SU1277292A1 - Device for protection of three-phase electric motor against operation with open and non-symmetrical phases in power supply network - Google Patents

Abstract

The invention relates to the field of electrical equipment for protection of three-phase electric consumers, in particular, can be used to prevent three-phase electric motors from working during open and asymmetrical phases of the supply network, phase breakdown on the housing, neutral of the neutral wire. The purpose of the invention is to increase the reliability of protection. The device contains a stabilized power source 1 on the basis of a ballast capacitor. Ys (L ND Y SO to

Description

An additional reed relay 10 is connected to source 1. In parallel, the 6,7,8 zener diodes of source 1 are turned on amplifier 12, which is controlled from the resistor star 21, 22, 23 connected to the phases of the supply network. An executive element 28 connected to the thyristor 27 is connected to the amplifier. The protection reliability is achieved by providing protection against the break of the neutral wire and protecting the interference from the star of the resistance 2), 22.23 from the stabilized source 1, as well as self control This goal is achieved by introducing an isolation transformer 25, an additional transistor 14 in the amplifier 12. The device provides noise immunity, thermal stabilization and tripping of the protection from the second control pulse. 1 il.

I

The invention relates to electrical engineering and can be used to protect three-phase electric motors from operation during breaks and asymmetry. power supply phase metrics, phase breakdown on the case, breakage of the neutral wire.

The aim of the invention is to increase the reliability of motor protection. ,

The drawing shows a circuit diagram of devices for protecting a three-phase electric motor against operation in the event of a break and asymmetry of the phases of the supply network. )

The circuit contains stabilized

power source I, made on the basis of the ballast capacitor 2, the discharge resistor 3, the surge bridge 4, the smoothing capacitor 5, the zener diodes 6.7, the additional zener diode 8 connected in series with the plus of the rapid bridge 4 included coil 9 of the executive relay 10 and with a reed switch 11. Parallel to the zener diodes 6, 7, 8, the amplifier 12 of the alternating current is switched on, based on the transistor 13, the additional transistor 14, the resistors 15-18, the tuning resistor 19 and additional diode 20 of which anode is connected to the base of additional transistor 14, and the cathode is - configured with a resistor 19 associated with the sinking circuitry. Between the midpoint of the star resistors is 21.22,

23, the emergency mode sensor 24 and the neutral wire N of the three-phase alternating current network include the primary winding of the isolation transformer 25, the secondary winding of which is connected to the emitter circuit of the additional transistor 14. The collector of the transistor 13 is connected via another additional diode 26 to the control transition of the executive thyristor organ 28. The cathode of the thyristor 27 is connected to the point of connection of the anode of the Zener diode 7 with the cathode of the additional Zener diode 8. Between the common minus of the circuit and the control electrode of the thyristor 27 on The capacitor 29 is operated. The thyristor anode 27 is connected via a resistor 30 by a rectifier bridge 4.

The device works in the following way.

Claims (1)

When a three-phase voltage is applied to the terminals A, B, .C, N on the stabilized power supply 1, a voltage appears, the reed switch I1 of the executive relay 10 closes its contact and does not prevent the magnetic starter and electric motor from turning on (not shown). When this additional transistor 4 of the amplifier 12 of the AC is closed, the transistor 13 is open, the thyristor 27 of the Executive body 28 is closed. The control signal, coming from the midpoint of the star resistors 21, 22, 23 to the primary winding of the developing transformer 25, is practically zero and does not interfere with the normal operation of the device. When one of the phases A, B, C, N of the supply network is broken or the voltage unbalance occurs, the potential appears at the midpoint of the star of the resistors 21,22,23 and the neutral wire appears on the secondary winding of the isolating transformer 25 the control of the auxiliary transistor 14. The AC amplifier 12 starts operating and the control signal is supplied to the control thyristor 27 electrode. The latter opens, the coil 9 of the executive relay 10 de-energizes its reed switch 11 opens the contacts in the magnetic coil circuit. starter, electric motor is disconnected from the network (in the diagram the magnetic starter and the electric motor are not shown). When the neutral wire N is broken, the voltage at the stabilized power supply 1 is disappeared, the coil 9 of the executive relay 10 de-energizes, which leads to the disconnection of the electric motor. To prevent a motor from being falsely disconnected by interference from various sources, the device provides for their suppression. The noise coming from the star side of the resistors 21,22,23 is partially quenched at the developing transformer 25, then - on the transistor 14 and the capacitor 29. The noise coming from the stabilized source 1 of the power supply is quenched partially on the coil 9 of the executive relay 10, then diode 26 and capacitor 29. If, however, a surge of overvoltage appears on the control electrode of the thyristor 27, a spurious motor disconnection does not occur because the disturbance signal is not sufficient to open the thyristor 27 because its cathode is connected to the cathode stabilitant at 8 and therefore, with an open transistor, 13 has a potential greater than the potential of the control electrode. In addition, the device performs self-checking, i.e. when de-energized from the circuit or when the device is triggered due to failure, the reed contact 1 1 of the executive relay 1 o opens, turning off the electric motor. The device can be used to protect an electric motor or electrical installation from phase disruption to the housing. In this case, it is connected together with a circuit breaker having a remote control coil. For example, during the breakdown of a phage of an electric motor or an electrical installation on a housing with a faulty re-grounding and the presence of a long 0.4 kV line, the neutral conductor N of a three-phase AC network receives the potential of the damaged phase. Therefore, a current flows through the primary winding of the isolation transformer 25. This leads to the operation of the device similarly to the mode of unacceptable asymmetry of the three-phase AC line voltage. During the breakdown of the motor or electrical installation on the case with good grounding and neutral wire N, the damaged phase A, B or C takes the potential of the neutral wire N. Asymmetry occurs in the network, the primary winding of the disconnecting transformer 25 turns out to be connected in parallel to one of the resistors 21,22, 23 sensors 24 emergency modes connected to the damaged phase. A current flows through the primary winding of isolation transformer 25. This triggers the device and disconnects the motor from the network. Thanks to the proposed scheme of a device for protection of a three-phase electric motor against operation during breaking and asymmetry of the supply mains phases, reliability of motor protection is increased due to increased noise immunity, improved thermal stability and adjustability, increased reliability of device operation, c. in the event of a failure of the first control pulse, as well as by providing self-monitoring of the device. In addition, the cost of the device is reduced by reducing the number of rejected thyristors when setting up at the factory. Apparatus of the Invention A device for protection of a three-phase electric motor against operation during the wrapping and asymmetry of the phases of the mains supply containing an emergency mode sensor, made in the form of star resistors. And connected by an input to the terminals of a magnetic actuator on the motor side and to the neutral wire, and an output to an amplifier whose transistor collector is connected to the control circuit of the actuator anode through a resistor with a stabilized power supply with two series-connected zener diodes at the output, characterized by a temr that, in order to improve reliability, an emergency A connecting transformer, the primary winding of which is connected between the zero point of the star resistors and the neutral wire, and the secondary winding is connected to the emitter circuit of the additional amplifier transistor, the base of which is connected through an additional resistor to the control electrode of the actuator thyristor, and through the first diode inserted - with the tuned resistor connected to the minus of the stabilized source power, the cathode of the actuator thyristor is connected to the cathode connection point additionally: an inserted Zener diode with an anode of the Stabilitron stabilized power source, and the control electrode of the actuator thyristor are connected via a second inserted diode to the collector of the amplifier transistor.