14_Bergmann_HV TR.pdf

HIGH VOLTAGE TESTING ON TRANSFORMERS

CEPED 2013, Bali, Indonesia

Dr. Ralf Bergmann

HIGHVOLT Prüftechnik Dresden GmbH

Table of contents

Motivation and Standards

Factory Testing – Latest Technology

On-Site Testing – Same principle

Summary

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MOTIVATION AND STANDARDS


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Motivation

Early recognition of:

Design issues

Production failures

Insulation degradation


Motivation

Transformer - Key component in electric energy system

Securing Transformers‘ quality essential for reliability of electric network

Extensive testing within development and testing of transformers Routine test Type test

Increase of old transformers in power grid Need to verify old transformers‘ condition


STANDARDS FOR FACTORY TESTING

Standards

Standards IEC IEC 60076-1…3

Standards IEEE IEEE C57.12.00 - C57.12.90 IEEE C57.152 (= old IEEE 62)

GOST GOST 1526, GOST 3484, GOST 52719-2007

On-Site Testing: No separate standards. use of same testing procedures, possible test voltage reduction for service aged

transformers


Possible Test`s on power transformers

Measurements of winding resistance Measurement of no-load loss and current

Dielectric tests Temperature-rise test

Determination of sound levels

Measurement of the harmonics of the no-load current

Measurement of insulation resistance

Measurement of turn ratio

Determination of capacitances Tests on on-load tap-changers

FACTORY TESTING - LATEST TECHNOLOGY


IMPULSE VOLTAGE TEST OF POWER TRANSFORMER ACCORDING TO IEC 60076-3, POS. 13-15 IEC 60060-1 2010

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10 High Voltage Testing on Trandformers

Sample of lightning impulses

Tail time

Front time

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0,9

0,3

1,0

U

B

A

0,7a

t T1

TC

a

D

C

0,1a

a – instant of chopping

Full lightning impulse Chopped lightning impulse


Accuracy is important:

Correctness of wave shape

Space is expensive:

Space saving solution

Time is money:

Quick test setup increasing output of factory

Requirements on impulse voltage test


Connection Point – The all in one solution

Test system consists of only two individual components: 1) Impulse generator 2) Connection Point HV divider Chopping gap and Overshoot compensation

Benefits of Connection Point: Space saving solution Integrated overshoot compensation Only one connection to the test object Only one test setup is used

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Space reduction using Connection Point

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Arrangement with Connection Point Arrangement with divider, overshoot compensation and chopping gap

MOST COMMON LAYOUT LAYOUT USING CONNECTION POINT

Example: Test system ULI=1800 kV USI= 1150kV Space required = 400 m² Space Required = 300 m²

25% space reduction

Test object

Divider

Chopping gap

Overshoot Compensat

ion

Impulse generator

Test object

Connectionpoint

Impulse generator

FACTORY TESTING - APPLIED VOLTAGE TESTING


Applied Voltage Test IEC 60076-3, pos. 11

15

Transformer based AC test system

- continuously duty cycle, high feeding power

- high test system costs

Resonant test system with variable inductance

- perfect sine wave, proven/robust technology

- less feeding power, less costs

Resonant test system with variable frequency

- perfect sine wave, proven/robust technology

- small components, lowest feeding power, best price

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Applied voltage test or separate source AC withstand voltage test can be performed with 3 different type of test systems


Example of Applied Voltage Test for 1200 kV


Test of transformer for 800 kV HVDC transmission at Siemens Nuremberg, Germany


ADVANTAGES

Compact

Easy extendable

Low power consumption

Operates according to IEC >80% of rated voltage

Lower Investment cost

Applied Voltage Test – Variable Frequency Test System

Test system at Siemens Dresden, Germany

System Concept for Applied Voltage Test


1 Control and feeding unit 2 Exciter transformer 3 HV reactor 4 Blocking impedance 5 Voltage divider

3

5

4

400V 50 kVA 50/60Hz

LV HV

Transformer to be tested

FACTORY TESTING - INDUCED AC VOLTAGE TESTING



Generation of test frequency

Solutions for Induced Voltage test

Since the test voltage Up for the induced voltage test is often higher than twice the rated voltage, the test frequency must be at least doubled to avoid over-excitation of the iron core.

Motor / Generator Set Static Frequency Converter


Induced AC Testing based on Static Frequency Converter

Different frequencies for loss measurement and induced voltage testing provided by static frequency converter – replacing several different motor-generator-sets

Fulfill all demands of standards

Efficient

Allows testing of transformers >1000 MVA

Expandable

Space-Saving

Easy to operate, intrinsically safe

ADVANTAGES



Block diagram of transformer test system



Transformer test system for induced voltage tests, based on static frequency converter, type WV 2000-4000/170

Static frequency converter build in

container Cooling system Step-up transformer High voltage filter


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Static Frequency Converter built in Container


THD Value < 5%

Test voltage and current waveform – no-load loss measurement with THDu < 3.5% and THDi = 52% (150 MVA transformer)

26

Sensitive PD Measurement

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PD Level < 10 pC according to IEC 60270

ON-SITE TESTING – SAME PRINCIPLE



NO STANDARDS FOR ON-SITE TESTING

HIGHVOLT on-site test systems allow tests appropriate to standards of factory testing On-Site Tests: Applied Voltage Test Induced AC Voltage Tests Optional: Impulse Testing

HV On-Site Testing

ON-SITE TESTING – APPLIED VOLTAGE TEST


Wide load range of power transformers 5 to 40 nF Variable test frequency 40 to 200 Hz Voltage 360 kV – Expandable to 720 kV Electric current 5 A


Test System for Applied Voltage Test

Resonant system with variable frequency

Standard 40 foot trailer

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Applied Voltage – Procedure and Test sequence

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Transportation to site

Test arrangement and connection of test object (approx. 50 min)

Start system and enter test parameters (approx. 10 min)

Start automatic test sequence Automatic search of test frequency at 10% of U test

(frequency shall be not less than 80% of rated frequency per IEC)

Increase the voltage up to U test Withstand voltage test Decrease the voltage up to 0 V

Finish test and print test report (HIGHVOLT Suite®)

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Summary – Applied Voltage Test

Dielectric test of the main insulation (between winding and iron core/ tank; between the winding systems)

Test voltage up to 360 kV with additional reactor up to 720 kV

Required power supply: 400 Volt (3~), 40 kVA

Only one HV lead to connect the transformer under test


ON-SITE TESTING – INDUCED AC VOLTAGE TEST


Setup for Induced Voltage Test


PD 1234

PLC

3 ~ 400V / 50~60 Hz

PD measuring system

HV capacitive compensation unit (Option)

Transformer to be tested

1234

1. Frequency converter 2. Step-up transformer 3. HV filter 1 4. HV compensation (Option) 5. HV filter 2 (Option) 6. Loss measuring system

1 2 3

4

5

6

Space for accessoiries

Design of Mobile Test System

Static frequency converter

Step-up transformer

Control room HV filter 1

Power supply cable, HV connection cable


CT’s and VT’s

Space for accessories, HV electrodes, etc.

HV test lead

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Induced voltage – Procedure and Test Sequence (IEC/ IEEE/customer specification)

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1. Transportation to site

2. Test arrangement and connection of test object (approx. 50 min)

3. Start system and enter test parameters U test and f test (approx. 10 min)

Typically: U test = 80% of U test at factory f test approx. 2 x f rated (between f rated and 200 Hz)

Choose frequency of test = f test :

a) Factory test frequency i.e. 120 Hz,180 Hz, etc. b) Or to minimize the power demand choose frequency to take

advantage of variable frequency to reach self compensation

4. Start automatic test sequence

5. Measure PD at test voltage levels specified

6. Finish test and print test report (HIGHVOLT Suite®)

APPLICATION

Required for reactive power compensation during short-circuit tests, load-loss tests and on-load tap-changer tests

SOLUTION

Capacitor bank on one trailer or in one 40-foot container for single phase and small three phase types

Capacitor bank on 2 trailers in four 20-foot containers for larger three phase types (3 containers for capacitors, 1 for measuring transducers)

Standard types: - up to 250 MVA test objects: 36 kV / 24 MVA, HVCC 24000/36 - up to 500 MVA test objects: 36 kV / 54 MVA, HVCC 54000/36

Capacitor Banks for Mobile Transformer Test Systems

Principle sketch of mobile capacitor bank HVCC 24000/36

power measurement: current transformer / voltage transformer

CT1…CT3: phase current measurement CT4: protection against unsymmetrical currents

Compensation units can be connected to form a 3-phase or a powerful single phase capacitor bank

HV capacitive compensation units

40 ft trailer

cable drums

All transformers up to highest ratings can be tested on site

Higher power by mobile capacitive compensation banks is available

Mobile capacitor bank HVCC 24000/36 inside a 40ft container

40

Output voltage: Up to 80 kV Output power: 1000 kVA / 620 kW

Power supply: 400 V (3~)

- 750 kVA mains supply or - 1200 kVA diesel generator Only 3 HV cables to connect the transformer under test

Easy set up: Within 1 hour ready to test

Summary – Induced Voltage Test


EXAMPLES OF TESTED TRANSFORMERS


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Test of a 500 MVA Single Phase Trans- former in a Nuclear Power Station


Test of 1phase main transformer with WV 620-1000/80

Power supply by mobile diesel generator

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Parallel connection of up to 3 test systems (total: 1.9 MW/3 MVA)

Parallel Operation for Testing up to 1200 MVA Transformers


Summary

Testing power transformers up to 1200 MVA

According to IEC and IEEE standards

Waveform distortion THD < 5%

Partial discharge (PD) noise level < 10 pC (with 2nd HV filter)

Free adjustable frequency 40 to 200 Hz (self compensation)

Modular design allows for future expansion

Easy and fast test set up


YOU DELIVER QUALITY OUR EQUPIMENT PROVES IT

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Documents

14_Bergmann_HV TR.pdf