Conference Proceedings of CMD2010
Application of Online PD Monitoring System Using HF/UHF PD Sensors for GIS and Cable Chen Min1*, Koji Urano1, Tang Jian1, Qui Zhongwei1, Atsuhide Jinno2 1
SE Technology Limited, Hong Kong, China 2 J-Power Systems Corp. Japan *E-mail:
[email protected]
Abstract—The internal type UHF PD sensor was made about 15 years ago for GIS to detecting or monitoring if any PD existing in GIS. In recent years, the external type UHF sensor has been newly developed and successfully used in the GIS online PD monitoring system. Meanwhile, external type of HF PD sensor has also been successfully applied for GIS PD detection and PD localization. The advantage of UHF PD sensor is its detection frequency band that reaches 3 GHz; and advantage of HF PD sensor is its high sensitivity area of PD detection that covers 3 GIS bays. Therefore, it is better to apply these two kinds of PD sensors in a GIS PD monitoring system. This paper describes the onsite verification test results based on an online PD monitoring system using HF/UHF PD sensors. Keywords – UHF PD sensor; HF PD sensor; GIS; Sealing end; online PD monitoring; Neural works; PD classification
I.
INTRODUCTION
A newly developed online Partial Discharge (PD) monitoring system using UHF PD sensor and HV PD sensor has been successfully applied for the whole of GIS equipments consists of 220kV GIS outdoor block and 110kV GIS indoor block in a power substation. As electrical PD detection method, the conventional PD measurement and PD condition monitoring for GIS is using internal UHF PD sensor installed inside GIS or external UHF PD sensor installed on outer edge of the insulation spacer of GIS to detect the electro-magnetic waves from the PD occurred inside GIS. For the single-phase GIS to keep the PD detection sensitivity high enough, at least six or nine UHF PD sensors are required for one circuit bay of 220kV GIS because of highly attenuation of UHF PD signal propagating in GIS. In recent years, it was reported that the PD existing in GIS was successfully detected and located with the HF PD sensor installed at the GIS sealing-end for cable circuit[1][2]. Applying pulse current measurement method to GIS PD measurement has been verified in commercial operation. It was also reported that the found PD was successfully monitored by an online PD monitoring system using HF PD sensor installed at the GIS sealing-end for years. The advantage of HF PD sensor is that it detect a PD of 10-20pC in the area of about three GIS bays at 20-30MHz, since PD signal less than 100MHz can propagate in GIS longer. As the same to the 220kV singlephase GIS to keep the PD detection sensitivity high enough, only three HF PD sensors are enough for monitoring one circuit bay. For the reason, the application of HF PD sensor to GIS PD measurement will be more and wider, particularly
with the development of intelligent identification and classification method for PD judgment. However, there are much more noise at the frequency less than 30MHz and this requires higher function of noise suppression for PD measurement. On the other hand, the application condition of HF PD sensor is that there should be the cable sealing-end in GIS. This paper introduces a newly developed online PD monitoring system for a 220kV and 110kV GIS substation in which there are more than 25 GIS bays and more 100 PD sensors including HF type and UHF type are used. The configuration, specification and the monitoring functions of the PD monitoring system are also shown, such as the automatic data save, automatic transmitting, the function of PD judgment, auto-alarming and the remote monitoring performance and its auto report creating function. II.
UHF PD SENSOR
A. External type of UHF PD Sesor The external type UHF PD sensor, as shown in Figure 1, has been developed and successfully used for detecting the PD in GIS. External UHF sensor usually consists of an electromagnetic wave (EM wave) antenna and a preamplifier, both of which can be fixed in small metal box. For GIS PD monitoring the sensor box is easily installed on the outer edge of the insulation spacer, no need any outage. When a PD exists in GIS, the EM wave signal emitted from the PD will propagate along the GIS enclosure and some EM wave signal can escape from the insulation spacer, and naturally the UHF
Figure 1. External UHF PD sensor
sensor can detect the PD signal. External UHF sensor also has a wide frequency band from tens of MHz to 3GHz so that
Conference Proceedings of CMD2010 detection frequency can be selected higher than 400MHz (to avoid the corona disturbance from Overhead equipment) and of the higher S/N rate. However, because the highly attenuation must happen when EW signal propagates in GIS, the effective PD detection sensitivity area of the UHF sensor is usually 2-8 meters long.
UHF antenna inside GIS Preamplifier
B. Internal type of UHF PD Sesor Comparing with the External UHF PD sensor described above, the internal UHF sensor was quite early developed and put in use of GIS PD monitoring, about 15 years ago. As shown in Figure 2, internal UHF sensor usually consists of an internal EW antenna and external preamplifier. Since the EM wave antenna is inside GIS it can directly catch the EM wave signal from PD and it has not only higher PD detection sensitivity but also higher resistance of outer disturbance. Internal UHF sensor also has the same wide frequency band from tens of MHz to 3GHz and its effective PD sensitivity area is more than 5 meters. However, because the internal EW antenna must be installed inside the GIS, it should be designed as a non gas leakage and reliable insulation part of the GIS. It means this type of UHF sensor should be usually installed in GIS and tested in GIS manufacture. In other words, it is difficult to install internal type UHF sensor on-site and it is difficult to use this type sensor for those GIS already in operation. III.
Figure 2. Internal UHF PD sensor
Ground wire HFCT
Figure 3. HFCT PD sensor at sealing end
HF PD SENSOR Capacitance lead wire (C-arms)
PD signal has a quite wide frequency distribution. The frequency component from hundreds of MHz to GHz is electric-magnetic wave that can be detected by UHF PD sensor. While the frequency component from several Hz to tens of MHz is traveling wave or so-called pulse current that propagates in coaxial cable including GIS and can be detected by HF PD sensor (or EHF sensor). PD measurement using HF PD sensor is also called pulse current method. HF PD sensor can be usually divided into two types: HFCT and capacitive coupler, as describes in the following.
PD detector
A. HFCT PD sensor HFCT means high frequency CT, of which the frequency band is from several Hz to tens of MHz. The frequency character is mainly determined by the CT core material and the turns of primary coil. HFCT is a kind of inductive sensor so its working principle is quite similar to the ordinary CT using in power system. Since the core of HFCT is usually made as opening ring, therefore, it is easy to install on the earth wire from GIS sealing end or on link cable for cross bonding to detect the PD signal pass through them, as shown in Figure 3. However, the attenuation of PD signal is direct proportion to the length of the earth wire or cable, the HFCT is better to use for the short earth wire or grounding wire.
the S/N rate. Here, the impedance of PD traveling wave is the key point for PD detection. If there is a GIS sealing end for connecting cable circuit, generally, the cable sheath is not directly connected with GIS case or the ending supporter while is earthed with grounding wire of several meters long. Therefore, an outer man-made capacitive by-pass (so-called capacitor arms) can be installed between the sheath terminal and the nearest grounding point of GIS or the ending supporter. In other words, a high frequency channel with low impedance can set up for pulse current detection at tens of MHz, as shown in Figure 4.
B. Capacitive coupler PD sensor Capacitive coupler is a kind of impedance matching detector. Since there are various strong noises in the substation site, especially concentrating in the frequency band below 5MHz, it is necessary to select higher PD detection frequency to higher
In order to apply PD sensor reasonably and effectively four kinds of the PD sensors are compared and summarized in Table 1. As examples, two on-site verification PD tests are shown as the following.
Figure 4. Capacitive coupler PD sensor at EB-G
IV.
COMPARISON OF UHF SENSOR AND HF SENSOR
Conference Proceedings of CMD2010 Table 2 Simulated PD Injection Result
Table 1 Comparison of UHF and HF Sensor for GIS Application PD sensor type External UHV Internal UHV HFCT CC PDD
PD signal property EM wave EM wave Pulse current Pulse current
Frequency band
PD detection sensitivity
Noise resistance
Effective detection
area
-3GHz
high
high
2-5 m
-3GHz
higher
higher
>5m
-100
high
MHz
-100 MHz
high
medium medium
3 bays 3 bays
Inject to X /detect at X
On-site installation
Easy, no outage Difficult , outage Easy, no outage Easy, no outage
A. UHF PD Measurement As shown in Figure 5, the PD measurement on GIS using 4 UHF sensors at the same time. There are total seven insulation spacers (ISP) in the GIS bay measured. It is evident that only from the ISP-2, ISP-3 and ISP-4 the same abnormal signal classified as PD can be detected by UHF sensor. The detection frequency was more than 600MHz. It is as shown as that the propagation distance of UHF PD signal is not so long, just several meters.
(injection at Circuit F)
PG Output (pC) 100 30 20 10
OSC
Inject to Z /detect at X
( injection at Circuit E)
OSC
(V)
Spectrum (MHz)
3.0 0.8 0.6
5-45 15-35 15-25
( injection at Circuit H)
OSC
(V)
Spectrum (MHz)
(V)
Spectrum (MHz)
1.0 0.4 0.2 -
15-32 15-32 15-32 -
0.8 0.3 0.2 -
15-34 20-33 20-32 -
signal from point X, Y and Z one by one and measure the propagating injected signal. The measurement results are summarized in Table 2. When only 10pC was injected to point X, it was detected with 0.6V at 15-25 MHz, but it could not be seen when injecting the same signal to point Y or point Z. While injected 20pC to point X, Y and Z, all the propagated signals were measured from point X as 0.8V at 15-35MHz, 0.2V at 15-32MHz and 0.2V at 20-32MHz. It is shown that the PD sensitivity area of HF sensor can cover 3 circuit bays. V.
-q-n signal pattern
Inject to Y /detect at X
ONLINE PD MONITORING SYSTEM
A newly operating online PD monitoring system for a GIS substation consisting of 220kV outdoor GIS and 110kV indoor GIS is introduced. The 220kV GIS block consists of overhead circuit bay, cable circuit bay, PT bay and bus connection bay, so does the 110kV GIS block. Based on the characteristics of UHF sensor and HF sensor at all the cable sealing end HF sensor were installed and for other GIS bays UHF sensor were used, as shown in Figure 7, and the PD signal processor unit in
Figure 5. Propagation distance of UHF PD signal
B. HF PD Measurement As shown in Figure 6, another PD measurement on GIS using 3 HF sensors at the same time. In order to evaluate how long the distance on GIS where the PD pulse current can propagate, the HF sensor were installed at the three GIS sealing-ends of cable circuit E, circuit F and circuit H respectively. For easy describing, circuit F was named as point X, circuit E named as point Y next to point X, and circuit H named as point Z, skipped over one bay circuit G. Then inject a simulated PD
Figure 7. HF sensor and UHF sensor on GIS
Local Station (LS)
Local Signal Processor
Channel Switch
PC User Interface
Ethernet Optical Units
Ethernet Units
Master Station (MS) Figure 6. Effective PD sensitivity area of HF sensor
Figure 8. Local station and master station of system
Conference Proceedings of CMD2010 the local station and the master station as user’s back stage are shown in Figure 8. The whole system configuration is shown in Figure 9. The GIS condition monitoring screen as the user interface is shown in Figure 10. As the key functions of the system, multiple logic gates are built based on the five PD factors including f (detection frequency), (PD phase position), q (signal magnitude), n (PD repetition rate) and t (continuous time). Furthermore, a set of neural works is also constructed for classifying PD and noise and for classifying sorts of PD if the PD is determined. For example, when abnormal signal is detected and is also judged as PD by -q-n logic gate there is a trigger signal output for alarming. Meanwhile, if the neural works also classified it as PD another trigger signal output for the same event. The total judgment program now will prompt up a PD alarming on the monitor screen. Then PD classification neural works will give the result of PD sort and show indicating massage on the screen. Figure 11 shows the configuration of the PD classification neural works and Figure 12 shows an example of neural works classifying PD pattern based on the -q-n graphic information.
external type UHF sensor is easy to install on GIS, no need any outage, particularly easy to use for those GIS in operation. 2) HF PD Sensor: Two kinds of HF PD sensors were also discussed. HFCT has the advantage of simplest structure and easy to install but it is not suitable to use for the long earth wire or ground cable; While the capacitive coupler PD sensor is better for this grounding condition. 3) Comparison of UHF and HF Sensor: UHF sensor has higher sensitivity but effective PD detection area is relatively small; While HF sensor is easily disturbed by lower frequency nois but its effective PD detection area can cover 3 GIS bays. 4) A newly developed online PD system: The system uses both UHF and HF PD sensor. It has strong function that can not only determine PD by multiple factors logic gate but also can classify PD sort by neural works.
Figure 11. Configuration of neural works for classifying PDs Figure 9. Configuration of online PD monitoring system for GIS PD classification by neural works
Figure 12. Example of neural works classifying PD with -q-n graphic
REFERENCES Figure 10. User interface – condition monitoring screen
VI.
[1]
CONCLUSION
1) UHF PD Sensor: Two kinds of UHF PD sensor were discussed. The internal type UHF sensor has the advantage of higher sensitivity but it is not easy to install on-site; While The
[2]
M. Chen, K. Urnao, K. Choy: “Application of Long-term Online Partial Discharge Monitoring System for GIS” in CMD2006 Proceeding, Changwon Korea. M. Chen, K. Urnao, YC. Li. Choy, A. Jinno: “Application of Combined PD Sensor for GIS PD Detection and Condition Monitoring ” in CMD2008 Proceeding, Beijing China
Conference Proceedings of CMD2010
