23_bergmann_hv testing on rot machines.pdf

HIGH VOLTAGE TESTING ON ROTATING ELECTRICAL MACHINES

CEPED 2013, Bali, Indonesia

Dr. Ralf Bergmann

HIGHVOLT Prüftechnik Dresden GmbH

High Voltage Testing on Rotating Electrical Machines

Content:

Why spend money on HV tests?

Physical background: Machine characteristics and test methods

Generation of continuous AC test voltages

Experience with continuous AC voltage testing

Summary

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WHY SPEND MONEY ON ON-SITE HV TESTS

High Voltage Testing on Rotating Electrical Machines 3 31/10/2013


Technical and Physical Point of View for Electrical Machine Testing On-site

Manufacturing D

amag

e

Mis

take

Test

ing

Test

ing

Dia

gnos

is

Transportation Installation

Test

ing

Power frequency 50/60 Hz

Operation Power frequency

50/60 Hz Electrical machine life →

Rep

air

Agei

ng

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Necessity for Evaluation of Machine Condition

Generators are an essential part of each power plant.

Failures usually result in the generating unit going off-line during repair, which may result in longer time periods without generation and immense costs.

Large electric motors are usually key components of industrial or power plants, and may be safety relevant (such as cooling water pumps in nuclear, but also conventional power plants, for example)

Their failure may halt production, lead to losses or even accidents

Consequently an evaluation of the condition of generators and large motors based on on-site testing is technically and economically recommended

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Root Causes of Generator Failures

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Mechanical 36

Bearings 3 Insulation 50

Thermal 11

Percentage of root causes of hydrogenerator failures

Hydrogenerator failures – results of the survey, Study committee SC11, EG11.02 Cigre 2002


Necessity for Evaluation of Machine Condition

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Requirements for On-Site Testing

Test results should cover

Evaluation of the machine insulation condition and its ageing

Estimation of remaining lifetime

Finding the cause and location of problems inside the machine

Requirements for test set-up

Designed for easy and frequent transportation, assembly and operation

Negligible ageing caused by on-site test

Load during on-site test should correspond to operational stress

Easy adoption to different test requirements as voltage, load capacitance, dielectric losses etc.

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Requirements for On-Site Testing

Technical point of view

System components are routine and type tested in factory

Check of transportation damages or assembling defects

Easy assembling and dismantling of the test system on-site

Lightweight, transportable and reliable

Physical point of view

Kind of testing stress ≈ operational stress ⇒ AC voltage (also recommended by IEC 60034-1 clause 9.2 for factory and on-site tests)

Acceleration of failure mechanism ⇒ testing stress > operational stress

Application of diagnostic measurements, e.g. PD, C/tan δ

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PHYSICAL BACKGROUND: MACHINE CHARACTERISTICS AND TEST METHODS



Tested Parameters and Test Methods used

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Tested parameter Test Method

Voltage withstand of insulation AC voltage test1)

General ageing of insulation, measurement of dielectric losses

Tan delta measurement during AC voltage test

Detecting the presence of insulation defects and their location

PD measurement during AC voltage test

1) According IEC 60034-1 DC testing will result in different surface potential along end winding insulation and different ageing mechanisms leading to breakdown.

In addition DC testing does not allow tan delta or sufficient PD measurement.


Voltage withstand test

Provides information, if the machine insulation is sufficient to withstand a certain AC voltage level

No breakdown / breakdown immediately provides a pass/fail criterion for the test without necessity of interpretation

Type of testing stress ≈ type of operational stress → same behaviour of all types of defect during test and operation

Amount of testing stress > amount of operational stress → acceleration of failure mechanism, defects break down in minutes that would in months during normal service

AC test voltage is basis for diagnostic measurements 12 31/10/2013


PD measurement

Provides information about insulation defects in a stadium, when they do not yet lead to breakdown

Requires interpretation

PD magnitude, inception and extinction voltages can be measured, giving additional information about the severity of the problem

PD patterns and their phase resolution give information about the type of defect and their location in the machine

The effort to find the problem is reduced, which avoids unnecessary disassembly and shortens the time needed for further investigation and repair

Trending can be applied to find out if and how fast problems are increasing over time

Basis: Variable AC voltage source 13 31/10/2013


Tan Delta measurement

Provides information about general insulation condition in a stadium, when no breakdown occurs yet.

Requires interpretation

In combination with PD measurement, or if tan delta measurement has been conducted before a fault it helps to determine if a machine should be repaired or replaced

Voltage dependence (tan delta tip-up) often reveals more than the actual tan delta value

Trending again gives valuable information about if and how fast problems are increasing

Basis: Variable AC voltage source

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GENERATION OF CONTINUOUS AC TEST VOLTAGES



Requirements for Test Voltage Source

Should generate AC test voltages according IEC 60034-1

Output voltage should be variable to:

Gradually increase test voltage

Measure PD inception and extinction voltage

Measure tan delta tip-up values

Should have low distortion and low PD level for sensitive measurement

Needs to be small enough for use inside of power plants

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Technical Requirements according standards

High voltage tests on rotating machines (motor & generators)

Test Frequency range of AC source accord. standard

Withstand voltage test 10 – 500 Hz Withstand voltage test combined with Partial discharge measurement

10 – 500 Hz

Power factor / tan delta measurement 45 < f < 65 Hz

Required test voltage level for AC Withstand voltage test and Partial Discharge Measurement

2 x Un+1000 V 1

Required test voltage level for Tan Delta Measurement

1 x Un

1 IEC 60034-1 (2004), Term: 9.2; recommended after on-site maintenance, cleaning and drying of generators is lower, only 1,5*Un for withstand voltage test Un – rated voltage of rotating machine (ph-ph)



Off-Line Voltage Test vs. On-Line Monitoring

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Feature Off-Line AC Test On-Line Monitoring AC test voltages according IEC 60034-1 + + – –

Gradual increase of test voltage + + – – Measuring PD inception and extinction voltage + + – –

Measuring tan delta tip-up + + – – Low distortion and low PD level + – Trending of PD values + + + Trending of tan delta values + O (unusual, high effort)

Requires outage – – + + Test equipment size – +

Different methods – different tasks. One cannot replace the other.


Technical Solutions for HV AC Test Voltage Generation

TR LC TH CH

CL

MD CC

AC

ACTC Compensated transformer

ACRL Resonant test system with tuned inductance as series resonant circuit

TR

LH

TE

CH

CL

MD CC

AC

TR TE LH CH

CL MD CC

AC

ACRL Resonant test system with tuned inductance as parallel resonant circuit

FC TE LH CH

CL MD CC

AC

ACRF Resonant test system with tuned frequency

AC f

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Parameters of Typical Test Objects

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Parameter Small turbo generator

Large turbo generator

Small hydro generator

Medium hydro generator

Rated voltage 13.8 kV 27 kV 6.3 15 Rated power 112 MVA 1300 MVA 12.5 MVA 270 MVA Test voltage 28.6 kV 55 kV 13.6 kV 31 kV Test capacitance 494 nF up to 1.5 µF 675 nF 1185 nF

Test current at 50 Hz 4.44 A 25.9 A 2.88 A 18.0 A

Test power at 50 Hz 127 kVA 1425 kVA 39 kVA 395 kVA

Generators of same power and voltages may differ in capacitance by factor 3 depending on the design – number of stator bars, geometry, insulation thickness etc.


Comparisons of different AC Test Systems

Mode of on-site test system

ACTC compensated transformer

ACRL variable inductance

ACRF variable frequency

Frequency 50 / 60 Hz 50 / 60 Hz 20 to 300 Hz

Quality factor of resonance (5)

40 to 60 80 to 200 (limited by tan delta of machine)

Power supply Single / two phase Single / two phase Three phases

Specific weight 15 to 20 kg/kVA 3 to 10 kg/kVA 0.5 to 2 kg/kVA

Sufficient for Small motors and

generators Test power ≤ 500 kVA

All motors and generators

All motors and generators

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EXPERIENCE WITH CONTINUOUS AC VOLTAGE TESTING

Particular Tests



Variable Frequency Test System for Testing of Rotating Machines Installed in a Van

Control and feeding unit

Test voltage lead

Exciting transformer

HV resonant reactor

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Voltage range: 30…50…100 kV Current range: 10…25…50 A Frequency: 20…300 Hz

On-site Resonant Test System Based on Variable Frequency

Application: Rotating machines Medium voltage cables Capacitor banks

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Voltage range: 30…50…100 kV Current range: 10…25…50 A Frequency: 20…300 Hz

On-site Resonant Test System Based on Variable Inductance, mounted in Container

Tests: Voltage withstand test PD measurement Tan delta measurement

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Application: Test of Turbo Generator

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Generator test in Power plant of Ruien, Belguim Cortesy of Laborelec, Belgium


Application: Test in Hydro Power Plant

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Compagnie Nationale du Rhone, Usine de Bourg les Valence 5 x 33 MVA, 10.5 kV, installed 1968

SUMMARY



Summary

On-site testing of rotating machines should be done with AC test voltages Same behavior of defects as under operating conditions Variable test voltage for overvoltage tests and voltage dependent

measurements available

Separate source testing can reveal more information than on-line monitoring, but is also more complex Both methods complement each other and have their valid application

Resonant test systems with variable inductance or frequency are the best solution Easy transportability and handling Low demand on feeding power

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TOP QUALITY: MADE BY YOU CERTIFIED BY HIGHVOLT


23_bergmann_hv testing on rot machines.pdf

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