SU792458A1 - Device for monitoring voltage of three-phase mains - Google Patents

Description

The invention relates to electrical engineering and is intended to control the operation of three-phase electrical networks. Devices for monitoring voltage of a three-phase network are known, comprising a sensor for a controlled voltage, a voltage source, a differential amplifier, a voltage divider, a diode, and a capacitor PZ. The closest technical solution to the invention is a device for signaling a voltage drop in a three-phase network containing a three-phase two-wave voltage rectifier, a blocking generator, an actuator and a source of reference voltage 2J. A disadvantage of known devices is the low accuracy of the voltage control in each phase in the phase voltage asymmetry mode. This is due to the fact that the voltage is monitored by the magnitude of the instantaneous value of the voltage at the time of equalization of the phase voltages. The absolute value of the instantaneous value of the voltage at the controlled point depends on the asymmetry of the phase voltages and does not reflect the actual state of the voltage of one of the phases (lower than the norm) and the increased voltage of the other two phases, the instantaneous value of the voltage at the moment of equality of phase voltages not only will not decrease, but may increase, as a result, the comparison device will not respond to a decrease in one of the phases below the norm and will not give a signal to the executive body. Therefore, the control results for asymmetry of phase voltages in known devices do not provide the necessary accuracy. The purpose of the device is to improve the accuracy of the device. The goal is achieved by the fact that a device for monitoring a three-phase network voltage containing a three-phase full-wave rectifier connected at the input to a monitored network, to the cathode group of which one end of the first voltage divider is connected, as well as the threshold element and the actuator, is equipped with a second divider a pulse shaper, a bidirectional key and an expander, with the anodic group of rectifiers Hstel connected to one end of the second voltage divider, the other end of which connected to the common bus and the other end of the first voltage divider, and the outputs are connected respectively to the collector and via RC to the base of the emitter follower transistor, the output of which is connected to the driver input and the port of the bidirectional switch connected to the midpoint of the first a voltage divider, and an output with a storage capacitor, which, through the threshold element, is connected to the input of the pulse extender, will output the output connected to flax element. . .

The schematic diagram of the device j described in Fig. 2 is a diagram of the voltages that explain its operation.

The device contains a three-phase two-full-phase rectifier 1 connected at the input to phases A, of the controlled network, rectifier 1 to the cathode and anode groups of the rectifier 1 are connected to the first voltage divider 2 and wto respectively at one end. voltage divider 3. The other ends of voltage divisors 2 and 3 are connected to each other and a common point. The outputs of the second voltage divider 3 are connected respectively to the collector and through the RC circuit 4 to the base of the transistor. Emitter repeater 5, the output of which is connected to the input of the driver 6, connected to the output of the bi-directional switch 7. The output of the key 7 is connected to the midpoint the first voltage divider 2, and the input - with a storage capacitor 8. The capacitor plates 8 through the threshold element 9 are connected to the input of the expander 10 pulses, the output connected to the executive body 11. Formed spruce b Impuls, bidirectional switch 7 and the expander 10 of the power pulse circuit connected to the source E.

On figa depicted diagrams of a three-phase AC network; Fig. 26 shows voltage diagrams at the lower shoulder of voltage divider 3; Fig. 2c shows voltage diagrams at the emitter follower 5; on Figg - pulses on the output of the pulse former b; Fig. 2e shows Ug — the response voltage of the threshold element 9; Ug is the voltage on the accumulative KOHjjeHTator 9 (the dotted line shows Ug when the voltage decreases when the voltage of each phase is within the normalized limits); in Fig. 2g, the input voltage of the actuator 11 when the voltage of each of the phases is within the normalized limits; FIG. 2Z shows the input voltage of the expander 10 at

decreasing the voltage of phase A; Fig. 2i shows the voltage at the input of the executive body 11 while decreasing the voltage of phase A.

The device works as follows.

The network voltage, rectified by the anode group of rectifier 1 (see Fig.26), is fed to the second voltage divider 3 and from its lower arm via a parallel RC circuit 4, which serves to pass a variable component, is fed to the input of the emitter follower 5. As a result, at the output of the emitter follower 5, an envelope of the rectified voltage is released (see Fig. 2c), which is fed to the input of the pulse shaper, performed, for example, on a Schmitt trigger with a matching transistor cascade connected to its output, At time points P ohozhdeni envelope voltage (sm.Fig.2v) through zero at the output of shaper b are formed by short duration pulses (cm.fig.2g) coinciding with the moment of passing the rectified group cathodic rectifier 1 through the voltage amplitude value. The control pulses from the output of the pulse generator 6 are fed to the control transition of the bidirectional switch 7, made, for example, in the form of a rectifying bridge with a transistor included in its diagonal. The key 7 at this moment opens and connects the storage capacitor 8 with the lower arm of the first voltage divider 2 connected via the power supply circuit to the cathode group of the rectifier 1. With the aid of a surge current through the double-ended key 7, the voltages on the storage capacitor 8 and the lower one are equalized. the shoulder of the first voltage divider 2. The instantaneous magnitude of this voltage is proportional to the amplitude value of the phase voltage, stored by the capacitor 8 until the next pulse arrives from the driver 6 pulses. Thus, a voltage Ug is formed on capacitor 8 (cf. figure 2 d), proportional to the amplitude value of the phase voltage. The voltage from the plates of the storage capacitor 8 through the threshold element 9 is fed to the input of the expander 10 pulses, made, for example, for a standby multivibrator with a connecting diode to its collector.

When there is a voltage in each re-phase of a three-phase AC network within the normalized limits, the voltage Us (see Fig.2 d, the solid line is greater than the threshold value Ug (pmfig d), therefore, the input transistor of the impulse spreading transducer.

opened by a positive signal (see fig.2e), is open at this time and its output transistor, and the executive body 11 is de-energized (see fig.2zh).

If the voltage of at least one of the phases decreases below a predetermined value (or one or more phases disappears), for example, the voltage of phase A decreases (see Fig. 2a, dashed line) below a predetermined value, the voltage of Ug on the capacitor plates decreases accordingly. 8 (see fig.2d, dotted line in the interval tj -tji) and becomes lower than the threshold U (see fig.2d) of the threshold element 9. At the same time, in the interval of time t -tg, the signal at the input of the pulse extender 10 disappears {see .fig.2z), its input transistor is locked, transmitting a signal to the performer The output unit 11. Simultaneously (in the time interval), the pulse expander is restored, and since time 1DO tj its tilting takes place, during which its output transistor closes and transmits a signal to the executive authority 11. If at time tj there is a confirmation at the input of the threshold element 9 on the voltage drop in one of the phases (see Fig. 2d, dashed line from the time tj), the processes in the circuit are repeated in the same sequence as described above from time t. In this case, the executive body 11 s. time t is under current (see fig, 2i).

Thus, in this device, the control and comparison of the magnitude of the phase voltages is carried out directly on the amplitude value of each of the phases of the supply voltage, therefore the asymmetry of the phase voltages does not affect the accuracy of measurement and control.

The effectiveness of this device is to increase the accuracy

voltage control at asymmetry of the phase voltage of the mains supply, 1 place in real conditions of operation.

Formula of invention

A device for controlling the voltage of a three-phase network, containing a three-phase full-wave rectifier connected to the input of the controlled network, to the cathode group of which one end of the first voltage divider is connected, as well as a threshold element and an actuator,

5 characterized in that, in order to improve the accuracy of the device, it is equipped with a second voltage divider, pulse shaper, bidirectional key and pulse spreaders, while the anode group of the rectifier is connected to one end of the second voltage divider, the other end of which is connected to common bus and the other end of the first voltage divider, and the outputs are connected respectively to the collector via an RC circuit to the base of the emitter follower transistor, the output of which is connected to the input of the pulse shaper, unity vyho0 house with the control of the bidirectional shift key, the input of which is connected to a midpoint of the first voltage divider, and output to a storage capacitor electrode ko5 torogo through said threshold element connected to the input of the dilator pulses output connected to the actuator body.

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Sources of information taken into account in the examination

1. USSR author's certificate No. 434532, cl. H 02 H 3/24, 1975.

2. Aatorskse certificate of the USSR No. 546984, cl. K 02 H 3/24, 1974.

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Claims (1)

Claim A device for monitoring the voltage of a three-phase network, comprising a three-phase half-wave rectifier connected to the input and the controlled network, to the cathode group of which one end of the first voltage divider is connected, as well as a threshold element and an actuator, characterized in that, in order to increase the accuracy of the device, it is equipped with a second voltage divider, a pulse shaper, a bi-directional switch and pulse expanders, while the anode group of the rectifier is connected to one end of the second case a voltage divider, the other end of which is connected to the common bus and the other end of the first voltage divider, and the outputs are connected respectively to the collector via an RC circuit to the base of the emitter follower transistor, the output of which is connected to the input of a pulse shaper connected by the output to the control transition of the bi-directional switch, input which is connected to the midpoint of the first voltage divider, and the output is with a storage capacitor, the plates of which are connected to the input of the expander through the said threshold element pulses output connected to the actuator body.