Dedicated Onsite Condition Monitoring ofHigh Voltage Power Cables震荡波法检测高压电缆局放.docx

1、Dedicated Onsite Condition Monitoring of High Voltage Power Cables 震荡波法检测高压电缆局放1Abstract - For advanced, non-destructive on-site condition monitoring of HV power cables up to 150kV by partial discharge detection and dielectric losses measurement it is necessary to energize the disconnected cable sys

2、tem. One of the methods available for this purpose is based on applying damped AC voltages up to 150kV. In this paper, the use of modern technological solutions in power electronics and signal processing as well as in technical design and production methods will be discussed on the basis of ultra li

3、ght system (300kg which is able to test cables up to 20km lengths.Index Terms damped AC voltages, diagnosis, dielectric losses, HV power cables, localization, on-site, partial discharges. I. INTRODUCTIONhe insulation failures in a cable network may be caused by lower dielectric strength due to aging

4、 processes and by internal defects in the insulation system. It is known that unlike voltage testing, measurements of the dielectric may give an absolute indicator for the quality level of the cable insulation. For HV power cables different on-site inspections/diagnostics are available 1, 2. In part

5、icular with regard to information as provided, conclusions about short- and long-term condition can be made (figure 1.The results of these measurements may have a direct relation to the average qualitative level of the insulation at the moment of measurement and can thus be applied as a trend- or fi

6、ngerprint measurement during future inspections. It follows from figure 1 that partial discharge diagnosis and dielectric diagnosis may play important role in short- and long-term condition assessment, figure 2.cable connection. In order to run the measurement partial discharges are ignited in the c

7、able insulation or joints by the application of a test voltage 3. The occurrence of partial discharges have physical character and it is described by such important parameters as PD inception voltage, PD pulse magnitudes, PD patterns and PD site location in a power cable. For utilities interested in

8、 applying PD diagnostics for E. Gulski is with Delft University of Technology, The Netherlands(e.gulskitudelft.nlP.P. Seitz is with Seitz Instruments AG, Switzerland (ppsseitz-instruments.ch B. Quak is with Seitz Instruments AG, Switzerland, (bqseitz-instruments.ch F. Petzold is with SebaKMT, German

9、y (petzold.f.F. de Vries is with Nuon Tecno, Alkmaar, The Netherlands(frank.de.vries parameters are of importance.In particular, analyzing PD parameters for different types of cable insulation and cable accessories can result in developing experience norms 4, 5. Such norms would very helpful in deve

10、loping knowledge rules to support AM decisions.of the loss factor of the insulation material 3, 4. This factor increases during the ageing process of the cable. The tan m easurement should be regarded as a diagnostic and/or supporting measurement. In practice, in HV insulation is known that in addit

11、ion to absolute value of tan at certain test voltage also the increment of tan delta as measured at twoDedicated On-site Condition Monitoring of High Voltage Power Cables up to 150kV E. Gulski, Senior Member, IEEE, P.P. Seitz, B. Quak, F. Petzold, Frank de VriesT2 condition assessment. The loss tang

12、ent is measured as function of voltage to check the quality of impregnation. The tanvalue of a cable is strongly influenced by the composition of the connection, the trace, and the deviations in joints and the actual m easurement is only applicable as trend measurement if composition circumstances o

13、f the trace and thermal conditions of successive measurements are virtually identical. For HV paper insulated cables the tan c an be an important indicator of possible thermal breakdowns 4. II. ON -SITE E NERGIZING O F HV P OWER C ABLES or complete on-site diagnosis of transmission power cables by P

14、D detection and dielectric losses measurement it is necessary to energize the disconnected cable system 8,9. The detection and measuring equipment is therefore directly connected to the cable conductors (or through the switchgear. In this way, the different phases of the cable circuit can be energiz

15、ed and the PD pulses can be coupled out. The capacitive power P = 2f Ccable U 2test needed to stress on-site the cable insulation is determined by the test frequency f , the cable capacitance C cable and the test voltage U test . In order to decrease the capacitive power demands for energizing cable

16、s as compared to 50Hz test voltages, different energizing methods using specific voltage shaped and frequencies have been introduced for PD diagnostics nowadays 11, 15, 16. As shown in 3, 16, 17 due to several important characteristics such as1. AC voltage type equivalence in PD inception processesf

17、or solid insulating materials,2. non-destructiveness of voltage stress during the diagnosis, 3. real-time advanced analysis of diagnostic data,4. sufficient immunity for on-site interferences and lowlevel of system background noise,5. IEC, IEEE standards conformity 2, 3, 4, 12, 13,6. test cost effic

18、iency based on investment and maintenancecosts, transportability and operation of the method in different field circumstances,the use of partial discharges and dielectric losses diagnosis at damped AC voltages (DAC has become important solution for on-site testing and diagnosis of HV power cables (f

19、igures 3,4.To generate on-site damped AC voltages up to 150kVpeak and to perform advanced diagnosis by meaningful PD parameters modular hardware/software solution has been developed (figure 4. In particular, by use of- modern solid-state technology and laser-controltechniques (HV Solid-State Switch,

20、- power electronics, digital signal processing (HV Solid-State Switch, HV source,- digital signal processing and filtering (PD detector,-wireless communication and embedded computer system (PD detector, Control unit, PD analyzernovel system OWTS HV -series type 150 has been developed for on-site PD

21、diagnosis of HV power cables up to 150kV (table 1.III. D AMPED A C V OLTAGE G ENERATIONor the generation of damped AC (DAC voltages, the power demand is low due to the charging the cable capacitance (figure 5 with a current of 10mA and aFTABLE IMAXIMUM TEST VOLTAGES OF A 150KV TEST SYSTEMNetwork vol

22、tage kV OWTS HV 150 x UF150 kV Switch150kV/ 7.1H Control HV DividerHV Power Cable150kV HV SourceInductor UnitUnitPD AnalyzerPD coupling capacitorPD Detector(a(bFig. 4: Examples of on-site testing and diagnosis of HV power cables using damped AC test system 150 kV:a after installation in substation d

23、uring testing a 9.6km long 50kV oil-filled cable,b after disassembling prepared for transportation (weight 300kg3 capacitance (represented as a capacitance Cc is switched by S in series with large inductance L, resulting in an sinusoidal damped AC voltage form with a frequency between 20Hz and few h

24、undreds of Hz (figure 6 In particular, the cable sample is linearly charged with continuously increasing HV voltage, directly followed by a switching process and period of several sinusoidal AC cycles, figure 7. As a result, during the charging time no steady state DC conditions occur in the cable i

25、nsulation 14. As soon as the cable is charged, the HV supply is disconnected and a specially designed 150kV solid-state switch connects the cable sample Cc to an air-core inductor L =7.1H in a closure time of less than 1s. In this way, and LC loop is created and an oscillating voltage wave is applie

26、d to test the sample.The test frequency of the oscillating voltage wave is approximately the resonant frequency of the circuit:f =21 This means that the test frequency of the applied DAC voltage is dependent on the cable capacitance, see figure 6. The HV power cable capacitance varies due to paramet

27、ers like thecross-section of the conductor and the thickness and the typeof the insulation. In table 2 examples are shown for differenttypes of HV cables and cable length and the damped ACfrequencies to be generated using system as shown in figure 2.Due to the low loss factor and design of the air-c

28、ore, theresonant frequency is close to the range of power frequency of the service voltage: 20Hz to 300Hz.The quality factor QC of the resonant circuit, which is responsible for the attenuation of the oscillations, can be expressed by:Q C = (L / (C * RA 2Here is R A the equivalent circuit resistance

29、. The quality factor Q of the resonant circuit remains high depending upon cable (30 to more than 100, as a result of the relative low dissipation factor of power cables. A slowly decaying sinusoidal waveform (decay time up to 0.3 second is applied as test voltage to energies the cable sample.IV. SY

30、STEM o support efficient on-site testing and diagnosis based on field experiences the following hardware/software solutions have been developed (figure 8. 150 kV HV Source: to load the power cable capacitance150kV HVDC voltage supply is used with a circuit effective load current of 10mA. During char

31、ging the test object the linear and continuously increasing HV voltage is controlled bythe computer. In figure 5 the charging time in function of the load capacities is shown. The switching discharge current ofTABLE IIEXAMPLES OF TYPICAL DAMPED AC VOLTAGE FREQUENCIES FOR DIFFERENT LENGTHS OF TWO TYP

32、ICAL 150KV POWER CABLESLength km XLPE (C=154pF/mHzOil filled (C=373pF/mHzTthe power supply are limited by 15k series resistor to max. 16A.150 kV HV solid-state switch: The function of the 150kV switch is to establish a series resonance circuit between charge HV power cable capacitance and the air inductor L. As a result sinusoidal damped AC voltages may occur in the cable sample. The switch is per