SU58787A1 - Device to control the electrical circuit - Google Patents

Description

Devices are already known for controlling an electrical circuit (e.g., the excitation circuit of a synchronous machine) from ground fault using an electrical measuring device or a relay connected to a wire that grounds one of a controlled circuit and contains a source of auxiliary (control) voltage.

In such devices, there is a direct electrical connection of the source of control voltage with a controlled electric circuit.

According to the present invention, such a connection of two circuits is eliminated due to the fact that a neon lamp is connected to the ground wire between the monitored circuit and the supervisory installation (measuring device or relay and auxiliary voltage source) so that in the normal state of isolation controllable (L1 of the circuit, it did not burn, but it caught fire with a sharp deterioration of the insulation or with the direct connection of the controlled circuit to the ground.

The invention is illustrated in FIG. 1 - 4 of which are shown: electrical circuits of various variants of the proposed device.

The monitored electrical circuit 1 (in the drawing, a circuit of the synchronous machine) is grounded through a control device consisting of a transformer 2, a relay 3 and 4 of a neon lamp 5.

The primary winding of the transformer 2 is connected to the AC network, and the secondary winding is connected in series with the specified devices between the controlled circuit and ground, and in this particular case, between the rotor of the machine and the machine body or, through a special brush, the rotor shaft (to avoid isolate the oil film in the HDDs).

It is not necessary for turbogenerags to be attached to the shaft}; connection to the generator case is quite enough.

Thus, the controlled excitation circuit is constantly under the control of the voltage of the secondary winding of this transformer. When on the ground connection of the excitation circuit

A neon lamp 5 is ignited, thereby creating a circuit shown in FIG. 1 dotted line.

The current flowing through the neon lamp actuates the telephone relay 3, which is triggered and gives the corresponding signal. The presence of voltage on the secondary winding of the transformer 2 is monitored by a special telephone relay 4. When the voltage on the transformer decreases or disappears, the relay 4 is activated and gives a signal. The voltage of the secondary winding of the transformer is chosen equal to the working voltage of the rotor.

Due to the inclusion of a neon lamp, in the normal state of isolation of the excitation circuit, there is no direct electrical connection of the circuit to the secondary winding of the transformer. This separation of the control device from the excitation circuit under normal conditions (normal isolation state) provides great advantages and allows for sensitive and reliable control. The control device is electrically connected to the excitation circuit and its operation is performed automatically by igniting a neon lamp with a sharp decrease in the insulation or direct connection of the excitation circuit to the ground.

Since the excitation circuit of high-power generators has a significant capacity, the circuit can be applied, according to fig. 2. This scheme works perfectly similarly to the scheme of FIG. 1, but here a cuprox rectifier 6 is included in the secondary circuit of the transformer; thus, the control is performed by rectified voltage. The inclusion of cuprox rectifiers can be made according to the scheme of rectifying one half-wave or two half-waves. The valve action of the circuit (i.e., such that the current can flow only in one direction) is much more convenient for the selection of equipment, and in addition, it is possible to measure the magnitude of the excitation circuit insulation with a special device.

The connection of the secondary winding of the transformer to the excitation circuit must be matched with the polarity of the driver in order to obtain the locking effect of the rectifier on the flow of current

from the machine exciter. As a rectifier, you can also use a conventional rectifying lamp 7, according to the diagram in FIG. 3. This scheme works the same as the previous ones.

In order to be able to systematically measure the value of the insulation, a circuit can be applied, according to FIG. four.

In the device according to this scheme, when the button 9 is turned off, the neon lamp is turned off and the measuring device 8 is turned on in the circuit. After measuring, the button 9 again closes the neon lamp circuit by disconnecting the device 8. The operation of this circuit when grounded is similar to the previous one. The connection to the excitation circuit with a rectifying lamp must also be matched with the polarity of the exciter, as in the circuit according to fig. 2

The pointing device can be made with a scale divided into three parts with inscriptions of the state of isolation, namely: "low," average, "high; over the divisions may be entered numbers of resistance in megohms.

The author points out that the schemes were tested by him experimentally and showed the following advantages over the commonly used control systems:

1) are simple, reliable, and require very little means to accomplish;

2) they do not have a dead zone {the control device operates when it is shorted to earth in any part of the excitation circuit);

3) allow control of the excitation circuit both when the generator is running and when the generator is stopped; there is absolutely no dependence on the presence and magnitude of the excitation;

4) they allow automatically notifying not only the presence of full ground, but also notifying of a decrease in the insulation resistance to a certain value (the burning intensity of the neon lamp will depend on the value of the insulation resistance);

5) allow monitoring and measurement of the insulation resistance with a special measuring device;

6) in the normal state of isolation, the direct electrical connection of the control device with the excitation circuit is eliminated;

7) the implementation of the control device is of the same type for all existing generators;

8) all elements of the control device can be located in one casing extremely compactly and can be mounted on the control panel protection panel.

Naturally, such a control can be applied not only to control the excitation circuits, but also to control individual isolated areas; so, for example, when using the above schemes, it is possible to protect the generator (stator) from earth fault when switching circuit. generator-transformer, etc.

The subject matter of the invention.

A device for controlling an electrical circuit, for example, an excitation circuit of a synchronous machine, against a ground fault using an electrical measuring device or a relay connected to a wire that grounds one of the points of the monitored circuit and contains an auxiliary (control) voltage source, characterized in that A neon lamp is connected in the ground wire in series with the device (or relay) and auxiliary voltage source, so proportional that, in the normal state of isolation of the monitored circuit, it It burned, but lights up at the sharp deterioration of the insulation or by direct connection controlled circuit to ground.