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Common selection methods for neutral point resistors in transformers
By Yang QiangMarch 15th, 2025358 views
Consider the capacitance current of the transformer and the capacitance current of the outgoing cable. Unless the cable has many and long outgoing lines, the capacitance current is generally around 3-6A. In order to prevent the capacitance current from acting between the stator and rotor of the generator for a long time, causing inter turn short circuits and burning out the generator, a grounding resistor of 10A is used in the design. The commonly used 10kV unit uses a 600 Ω resistor with a 10A parameter.
Due to the use of backup transformers directly in the system, there are many cables and the transformer does not have a neutral point resistor. Considering that the current generated when one phase of the cable is grounded is relatively high, if a 10A grounding resistor is used, the voltage of the healthy phase will rise too high, causing imbalance and putting the system into a protective state, which is not conducive to delayed operation. If a larger current neutral point resistor is used, the three-phase imbalance difference will be small, and it can still work for a period of time. When it is briefly grounded and can be restored, it can continue to work.
