SU1034117A1 - Device for two-phase operation protection of three-phase induction motor - Google Patents

Abstract

DEVICE FOR PROTECTION tPEXYLZNOGr ASYNCHRONOUS ELEKTRODVIGA, therefore, obliged to-working two FDZAH, comprising three current transformers, the primary of vpitayu1 e wires motor, the secondary windings are connected S open delta, the output of which is operably linked to tirystornym key and the magnetic actuator and / Stabilized A power source, characterized in that, in order to increase the operational reliability of the device, it is additionally equipped with a full-wave rectifier bridge, It is equipped with a potentiometer and a time delay unit, and a current transformer is made on a core of transformer steel, between the output of an open triangle and a voltage regulator, the zener diode of which is connected to a thyristor switch control switch connected to a coil mains voltage, a full-wave rectifier bridge connected, a potentiometer, is connected (our extreme terminals to the bridge, and a time delay unit connected between the output of the adjusting potentiometer and the common point of the anode of the Zener diode and the cathode of the thyristor of the thyristor key. oo 42

Description

FIELD OF THE INVENTION The invention relates to the protection of electric motors against abnormal work patterns, in particular against phase failure, electric drives, industrial and agricultural workers.

Various types of protection are known that use current transformers as sensors, which are connected to controlled circuits by primary windings. Secondary windings to provide measurement mode of current transformers (to ensure the unsaturated magnetic circuit) are loaded by phase solutions connected either directly to the secondary terminals or through Heavy devices l -.7. 2

The signal from the current transformers is fed either to a preamplifier having a threshold element, with a further output to the actuator, or directly to the relay, performing the function of the threshold element and the executive mechanism.

The closest to the proposed device is to protect the three-phase electrical installation from working on two phases, in which three current transformers with a rectangular hysteresis loop are connected in an open triangle and connected to an actuator in the form of a half-wave SCR. . .

However, current transformers must be available with different primary currents for different electric motors.

Control of the size of the control pulses is not possible.

In addition, the device is inconvenient in operation due to the fact that in case of an accidental short-term disappearance of 4i, i3bi, the electric motor is disconnected, and during start-up, the circuit of the coil of the switching apparatus will be interrupted by the contacts of the actuator's actuators operating on currents above nominal.

The executive units are of considerable size due to the fact that, firstly, the thyristor switch is half-wave, and secondly, the thyristor opens with positive impulses, while impulses of different polarities are applied to it. . The polarity of the latter corresponds to the polarity of the fauna controlled by Ci. At the same time, the actuator is connected to the linear voltage of phases A and B. Analysis of the vector diagrams shows that the vector of the linear voltage A B is ahead of the vector of phase A (the alternation of the phases is taken from left to right) by 30 ° and lags behind

from the vector of phase B by 90, and from the vector of phase C by 210 °. Positive pulses from current transformers come after the passage of sinusoids of phases A and C of the network O, 120, 240, 5 360, 480. ..; negative pulses that do not open the thyristor after passing the phases С L In the network 60, 180, ZOR, 420, 540% ... Consequently ,. impulses of phases A and C.

Q thyristor connected to phases A B does not open. It opens only with positive and strong B phases, i.e. at oi 120, 480, 840 °, ... in the area of maximum value

 voltage A V. Thus, in each half-period the thyristor remains open only 90 °. This caused in the prototype to shunt the coil of the actuator relay with a capacitor of significant capacitance to a voltage not lower than 500 V connected in series with a powerful (W) current-limiting resistor.

Condenser coil running

near the resonance of the currents, which puts the key thyristor in severe conditions and reduces the operational reliability of the protective device.

When the motor starts, a high-power impulse comes to the control transition, which also reduces operational reliability.

The purpose of the invention is to increase the operational reliability of the device.

The goal is achieved by the fact that the device for protection of a three-phase asynchronous electric motor against operation on two phases, containing three current transformers, is on. The primary windings into the power wires of the electric motor, the secondary windings of which are connected in an open triangle, are output, the output of which is functionally connected to the tiris switch and the magnetic starter, and the stabilized source is fed, additionally equipped with a full-wave rectifying bridge, an adjusting potentiometer and a time delay unit , and current transformers are made on a core of transformer steel, and between the output of an open triangle and a voltage stabilizer, the throne of which is connected to the thyristor key thyristor control transition connected together with the magnetic starter coils to the phase mains voltage, 0 includes a full-wave rectifier bridge, an adjusting potentiometer connected to the bridge by the extreme terminals, and a time delay unit connected between the adjustment output potentiometer and common point of the anode of the Zener diode and the cathode of the thyristor thyristor key.

The drawing shows a diagram of a device for protecting an electric motor against operation on two phases.

The device contains three current transformers 1 connected to a full-wave rectifier bridge 2, the output of which is connected to an adjusting potentiometer 3, a limiting resistor 4 and a capacitor 5 time delay block, which are connected between the motor of potentiometer 3 and the plus rectifier bridge 2, a ballast the resistor is connected at one end to the point where the resistor 4 is connected to the capacitor 5, and the other end to the A. zener diode 7 voltage stabilizer, whose cathode is connected to the plus of the rectifying bridge 2 and controlling Transistor thyristor 8, which together with diodes 9-12 constitute a thyristor key 4, connected in parallel with a start button 13 of a button station, having, besides the button, a stop button 14, and in series with a coil 15 of a magnetic starter whose power contacts 16 switch the stator winding of an electric motor - 17 ..

The current transformers are made in such a way that, at the rated current of the motor 17, the number of primary current turns out to be sufficient to magnetize the iron to saturation. The secondary windings are connected to a load with a large input resistance and low current. In this case, the transformer when applying a sinusoidal current to the primary winding transfers it to the secondary winding with distortion. The current will contain the first, third, fifth, seventh (harmonics, etc., etc.). When connecting the secondary windings of a current transformer into an open triangle, harmonics 1, 5, 7, 11-13 do not multiply by three disappear, but harmonics are multiples of three. , adding in phases give the value of Zi, where UQ is the voltage of harmonics that are multiples of three separate phases.

The device works as follows.

When the locking button 13 is pressed, the magnetic puller with the coil 15 and the contacts 16 is activated, and the motor 17 is connected to the network. A starting current flows through the stator and at terminals d, 2 a potential appears up to 70 V. After acceleration of the electric motor, the potential is set to 20 - 35 V. Depending on the magnitude of the primary rated current, adjusting potentiometer 3 sets the supply voltage of circuit 18. From the Zener diode 7, the power of the thyristor control switch B to the thyristor switch 8-12, which bypasses the closing button 13, is powered. The magnetic starter remains on, the motor starts up normally. A 5 fO capacitor and a resistor 4 serve to delay

time of circuit disconnection at short-term disappearances of the network phase and for smoothing the ripple of rectified voltage.

When a phase is broken, the direction of the current in one of the remaining phases of the motor changes, and therefore, in the secondary windings of transformers of these phases, the current vectors are directed oppositely. Their subtraction leads to

that the voltage at terminals A, B disappears. If the disappearance-phase was not accidental and the symmetry in the network was not restored, then after the discharge

25 of the capacitor 5, the thyristor 8 is closed, de-energizing the coil of the 15-starter and disconnecting the electric motor 17 from the damaged network. Restarting is possible only after restoring the symmetry of the network voltage, since the harmonic vectors are multiples: the three in the two remaining phases are directed oppositely and the potential at the terminals is equal to

35 zero.

The use of current transformers with a core of transformer steel, connected in an open triangle and operating in a saturated mode, as a power source for the thyristor control circuit and phase break sensors, introduction to the circuit

45 of the full-wave rectifying bridge, time delay block, adjustment potentiometer and connection of the output of the thyristor key and the coil of the magnetic start of the bodies to the phase voltage of the network favorably distinguish the proposed device to protect the motor from two phases from the prototype using a two-wave rectifier, capacitor

55 of the time delay block and the connection of the thyristor key and the coil actuator for phase 1 April, the thyristor is opened for the entire period, adjusted by the starter to the sixth dimension inclusive, and the time delay block leaves the motor in operation during random short-term phase losses. In addition, if the con-Densator takes a splash

.tokov when starting the engine. Exclusion from the circuit of the capacitor and resistor, shunt the coil of the relay, posl

d

improve the efficiency and UA4s11It dimensions of the device.

l

Claims (1)

2. Copyright certificate of the USSR No. 612339, cl. Н 02 Н 7/08, 1976. i 3 * Authrr certificate of the USSR No. 547901, cl. N 02 N 7/00, 1975. 1 (54) (57) A DEVICE FOR PROTECTING A THREE-PHASE ASYNCHRONOUS ELECTRIC MOTOR FROM 'OPERATION ON TWO FDZA, containing three current transformers, connected by primary windings, soaked wires of the electric motor, the secondary windings of which are connected at one time by a triangle which is operably linked to a thyristor key and the magnetic actuator ^1, and a stabilized power supply, characterized in that, in order to improve the operational reliability of the device ^ it is further provided with a full-wave rectifier a bridge, adjustable by a potentiometer and a time delay unit, and current transformers are made on a core made of transformer steel, and between the output of an open triangle and a voltage regulator, the zener diode of which is connected to the thyristor switch thyristor control switch connected together with the magnetic starter coil to the mains phase voltage, a half-wave rectifier bridge, an adjustment potentiometer connected by extreme terminals to the Bridge, and the unit is temporarily a delay coupled between the output and adjusting potentiometer common point of the anode of the zener diode and the cathode of the thyristor of the thyristor switch.