PowerPoint-Pr

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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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Reasons PD Monitoring of Power Transformers

• Technological reasons for PD generation
• contamination, manufacturing errors, incorrect
  design
• aging due to electrical, thermal and mechanical
  stresses in operation
• General complete information about a PD activity
• its intensity (might be apparent charge q)
• its type (voids, etc. failure identification)
• its location (appraise the severity of the
  fault)

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PD Yes/No?
PD If yes, where?
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Partial Discharge Detection Principles
Macroscopic-Physical Effects
Detection Methods
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Electrical PD diagnostic techniques
PD measuring circuits according to IEC 60270
often applied in on-site/on-line 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
ComponentsAC 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 lt 60 kHz
• Additional voltage signal for phase-resolved
  measurements
• 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)

500 kV Transformer Bushing
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Advanced tools for PD monitoring
Acoustic and electromagnentic PD measuring
principle
Electromagnetic (UHF) method
Acoustic method
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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 -gt
  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 120C warm oil
  with 5 bar compression)

View from inside the transformer
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Type-Test Cone-shaped active drain valve
UHF-sensors

• Mechanical pressure test

• Oil pressure estimation

• Standard Antenna Factor

• Combined temperature/pressure test

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Performance Check
output path
input path
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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System Check for UHF (on transformers)

• Performance Check
• Functional check of the whole measuring path
  including sensors and partial discharge (PD)
  acquisition system
• not necessarily transmission of electromagnetic
  waves through the test object , one-port
  solutions are possible
• Sensitivity Check
• Emission of electromagnetic waves into the test
  object necessary and known distance between
  sensors and injection location
• Pulse Generator injection necessary to determine
  relation between the apparent charge (pC) and
  measured quantities (e.g. V,W,J) through
  simultaneous measurement
• one-port solutions might be possible in
  relation to the wave length (for compact objects,
  not for extended objects)

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Performance Check
Performance check at 750 MHz
Phase-resolved view in UHF PD device LDS-6/UHF
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Steps of the on-site/on-line procedure UHF PD
Test

• Mounting of UHF PD probe
• Performance Check (functional test)
• Perform measurement/diagnosis

Ensure tight closure of the drain valve/dismantle
blank flange
Measure the distance tank wall ? flange sealing
surface
a) Check needed rod insertion depth b) Check
o-ring sealing c) Apply probe with venting screw
in upward position d) Venting open the upper
venting screw, slightly open the drain valve and
bleed the air. When oil is leaking from the
bleeding screw tighten it immediately.
a) Open drain valve completely b) Insert the
probe into the drain valve up to a position
maximum aligned with tank wall. Fix the rod by
using the retaining screw.
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Advanced tools for PD monitoring Electromagn.
PD Tests
Case study A - test laboratory UHF PD
measurement of a 450 MVA autotransformer
UHF PD pulse recorded at max. 70 pC electr. PD
level
corresponding UHF PD spectrum up to 1 GHz
top view of the 3-phase 400kV transformer, with
position of the gate-valve UHF-sensor
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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
380/220kV, 200 MVA single-phase transformer and
position of the gate-valve UHF-sensor
UHF pulse recorded on-line
corresponding UHF PD spectrum up to 1.5 GHz
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Advanced tools for PD monitoring Electromagn.
PD Tests
Case study C - on-line UHF PD measur. of a
3-phase power transformer 600 MVA
gate-valve UHF-sensor used at the 3-phase power
transformer 600 MVA, 21/380kV
UHF pulse recorded on-line
corresponding UHF PD spectrum up to 1.0 GHz
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UHF PD Measurements and delivered UHF PD Probe
DN50/80

• Taiwan
• Taipeh
• China
• Shangai
• Belgium
• Linkebeek
• Germany
• Berlin
• Heidenau
• Riesa
• Ireland UK
• Ardnacrusha
• Cashla
• Dublin
• Louth

• Philippines
• Manila
• Saudi Arabia
• Jeddah
• Jizan
• UAE
• Dubai
• Egypt
• Kairo
• Colombia
• Bogota

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• Latest UHF PD measurements in
• Riesa, Germany
• Heidenau, Germany
• Louth, Dublin, Ardnacrusha, Cashla in Ireland
• Jizan, Saudi Arabia

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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
Mounting of the UHF Probe DN50 (with Adapter
DN50/DN80)
Measuring System LDS-6/UHF
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UHF PD measurement in Louth, Dublin, Ardnacrusha,
Cashla (Ireland)
Louth
Left drain valve 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
T2xxx
Left drain valve 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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• Acoustic PD location

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Advanced tools for PD monitoring Acoustic PD
location
Alternatives of arrival time based positioning
triangulation
1. Mixed-acoustic methods

• electro-acoustic (test laboratory or
  on-site/off-line)
• electromagnetic- acoustic (test laboratory or
  on-site, off-line or on-line)

schematic view of a transformer tank with
acoustic sensors
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Advanced tools for PD monitoring Acoustic PD
location
UHF-triggered 'Averaging' as de-noising method
Prerequisites
(i) the signal which should be de-noised is
repetitive(ii) signal and noise are
uncorrelated and(iii) the noise is supposed to
be white
acoustic 132 pC single PD pulse (black line) and
500 superpositions of maximum 9 pC (orange line)
During averaging process

• noise tends against statistic mean value (zero)
• acoustic signal superimposed constructively

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Advanced tools for PD monitoring Acoustic PD
location
UHF-triggered 'Averaging' as de-noising method
Start noise level
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Advanced tools for PD monitoring Acoustic PD
location
Case study A - Acoustic PD localization on a 200
MVA transformer
Measurement goals

• gas-in-oil diagnosis indicated PD
• customer wanted to confirm PD indication and
  locate the PD site

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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 AG Rheinfelden, Switzerland Tel. 41
61 836 8000 www.ldic.ch
Doble Lemke GmbH Kesselsdorf/Dresden,Germany Tel.
49 35204 3900 0 www.ldic.de