.10 Kv With A Grid Flexible Neutral Point Grounding Mode And The Ground Fault Detection System

On the basis of fault characteristic analysis for distribution networks and by comparing both the advantages and disadvantages among the three different neutral ground modes, such as ungrounded, Petersen coil grounded as well as resistor grounded, a neutral flexible ground method is proposed in this paper. For such method, the neutral equipment consists of a auto-tuned Petersen coil and a paralleled automatically switched resistor. The Petersen coil is mainly used to compensate the capacitive current and then to increase the self-restoration probability after single phase fault, while the resistor is used to restrain the over voltage due to arc grounding and resonance. Further more, the paralleled ground resistor can be adjusted to produce enough active component in the fault current that can help to identify the faulty feeder from other feeders in a substation, and even the fault location on the feeder. Consequently, the reliability and availability of distribution network can be improved considerably.The above neutral flexible ground method can also be applied in cases of such lOkV distribution networks with lower capacitive current where Petersen coil is not needed according to DL/T620-1997, a standard for the electric power industry. In such cases, a two tapped Petersen coil is enough for automatic adjustment to ensure over-compensation to the network. For the networks with capacitive current greater than 100A, the Petersen coils should consist of a fixed part and an auto-tuned part.Through numerical calculations and analysis of the single phase to ground fault of a flexible ground system by the ATP, an Alternative Transient Program to the Electro-Magnetic Transient Program (EMTP), a new simple detection method for the faulty feeder is put forward based on both the value and direction of the active component of zero-sequence current. The method ensures correct selection of faulty feeder in a network for a faulty resistance lower than 3000Q. This paper also proposed a new fault locating method based on either the active component increment or the amplitude increment of zero-sequence current. In addition, a 380V experiment model was built up with which some propositions are proved by experiment.Neutral equipment parameters, the measures as well as the control rules for the flexible ground networks are also presented in the paper. The parameters and control rules has been tested by experiment in a real lOkV network in Xueying substation managed by Langfang Power Supply Bureau. And the test results proved that the performance is satisfied.