SU748627A1 - Device for protecting electric mains with electric motors from short-circuiting current - Google Patents

Description

(54) DEVICE FOR PROTECTION OF ELECTRIC NETWORK WITH ELECTRIC MOTORS FROM SHORT CIRCUIT CURRENT

The invention relates to electrical engineering, in particular to the protection of electrical networks from short-circuit currents. A device for protecting electrical networks from short-circuit currents is known, which contains a current sensor, a threshold element for comparing the magnitude of the current in the protected network with the installation, and a shutdown unit 1. During start-up mode act. protection is blocked. However, the protection blocking channel contains a sensor of the magnitude of the higher harmonic components of the unbalance current, which causes difficulties in the technical implementation of this device and, moreover, causes a false operation of the device due to the effect of interference. It is also known to protect electrical networks from short-circuit currents, which contains a network current sensor, a threshold element and a disconnecting unit. This device has a blocking effect on the protection of the engine starting time, while the starting mode sensor is an aperiodic component of the monitored current pickup sensor 2. The disadvantage of this device is also low noise immunity and reliability due to the difficulty of distinguishing interference from the useful signal. This leads to false positives of protection, disruption of uninterrupted power supply to consumers, and excessive use of motor potential. The purpose of the invention is to increase the reliability of the protection device by eliminating false alarms when a starting network of motors is protected in the protected network. This del is achieved by the fact that, in a known device containing a current sensor, a threshold element, the output of which is connected to the input of a magnetic actuator via a key, the control input of which is connected to the output of the blocking signal forming element of the protection lock channel the starting mode of the electric motor, the element of comparison and the element of forming a blocking signal, the sensor of the starting mode

the electric motor is installed in the immediate vicinity of the engine inlet to be connected to it and to the output of the power contact of the magnetic actuator. In this case, the motor starting mode sensor can be made in the form of a current sensor connected in series between the magnetic actuator output and the motor input, as well as a rectifier connected in parallel with the power contact contacts of the magnetic actuator. In this case, the comparison element can be made in the form of a storage ring. -doeator energy. Moreover, when a blocking signal forming element is executed in the form of a trigger, the output of the blocking element forming element can be connected to the control input of the key directly or when the blocking signal forming element is executed as a pilot generator, the output of the specified formation element can be connected a magnetic actuator contact and an additional pilot selector input connected to the output of said current sensor. FIG. 1 shows a diagram of the device, when used as a start-up mode sensor, a current sensor installed directly at the input of an electric motor; in fig. 2 is a diagram of the device when using a rectifier connected as a sensor in the starting mode, connected in parallel with the power contact of the magnetic starter; in fig. 3 is a diagram of the device when using the network as a communication channel.

The device consists of a starting mode sensor of the electric motor 1, rectifier 2 (if necessary), comparison element 3, blocking signal generation element (pilot signal generator) 4, matching unit 5 (if necessary), sensor 6 current of the pilot signal selector 7, threshold element 8 ,. key 9, block 10 off, made in the form of a magnetic actuator and the line for, p, the holders 11 (if necessary).

The output of the start-up mode sensor of the electric motor 1, which is located directly at the engine inlet, through the rectifier 2 is connected to the input of the comparison element 3, the output of which is connected to the input of the block forming element (pilot signal generator). 4. The output of the pilot signal generator 4 through the matching unit 5 is connected to the protected electrical network. The output of the current sensor (or current derivative) 6 through the pilot signal selector 7 is connected to the input of the threshold element 8 and in parallel with the control input of the key 9. The output of the threshold element 8 is connected through a switch 9

connected to the input of the block 10 shutdown (magnetic starter).

In order to increase the reliability of blocking the shutdown unit 10, a signal that carries information about the presence of a blocking signal (pilot signal) in the network is fed to a controllable key input 9 with advance as far as the signal that carries information about the current in the network (or speed change this current) setting level. This is achieved by supplying the specified overflow information to key 9 via delay line 11.

The work is as follows.

When connecting (starting) to the motor network, for example, when the switch is closed at the output of sensor 1, a signal appears, pro. portioned value (or derivative) of the current in the network. This signal, if necessary, is rectified using rectifier 2 and fed to reference element 3.

At the moment when the signal at the output of the rectifier 2 of a predetermined trigger level of the comparison element 3 is exceeded, a trigger signal is sent to the input of the pilot signal generator 4, which causes the generation of the pilot signal, which is fed into the protected network through the matching unit 5.

Thus, in the electrical network, along with the starting current, a signal appears a tag that carries information that there is an excess of the threshold for triggering the level setpoint (or derivative) 8, which receives information about the value (or derivative) of the current in the network from the current sensor 6 (or derivative) 6 through the pilot selector signal 7, is not the result of a short circuit in the network, but the result of connecting (starting) the motor, for example, asynchronous. This pilot signal allocated from the electrical network by means of the sensor 6 is fed through the selection unit 7 to the controlled input of the key 9 and releases the key.

Thus, the access to information about the magnitude of the current (or derivative of the current) in the network of an a priori predetermined level (or derivative) is interrupted, and the shutdown unit 10 does not operate.

If the overcurrent in the network occurs as a result of a short circuit, and not the connection (starting of the motors). The key 9 will remain closed, and the signal carrying the information that the current (or the current derivative) in the network has exceeded the permissible level, I post via key 9 to the input of block 10, switch off, which will cause the network to shut down.

The blocking signal can be fed to the controlled input of the key 9 and through a specially organized communication channel.

Thus, the sensor 1 located directly at the motor input does not react to the short circuit current itself, it has a place at any other point of the protected network.

However, besides the starting current of the motor, the indicated sensor could react to a short circuit current only in two cases:

when a short circuit occurs directly inside the engine;

when, due to the presence of a short circuit at other points of the monitored network, the motor enters a generator mode, which is accompanied by a short-term current surge of a significant magnitude.

But both cases are easily recognized and are eliminated from the logic of the sensor 6 locking system. Indeed, a short circuit inside the engine that took place before it was connected to the network can be determined by known methods (i.e., using pre-start test signals) although it is not necessary.

In the event that a short circuit in the motor occurred at the time or after starting (or occurred earlier), this fact is easily determined by the skew (asymmetry) of the voltages (currents) in the phases (windings) of the motor, tel.

The presence of signals about these situations with the help of logic circuits (not shown in the figure) prevents the protection from being blocked by the analyzing device described in the application.

For the case of identifying the transition of the engine to the generator mode (due to a short circuit in the network), which is accompanied by a short-term (compared with the starting currents and short-circuit currents) inrush current, use either a reverse power relay or filtering (integrating) stages at the exit, supra mitel. Both in that and in the Other case, the blocking of protection by launching a pilot signal is not carried out, the main sensor of protection 6 performs the tasks assigned to it.

Thus, the protection lock of sensor 6 is only performed at the time of starting the engine for the duration of the presence of inrush current, and in all cases this blocking is not carried out.

When using information on the state of the POWER contact of the magnetic starter, the current (or derivative) 6

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through the threshold element 8 and the key 9 is connected f with the control input of the shutdown unit 10. Inputs are up to 12, used in ka. As a start-up sensor, 5 are connected to different outputs of the power contact of the magnetic actuator 10 (switch-off unit), and the outputs of the sensor 12 through the filter 13 and the comparison element, made in the form of an electric power metering accumulator 3, are connected 10 to the input of the amplifier 14, the output of which to the mono-signal generator 4. The output of the pilot-signal generator 4 is connected to the y | | additional key input 9.

In the case of using communication as channel 15 for supplying a pilot signal of the protected electrical network between the current sensor (or derivative) 6 and the threshold element 8. the pilot signal selector 7 is entered (see Fig. 3), one input of which is connected to the output 20 of the current sensor (or derivative) 6, and the first output - to the input of element 8, the second output of the signal selector 7 is connected to the control input of the key 9. The pilot input 4 of the generator 4 in this case is connected to the protected electrical network.

The work is as follows. After installing the current sensor 6 and the disconnecting unit 10 at the designated points of the protected network, the rectifier 12 charges the electric power 30 batch 3 via the rectifier 12. The signal, which then passes through the storage unit of the electricity meter at the first moment, carries information only that the device is connected to the feeder.

35 After closing the power contact of the magnetic actuator, the portions at the rectifier inputs will become zero. The electricity metering accumulator will begin discharging along the discharge circuit (for example, through a resistor and input 40 of amplifier 14). From the output of amplifier 14, the signal goes to the pilot signal generator 4, which supplies it (via the network or directly) to control input of key 9, causing it to open.

5 Thus, for the time the pilot signal is present, the trip unit 10 will be disconnected from the current (or derivative) sensor 6. In the case of the absence of a pilot signal through the threshold element 8 and the key 9, a signal will be received at the input 0 of the shutdown unit 10, which will trigger the protection.

The scientific and technical effect of the proposed solution is very high in noise immunity. reliability and protection, which excludes the False positives of protection when the engine starts, which in turn

Claims (2)

, leads to the provision of uninterrupted power supply to consumers, preservation of the service life of the releasers and reduction of the received noise. In addition, the protection setup is simplified. Claims 1. A device for protecting an electrical network with electric motors against short-circuit current, comprising a current sensor, a threshold element, the output of which is connected to the input of a magnetic starter via a switch, the control input of which is connected to the output of the blocking element of the blocking channel of protection, made in the form of a successively coupled sensor of the starting mode of the electric motor, the comparison element and the blocking signal forming element, characterized in that, in order to increase the reliability The operation of the motor starting mode sensor is installed in the immediate vicinity of the engine input and is connected to it and to the output contact of the magnetic starter 2. The device according to claim 1, characterized in that the 4HJ sensor of the motor starting mode is designed as a current sensor connected in series between the output of the magnetic starter and the input of the electric motor. 8 3. The device according to claim 1, that is, that the sensor of the starting mode of the electric motor is designed as an overhead switch connected in parallel with the terminals, the sludge contact of the magnetic actuator, and the comparison element is designed as an energy metering accumulator. 4. The device according to claim 1, characterized in that the blocking signal forming element is designed as a trigger and its output is directly connected to the control input of the key. 5. The device according to claim 1, characterized in that the blocking signal generation element is designed as a pilot signal generator and its output is connected to the control input of the key through the output of the POWER contact of the magnetic actuator and the additional pilot signal selector connected to the output current sensor. , Sources of information taken into account during the examination 1.Atabekov GI. Differential relay with braking action from high harmonic components of unbalance current, journal Electric stations, No. Sh, 1938. 2. Application of electronic equipment in control systems of electrical devices, Proceedings of VNIIZhT, V.336. with. 79-182. " uh