case study 2 - cruise ship scrubber project

SPECIALISTS IN ELECTRO-MECHANICS

A R M A T U R E E L E C T R I C L I M I T E D

100 – 3811 NORTH FRASER WAY, BURNABY, BRITISH COLUMBIA, V5J 5J2

Tel: 604-879-6141 Fax: 604-879-6974

Toll Free: 1-800-539-3556 Toll Free Fax: 877-879-6974

Service Report

Installation of Cool Blue Inductive Absorbers

5 x 300KW & 3 x 66KW VFD’s

Scrubber Project

Performed on September 26th 2016

Service Report – Cool Blue Inductive Absorber Installation for Scrubber

Project (Cont’d)

Overview

AC Motor Drive systems utilizing variable frequency controls produce high

frequency electrical noise. The noise is superimposed on the power drive lines

of the motors in the form of common mode noise. The common mode noise

creates a voltage (dv/dt) across the rotor/stator of the motor resulting in a

discharge current through the lubrication and motor bearings to the motor

raceway, and into the ground system.

A prominent cruise liner contacted us regarding issues on board since installing

a new Scrubber system. Upon commissioning of the variable frequency drives,

they experienced some disturbances on some mA sensor lines and

communications errors on nearby equipment.

We recommended installing Cool Blue Inductive Absorbers to reduce the

common mode noise that could be disturbing the nearby equipment.

Inductive absorption is an electrical solution whereas inductive components are

placed over the drive cables to absorb the transient voltage and common mode

currents. The inductive components need to have high permeability, high

saturation, and low power loss. They do not affect the symmetrical power

currents but efficiently dampen the asymmetrical EMI noise currents. This

creates a common mode choke.


Project (Cont’d)

Installation & Results

1FC1

Using a Rogowski Coil and Oscilloscope, the common mode currents were measured. Using

a piece of wire run through the main chokes, we are able to defeat the chokes to simulate the

currents before the chokes were installed. The Rogowski coil’s output is 50mV=1A. With the

scope set to 5V per division on 10x scale we can see current peaks of 25 Amps before and

after we have a steady current of 4-6 Amps. Note that the overshoots are a lot less erratic

than before. We have reduced this noise to 20-25% of the original.


Project (Cont’d)

2FC1

Here we see similar results. With the chokes defeated we see many overshoots just over 20

Amps, with one off the scale over 40 Amps. With the Cool Blue’s installed we see a constant

of around 5 Amps, with just one overshoot at around 10 Amps. Overall current is reduced to

25% of original.


Project (Cont’d)

3FC1

The leads were too short on this unit to fit all 4 chokes under the bus bar. 2 were installed

above the bus bar to accommodate all the chokes and line absorbers required.

Because the chokes were split into 2 pairs before and after the bus bar, it was difficult to

defeat the chokes properly to show the full common mode current before they were installed.

What we see here is 2 out of 4 chokes defeated on the left, meaning there were still 2 chokes

absorbing common mode currents. So, while it doesn’t seem that there is much change, there

most likely was similar amounts of currents present as the other units before the chokes were

installed. The current readings with the cool blues installed are steady around 6 Amps.


Project (Cont’d)

4FC1

Here we see quite a few overshoots above 30 Amps with the chokes defeated. Afterwards,

we see a steady current of 7.5 Amps. Again, current is reduced to 25% of original.


Project (Cont’d)

5FC1

The ship was unable to run 5FC1 while we were on board, however below is a picture that

was taken during the initial meeting between us and the customer on September 11th 2016.

Currents measured were quite significant, with some overshoots above 40 Amps, and we can

see one in this picture above 60 Amps. Based on our experience, and the results measured

from the other units on this ship, we expect that these currents were reduced to approximately

25% of original values.


Project (Cont’d)

13FC1

For the (3) 66KW units, motor Cables were extended inside the VFD cabinet to

accommodate the cool blue inductive absorbers.

With the chokes defeated, observed common mode currents peaked over 16 Amps. With

Cool Blue’s installed, we saw a steady current just below 4 Amps, with an occasional

overshoot around 8 Amps. Overall, currents were reduced to 25% of original.


Project (Cont’d)

13FC2


Cool Blue’s installed, we saw a steady current of 4 Amps. Overall, currents were reduced to

25% of original.


Project (Cont’d)

13FC3


Cool Blue’s installed, we saw a steady current of 4 Amps. Overall, currents were reduced to

25% of original.


Project (Cont’d)

Summary

After installing Cool Blue Inductive Absorbers with NALA Differential Line

Absorbers on the Scrubber VFD’s, we consistently observed reduction in

common mode currents to 25% of original levels. This reduction should be

enough to mitigate the disturbances and communication errors previously

experienced since the scrubber system installation.

End of Report

case study 2 - cruise ship scrubber project

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