23_bergmann_hv testing on rot machines.pdf
TRANSCRIPT
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
High Voltage Testing on Rotating Electrical Machines
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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High Voltage Testing on Rotating Electrical Machines
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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High Voltage Testing on Rotating Electrical Machines
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
High Voltage Testing on Rotating Electrical Machines
Necessity for Evaluation of Machine Condition
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High Voltage Testing on Rotating Electrical Machines
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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High Voltage Testing on Rotating Electrical Machines
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
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High Voltage Testing on Rotating Electrical Machines
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.
High Voltage Testing on Rotating Electrical Machines
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
High Voltage Testing on Rotating Electrical Machines
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
High Voltage Testing on Rotating Electrical Machines
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
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High Voltage Testing on Rotating Electrical Machines
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)
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High Voltage Testing on Rotating Electrical Machines
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.
High Voltage Testing on Rotating Electrical Machines
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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High Voltage Testing on Rotating Electrical Machines
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.
High Voltage Testing on Rotating Electrical Machines
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
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High Voltage Testing on Rotating Electrical Machines
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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High Voltage Testing on Rotating Electrical Machines
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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High Voltage Testing on Rotating Electrical Machines
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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High Voltage Testing on Rotating Electrical Machines
Application: Test of Turbo Generator
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Generator test in Power plant of Ruien, Belguim Cortesy of Laborelec, Belgium
High Voltage Testing on Rotating Electrical Machines
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
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High Voltage Testing on Rotating Electrical Machines
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
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