skip weld F Ceiling panel

C #14 Tek screws G Drip shield

D Wall panel H12-gauge galvanized wall cap

roof and ceiling support

AAC

B

B

D D

C

G

E

F

H H

4

Other construction features

Typically, PECs are provided with interior and exterior lighting, heating, ventilation and duplex receptacles.

PECs can also be provided with air conditioning, humidity control and pressurization/purge systems (NFPA 496).

Additionally, most features available in a site-built facility are available in a PEC; including offices, bathrooms, communications rooms and battery rooms.

Figure 7: Typical PEC equipment layout including lighting on page 6 illustrates some of these details.

Resistance to environments

The interlocking panel design provides a barrier against water entering the PEC by providing two 90° bends at seams between the exterior and interior walls of the PEC. Additional weatherproofing is also provided to ensure enclosure integrity.

After assembly of the wall system, all seams are sealed with an industrial grade silicone sealant. Roof sealing putty is used at all wall-to-roof joints and at joints on peaked-roof enclosures. All roof panels are also individually sealed with silicone sealant.

The paint system consists of surface preparation, primer on the base steel, underside coatings, finish paint or coatings and sealant. The finish coat on base steel is typically epoxy-based. For wall, ceiling and roof steel, an electrostatically applied and thermally set polyester powder coat finish is used. Each provides outstanding resistance to chemicals, moisture and abrasion.

These coatings are highly resistant to the deteriorating effects of many acids, alkalis, solvents, greases, oils and other active chemicals. Other coating systems can also be considered.

The resulting enclosure can be designed for extreme ambient temperature and humid environments, ranging from minus 40 °C to 50 °C, while allowing the use of lower cost indoor types of switchgear and electronic equipment.

Grounding system

The PEC is furnished complete with suitable factory installed grounding provisions. Through appropriately sized ground buses and bonding jumpers, all electrical equipment enclosure frames and ground buses are in turn bonded to the building frame. Four two-hole ground pads are provided, with one located at each corner of the PEC exterior. Two of the ground pads are bonded to the interior ground bus.

A separate ”quiet” or isolated instrument ground bus can also be provided.

Figure 5: Section view through an insulated wall Figure 6: Typical wall-floor connection

Item Description

A 3” (76 mm) fiberglass insulation

B Inner wall

C All seams silicone sealed

D Outside of interlocking wall panels

E #14 Tek screws

A

32” (813 mm)

B

C D E

E

3” (76 mm)

Item Description

A Interior wall

B1/4” (6 mm) floor plate

C Perimeter channel

D #14 Tek screws

D

A

B

C

3” (76 mm)

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PEC application benefits

One of the significant advantages of the PEC alternative is minimal field erection and commissioning time and expense. All equipment is interconnected and tested before shipment from the factory, including switchgear, DCS systems, power panels, heat trace panels, lighting panels, HVAC and battery systems. In the case of conventional buildings, the purchaser or contractor must coordinate and provide field labor to install, interconnect and test all equipment on site.

With the PEC option, a major part of the engineering, drafting and coordination is transferred to the PEC manufacturer under one purchase order early in the project. Whereas, even a small site-built facility has all the elements of a major project requiring project management and coordination. Furthermore, for a conventional building project, a series of purchase orders will be required that can complicate the coordination effort. Numerous meetings for evaluation, review and coordination are necessary, and require additional allocation of the purchaser’s resources.

Engineering, fabrication and planning can proceed while waiting for equipment arrival at the PEC manufacturer’s location. Experience has shown that up to four times the man-hours must be allotted for site equipment installation because of the additional work done in the field, in contrast to a PEC which arrives complete, pre-tested and ready for installation.

PECs can be installed on field erected piers which allows for them to be elevated to avoid flooding ‒ an advantage for installations near bodies of water or rivers. Having the PEC located on piers also provides the ability to install cable tray and bus duct systems below the building without the need for ground excavation. PECs can also be relocated and are not considered permanent structures as conventional buildings are.

With a site-built facility, commercial warranties may be affected by staggered lead times that do not run concurrently with the overall system commissioning date.

Applications

Application of a PEC is usually compared with conventional outdoor electrical/instrument enclosures such as concrete block facilities and sheltered-aisle switchgear. Evaluation is centered on the issues of effective application, initial installation costs and total life cycle costs.

Specific construction and procurement factors provide the basis for a more detailed technical and commercial comparison of alternatives.

PEC vs. conventional building

PECs are primarily used in applications that have traditionally favored electrical rooms constructed at the site utilizing conventional construction techniques. Table 1: Comparison of PECs and conventional site-built enclosures on page 8 elaborates the advantages of a PEC compared to the most common alternative, a concrete block building.

Item Description

A 10” (254 mm)

B 4’ (1.2 m)

C 7’ (2.1 m)

D Light

EMedium-voltage

switchgear

F 15” (381 mm)

G 3’ (914 mm)

H Fire extinguisher

I Electric unit heater

JUtility transformer (transformer and

panel)

K 8” (203 mm)

L 2’ (610 mm)

M 14’ (4 m)

D

Figure 7: Typical PEC equipment layout including lighting

D D D D

D

D

D

E

H I

J

Rear access

31’ (9.4 m)

9’ (2.7 m) auxiliary equipment area

A

G

K

L

M

F G G G G G G G

A

B

C

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PEC vs. NEMA type 3R sheltered-aisle enclosure

Most major switchgear suppliers, including Siemens, offer a line of sheltered aisle in single-row or double-row arrangements that typically comply with NEMA 3R requirements for outdoor installation.

Single-row installations consist of a lineup of outdoor switchgear adjacent to a weatherproof walk-in aisle. The overall design provides weather protection and good economy of space, but is limited in application flexibility and room for auxiliary equipment.

Table 2: Comparison of PECs and NEMA 3R sheltered-aisle switchgear on page 9 provides a more detailed comparison of PEC construction and application as an alternative to NEMA 3R sheltered-aisle switchgear enclosures.

Additionally, a PEC provides superior weather protection and can be insulated and air conditioned to protect sensitive electronic equipment. Sheltered-aisle switchgear is limited to the type of non-switchgear equipment that can be housed in the enclosure.

PEC and high-voltage switchgear

Through the use of SF6 gas-insulated switchgear, a PEC can also be used for housing primary (transmission and substation) switchgear. A double-feed station, or H configuration can be housed in a single PEC. This configuration provides enormous space savings, higher reliability and less maintenance than a typical air-insulated substation. All the advantages of a PEC (single-point engineering, procurement, fabrication and testing) are applicable to high-voltage switchgear. In combination with a secondary switchgear PEC, an entire substation could consist of two PECs and transformers.

Special applications

PECs can be designed for high-wind loading (up to 150 mi/h), seismic zone 4 applications and high-snow loading. Fireproofing can be installed on exterior walls to protect switchgear from transformer failures. Special exterior finishes can be provided to better integrate a PEC with the surrounding environment. To eliminate additional facilities, options such as offices, battery rooms, bathrooms or maintenance rooms, can be added within a PEC.

With most PEC installations, the warranty period for all the equipment inside the PEC will last for a predetermined number of months after shipment from the PEC manufacturer or from time of commissioning, whichever occurs first.

Also, shipping time differs for each type of electrical equipment being installed. The total shipping time for PECs is only four to six weeks longer than for individually procured indoor equipment of the same type.

Finally, the sum of individual equipment prices is not typically as low as equipment purchased as a package from a single supplier.

Buying integrated PEC systems from one supplier in lieu of the conventional “Built on site” type of buildings can result in coordination simplicity, application flexibility, cost savings, quicker delivery and installation.

Figure 8: Type Siemens interlocking panel (SIP) PEC with HVAC system

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Table 1: Comparison of PECs and conventional site-built enclosures

Feature PEC Conventional site-built construction

Major electrical equipment Same Same

SourcingManufacturer responsible for all equipment inside the

PECSeparate solicitation, analysis (and often) sourcing of switchgear, building, battery systems, bus duct, etc.

Design engineeringComplete package designed and engineered by

manufacturerPurchaser must design and engineer

ConstructionVariety of materials, depending on application

environment and structural requirements including galvanized steel, stainless steel and aluminum

Typically concrete block

Foundation Minimum foundation (for example, curb or pier type)Requires full slab foundation with relatively large

stem walls and footings

BaseSelf-supporting; allowing all equipment to be factory

leveled before shipmentPurchaser provides channel base and grouting for

leveling all equipment

AccessCan be provided with hinged switchgear doors in rear

for access to terminations (rear aisle inside PEC not required)

Must be 25 percent to 40 percent larger than an equivalent PEC to permit access to switchgear bus

area and terminations

Internal wiring Factory wired complete with wiring schematicsJobsite interconnection of control wiring in addition

to major equipment

Main bus Coordinated by manufacturerPurchaser coordinates the match up of main buses for

different types of equipment

Bus duct from transformers Checked for ease of assemblyPurchaser coordinates and assembles bus to

switchgear in field for first time

Grounding system Integral to PEC Must be planned and built into foundation

External connectionsEasily adaptable to overhead or underground conduit

systemsSlab floor mandates detailed and exact conduit

location; changes are difficult

TestingPEC is factory tested; customer can complete many pre-energization tests before installation. Witness

testing can be performed at one location.

Each type of equipment is tested at different factories. Witness testing requires more time and

travel.

ChangesChanges can be made after functional testing and

inspection in a controlled factory environmentRequires coordination among various trades, often

after initial construction is complete

Receiving, handling and storageArrives ready for installation or secure storage with

minimal preparation

Purchaser must provide for receiving and storing of material and equipment at different times by different suppliers. Often this involves redundant handling for storage, truck to intermediate locations and requires storage to protect from weather, pilferage and other

loss.

Installation Involves minimum number of craftsRequires multiple crafts (for example, carpenters,

ironworkers, cement finishers, bricklayers, electricians - all with foremen and helpers)

ExpansionModular construction results in convenient

expandability as system growsSpace for expansion must be included in initial

installation

Commercial Typically taxed same as weatherproof equipment1

Treated as real estate improvement necessitating higher tax schedule, permits, progress inspections,

bonding and insurance1

Footnotes:1. This is an illustration and does not constitute

tax or legal advice. Please contact a qualified tax consultant to confirm tax treatment of a PEC in your area.

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Table 2: Comparison of PECs and NEMA 3R sheltered-aisle switchgear

Feature PEC Shelter-aisle switchgear

Major electrical equipment Same Same

SourcingManufacturer responsible for all equipment inside the

PEC and PEC can accommodate various types of electrical equipment

Separate enclosure must be sourced for each type of electrical equipment

Design engineeringComplete package designed and engineered by

manufacturerPurchaser must design and engineer

ConstructionVariety of materials, depending on application

environment and structural requirementsTypically manufacturer’s standard steel construction,

paint and finish

Foundation Minimum foundation (for example, curb or pier type) Same

BaseSelf-supporting; allowing all equipment to be factory

leveled before shipmentPurchaser provides level foundation or piers and

grouting for leveling all equipment

Internal wiring Factory wired complete with wiring schematicsJobsite interconnection of control wiring in addition

to major equipment

Main bus interconnections Coordinated by manufacturer Purchaser completes in field at every shipping section

External connectionsEasily adaptable to overhead or underground conduit

systems

Slab foundations require exact conduit location making changes difficult. Not suitable for overhead

tray installations.

TestingPEC is factory tested; customer can complete many pre-energization tests before installation. Witness

testing can be performed at one location.

All field reconnections require retesting by field personnel

Receiving, handling and storageArrives ready for installation or secure storage with

minimal preparation

Purchaser must provide for receiving and storing of multiple pieces requiring re-assembly. Often involves

redundant handling for storage, trucking to intermediate locations, and protection during storage from pilferage, other loss or lost time due to weather.

Installation Involves minimum number of craftsNEMA 3R construction must be field assembled or

connected to shipping groups

Transom

24’ (7.3 m)

15’ (4.6 m)

75’ (22.9 m)12.7’

(3.9 m)

Shipping limited based on combination of:

Length

Width

Height

Destination.

Dimensions in feet (meters).

Larger sizes available. Consult factory.

4080 Door HVAC

Figure 9: PEC dimensions

9

Summary

A PEC provides the end user with a self- contained, pre-engineered, prefabricated solution to enclosing various forms of equipment, such as switchgear, auxiliary electrical equipment, instrument/control panels, DCS systems, heat trace panels and UPS systems.

Of particular significance is:

The ability to provide rugged, reliable enclosure construction in accordance with established standards

The ability to acquire the complete outdoor electric/instrument equipment package from a single supplier with design and engineering responsibility

The ability to provide complete pre-delivery interconnection and testing, to include switchgear control wiring, lighting transformers, power panels, lighting panels, lighting fixtures, receptacles, exterior lighting, batteries and chargers.

Modular construction from interlocking materials contributes to flexibility as well as cost effectiveness. PECs are designed to reduce engineering, procurement and field costs as compared to other enclosure technologies, without decreasing reliability, maintainability or performance.

Siemens provides a single-source solution for PEC and electrical equipment requirements. No other PEC manufacturer has the range of products and application experience that Siemens can deliver.

The solution

A key advantage of the PEC is the flexibility to provide a variety of equipment (switchgear, relay panels, RTU, supervisory control and battery systems, data logging, event recorders, etc.) installed and interconnected in the same enclosure.

Figure 10: Type Siemens crimp plate (SCP)

10

Figure 11: Sketch area

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Published by and copyright © 2011:Siemens AGEnergy SectorFreyeslebenstrasse 191058 Erlangen, Germany

Siemens Energy, Inc.6510 Bourgeois RoadHouston, TX 77066-3111, USA

For more information, please contact: Phone: +1 (281) 444-1200Toll-free: +1 (800) 347-6659www.usa.siemens.com/energy

Order No. E50001-F710-A394-X-4A00Printed in USATB 2494T BR 0911.2

All rights reserved. Trademarks mentioned in this document are the property of Siemens AG, its affiliates, or their respective owners.

Subject to change without prior notice. The information in this document contains general descriptions of the technical options available, which may not apply in all cases. The required technical options should therefore be specified in the contract.