Holding circuit having bus residual voltage

Abstract

A holding circuit with busbar residual voltage relates to the technical field of power systems. It is characterized in that it includes a Rock coil, a measurement and control unit, a converter, a cut-off switch, a current limiting impedance, a microcomputer integrated protection device, and a current transformer. One end of the measurement and control unit is connected to the Rock coil, and the other end is respectively connected to a computer. One end of the comprehensive protection device, one end of the inverter, one end of the disconnect switch and one end of the current limiting impedance, the other end of the microcomputer integrated protection device is connected to the current transformer, one end of the current limiting impedance is connected to the disconnect switch, and the other end is connected to the other end of the inverter. It can replace branch circuit breakers and ordinary series current-limiting reactors. It can quickly switch on the current-limiting impedance, and the residual voltage of the busbar is high, which can meet the requirements of maintaining important loads to continue running without being affected.

Description

technical field [0001] The invention relates to the technical field of electric power systems, in particular to a holding circuit with busbar residual voltage. Background technique [0002] At present, in the power supply system of a certain voltage level of the medium-voltage power grid in many enterprises, if a short circuit occurs in a certain branch, the voltage on the bus connected to the branch will drop sharply, and the residual voltage of the bus is generally lower than 20% of the rated defined voltage. , only when the branch circuit breaker is disconnected and the short-circuit fault is removed, the bus voltage can recover. The period from the steep drop to the recovery of the bus voltage is the time for the circuit breaker to open the short-circuit fault, which is about 0.1 seconds, that is, the microcomputer The time for the comprehensive protection to judge the fault (20ms-30ms), plus the inherent action time of the circuit breaker (40ms-80ms), plus the arc zero-...

AI Technical Summary

Problems solved by technology

During the occurrence of "power shaking", the residual voltage of the bus is very low, which interrupts the operation of some loads that have not experienced short-circuit faults, such as frequency converters, motors, relays, solenoid valves, etc. These loads that respond obviously to "power shaking" are called sensitive. The load is characterized by mechanical movement and the presence of electric energy or magnetic energy storage components. The motors used in the enterprise are mostly asynchronous motors, and the maintenance of the rotating magnetic field of the asynchronous motor comes from the reactive power support of the power grid. When a branch is short-circuited The residual voltage of the busbar is very low, and the asynchronous motors on other branches cannot receive reactive power support, and the short-circuit point needs to output short-circuit current. The short-circuit time constant of the asynchronous motor is below 30ms, and the "shocking" time is close to 3T, which decays according to the exponential law The magnetic field of the asynchronous motor is exhausted, and at the moment when the voltage recovers after the short-circuit fault point is removed, the power grid has an impact of 5-7 times the rated current on the rebuilt magnetic field of the asynchronous motor, causing relay protection to malfunction

[0003] Usually, when the residual busbar is below 50%, the tolerable "shock" time of the sensitive load is no more than 30ms. When a short-circuit fault occurs in the external network, all loads or some important loads of the internal network can be switched to another external network. However, if a short circuit occurs in a certain branch in the intranet, it cannot be switched as a whole, but only partially. It can solve the problem of outage of important loads caused by the short circuit of the intranet. The necessary condition is to have a suitable extranet that can be switched. If there are many important sensitive load branches in the intranet, the cost of partial switching will be too high

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