A zero-sequence overcurrent protection method blocked by resistance-capacity ratio

Abstract

The invention discloses a zero-sequence overcurrent protection method blocked by a resistance-capacity ratio condition, which is suitable for a neutral point grounded system through a small resistance. Step 1: collect zero-sequence voltage and zero-sequence current, and calculate the absolute value of the resistance-capacity ratio in real time; Step 2: Compare the absolute value of the zero-sequence current and resistance-capacity ratio with the corresponding threshold value to determine whether a ground fault has occurred; Step 3: If it is determined to be a ground fault, it will trip after a set delay. The resistance-capacity ratio threshold used in this method is calculated based on the neutral point grounding resistance of the neutral point through a small resistance grounding system and the total capacitance current level of the system to ground.

Description

technical field [0001] The invention relates to a grounding fault protection method for power transmission and distribution in a power system, in particular to a zero-sequence overcurrent protection method blocked by a resistance-capacity ratio condition. Background technique [0002] When the distribution network adopts the grounding method of the neutral point through a small resistance, if a single-phase metallic grounding fault occurs, the fault point and the small resistance of the neutral point form a zero-sequence current path, so the fault current is relatively large, and the zero-sequence overcurrent protection can be used Quickly remove the ground fault; and for the neutral point ungrounded system or the neutral point through the arc suppression coil system, even if a metallic ground fault occurs, the fault current is still small, and the conventional zero sequence protection cannot quickly remove the fault, so it is generally allowed to operate 2 hours. In view o...

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Problems solved by technology

In addition, due to the expansion of the scale of the power grid, the capacitive current of the system to the ground continues to increase, resulting in insufficient compensation capacity of the arc suppression coil. Some substations have gradually switched to the neutral point through a small resistance grounding method because of the difficulty in expanding the capacity of the arc suppression coil.

[0003] However, for the 10kV system whose neutral point is grounded through a small resistance, due to the consideration of selectivity, the zero-sequence overcurrent protection can only respond to the grounding fault with a transition resistance below 100Ω when setting the value. Fault, not only the zero-sequence protection cannot trip, but also because the open triangle voltage (secondary rated value 100V) is less than 10V at this time, and it cannot reach the threshold for sending a zero-sequence voltage alarm signal, so the system is in a state where it cannot trip and there is no alarm The fault state indicated by the information can only be tripped after the fault develops more seriously and reaches the protection action condition. In some areas, even the wire fell into the pond and boiled the water without protection action.

[0004] The neutral point grounding method through a small resistance is generally used in systems with many cable lines, and there are few cases of high-resistance grounding. With the promotion, the cases involving overhead lines have also increased. If the distribution line falls On wet sandy land, dry grassland, turf and other media, if the transition resistance is in the range of 200-500Ω, it will enter a high-resistance ground fault state with no tripping or alarm information, which will easily leave long-term safety hazards

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