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PowerPoint Presentation: 

1 Advanced PD Monitoring of Power Transformers Supporting Asset Management www.ldic.de Gregor Pudlo Doble Lemke Germany Switzerland

Abstract: 

2 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

Reasons: PD Monitoring of Power Transformers: 

3 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

Reasons: PD Monitoring of Power Transformers: 

4 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) [1] PD –Yes/No? PD – If yes, where? especially in transformers, the PD site is of great importance

Partial Discharge Detection Principles: 

5 Partial Discharge Detection Principles Optical Mechanical Chemical Acoustic Opto-acoustic HV Electrical IEC 60270 HF/VHF/UHF Optical Effects (Light) Pressure Wave (Sound) Discharge Effects Dielectric Losses High Frequency Waves Chemical Effects Heat Macroscopic-Physical Effects Detection Methods Draft IEC 62 478

Electrical PD diagnostic techniques: 

6 Electrical PD diagnostic techniques PD measuring circuits according to IEC 60270 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 C K , measuring impedance Z m , a measuring instrument M and generalized test object C a . [König, 1993] frequently used circuit in test laboratories often applied in on-site/on-line PD investigations

Electrical PD diagnostic techniques: 

7 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 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

Advanced tools for PD monitoring: 

8 Advanced tools for PD monitoring Acoustic and electromagnentic PD measuring principle Acoustic method Electromagnetic (UHF) method Sound field (acoustic wave) Piezo-Sensor PD (partial discharge) ) ) ) Electromagnetic wave example sensor „monopole“ Key characteristics:

IEC 62478 - Draft level: 

9 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

Advanced tools for PD monitoring – Electromagn. PD Tests: 

10 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

Type-Test Cone-shaped active drain valve UHF-sensors: 

11 Type-Test Cone-shaped active drain valve UHF-sensors Oil pressure estimation Mechanical pressure test Combined temperature/pressure test Standard Antenna Factor

PowerPoint Presentation: 

12 Performance Check 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. Cone-shaped active UHF-sensor (DN 50/80 oil gate-valve) UHF PD spectra for grounded and ungrounded sensor head input path output path

System Check for UHF (on transformers): 

13 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)

PowerPoint Presentation: 

14 Transformer Drain valve UHF PD probe DN80 Output Input Pre-amplifier High-pass filter Performance Check Performance check at 750 MHz Phase-resolved view in UHF PD device LDS-6/UHF

Steps of the on-site/on-line procedure ‘UHF PD Test’: 

15 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.

Advanced tools for PD monitoring – Electromagn. PD Tests: 

16 Advanced tools for PD monitoring – Electromagn. PD Tests Case study A - test laboratory UHF PD measurement of a 450 MVA autotransformer top view of the 3-phase 400kV transformer , with position of the gate-valve UHF-sensor UHF PD pulse recorded at max. 70 pC electr. PD level corresponding UHF PD spectrum up to 1 GHz customer wanted to assure that sporadic electrically recorded heavy PD are external to transformer clear UHF signals during moderate PD activity and no UHF signals during activity which where visible as noise in the electrical PD measurement Application benefit:

Advanced tools for PD monitoring – Electromagn. PD Tests: 

17 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 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 Application benefit:

Advanced tools for PD monitoring – Electromagn. PD Tests: 

18 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 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 Application benefit:

PowerPoint Presentation: 

19 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

PowerPoint Presentation: 

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

PowerPoint Presentation: 

21 UHF PD measurements in Ireland

PowerPoint Presentation: 

22 UHF PD measurements in Ireland 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 Locations: Louth Dublin Ardnacrusha Cashla

PowerPoint Presentation: 

23 Drain Valve Applied UHF Drain Valve Sensor Mounting of the UHF Probe DN50 (with Adapter DN50/DN80) Measuring System LDS-6/UHF 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 UHF PD measurements in Ireland

PowerPoint Presentation: 

24 V ≈ 550 mV at measuring frequency 560 MHz V ≈ 238 mV at measuring frequency 560 MHz Left drain valve Right drain valve V ≈ 139 mV at measuring frequency 560 MHz V ≈ 128 mV at measuring frequency 520 MHz UHF PD measurement in Louth, Dublin, Ardnacrusha, Cashla (Ireland) Louth T2xxx Left drain valve Right drain valve The measurements on both valves showed PD activity from inside the transformer. Not any critical PD levels above the detection sensitivity have been measured in Dublin, Ardnacrusha and Cashla .

PowerPoint Presentation: 

25 UHF PD measurements in Jizan, Saudi Arabia

PowerPoint Presentation: 

26 UHF PD measurements in Jizan, Saudi Arabia Drain Valve Power Transformer 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

PowerPoint Presentation: 

27 UHF PD measurements in Jizan, Saudi Arabia PRPD Pattern at the measuring frequency of 400 MHz V = 177 mV “A” PRPD Pattern at the measuring frequency of 400 MHz V = 288 mV “B” Not any critical PD levels above the detection sensitivity have been measured. 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

PowerPoint Presentation: 

28 Acoustic PD location

Advanced tools for PD monitoring – Acoustic PD location: 

29 Advanced tools for PD monitoring – Acoustic PD location Alternatives of arrival time based positioning electro-acoustic (test laboratory or on-site/off-line) electromagnetic- acoustic (test laboratory or on-site, off-line or on-line) 1. Mixed-acoustic methods: all-acoustic (test laboratory or onsite, off-line or on-line with reduced sensitivity) 2. All-acoustic methods: schematic view of a transformer tank with acoustic sensors Observation equations: unknowns x, y, z Input parameters: sensor coordinates, sound velocity, meas. time difference triangulation

Advanced tools for PD monitoring – Acoustic PD location: 

30 Advanced tools for PD monitoring – Acoustic PD location UHF-triggered 'Averaging' as de-noising method (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 Prerequisites noise tends against statistic mean value (zero) acoustic signal superimposed constructively During averaging process … acoustic 132 pC single PD pulse (black line) and 500 superpositions of maximum 9 pC (orange line) acoustic arrival times can be determined sensitively

Advanced tools for PD monitoring – Acoustic PD location: 

31 Advanced tools for PD monitoring – Acoustic PD location UHF-triggered 'Averaging' as de-noising method Start noise level

Advanced tools for PD monitoring – Acoustic PD location: 

32 Advanced tools for PD monitoring – Acoustic PD location Case study A - Acoustic PD localization on a 200 MVA transformer gas-in-oil diagnosis as well as off-line electrical PD measurement with 600pC confirmed PD location with various sensor positions and different measurements gave similar result risk assessment possible (contacted transformer manufacturer verified suspicious position) Application benefit: 28.10.03 (offline a,b,c,d) 21.04.2004 (c, d, e, f, g) PD-origin calculated x [m] y [m] z [m] 1.40 3.12 2.27 1.25 3.19 2.23 1.27 2.19 3.22 21.04.2004 (a,c,d,e,f,g) gas-in-oil diagnosis indicated PD customer wanted to confirm PD indication and locate the PD site Measurement goals:

PowerPoint Presentation: 

33 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 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