On-line monitoring of reactive power switching in substation based on high frequency transient voltage monitoring of PT secondary voltage of substation bus

In recent years, the damage of substation equipment caused by reactive power switching and the fire of dry-type air-core reactors have occurred frequently, which seriously affects the safe operation of the power grid.The opening overvoltage generated during the opening process of the circuit breaker is one of the main reasons for equipment failure. The frequency and amplitude of the transient overvoltage caused by re-ignition are much higher than the normal switching transient voltage. Therefore, it is necessary to Attention and assessment of re-ignition and its impact on equipment insulation. Whether the circuit breaker (especially for the vacuum short-circuit circuit breaker) switching reactive equipment produces re-ignition is related to two factors: the reactive switching characteristics of the circuit breaker itself,and the parameters of the reactive circuit (including cable length and equipment equivalent capacitance, etc.), the unreasonable selection and the mismatch between the two lead to the main reason for the high frequency of re-ignition. In the design stage of the substation, the selection of parameters of reactive power circuit equipment, conductors, and whether to install a voltage limiting device has not been specified from the perspective of suppressing reactive switching transient voltage. The characteristics of the switching reactive power equipment of the vacuum circuit breaker itself do not require factory and new installation tests. The dispersion of different equipment parameters leads to differences in transient overvoltage levels, which need to be evaluated; The magnitude of the overvoltage and its hazard are also lack of monitoring and control, resulting in frequent transient faults of reactive power equipment during operation, and the cause of the fault is difficult to trace. In response to this problem, this paper discusses the re-ignition rate of reactive power circuit switching and the peak oscillation voltage as evaluation indicators to measure the operating state of reactive power equipment. And the necessity to carry out the monitoring of transient characteristics of reactive power equipment switching in the actual operating state,Aiming at the problem of lack of online monitoring methods for reactive power switching, an online monitoring method for reactive power switching transient process based on high-frequency response of bus PT is proposed, which fills the gap of reactive power equipment operating status monitoring.

I. Introduction

On-line monitoring of reactive power switching in substation based on high frequency transient voltage monitoring of PT secondary voltage of substation bus. However, in recent years, many operating units have experienced problems such as damage to the low-voltage side busbar equipment caused by switching reactive power, and dry-type air-core reactors catching fire, which seriously affects the safe operation of the power grid ^[1]–[3]. Investigations show that most faults of shunt reactors are caused by inter-turn short circuit caused by insulation breakdown. The relevant literature^[4] analyzes the causes of reactor damage and believes that the reactor failure is formed under the action of electrical stress, mechanical stress, thermal stress and other factors[^5-7]. But no matter which reason is dominant, the final failure form is the insulation breakdown between turns under the action of overvoltage. Relevant literature points out that the overvoltage amplitude of the reactor opening is low when no re-ignition occurs, and it is considered that this value is safe. However, if re-ignition occurs during the opening process, a re-ignition over-voltage with an amplitude and frequency much higher than the normal switching over-voltage will be generated, resulting in a decrease in the inter-turn insulation of the equipment.