RU2137278C1 - Method and device for protecting saturation-controlled reactor against internal short circuits - Google Patents

Abstract

FIELD: electrical engineering. SUBSTANCE: protective gear responds to ac voltage appearing upon occurrence of any internal short circuit across points of reactor control windings electrically balanced with respect to ac current connected to reactor saturation source. Emergency current starts flowing in thyristors connected to these points in parallel opposition and in current transformer arranged around their bus system at output of saturation source; overcurrent relay operates in response to this current and passes signal for disconnecting reactor from supply mains. EFFECT: improved speed of response and simplified design of protective gear. 2 cl, 1 dwg

Description

 The invention relates to the field of electrical engineering and can be used to protect against windings and short circuits on the body of windings controlled by magnetization of reactors.

 Known traditional methods for protection against short circuits of reactors and transformers, using maximum current, gas or differential protection.

 Maximum protections have insufficient sensitivity, gas protections have low speed, therefore, both cannot serve as the main high-speed protection against internal damage during short-circuiting of the windings.

 In powerful transformers and reactors, differential longitudinal and transverse protection are widely used as the main ones, having high speed and increased sensitivity. However, for their implementation they require two-sided coverage of all branches of the windings with current transformers, as well as detuning from unbalance currents and transients, which significantly complicates the protection and leads to its insufficient sensitivity with windings of less than 10% of the winding.

 The aim of the proposed method is to increase the sensitivity of the main protection of the reactor from internal short circuits and its simplification.

 This goal is achieved by the fact that as the main parameter that allows to detect any internal circuit of the reactor windings, voltage is applied between two points of the control windings electrically balanced by alternating current connected in a triangle, to which a constant voltage is supplied from the reactor magnetization source.

 The drawing shows an electrical diagram of the windings of a reactor controlled by magnetization. The network windings of the half-phases of the reactor are connected in a double star, the control winding is connected in a triangle and connected to the source of magnetization of the reactor. In this case, the corresponding network windings and control windings of the half-phases are located coaxially on each of the six rods of the magnetic system of the reactor.

 In normal operating conditions of the reactor and with external short circuits in the network, the sum of the voltage vectors in the control windings connected in a triangle is zero, and only DC voltage is present at the connection points of the magnetization source of the reactor electrically balanced by alternating current. If a half-wave rectifier is used as the magnetization source of the reactor, this voltage also contains the sixth harmonic. There is an industrial frequency voltage of 50 Hz in these modes at the terminals of the magnetization source of the reactor and at the points of its connection to the control windings.

 In the event of internal short circuits, both winding, and to the body or magnetic circuit of any reactor winding, voltage of an industrial frequency of 50 Hz appears on the terminals of the reactor magnetization source, corresponding to the number of closed winding turns. This is due to the fact that the control windings connected in a triangle reveal any asymmetry in the magnetically connected reactor windings.

 Due to this property, the fast-acting reactor protection against all types of internal short circuits is effectively and simply implemented. To do this, it is enough to connect two counter-parallel connected uncontrolled thyristors of class 1 ... 2 (depending on the rated bias voltage) or a zener diode to the terminals of the bias source of the reactor, passing their busbar through a standard current transformer with a transformation coefficient, for example, 100/5 and connecting a current relay to the current transformer with the effect of opening the circuit breaker and removing the pulses of the control system.

 A device that implements the proposed method consists of two counter-parallel connected uncontrolled thyristors or zener diodes at the terminals of the bias source of the reactor, a current transformer, covering the busbar of these thyristors or zener diodes, and a maximum current relay connected to the secondary winding of the current transformer with the action of its output contacts to trip network switch and reactor control system.

 The device operates as follows. When an internal short circuit occurs in any winding with a number of closed turns of more than 5%, the on-switched uncontrolled thyristors generate a voltage sufficient for their spontaneous opening or breakdown, which is accompanied by a surge of short circuit current through the thyristor in one of the directions and, accordingly, through the primary winding of the current transformer. The secondary current appearing at the output of the current transformer leads without delay to the operation of the maximum current relay and to the shutdown of the control system and network switch. With a significant asymmetry voltage and, accordingly, a large short-circuit current, almost simultaneously with the action of the relay, a complete breakdown or overlap of on-connected thyristors of a low voltage class occurs. This allows, firstly, to prevent the passage of high emergency overvoltages to the source of magnetization of the reactor, secondly, it activates the maximum current protection of the source of magnetization of the reactor by shorting its conclusions and, thirdly, reserves and accelerates the main protection of the reactor, including the current relay in the described device, by increasing their trip current.

 Studies of the layout of the device that implements the described method showed that the sensitivity of the protection is sufficient to reliably detect the circuit of more than 5% of the turns of any of the windings of the reactor. With the number of turns in the windings of controlled reactors of voltage classes of 110 ... 500 kV of the order of one or two thousand, protection covers more than 95% of the turns of both the network winding and the control winding, which significantly exceeds the performance of traditionally used transformer and reactor protectors. In this case, the most probable short circuits of the coils and layers of any winding are reliably detected, since the number of turns in them exceeds the specified 5% of the protection sensitivity.

 Moreover, the circuitry for the implementation of the proposed method of protection is simple, reliable and can be performed on any element base - electromechanical, semiconductor or digital. In the event of failure of the on-connected thyristors, they are easily replaceable due to their low cost and location outside the reactor tank. Zener diodes or other similar devices of the corresponding class in voltage and current can also play their role.

Sourse of information
Fedoseev A.M. Relay protection of electrical systems. - M .: Energy, 1976.

Claims (2)

 1. A method of protecting a reactor controlled by magnetization from internal short circuits, which consists in the fact that when an alternating voltage occurs between the points of the reactor control windings electrically balanced by alternating current connected in a triangle to which the magnetization source of the reactor is connected, in additionally connected thyristors at the source terminals magnetization of the reactor and in the current transformer, covering their busbar, a current appears, leading to the operation of the maximum current relay and applying a signal to shut down the reactor and its control system.  2. The device for protecting the controlled magnetization of the reactor from internal short circuits for implementing the method according to claim 1, comprising two counter-parallel connected uncontrolled thyristors or a zener diode at the terminals of the magnetization source of the reactor, a current transformer covering the busbar of these thyristors or zener diodes, and a maximum current relay connected to the secondary winding of the current transformer and acting by its output contacts to disconnect the network switch and the reactor control system.