RU169659U1 - DEVICE FOR PROTECTION AGAINST VOLTAGE IN THE WINDING OF EXCITATION OF A SYNCHRONOUS MACHINE WITH A BRUSHLESS-FREE EXCITATION SYSTEM - Google Patents

Abstract

The inventive utility model relates to electrical engineering and relates to the design features of the device for surge protection on the excitation winding of a synchronous machine with a brushless excitation system. The technical result achieved by using the claimed utility model is to reduce the rate of rise of the discharge current di / dt of the capacitor of the protective RC circuit through the thyristor of the device for surge protection on the excitation winding of the synchronous machine, which increases the life of the thyristor and, accordingly, will improve the operational characteristics of the claimed devices. The problem is solved in that in the device for overvoltage protection on the excitation winding of a synchronous machine with a brushless excitation system containing a thyristor, connected in parallel with the rectifier diodes of the brushless exciter and protected against switching overvoltages by an RC circuit, a thyristor control unit connected in series with a threshold element, in the circuit of the anode or cathode of the thyristor includes a switching reactor. 2 ill.

Description

The inventive utility model relates to electrical engineering and relates to the design features of the device for surge protection on the excitation winding of a synchronous machine with a brushless excitation system.

The prior art various embodiments of devices for similar purposes.

So, it is known a device, namely, an overvoltage protection unit in an electric machine, disclosed in the description of the utility model "Brushless excitation system of a synchronous machine" of the Russian Federation according to patent No. 134716. This device provides overvoltage protection blocks from the rotor and switching overvoltages. These blocks are mounted on the radiator section between two thyristors on the one hand and one of the rectifier diodes on the other. Two tape thyristor protection resistors are located on the pathway hub under the rectifier diodes. The findings of the resistors are connected to the corresponding thyristors.

This device is characterized by the presence of two thyristors, two tape resistors, a device for controlling two thyristors and its installation in the limited dimensions of the rotor of the brushless pathogen is not always possible or causes certain difficulties.

The closest in technical essence to the claimed utility model is a device for overvoltage protection on the excitation winding of a synchronous machine with a brushless excitation system in which the thyristor is connected counter-parallel to the rectifier diodes of the brushless exciter (AS USSR No. 534010).

A disadvantage of the known devices is the lack of elements limiting the rate of rise of the discharge current di / dt of the capacitor of the protective RC circuit intended for protection against switching overvoltages of the semiconductor rectifier through the thyristor when it is opened. The slew rate of the discharge current di / dt of the capacitor of the protective RC circuit in these devices can significantly exceed the critical slew rate of the current in the open state for the applied thyristors since it is limited only by the parasitic inductance of the discharge circuit. This circumstance causes a limited resource of operation of power thyristors in these devices for overvoltage protection on the excitation winding of a synchronous machine with a brushless excitation system.

The objective of the proposed technical solution is to reduce the slew rate of the discharge current di / dt of the capacitor of the protective RC circuit through the thyristor.

The technical result achieved by using the inventive utility model is to reduce the rate of rise of the discharge current di / dt of the capacitor of the protective RC circuit through the thyristor, which will improve the operational characteristics of the claimed device by increasing the life of the thyristors.

The problem is solved in that in the device for overvoltage protection on the excitation winding of a synchronous machine with a brushless excitation system containing a thyristor, connected in parallel with the rectifier diodes of the brushless exciter and protected against switching overvoltages by an RC circuit, a thyristor control unit connected in series with a threshold an element, according to the technical solution, a switching reactor is included in the circuit of the anode or cathode of the thyristor.

The inductance of the reactor allows to reduce the rate of rise of the discharge current di / dt of the capacitor of the protective RC circuit through the thyristor.

The inventive utility model is illustrated by the following drawings, where:

in FIG. 1 is an electrical schematic diagram of a rotor of a brushless pathogen with the claimed device for surge protection with a switching reactor included in the thyristor anode circuit; but

in FIG. 2 is a schematic electrical diagram of the rotor of a brushless pathogen with the claimed device for surge protection with a switching reactor included in the thyristor cathode circuit.

The circuit of the device includes a winding 1 of the rotor of the brushless exciter, a semiconductor rectifier 2, a resistor 3 and a capacitor 4 of the RC circuit for protection against switching overvoltages of the semiconductor rectifier, thyristor 5, control unit of thyristor 6, threshold element 7 and reactor 8.

The inclusion of the reactor in the circuit of the anode or cathode of the thyristor (see figure 1 or 2, respectively) depends only on the design features of the rotor of the brushless pathogen.

The inventive device operates as follows.

When exceeding the voltage induced in the rotor of the synchronous machine, for example, when starting the synchronous motor, the voltage of the threshold element 7, the thyristor control unit 6 generates a control pulse that opens the thyristor 5, as a result of which the thyristor 5 shunts the rotor of the synchronous machine, but the capacitor 4 of the protective RC circuit is discharged to the thyristor through resistor 3 and reactor 8. The voltage on the capacitor at this point in time is almost equal to the voltage of the threshold element 7.

Consider the principle of limiting the rate of rise of the discharge current dI / dt of the capacitor 4 through the thyristor in the presence of a reactor thyristor in the circuit.

At the initial moment of time, in the discharge circuit, consisting of a capacitor 4, a resistor 3, a reactor 8, and a thyristor 5, in addition to a current source - a capacitor 4 with an EMF “E”, the self-inductance EMF “Ec” will also act due to the discharge current of the capacitor 4 reactor 8, respectively, and Ohm's law for this circuit will have the form:

I = (E + Ec) / R,

where I is the discharge current of the capacitor 4 through the thyristor;

E - EMF source - voltage across the capacitor 4;

Ec - EMF of reactor self-induction 8, where Ec = -L (dI / dt);

L is the inductance of the reactor 8;

dI / dt — slew rate of the discharge current of capacitor 4;

R is the resistance of the resistor 3;

then the discharge current of the capacitor 4 through the thyristor is equal to:

I = (E - L (dI / dt)) / R,

accordingly, the slew rate of the current through the thyristor is equal to:

dI / dt = E / L-I (R / L).

At the initial moment of time, we have the maximum slew rate of the discharge current of the capacitor 4 through the thyristor dI / dt = E / L, and in this technical solution it is limited by the inductance of the reactor 8.

The inductance of the reactor is selected so that the slew rate of the anode current of the thyristor 5 from the discharge of the capacitor 4 is lower than the critical slew rate of the current in the open state for the installed thyristor and is usually equal to units of microgenry.

So when using a threshold element with a trip voltage of 1500 V and a thyristor with a critical slew rate of current in the open state of 320 A / μs, reactor 8 should have an inductance L of at least 4.7 microgenry (1500/320 = 4.7).

Thus, the inclusion of the reactor in the anode or cathode of the thyristor allows you to limit the rate of rise of the discharge current di / dt of the capacitor of the protective RC circuit through the thyristor of the surge protection device on the excitation winding of the synchronous machine, which ensures reliable operation of the thyristor, increases its life and, accordingly, increases reliability the whole pathogen as a whole.

Claims (1)

A device for overvoltage protection on the excitation winding of a synchronous machine with a brushless excitation system, comprising a thyristor connected in parallel with the diodes of the rectifier brushless exciter and protected from switching overvoltages by an RC circuit, a thyristor control unit connected in series with a threshold element, characterized in that The circuit of the anode or cathode of the thyristor includes a switching reactor.

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