State Grid Tianjin Electric Power Company Cable Branch Cable Transportation Inspection Northern Center Cable Test Class was established in September 2019, mainly engaged in the live detection of high-voltage cables within the jurisdiction of State Grid Tianjin Cable Company. The team currently has 11 employees, including 8 masters, accounting for 72.8% of the total number, 7 young party members under 35 years old, accounting for 63.6% of the total number. The team is equipped with various sophisticated testing equipment, which is a highly skilled and courageous team. The first live line inspection team. The daily work covers 770 kilometers of 110kV cables, 334 kilometers of 220kV cables, high-frequency partial discharge detection, ground current detection, infrared detection and other live detection tasks. Committed to timely discovering potential operating hazards of cable equipment, reducing the number of unplanned power outages, and providing important guarantees for the safe and stable operation of cable equipment.
Team Contact: Wei Wenting
Email: weiwttt@163.com
Cable High Frequency Partial Discharge Detection Technology (Part 2)
4Introduction of commonly used equipment manufacturers
PD CHECK is currently the most widely used high-frequency detection equipment in China. It adopts a broadband detection method. Most power supply companies, electrical research institutes, and universities are equipped with this equipment. The high-voltage state detection technical specifications and other related testing procedures are also based on the equipment map as an example , It has the advantages of high detection accuracy, easy analysis, simple operation, easy to carry, etc., suitable for general cable survey work. PD CHECK adopts the method of calculating the equivalent frequency and equivalent duration of the signal to classify the collected signals. A certain aggregated signal can be selected for analysis, which can distinguish signals from different sources. The classification method is shown in Table 1.
5Typical case
5.1 Anomaly Overview
In December 2017, the cable company found that a certain 35kV cable had a partial discharge abnormality during the live detection of the 35kV cable outlet of a 220kV substation. The PRPD spectrum has obvious power frequency phase correlation, and the discharge amplitude is large. , Showing the characteristics of insulation defects.
5.2 Test objects and items
The specific situation of the cable line is shown in Table 2. The test item is high-frequency partial discharge test.
5.3 Testing equipment and standards
See Table 3 for information about the equipment used in the test.
The determination of the test results is based on the following standards:
1. Q/GDW 11400-2015 "Guidelines for the Field Application of High Frequency Partial Discharge Detection Technology for Power Equipment"
2. Q/GDW 11223-2014 "Technical Specification for High Voltage Cable Condition Detection"
3. Q/GDW11224-2014 "Technical Specification for Partial Discharge Detection Equipment for Power Cables"
4. DL/T664-2016 "Application Specification for Infrared Diagnosis of Live Equipment"
5.4 Testing conditions
The working conditions of the test day are shown in Table 4.
5.5 Test data and analysis
On December 20, 2017, the operator found that the cable had a suspected partial discharge abnormal signal, the time domain map had discharge characteristics, and the PRPD map showed obvious power frequency phase correlation. The partial discharge test results are shown in 5.
It can be seen from the table that the PRPD spectrum of the cable has obvious power frequency phase correlation. The A-phase discharge amplitude of No. 1 cable is 140mV, the B-phase discharge amplitude of No. 1 cable is 210mV, and the C-phase discharge amplitude of No. 1 cable. The value is 600mV, and the three-phase discharge amplitudes of No. 2 cables A, B, and C are 40mV, 15mV, and 245mV, respectively. It can be preliminarily concluded that the partial discharge signal comes from No. 1 cable. Further analysis of cable No. 1 showed that the discharge amplitude of phase C was significantly higher than that of phase A and phase B. The power frequency phase was opposite to phase C. From this, it can be preliminarily determined that the partial discharge signal originated from phase C. Other phases are related to other lines. The signals are all caused by the C-phase discharge of No. 1 cable. From the above analysis results, it can be preliminarily concluded that the line is suspected to have insulation defects.
5.6 Conclusions and recommendations
According to the comprehensive judgment of the detection map, the suspected partial discharge signal originated from the C-phase of the 1st cable, showing the characteristics of insulation defects, and other phase-related signals were all caused by the 1st-cable C-phase discharge. It is recommended to retest the No. 1 cable of this line and other related lines to observe its development trend. At the same time, it is recommended to use the means of oscillating wave to detect the power failure of the upper cable, and locate and verify the abnormal signal detected above.
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