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Multi-mode Grounding Renovation Project of Zhongshan

The 110 kV Baishi Substation of Zhongshan Power Supply Bureau has three main transformers and four 10 kV busbar sections, among which 2AM and 2BM busbar sections operate in parallel. Currently, its eighteen 10 kV outgoing lines (and 17 lines for standby) consist of overhead lines and cables.Before renovation, there were three arc suppression coils, among which two were of the multi-tap type and one was of the high-impedance type. They were supplied by different manufacturers and had inadequate capacity. As a result, the line selection accuracy for earth faults was less than 60%. In the renovation of the Baishi Substation, the application of three intelligent multi-mode neutral grounding systems offers a full automatic and whole-process solution for its 10 kV distribution network.
 
1. Commissioning Test & Verification of Intelligent Multi-mode Neutral Grounding Systems

On November 2, 2012, such systems before operation were given two metallic grounding tests at the 110 kV Baishi Substation. An artificial grounded single-phase short circuit was made by closing switches in the substation to verify the action reliability of such grounding systems.The manual remote control requiring more time could not result in remote-controlled switch closing and opening within 10s. For both grounding tests, low resistors were automatically used into the systems after 10s. Protective devices achieved the switch tripping in grounded lines. After faults were isolated, the normal operation of those systems was recovered. The systems ran correctly, with records shown below.

 

Multi-mode Grounding Renovation Project of Zhongshan
1st artificial grounded single-phase short circuit 

 

Multi-mode Grounding Renovation Project of Zhongshan               

2nd artificial grounded single-phase short circuit

   

The data on this commissioning test and verification are shown as follows. In both grounding tests, the arc suppression coils are going into the compensation state and fulfilling accurate compensation as per given parameters the moment that earth faults occur. After compensation, the residual currents are less than 5 A, without any arc grounding overvoltage.

     

Multi-mode Grounding Renovation Project of Zhongshan

System Actions of the 10 kV Lines in the Baishi Substation during Two Artificial Grounded Single-phase Short Circuits 
During grounding for more than 10s (set point), low resistors from the complete unit are used, so that strong current signals generated enable the line protective devices to accurately trip those faulty lines. Consequently, faults are successfully isolated and the systems operate normally again.

            

 

Analysis on the Operation of  Intelligent Multi-mode Neutral Grounding Systems

Since its operation on November 3, 2012 till December 18, 2015, the 110 kV Baishi Substation has had totally 159 single-phase groundings on its 10 kV lines, among which 148 were transient earth faults less than 10s, amounting to 93%.There were 11 permanent earth faults, in which the low resistors were used for Intelligent Multi-mode Neutral Grounding System #2 in nine cases and for System #3 in two cases. This was consistent with protective actions of the zero-sequence current on its lines.

For all earth faults, the arc suppression coils in such intelligent multi-mode neutral grounding systems have made fast and accurate compensation. For those faults with grounding more than 10s, the correct application of low resistors and protective actions of the zero-sequence current lead to the accurate protection from faulty lines and the fast recovery of normal system operation. These 11 permanent earth faults involve similar metallic grounding (voltage = 4802 V) and high resistance grounding (voltage = 1351 V). After the application of low resistors, the zero-sequence current can act correctly and protect from faulty lines.

 

 

 

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