Advanced PD Monitoring of Power Transformers
Supporting Asset Management
Gregor Pudlo
Doble Lemke
Germany
Switzerland
www.ldic.de
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Abstract
• Reasons for (PD) monitoring of transformers
• Partial Discharge Detection principles
• Electrical PD diagnostic techniques
• PD measuring circuits according to IEC 60270
• Advanced tools for PD monitoring
• Acoustic and electromagnetic PD measuring principle
• Cone-shaped drain valve UHF-sensors / Performance Check
• Case studies – UHF PD measurements
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Reasons: PD Monitoring of Power Transformers
• Power transformers are the most important and expensive
pieces of equipment in substations.
• A new power transformer costs millions of dollars.
• Unplanned outage and repair costs, penalties, etc. sum up
• Transformers design life is 20-35 years.
• With proper maintenance they can remain in service for 60
years.
• As transformers age, their internal conditions degrade which
increases the risk of failures.
• Time-based maintenance changes to condition-based
maintenance approaches
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Partial Discharge Detection Principles
Macroscopic-Physical
Effects
HV
Detection Methods
Optical Effects
(Light)
Optical
Pressure Wave
(Sound)
Mechanical
Discharge Effects
Dielectric Losses
High Frequency
Waves
Acoustic
Opto-acoustic
Draft IEC 62 478
Electrical
IEC 60270
HF/VHF/UHF
Chemical Effects
Chemical
Heat
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Electrical PD diagnostic techniques
PD measuring circuits according to IEC 60270
often applied in on-site/online PD investigations
frequently used circuit in
test laboratories
[König, 1993]
a) coupling device in series with the coupling capacitor
b) measurement at a bushing tap
Components:
AC voltage source U, optional blocking impedance Z, coupling capacitor CK,
measuring impedance Zm, a measuring instrument M and generalized test object Ca.
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Electrical PD diagnostic techniques
PD Measuring Impedance for Bushing Tap Installation
•
Decoupling of PD signals from the bushing tap
•
in a wide frequency range up to 30 MHz
•
Lower cut-off frequency < 60 kHz
•
Additional voltage signal for phase-resolved
measurements
500 kV Transformer Bushing
•
Superimposed PD and test voltage signal
•
Very fast and safe over-voltage protection
•
TNC-socket for signal output
•
Dimensions: diameter 125 mm, length 120 mm;
Weight: 2 kg
•
Special feature for continuous PD monitoring (IP 68)
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IEC 62478 - Draft level
"Non-conventional PD-measurements“:
• Electromagnetic PD Detection in the (HF/VHF/UHF) - range
• Acoustic PD measurements
• Mixed acoustic and electromagnetic method
-> PD location in Power Transformers and Reactors
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Advanced tools for PD monitoring – Electromagn. PD Tests
Cone-shaped active drain valve UHF-sensors
•
for the decoupling of electromagnetic PD signals
from the inner of an oil-paper-insulated transformer
•
PD-signals in the UHF frequency range
(mainly 300 MHz – 1 GHz)
•
sensors support „Performance/Sensitivity Check“
(high-frequency test impulses can be injected with
additionally integrated electrode)
•
sensor head is grounded (for lower frequencies)
•
sensor application at oil valves, which are available
e.g. for oil filling or draining (liquid tightness is
tested for 120°C warm oil with 5 bar compression)
View from inside the transformer
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Performance Check
grounded probe
Performance Check
output path
input path
normalized amplitude
1,0
0,8
0,6
0,4
0,2
0,0
0,00
0,25
0,50
0,75
1,00
1,25
frequency / GHz
Cone-shaped active UHF-sensor
(DN 50/80 oil gate-valve)
UHF PD spectra for grounded
and ungrounded sensor head
• Functional check of the whole measuring path including sensors and partial discharge (PD)
acquisition system through injection of high-frequency test impulses
• „single-port“ solutions are possible
• the Performance Check „controls“ e.g. the effect of a contact to grounded elements within
the oil valve.
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Performance Check
Performance check at 750 MHz
Phase-resolved view in UHF PD
device LDS-6/UHF
Drain valve
Output
Pre-amplifier
UHF PD probe DN80
High-pass
filter
Input
Transformer
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Advanced tools for PD monitoring – Electromagn. PD Tests
Case study B - on-line UHF PD measur. of a 200 MVA single-phase transformer
40
30
UHF pulse
recorded
on-line
amplitude (V)
380/220kV, 200 MVA singlephase transformer and
position of the gate-valve
UHF-sensor
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10
0
-10
-20
-30
0
50
100
150
200
time (ns)
0.6
corresponding
UHF PD
spectrum up
to 1.5 GHz
Application benefit:
amplitude (Vs)
0.5
0.4
0.3
0.2
0.1
0.0
0.00
•
customer wanted to verify the hydrogen measurements and locate potential PD
•
full in-service sensor application and measurement
•
UHF PD signal could be used to enhance acoustic PD measurements
0.25
0.50
0.75
1.00
1.25
frequency (GHz)
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1.50
Advanced tools for PD monitoring – Electromagn. PD Tests
Case study C - on-line UHF PD measur. of a 3-phase power transformer 600 MVA
150
100
UHF pulse
recorded
on-line
amplitude (mV)
gate-valve UHF-sensor used
at the 3-phase power
transformer 600 MVA,
21/380kV
50
0
-50
-100
-150
-500
-250
0
250
500
750
1000
time (ns)
Application benefit:
12
10
amplitude (Vs)
corresponding
UHF PD
spectrum up
to 1.0 GHz
8
6
4
2
0
0.00
0.25
•
gas-in-oil hydrogen indication „useless“ due to active hot spot
•
customer wanted to test for PD and check a potential load dependency of PD
•
full in-service sensor application and measurement
•
Inception and extinction voltage could be identified, load dependency excluded
0.50
0.75
1.00
frequency (GHz)
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UHF PD Measurements and
delivered UHF PD Probe DN50/80
Taiwan
Taipeh
China
Shangai
Philippines
Manila
Belgium
Linkebeek
Saudi Arabia
Jeddah
Jizan
Germany
Berlin
Heidenau
Riesa
UAE
Dubai
Ireland & UK
Ardnacrusha
Cashla
Dublin
Louth
Egypt
Kairo
Colombia
Bogota
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UHF PD measurements in Ireland
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UHF PD measurements in Ireland
Locations:
• Louth
• Dublin
• Ardnacrusha
• Cashla
Application benefit:
• Tested measurements have been performed using non-conventional decoupling methods taking
advantage of electromagnetic field coupling
• PD measurements on the power transformers have been functioned on the drain valves of the 3- phase
110/225kV power transformers with the help of the UHF probe DN 50
• Three transformers found with minor PD activity, one transformer with clear PD
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UHF PD measurements in Ireland
Measuring Instrument:
•
•
•
•
PD Measuring System LDS-6/UHF
UHF Probe DN50 (with Adapter DN50/DN80)
UHF Calibrator LDC-6/UHF
Pre Amplifier LDA-5/GIS
Drain Valve
Applied UHF Drain
Valve Sensor
Measuring System
LDS-6/UHF
Mounting of the
UHF Probe DN50 (with
Adapter DN50/DN80)
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UHF PD measurement in Louth, Dublin, Ardnacrusha, Cashla (Ireland)
Left drain valve
Louth
Right drain valve
The measurements on both valves showed
PD activity from inside the transformer.
V ≈ 550 mV at measuring
frequency 560 MHz
V ≈ 238 mV at measuring
frequency 560 MHz
Left drain valve
T2xxx
Right drain valve
Not any critical PD levels above the
detection sensitivity have been measured in
Dublin, Ardnacrusha and Cashla.
V ≈ 139 mV at measuring
frequency 560 MHz
V ≈ 128 mV at measuring
frequency 520 MHz
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UHF PD measurements in Jizan, Saudi Arabia
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UHF PD measurements in Jizan, Saudi Arabia
on 33/13,8 KV Power Transformers “A” and “B”
Measuring Instrument:
• UHF Probe DN50
• Calibrator LDC-6/UHF
• PD measurement instrument
LDS-6/UHF
Drain Valve
Power Transformer
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UHF PD measurements in Jizan, Saudi Arabia
“A”
“B”
Not any critical PD levels above the
detection sensitivity have been
measured.
PRPD Pattern at the measuring
frequency of 400 MHz V = 177 mV
PRPD Pattern at the measuring
frequency of 400 MHz V = 288 mV
Application benefit:
• For examination and diagnostics of the insulation quality of high voltage apparatus the measurement
of PD is accomplished by sensitive UHF method on-site
• UHF probe applied in full operation of transformer, no outage needed
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Conclusion
• sensitive UHF PD measurement with UHF probes applicable in
service provide advantageous robust and easy PD decoupling
• PD location - especially in transformers of great importance is possible in mixed and all-acoustic way
• significant diagnostic information are derived from advanced
tools for PD monitoring
• valuable application benefits e.g. on-line quick start of PD
monitoring, enabling time-based maintenance, “diagnostic
double checks”, etc. are at hand
Doble Lemke GmbH
Kesselsdorf/Dresden,Germany
Tel.: +49 35204 3900 0
www.ldic.de
Doble Lemke AG
Rheinfelden, Switzerland
Tel.: +41 61 836 8000
www.ldic.ch
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