On-site testing with AC voltages
Stefan Bergmann
HIGHVOLT Prüftechnik Dresden GmbH
On-site testing with AC voltages
Growing power demand and the impact on the grid
forecast of required electrical energy Consequences for the grid:
120
100 ▪ Extension of grid capacity
electric power in TWh
80
60 ▪ Higher loading on installed
40 equipment
20
0 ▪ Additional stress leads to
2015 2017 2019 2021 2023 2025
increased ageing and thus
Sold energy Purchased energy Losses
a reduced lifetime
Transmission development plan 2014 – 2015
Final report, issued December 2016
06.12.2019 Vortragstitel 2
On-site testing with AC voltages
Growing power demand and the impact on the grid
Quantity of Power transformers to be Consequences for the grid:
maintained
45 ▪ A large number of HV components
40
35 are reaching their end of life
Number of units
30
25
20
▪ The probability of failures or
15 defects increases
10
5
0 ▪ A regular maintenance plan
2015 2016 2017 2018 2019 2020 should include a proper testing
Transmission development plan 2014 – 2015 program
Final report, issued December 2016
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On-site testing with AC voltages
High voltage tests - Part of a reliable quality assurance program
▪ Validation of a correctly designed HV component
▪ Validation, that the component has been produced
according to specified values
▪ Validation of a correct installation and commissioning
▪ Regular diagnosis & validation after repair measures
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On-site testing with AC voltages
High voltage tests - Steady part of the high voltage component’s life
Deviation Manufacturing
Routine test
Damage Transport
Mistake Installation / Commissioning
Site acceptance test
Ageing
Maintenance test
Operation
Defect Test after repair
06.12.2019 Vortragstitel 5
On-site testing with AC voltages
High voltage tests - Steady part of the high voltage component’s life
Deviation Manufacturing
Routine test
Damage Transport
Mistake Installation / Commissioning
Site acceptance test
Ageing
Maintenance test
Operation
Defect Test after repair
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On-site testing with AC voltages
On-site tests: What are the benefits?
Major assets of on-site testing:
▪ Avoid long-lasting and
sophisticated transports to a
test shop
▪ Decide, if and when a
repair can be done on-site
Diagnostic test of power transformer,
▪ Plan repair measures in advance
using a frequency-converter based test system
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On-site testing with AC voltages
On-site tests: What are the benefits?
Major assets of on-site testing:
▪ Test the fully installed system
in its operational environment
▪ Assess the quality of site works
e.g. jointing
▪ Detect failures, that might have
Commissioning test of 400 kV XLPE cable,
occured during installation
using 4 frequency-variable resonant test systems
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On-site testing with AC voltages
Purchasing a system for field testing…
▪ …is usually a unique acquisition.
Test objects?
Type test? Test field layout?
Prices? Test on tap changer?
Options? Routine test?
Ambient conditions?
Add-ons?
Delivery times? Shunt reactors?
Factory test? On-site test?
Automatisation?
Technical details? Consultancy?
Shielded test field?
Power measuring?
▪ A good knowledge of the main parameters of test objects and the test
location is decisive to select a suitable test system.
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On-site testing with AC voltages
Cable tests: test object
to be applied shall be subject to agreement between the purchaser and
the contractor. The waveform shall be substantially sinusoidal and the frequency shall be
between 20 Hz and 300Conductor Conductor
Hz. A voltage according to Table 4, column 10, shall be applied for 1 h.
Inductance Resistance Cable length (km)
(mH / km) (Ω / km)
Insulation Insulation
Resistance capacitance
(MΩ / km) (µF / km)
„The a.c. test voltage to be applied shall be subject to agreement between
the purchaser and the contractor. The waveform shall be substantially
sinusoidal and the frequency shall be between 20 Hz and 300 Hz. A voltage
[…] shall be applied for 1 h.“ (IEC 60480)
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On-site testing with AC voltages
Cable tests: Resonant test circuit
to be applied shall be subject to agreement between the purchaser and
the contractor. The waveform shall be substantially sinusoidal and the frequency shall be
between 20 Hz and 300 Hz. A voltage according to Table 4, column 10, shall be applied for 1 h.
reactor voltage
Power
Source
frequency
1
Simplified resonant test circuit 𝑓𝑟𝑒𝑠 =
2𝜋 𝐿 ∗ 𝐶
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On-site testing with AC voltages
The test system shall supply:
▪ Active power
to feed the losses
to be applied shall be subject to agreement between the purchaser and
▪ Reactive power
the contractor. The waveform shall be substantially sinusoidal and the frequency shall be
between 20 Hz and 300 Hz. A voltage according to Table 4, column 10, shall be applied for 1 h.
to form the resonant circuit
together with the cable capacitance
▪ Required information:
Test voltage and -duration, test load or cable parameters,
losses and load cycles
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On-site testing with AC voltages
Transformer tests: test objects
to be applied shall be subject to agreement between the purchaser and
the contractor. The waveform shall be substantially sinusoidal and the frequency shall be
Inductance Resistance Inductance Resistance
between 20 Hz and 300 Hz. A voltage according to Table 4, column 10, shall be applied for 1 h.
of prim. of prim. of sec. of sec.
winding winding winding winding
Core Main
resistance reactance
No determined procedure for on-site testing in IEC or IEEE standards
Guidelines and suggestions for testing, e.g. IEEE C57.152-2013
“IEEE Guide for Diagnostic Field Testing of Fluid-Filled Power Transformers,
Regulators, and Reactors”
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On-site testing with AC voltages
Transformer tests: test objects – no load condition
to be applied shall be subject to agreement between the purchaser and
the contractor. The waveform shall be substantially sinusoidal and the frequency shall be
between 20 Hz and 300 Hz. A voltage according to Table 4, column 10, shall be applied for 1 h.
▪ Relevant for:
induced voltage test (> 2 times power frequency)
no-load loss measurements (power frequency)
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On-site testing with AC voltages
Transformer tests: test objects – short-circuit condition
to be applied shall be subject to agreement between the purchaser and
the contractor. The waveform shall be substantially sinusoidal and the frequency shall be
between 20 Hz and 300 Hz. A voltage according to Table 4, column 10, shall be applied for 1 h.
▪ Relevant for:
load loss measurements (power frequency)
measurements of short-circuit impedance (power frequency)
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On-site testing with AC voltages
Transformer tests: test objects – applied voltage condition
to be applied shall be subject to agreement between the purchaser and
the contractor. The waveform shall be substantially sinusoidal and the frequency shall be
between 20 Hz and 300 Hz. A voltage according to Table 4, column 10, shall be applied for 1 h.
▪ Relevant for:
applied voltage tests (> 0.8 times power frequency)
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On-site testing with AC voltages
The test system shall supply:
▪ Active power
-to feed the no-load losses
-to compensate saturation
to be applied shall be subject to agreement between the purchaser and
the contractor.
conditionsThe waveform shall be substantially sinusoidal and the frequency shall be
between 20 Hz and 300 Hz. A voltage according to Table 4, column 10, shall be applied for 1 h.
-to provide transient power during
OLTC switching
-to suppress harmonics
▪ Reactive power
to compensate the load-loss
conditions
-to suppress harmonics
▪ Required information:
Transformer parameters, losses and impedances, Test conditions
and duration
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On-site testing with AC voltages
On-site diagnostic tests
Fault location detection during dielectric tests with AC voltages
measuring device
(transient recorder) l
Time domain reflectrometry-based measuring circuit
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On-site testing with AC voltages
On-site diagnostic tests
Fault location detection during dielectric tests with AC voltages
left side: setup for HV cable test; right side: typical breakdown pattern, detected with fault locator
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On-site testing with AC voltages
On-site diagnostic tests
On-site PD diagnostic during maintenance of wind power transformer
Box 1 Box 2 Box 3
Test
object
CEE 32
1 2 3 4 5
6 7 8
1 – Static Frequency Converter 6 – Operator Panel
2 – Power Sine Wave Filter 7 – Control Computer Unit
3 – Step-up Transformer 8 – Measuring Unit
4 – PD Filter
5 – Current and Voltage Sensors
Test source for diagnostic tests on wind power transformers
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On-site testing with AC voltages
On-site diagnostic tests
On-site PD diagnostic during maintenance of wind power transformer
Test source for diagnostic tests in the field
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