Generally, two kinds of abnormal conditions are presented when the power transformer core is grounded at multiple points.
1. The change of dissolved gas in the core of the power transformer
When the dissolved gas in the transformer causes the multi-point ground fault of the iron core, the chromatographic analysis results show that the following characteristics are generally available:
(1) The total hydrocarbon content is high, often exceeding 150 ppm, and the composition of its constituent gas content is decremented according to the order of C2H4-CH4-C2H6-C2H2.
(2) C2H4 is the main characteristic gas of multi-point ground fault of iron core. If we calculate the ratio of hydrocarbon composition to total hydrocarbons, we calculate the highest C2H4 ratio.
(3) The rate of total hydrocarbon generation often exceeds the value of the regulation, during which the rate of ethylene increases sharply.
4) When using the IEC three-ratio method, the ratio of the characteristic gas is generally 0, 2, 2
(5) The temperature at the fault point of the budget is generally higher than 700 degrees, less than 1000 degrees.
2. The power transformer core grounding current changes
State Grid Corporation Enterprise Standard Q/GDW534-2010 "Technical Guidelines for Online Monitoring System for Substation Equipment"
It is necessary to use the variable power transformer core grounding current online monitoring system to monitor the grounding current of the transformer core in real time whether it exceeds the "Progressive Experimental Regulations for Power Equipment". The grounding current of the transformer core in the regular operation in DLT/596-1996 is not more than 0.1A, if the iron core is multi-point grounded and the circulation is large, the current flowing through the core grounding wire will increase significantly, and some can reach several amps or even tens of amps. For example, in March 2012, a certain power supply bureau used the JTX-type transformer core grounding current online monitoring system of Zhuhai Jisen Electric Co., Ltd. At 3:23 pm on July 18, 2012, the grounding current of the A-phase iron core of the 500KV main transformer was detected to be 15.3A. After a useful investigation, it was found that the iron core was grounded due to metal foreign matter. And useful to remove the danger of the transformer.http://www.wenergytech.net/