Locating Winding Insulation Defects in Large Electrical Machines

Dragana Popovic Renella & Marjan Blagojevic

CWIEME 5th June 2013, Berlin

Outline

• Magnetic Measurement Instruments

• Current Sensors

• Insulation Defect Locator

• Outlook

5/23/13 2

Digital Teslameter / Gaussmeter

5/23/13 3

• Integrated 3-axis Hall Probe • Very high resolution: 1ppm • Accuracy: 0.001% • High f-bandwidth • High temperature stability

Applications

5/23/13 4

• Magnetic Field Mapping, e.g. in Particle Accelerators • Characterization of Permanent Magnets

Application: Monitoring Electrical Machines

5/23/13 5

Detecting rotor winding shorted through measurement of: • Main Rotor magnetic field • Stator Reaction magnetic field • Rotor Slot Leakage magnetic field • Air-gap magnetic field

6/10/2013 6

SENIS’ Teslameter

reso

lutio

n &

acc

urac

y (p

pm)

field (T) *Luca Bottura of CERN; Revised by SENIS 2011

Magnetic Measurement Technologies

5/23/13 7

Current Sensing using Magnetic Field

Application: Current Sensors

5/23/13 8

I = 0.2A …10A

B I

I = 200A …3000A

5/23/13 9

Application: Clamp-On MicroAmmeter

Key Features ▪ Measurement range ± 100mA (100μT)

▪ Offset Drift IOF,RMS< 10μA (10nT)

▪ Sensitivity 100V/A (100’000V/T)

▪ Withstanding voltage 50kV

▪ Jaw opening Ø50mm

SENIS Hall sensor inside

5/23/13 10

Application: Insulation Defect Locator

IDL – Theoretical background

Typical current stator slot cross section

IDL – Theoretical background

Predicted diagram of leakage current based on simplified schematic diagram. Current limit for controllable high voltage source is about 15mA.

IDL – Theoretical background

Control voltagefor HV source

Leakage current of coil

Current of HV source

HV so

urce

ope

rates

like

vol

tage s

ourc

e

HV source operates like current source

Rise time Fall time

Trailing edge

Width time

Leading edge

Current limit

Current Limiter

Stat

or C

oil C

Leakage Resistance

High Voltage Generator

5/23/13 14

IDL Consisting Parts

Measurement diagram for one phase of generator

IDL – Measurement Procedure

Rins

ulat

ion

Hig

h V

olta

ge D

C G

ener

ator Win

ding

und

er te

st

Multifunction DAQ

DC

Clam

p-O

n M

icro

amm

eter

1

DC Clamp-On Microammeter 2

R

#1 #2 #12

CT

CT

CT

CT

1

2

9

10

11

A

B

C

D

Technical Challenges

Very low magnetic resolution order of nT

=> Minimization of noise and offset fluctuation

Influence of external magnetic field

=> Dual core

Remanet magnetic field

=> Degaussing & material with low Br

High voltage compatibility

=> Fiber-optic transfer data

Case Story - Twin Lakes Colorado

Case Story – Grand Coulee

5/23/13 19

Case Story – Buffalo Bill G2 Plant

5/23/13 20

Case Story – Buffalo Bill G2 Plant

5/23/13 21

SENIS’ Current Sensors - Outlook

• Development of a New generation of Clamp-On MicroAmmeters for leakage current detection.

- Objective: Offset fluctuation and drift <3µA over 10min - Deadline: End of 2013 • High-Accuracy Clamp-On DC/AC Current Transducers for Test

and Measurement applications, ranges from 100A to 1000A - Objective: Absolute accuracy better than 0.2% (now the best

on the market: 1%); major improvement of repeatability and immunity to external magnetic fields.

- Time: Mid-2014

5/23/13 22

Demonstration

Booth No. 4333, Hall 4.2

Thank you!

www.senis.ch