Abstract-- For advanced, non-destructive on-site condition monitoring of HV power cables up to 150kV by partial discharge detection and dielectric loss measurement it is necessary to energize the disconnected cable system. One of the methods available for this purpo is bad on applying damped AC voltages up to 150kV. In this paper, the u of modern technological solutions in power electronics and signal processing as well as in technical design and production methods will be discusd on the basis of ultra light system (300kg) which is able to test cables up to 20km lengths.
Index Terms— damped AC voltages, diagnosis, dielectric loss, HV power cables, localization, on-site, partial discharges.
I. I NTRODUCTION
he insulation failures in a cable network may be caud by lower dielectric strength due to aging process 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 particular with regard to information as provided, conclusions about short- and long-term condition can be made (figure 1).
The results of the 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 fingerprint 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 asssment, figure 2.
巫蛊师The partial discharge diagnosis may indicate weak spots in a cable connection. In order to run the measurement partial discharges are ignited in the cable 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 pul magnitudes, PD patterns and PD site location in a power cable. For utilities interested in applying PD diagnostics for
E. Gulski is with Delft University of Technology, The Netherlands
浙江省地图(e.gulski@tudelft.nl)
P.P. Seitz is with Seitz Instruments AG, Switzerland (pps@itz-instruments.ch)
B. Quak is with Seitz Instruments AG, Switzerland, (bq@itz-instruments.ch)
F. Petzold is with SebaKMT, Germany (petzold.f.@ba.com)
F. de Vries is with Nuon Tecno, Alkmaar, The Netherlands
(frank.de.)
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 developing knowledge rules to support AM decisions.
The tan δm easurement can be applied for the determination of the loss factor of the insulation material [3, 4]. This factor increas during the ageing process of the cable. The tan δm easurement should be regarded as a diagnostic and/or supporting measurement. In practice, in HV insulation is known that in addition to absolute value of tan δ at certain test voltage also the increment of tan delta as measured at two
Dedicated On-site Condition Monitoring of
High V oltage Power Cables up to 150kV
E. Gulski, Senior Member, IEEE, P.P. Seitz, B. Quak,
F. Petzold, Frank de Vries
T
condition asssment. The loss tangent is measured as function of voltage to check the quality of impregnation. The tan δ
v
alue 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 of the trace and thermal conditions of successive measurements are virtually identical. For HV paper insulated cables the tan δ c an be an important indicator of possible thermal breakdowns [4].
II. O N -SITE E NERGIZING O F HV P OWER C ABLES
or complete on-site diagnosis of transmission power cables by PD detection and dielectric loss 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 phas of the cable circuit can be energized and the PD puls can be coupled out. The capacitive power P = 2π•f• C cable •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 decrea the capacitive power demands for energizing cables as compar
ed 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 veral important characteristics such as
1. AC voltage type equivalence in PD inception process
for 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 low
level of system background noi,
5. IEC, IEEE standards conformity [2, 3, 4, 12, 13],
6. test cost efficiency bad on investment and maintenance
costs, transportability and operation of the method in different field circumstances,
the u of partial discharges and dielectric loss diagnosis at damped AC voltages (DAC) has become important solution for on-site testing and diagnosis of HV power cables (figures 3,4).
To generate on-site damped AC voltages up to 150kV peak and to perform advanced diagnosis by meaningful PD parameters modular hardware/software solution has been developed (figure 4). In particular, by u of
- modern solid-state technology and lar-control
techniques (HV Solid-State Switch),
- 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 analyzer)
novel system OWTS HV -ries type 150 has been developed for on-site PD diagnosis of HV power cables up to 150kV (table 1).
小图片头像
III. D AMPED A C V OLTAGE G ENERATION
or 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 a
F
TABLE I
MAXIMUM TEST VOLTAGES OF A 150KV TEST SYSTEM
Network voltage [kV] OWTS HV 150 [x U 0
]
50 3.6
66 2.7
110 1.6 132 1.4 150 1.2
F
Dielectric loss State Switch
Process Control Unit
Data Storage PD Analysis estimation
HV Source
HV Solid-Inductor Test Object: Power Cable
HV Divider
PD Coupling Capacitor
PD detector
C c
L
S Fig. 3: Schematic view of the damped AC circuit inclusive the partial discharge and dielectric loss measuring system.
150 kV Switch
150kV/ 7.1H Control HV Divider
HV Power Cable
150kV HV Source
Inductor Unit
Unit
PD Analyzer
PD coupling capacitor PD Detector
(a)
(b)
Fig. 4: Examples of on-site testing and diagnosis of HV power cables using damped AC test system 150 kV:
a) after installation in substation during testing a 9.6km long 50kV oil-filled cable,
b) after disasmbling prepared for transportation (weight 300kg)
capacitance (reprented as a capacitance C c ) is switched by S in ries with large inductance L, resulting in an sinusoidal damped AC voltage form with a frequency between 20Hz and few hundreds 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 veral sinusoidal AC cycles, figure 7. As a result, during the charging time no ‘‘steady state’’ DC conditions occur in the cable insulation [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 C c to an air-core inductor L =7.1H in a closure time of less than 1μs. In this way, and LC loop is created and an oscillating voltage wave is
applied to test the sample.
The test frequency of the oscillating voltage wave is approximately the resonant frequency of the circuit:
C L f ⋅=π21 This means that the test frequency of the applied DAC voltage is dependent on the cable capacitance, e figure 6. The HV power cable capacitance varies due to parameters like the
cross-ction of the conductor and the thickness and the type
of the insulation. In table 2 examples are shown for different
types of HV cables and cable length and the damped AC
frequencies to be generated using system as shown in figure 2).
Due to the low loss factor and design of the air-core, the
resonant frequency is clo to the range of power frequency of the rvice voltage: 20Hz to 300Hz.
二年级班主任工作总结The quality factor Q C of the resonant circuit, which is responsible for the attenuation of the oscillati
ons, can be expresd by:
Q C = √(L / (C * R A 2)
Here is R A the equivalent circuit resistance. 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 cond) is applied as test voltage to energies the cable sample.
IV. S YSTEM o support efficient on-site testing and diagnosis bad on field experiences the following hardware/software solutions have been developed (figure 8). 150 kV HV Source : to load the power cable capacitance
150kV HVDC voltage supply is ud with a circuit effective load current of 10mA. During charging the test object the linear and continuously increasing HV voltage is controlled by
the computer. In figure 5 the charging time in function of the load capacities is shown. The switching discharge current of
TABLE II
关于新年的诗词EXAMPLES OF TYPICAL DAMPED AC VOLTAGE FREQUENCIES FOR DIFFERENT LENGTHS OF TWO TYPICAL 150KV POWER CABLES
Length [km] XLPE (C=154pF/m)
[Hz]
Oil filled (C=373pF/m)
[Hz]
0.25 300 194 0.5 213 137 1 151 97 2 107 69 4 76 49
8 53 34 16 38 24 20 34 22
T
(a)
(b)
Fig. 7: Example of sinusoidal damped AC voltages as generated to energize at 100kV a capacitive load of 0.5μF and the measured PD
pattern: (a) full AC wave of 86Hz, (b) single AC cycle of 12ms
the power supply are limited by 15k Ώ ries resistor to max. 16A.
150 kV HV solid-state switch : The function of the 150kV switch is to establish a ries 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 permanently installed on the HV power supply.
150kV Inductor Unit : the system inductor consists of three in ries connected air coils with a total inductance of 7.1H. To make it sure that the damping of the voltage waves is mainly depending on the test object loss the inductor is air core type. Also the epoxy insulation of the windings provides PD freedom of this part.
HV Divider / PD coupling capacitor : to measure the damped AC voltages and to couple PD signals a PD free AC/DC divider C= 1nF/R= 800 M Ώ is integrated in the unit costing the PD detection system.
PD detection system : to detect PD signals a coupling device is connected to a PD-free coupling capacitor 1nF. The signals as detected in this way are process by digital PD detector. In particular this embedded system controlled by the PD Analyr Control Unit consists of IEC60270 conform signal processing and display in [pC] and to provide HF signals for localisation purpos wideband signal amplification and processing is ud.
PD Analyr Control Unit : Using special Ur interface software installed on a laptop the HV generation process, data measurement process, data storage and analysis are possible. Moreover, this unit communicates with PD detection system by wireless or optical link.
The operation of the hardware system as described in previous ction is supported by software concept as shown in figure 9. It follows from this figure that the whole on-site process of testing and diagnostic data gathering is divided into four steps. Cable System Definition : for practical reasons, a cable ction may be constructed from multiple parts of cable, which are connected to each other with cable joints.
Moreover such relevant information as the voltage ratting, insulation type, type and the position of the accessories are ud to identify particular test, figure 8.
Test Circuit Calibration : PD calibration of a measuring circuit means the reading adjustment of the PD detector. This calibration consists of a process where two calibrations procedures are automatically performed:
- Calibration of the PD reading; in accordance to IEC60270
Fig. 8: Example of cable system definition.机器人布里茨
Ur functions
Fig. 9: Example of test circuit PD calibration.
Actual DAC test voltage curve
PD numeric display
Actual PD pattern
Test object capacitance DAC voltage display mode
Ur functions DAC test frequency
Dielectric loss numeric display
Default PD range
Selected DAC test voltage
Actual DAC test voltage V peak [kV]
System status
Fig. 10: Example of the ur main screen during on-site testing.吉林农业大学排名
Fig. 11: Example of PD mapping (PD activity versus cable length) as obtained during on-site tests using OWTSHV 150 system up to 2xU 0 for three phas (red, yellow, and blue) for a 6.7km long 50kV oil-filled HV power cable. The X-axis reprents the length of the power cable including the position of the individual joints (black dots).
recommendation a PD pul calibrator as defined in the IEC 60270 has to be ud.
- Calibration of the PD pul propagation velocity reading: for this purpo the same as in 1 mentioned PD pul calibrator can be ud.
If possible in particular cas, on the basis of additional reflections as obrved on the calibration signals the location of individual joints can be done (figure 9).
voltage to the test object diagnostic parameters are measured (figure 10). The test voltage level lection and a correct lected PD measuring range are important parameters in obtaining correct measuring data. In particular, real-time registration of PD inception voltage (PDIV), PD extinction voltage (PDEV), PD-patterns is crucial for the execution of the on-site tests. For instance, during increa of the test voltage a sudden increa of PD activity may be ud to identify and real-time localize rious discharging defects.
Data Analysis; after during an on-site test diagnostic data have been collected analysis of data can be done. In particular with regard to PD data the location of discharge sites can be determined on the basis of VHF records. As a result, PD mapping can be obtained shown on the power cable the PD levels and PD concentration in function of the applied test voltages (figure 11). This information and all other data [21] can be ud to ass the condition status of a particular HV cable system.
Also bad on the dielectric loss measurements as performed at different voltage levels information can be obtained about the insulation degradation of particular cable ction (figures 12, 13). It is known that in addition to analyzing the differences between particular phas also evaluation of the increment of tan delta as measured at two designated voltages so called Δ tan δ or tip-up may be important for condition asssment of rvice aged cable system.
V. C ONCLUSIONS
n this contribution novel solution for on-site testing and diagnosis of HV power cables up to 150kV is prented. In particular the following can be concluded.
1.Applying modern solid-states materials, power electronics
technology and advanced signal processing allows
developing compact system to generate on-site damped
AC voltages up to 150kV.
2.PD and dielectric loss diagnosis at damped AC voltages
can be ud for non-destructive on-site testing of new and
rvice aged HV power cables.
名词英语3.Due to digital signal processing and filtering as well as
due to the fact that during application of damped AC
voltages no active voltage sources are switched on,
nsitive on-site PD detection (few pC’s) can be
achieved.
4.The complete solution for on-site testing and diagnosis
complies with international standards and recommendations [9, 10, 11, 18, 19].
5.Testing, measuring, analyzing and reporting process are
supported by embedded hardware/software solutions as
well signal processing tolls like wavelets and digital
filters.
6.Such characteristics like
- AC sinusoidal and non-destructive stress,
-
the available testing power (cables with length up to more
than 20km) and voltages (up to 250kV),
- efficiency in transportation (300kg… 400kg) , tting up
and on-site test execution (1/2 hrs/pha),
- diagnostic information as generated for HV power cables:
PD detection localization, dielectric loss [21],
I
