Research On Neutral Point Compound Grounding Mode Of 10kV Distribution Network

Neutral point grounding mode of distribution network is always the focus of attention, which plays an important role in the safe and stable operation of the distribution network and the power reliability of the users. With the rapid development of economy, distribution network structure gradually changes and the grounding capacitance current is increasing. The traditional neutral grounding mode has many problems, so it is of great significance to the safe and stable operation of the system to choose a suitable neutral grounding mode.The paper establishes a simulation model of single-phase earth fault under different neutral grounding mode based on EMTP(electromagnetic transient simulation software). The influence of ground resistance, load and distribution network structure is studied to different neutral grounding modes and neutral compound grounding mode is put forward for 10 k V distribution network. The single-phase earth fault diagnostic device is designed based on the Multisim(electronic circuit design software) and the effect of the putting time of the neutral grounding device on the system is simulated and studied. The main results obtained are as follows:(1)The proportion of cable in distribution network is higher and the system grounding capacitance current is larger,neutral non-grounded system is not effective in extinguishing arc and is easy to produce arc grounding overvoltage. Even though large ground resistance can effectively reduce the arc grounding overvoltage and fault current,it will lead to low zero sequence voltage and even can't start the fault alarm for low-resistance grounding system. The larger system load, the smaller the single phase to ground fault overvoltage and the fault point current, which is beneficial to the system.(2) Neutral point compound grounding mode is put forward for 10 k V distribution network. The neutral of the system is not grounded in normal operation; the neutral of the system is grounded via arc suppression coil if intermittent arc grounding occurs and is not grounded if intermittent arc grounding disappears; the neutral of the system is grounded via small resistance if permanent phase-to-ground faults occurs, then carry out the fault line selection and remove the fault line, the line selection is completed to withdraw from low resistance. Research shows that it doesn't have a dramatic impact on the system that putting arc suppression coil or small resistance and verifies the feasibility of neutral point compound grounding mode. Taking IEEE RBTS Bus2 as an example, the reliability of distribution network under different neutral grounding modes is evaluated, which proves that neutral point compound grounding mode is more reliable than the other grounding methods of neutral point.(3) The single-phase earth fault diagnostic device is designed based on the Multisim. The simulation results show that the device can effectively put the arc suppression coil to suppress arc grounding overvoltage when intermittent arc grounding occurs and can put the small resistance when permanent phase-to-ground faults occurs. Neutral device does not operate to normal operation,low frequency resonant and high frequency interference system.