SU663014A1 - Method and apparatus for protecting three-phase consumers from incomplete operating modes - Google Patents

Description

one

The invention relates to the protection of three-phase consumers from abnormal operation and can be used to increase the level of reliability and safety of operation of current collectors in three-phase electrical networks.

Various methods are known for protecting current collectors from abnormal operation.

The closest in technical essence and the achieved result. The proposed invention is a method of protecting three-phase consumers from incomplete-phase modes of operation, based on measuring the ripple of the rectified voltage of a three-phase network, by forming the difference of two signals, one of which is proportional to the instantaneous values of the rectified phase voltages, and obtaining an output signal when the difference exceeds the threshold value, and a device for carrying out this method, comprising a capacitor, a field conductor devices, the executive body and the transistor, which are connected with the source electrodes

rectified phase voltages and a source of constant voltage 3.

The disadvantage of this method is that it does not allow the protection device to provide self-monitoring of the operability of the elements of their electrical circuits.

The purpose of the invention is to increase the reliability of the protection of three-phase consumers from abnormal operation.

This goal is achieved in the way to shield three-phase consumers from non-phase-mode operation based on measurements of the ripple of a rectified voltage of a three-phase network by forming the difference between two signals, one of which is proportional to the instantaneous values of rectified phase voltages, and obtaining an output signal at exceeding the threshold value, a constant signal in the range of amplitude variation of the instantaneous values of rectified phase signals is taken as another compared signal zheny, and their difference is formed into a rectangular signal, which frequency is obtained at the output umenschenii.

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In a device for carrying out the described method comprising a capacitor, semiconductor devices, an actuator and a transistor, the electrodes of which are connected to a source of rectified phase voltages and a source of constant voltage, both mentioned; the source is connected to a semiconductor device, shunting it to the input of a transistor, to the output of which an executive organ connected by a semiconductor device connected by a constant voltage source is connected through a capacitor, and a semiconductor device for shunting the executive organ is used a zener diode.

FIG. 1 shows a diagram of the temporal characteristics of the currents obtained with the proposed method of protection of three-phase consumers; in fig. 2 is an electrical circuit of a protection device implementing the proposed method.

The proposed method of protection is as follows.

 To measure the pulsations (Fig. 1), the difference between the current proportional to the instantaneous values of the rectified phase voltages ia, it, ic, and the current proportional to the amplitude value of the constant voltage in is formed. The difference is formed in the form of a quantity proportional to the instantaneous value of the square-wave signal, and the frequency of this signal is monitored.

A device for carrying out the proposed protection method (Fig. 2) consists of a capacitor 1, semiconductor devices 2 and 3, an executive element 4 and a transistor 5, the electrodes of which are connected to a source of rectified phase voltages 6 and a source of constant voltage 7. -. .... g „- ,,:.-... .-:, ...,.,. : ь, ......,.

Both sources 6 and 7 are connected to a semiconductor device 2, shunting the input of the transistor 5. To the output of the specified transistor 5, through the capacitor 1 is connected an actuator 4, which is clamped by a semiconductor device 3, connected according to a constant voltage source 7.

During normal operation, the consumer transistor periodically opens and closes (to, tj, respectively, the duration of the open and closed, the state of the transistor 5) and, working as a switch, connects the capacitor 1 to a constant voltage source 7, then to the actuator 4. The capacitor 1 in the open state of the transistor 5 is charged through the semiconductor device 3 to the voltage source 7, and in the closed state of the transistor 5 is discharged through the actuator 4 and the resistor included in the collector circuit is specified transistor.

As a result, an average current flows through the executive (relay coil) over the period of the industrial frequency, caused by three discharge pulses of the capacitor 1, which correspond to three closed

the ts states of the transistor 5.

The magnitude of this current, which is determined by the pulse frequency of the capacitor 1, is sufficient to attract the relay's core and hold it. The duration of the discharge pulses is determined only by the parameters of the capacitor 1, the actuator 4 and the resistor included in the collector circuit of the transistor 5, and therefore does not depend on the state of the consumer being monitored. The criterion for the normal functioning of the device and the controlled consumer is the specified frequency of the following rectangular impulses generated by the open and closed state of the transistor 5.

At violation of the mode of operation (break

0 phase, decreasing the phase voltage or the phase angle of the mains voltage) during the industrial frequency period, a maximum of two discharge pulses pass. As a result, the current through the actuator 4 becomes less than the holding current of the core in an induced state and the relay 4 disappears, causing the consumer to be turned off (signaled). That is, the threshold value is YiponycK (absence) for the period of the industrial frequency of at least one of

rectangular pulses due to the above current difference.

FIG. 1, for example, shows the occurrence of a phase B shift, as a result of which the frequency of following square-wave pulses has reached a threshold value.

Adjustment of the pickup setpoint, which takes into account the possible unbalance of phase voltages in the network, is made by the resistor 8, whose parameters are determined by -, the current in.

0 Implementing the described method of protection

Three-phase consumers allow the protection device to provide the function of self-monitoring of the health of the elements. When a rectifier, bridge 6 (breakdown, break) or resistors forming an artificial zero point fail, the frequency of the capacitor discharge pulses 1. reaches a critical value (one of the phase straightened out strains is missing) and the executive body disappears. With

0 failure of the remaining elements of the device (breakdown or open circuit of the transistor 5, both semiconductor devices 2, 3, capacitor 1), the current through the actuator falls to zero.

Claims (3)

Thus, any damage to the elements of the device leads to the disconnection of the network, i.e., it is excluded the possibility of operating three-phase consumers with a defective protection device. In order to limit the current in the actuator 4 while increasing the supply voltage in the network, a Zener diode is used as a semiconductor device 3 that shunts the actuator. The described technical solution allows the protection devices to work stably in a wide range of ambient temperatures, because the transistor operates in a key mode and its gain change with temperature does not practically affect the setpoints at which the network is disconnected. The protection device ensures efficient operation, regardless of the connected load, as the three-phase voltages supplied to the consumer are controlled both in amplitude and in their phase shifts. This allows the protection of three-phase consumers with asymmetrical phase loads, as well as single-phase consumers connected to a three-phase current system, whose functional operation depends on each other. Claim 1. A method of protecting three-phase consumers from non-full-phase modes of operation, based on measuring the ripple of a rectified voltage of a three-phase network, by forming the difference between two signals, one of which is proportional to the instantaneous values of rectified phase voltages, and obtaining an output signal when it is equalized threshold value, in that, in order to enhance the functional reliability of protection, by introducing a minimum control, as another comparable the signal is received by a constant signal in the range of variation of the amplitude of the instantaneous values of the rectified phase voltages, and their difference is formed as a square wave signal, with decreasing frequency of which the output signal is obtained. The device for implementing the method of claim 1, containing a capacitor, semiconductors, an actuator and a transistor, the electrodes of which are connected to a source of rectified phase voltages and a source of constant voltage, characterized in that, in order to increase the reliability implementation of protection by ensuring the self-control of the health of the elements, both of these sources are connected to a semiconductor device, bypassing the input of the transistor, to the output of which, through a capacitor, an actuator connected by a semiconductor device connected according to the source of constant voltage is connected. 3. The device according to claim 2, characterized in that a zener diode is used as a semiconductor device shunting the actuator. Sources of information taken into account in the examination 1. Yu.A. Karinsky (S. Krivtsov. Principles of implementation of current protection with braking from asymmetrical modes of operation of three-phase units. 2. USSR author's certificate number 349056, cl. H 02 H 3/26, 1973. 3. USSR author's certificate number 375330, cl. H 02 H 3/24, 1975. tp ij R at to is / / / I