Activities on AC Motors in 2007

Measurements on AC Motors in 2007June to Nov 2007

Power Electronics and Electrical Drives

Ernst SchimanekConsultant Engineerwww.ingenieurbuero-schimanek.com

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Peak voltage on AC-Motors / June to November 2007


Ernst Schimanek Consultant Engineer



- General discription of the physical effects

- Summary of the taken peak voltage measurements on site

- Summary of Partial Discharge Inception Voltage

- Recommendations

Table of contents

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Fast switching elements in conjunction with long motor cableslead to voltage stress of the winding insulation of the motor.The measurements should give an overview of the actual situationin terms of peak voltages at motor and inverter side.

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VVvoltagepeak 9762690_ ==

690Vrms

VVvoltagelinkdc 93035,1690_ ==

976V without load

930Vdc

930V with load

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Vvoltagelinkdc 930_ =

930Vdc

930V with load

690V operating voltage


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930Vdc



appr. 2kVpeak

Motor

DC-link-voltage

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Sketch of motor-winding

Uniform voltage distributionalong the turns of a windingif the motor is fed withline frequency voltage

Non-uniform voltage distributionalong the turns of a windingif the motor is inverter fed.This can cause PD in the insulationsystem of the first turn of the winding

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Electrical treeing within an organic isolation material due to PD

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Peak Voltage measurements on AC-Drives were taken

Chirag1 Top Drive in April 2007

West Azeri Central Azeri All Drives in July August 2007 East Azeri

Partial Discharge measurements on AC-Motors were taken

at Bentec in October 2007on various motors

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dv/dt peakvoltage

DC-link voltage

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Top Drive peak voltage at motor terminals - initial incoming voltage 720Vac

dv/dt = 4kV/1,85s = 2,2kV/s

peak voltage = 1.96kV DC-link voltage = 1010V

Central Azeri

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Central AzeriTop Drive voltage at motor terminals - reduced incoming voltage 700V

dv/dt = 4kV/1,85s = 2,2kV/s

peak voltage = 1.84kV

DC-link voltage = 940V

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Short on and off times lead to a higher peak voltage as seen at WA Cement pumps ABB ACS 600 Paramterer Lang Distance Mode= OFF

dv/dt = 4kV/0,64s = 6,3kV/sWA_pvfCem Pump_2_mot = 2,1

peak voltage = 2,05kV

DC-link voltage = 980V

Voltage phaseto phase

voltage phaseto ground

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Discharge within the motor during the first minutes of operation!

peak voltage = 2,17kV

voltage phaseto phase

voltage phaseto ground

EA_pvfCem-P1-mot = 2,2

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The theoretical peak voltage at the motor terminalsis 2 times the DC-link voltage (if no filters are between inverter and motor)

The DC-link voltage varies with the load of the DC-bus.The measurements are taken with different DC-load conditions.To have a possibility to compare of the measurement results, a peak voltage factor is introduced.

peak voltage factor = peak voltage / DC-link voltage

Discussion of voltage peaks

The overvoltage factor is constant for a certain configuration of - specific dv/dt- cable length- type of cable- maybe connections of cable shield to ground- etc

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Central Azeri PVF

0,00,20,40,60,81,01,21,41,61,82,0

Top D

rive

Draw

works

1Dr

awwo

rks 2

Mud P

ump 1

AMu

d Pum

p 1B

Mud P

ump 2

AMu

d Pum

p 2B

Mud P

ump 3

AMu

d Pum

p 3B

Ceme

nt Pu

mp 1

Ceme

nt Pu

mp 2

CRI P

ump

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PVF-motPVF-inv

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West Azeri PVF

0

0,5

1

1,5

2

Top D

rive

Draw

works

ADr

awwo

rks B

Mud P

ump 1

AMu

d Pum

p 1B

Mud P

ump 2

AMu

d Pum

p 2B

Mud P

ump 3

AMu

d Pum

p 3B

Ceme

nt Pu

mp 1

Ceme

nt Pu

mp 2

CRI P

ump

p

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PVF-motPVF-inv

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East Azeri PVF

0

0,5

1

1,5

2

Top D

rive A

Top D

rive B

Draw

works

ADr

awwo

rks B

Mud P

ump 1

AMu

d Pum

p 1B

Mud P

ump 2

AMu

d Pum

p 2B

Mud P

ump 3

AMu

d Pum

p 3B

Ceme

nt Pu

mp 1

Ceme

nt Pu

mp 2

CRI P

ump

p

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PVF-motPVF-inv

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Partial Discharge Inception Voltage measurement in Bad Bentheimwith two methods of measurement

Sinusoidal voltage 50Hz

Surge voltagewith a dv/dt of about 5kV/srepitition rate of 8Hz

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Result of measurement

0

500

1000

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5000

General electric/ GEB20B2 TT

04030034

General electric/ GEB22 TT02080110

General electric/ GEB22-1

BP98030009

General electric/ GEB20B3

VV07010007

Bentec / 711490

Reliance / DL2814

*ATP / 47139002

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PDIV sine 19C/58%PDIV sine 28C/35%PDIV pulse 19C/58%PDIV pulse 28C/35%IR 19C/58%IR 28C/35%

max.voltage phase to ground

max. voltage phase to phase

**

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Recommendation- Parameter Long Distance mode ON on all ABB Drives to avoid short off-times

- Polution in conjunction with high humidity leads to surface dischargeinside the motor

- avoidance of pollution inside the motor keeps the IR at high values

- Motors with round wire windings like the Reliance motors on Chirag1 must beimproved in terms of PDIV otherwise these motors will fail again after a short periode of time

- GEB20/22 motors should withstand the high voltages in general. If possiblean online PD measurement should be taken to ensure that there is no PD in normal operation.

Documents

Activities on AC Motors in 2007