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"Integrated Earth Fault Solution" for Sinopec Fujian

Total Buck Transformer Substation 1# of Fujian Refining & Chemical Co., Ltd. is a 110 kV substation consisting of two 110 kV main transformers and two 6 kV busbar sections. It has secondary substations respectively for treated water, polypropylene, coking, hydrogenation, constant voltage, catalysis and circulating water. The 6 kV grid system is a resonance grounding system with the neutral point earthed via an arc suppression coil. The earth fault line selection devices for the microcomputer low current system are used for the single-phase grounding protection of each outgoing line circuit. Since their operation in 1997, the original air gap inductance regulation air-suppression system and its line selection devices have shown many problems, mainly including:
  
The grid capacitive current of two system sections measured at the total buck transformer substation is 47.9 A and 38.9 A respectively. Apparently, the 182 kVA / 50 A air suppression coil cannot meet current needs;
  
Due to outdated technologies and severely aged components and parts, the automatic tracking unit of the original arc suppression coil can never fulfill automatic tracking or compensation. The manual regulation and fixed capacitor compensation are combined as current mode. Accordingly, accurate compensation is impossible;
  
The action principle of the original earth fault line selection devices for the microcomputer system has big problems. Specifically, those devices cannot accurately indicate the fault state, but give poor results in respect of accurate action rates. They have delayed the troubleshooting and handling time of single phase-to-ground faults.
   
The leaders, maneuvering division and power supply workshop of Fujian Refining & Chemical Co., Ltd. have attached much more importance to the aforesaid issues. In particular, "Eliminating Hazards of Single-phase Grounding to System Operation and Production" has been considered as one of key aspects of "Ensuring Safe and Reliable Operation of Power Supply System", which was its critical program in 2003. Consequently, it was decided to replace and renovate its two arc suppression systems and line selection devices. Relevant personnel were organized to investigate the arc suppression coils and line selection devices popular in the current market with respect to the strength, technological force and production processes of their manufacturers, the product quality reliability, action principles of their arc suppression coils and line selection devices, and profiles of their users. It was concluded that the "Integrated Earth Fault Solution" integrating Type KD-XH arc suppression coils and the supporting Type DDS-02 line selection devices from Guangzhou Zhiguang Electric Co., Ltd. was featured by its excellent performance and thus ideal for renovation works.
  
Subject to a contract concluded in July 2003, a Type KD-XH01-400 / 6.3 arc suppression coil unit (range of offset current per unit: 0-110 A) was installed respectively on both busbar sections of the total buck transformer substation. Totally six Type DDS-02 line selection devices were installed in such substation and its five 6 kV secondary substations (for circulating water, hydrogenation, coking, and treated water). Due to few outgoing lines, other 6 kV secondary substations were not equipped with such line selection devices. Also, those original arc suppression coils and line selection devices were removed. On November 20 in the same year, all equipment were debugged, accepted and then put into operation. The system capacitive current measured at such arc suppression units conformed to the actual value. Since their operation, these arc suppression coil units and lower current grounding line selection devices have been operating normally without any fault.

 

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