Protection device for a three-phase electric motor from open-phase operation in case of an open circuit of the power fuse. Encyclopedia of radio electronics and electrical engineering

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The article describes a simple device for protecting a three-phase electric motor from open-phase operation, which occurs when the power fuse circuit is broken, made on thyristor optocouplers that control the integrity of the circuit of fuse links in the phases of the electric motor during its operation.

It is known that the operation of a three-phase asynchronous electric motor (AM) in two phases leads to its overload and failure [1].

Previously, a device was proposed to protect the IM from open-phase modes of operation [2], which provided its protection in the event of a blown fuse insert or poor contacts in switching devices.

Below is a description of a simpler device for protecting blood pressure from open-phase operation. The device belongs to electrical engineering and is intended for use in power supply circuits of three-phase IM protected by fuses (see figure). The proposed technical solution is protected by copyright [3].

A device for protecting a three-phase IM from operation in two phases in case of an open circuit of the RSh-RSh power fuse, connected to the power line of the IM phase from the mains, contains shunt chains 1, 2 and 3 according to the number of controlled fuses, each of which is made on a diode VD1 (VD2 , VDЗ) resistor R1 (R2, RЗ) and optocoupler U1 (U2, U3) according to the number of controlled fuses. The device also contains a reacting body K with a break contact K1, which is included in the IM control circuit.

Each shunt chain 1, 2 and 3 is provided with the first terminal 7 for connection to the fuse terminal on the mains side and the second terminal 8 for connection to the fuse terminal on the BP side.

The LEDs 9, 10, 11 of the optocouplers are connected in accordance with the diodes VD1-VDZ of the corresponding shunt chain 1, 2 and 3. The anode terminal of each of the photothyristors 4-6 of the optocouplers is connected to the first terminal 7 of the corresponding shunt chain 1, 2 and 3. The cathodes of the photothyristors are connected between itself and connected to the first output of the reacting organ K and to the cathode of the additional diode VD4, the anode of which is connected to the second output of the reacting organ K and connected to the network neutral N. Diode VD4 ensures the flow of current through the reacting organ K in the negative half-cycle of the mains voltage due to the EMF of the electromagnetic induction, which increases the reliability of its operation. Zener diodes VD5-VD7 protect the LEDs of 9-11 optocouplers from overload when the engine load changes and, accordingly, ensure the device's operability with these changes.

Connection of IM to the network is carried out by contacts 1K1-1KZ of the magnetic starter included in the control circuit of the electric motor.

The device works as follows. In the initial operating state, the fusible link of a good fuse short-circuits terminals 7 and 8 of chains 1, 2 and 3 in each phase of the IM. The photothyristors 4, 5 and 6 of the optocouplers are closed, the winding K of the reacting element is de-energized, the contact K1 in the IM control circuit is closed, which makes it possible to start the electric motor.

Failure of any of the fuses, for example, in phase A during IM operation, leads to the appearance of voltage between terminals 7 and 8 of the shunt circuit 1. As a result, current flows through LED 9, photothyristor 4 opens, which leads to the operation of the reacting organ K. Contacts K1 open the circuit power supply of the 1K coil (not shown in the diagram) of the magnetic starter, which disconnects the IM from the network with power contacts 1K11KZ. The device works similarly if the fuse fails in phases B and C.

The device uses low-power optocouplers of the 3ОУ1ОЗГ type with forward and reverse voltage on a 400 V photothyristor. Resistors R1-RЗ of the MLT-0,5 type. Diodes type KD105 with any letter index. It is possible to replace with diodes D226B, D209-D211 and D237 with letter indices B, C, G. The reacting element K is a 220 V AC relay of the RP-21, RP25 or MKU-48 type. It is possible to use relays and lower voltages within the allowable current of the photothyristor, since the device is energized for a short time, only for the period when the IM is disconnected from the network. As zener diodes VD5-VD7, stabistors of the KS119A (2S119A) type were used with their direct connection. They can be replaced by a chain of two series-connected stabistors of the D219S or D223S type, as well as a KS107A, (2S107A) stabistor and a KS113A (2S113A) stabistor connected in series.

To increase the reliability of the device and the possibility of using optocouplers with a lower reverse voltage, it is necessary to connect the anode terminals of the thyristors 4-6 of the optocouplers, respectively, to the terminals of the cathodes of the diodes VD1-VD3, and not to the terminals of 7 shunt chains 1, 2 and 3, while shunting the diode and thyristor of each chains with a resistor of the MLT-0,5 type with a resistance of 100 ... 200 kOhm.

The device is mounted on a printed circuit board, which is installed in the body of the reacting element K (relay RP-25). It is also possible to install a printed circuit board directly in the case of a 1K magnetic starter, but in this case it is necessary to use a small-sized AC relay, for example, RP-21 for a voltage of 220 V.

The device is set up as follows. Terminal N is connected to pin 8 of shunt chain 1, and pins 7 and 8 of the same shunt chain are connected to the output of an adjustable autotransformer (AT), the primary winding of which is connected to a 220 V network. Turning the AT handle, set its output to 180 V, with this relay K should work, and its contacts K1 open. If the relay K does not work, then it is necessary to reduce the resistance value of the resistor R1, achieving the relay operation. The shunt chains of phases B and C are adjusted in a similar way.

It is possible, when setting up, instead of optocouplers, to turn on LEDs of the AL307 type and achieve their normal glow by changing the resistance value of the resistor R1, and then turn on the optocouplers and check the reliable operation of the relay K from each shunt chain.

In the absence of AT, tuning can be done by connecting pins 7 and 8 of the shunt chain directly to a 220 V network, achieving the LED to glow and the relay to operate by changing the resistance value of resistor R1. After that, the value of the found resistance of the resistor R1 must be reduced by 2 ... 3 kOhm. This completes the device setup.

A distinctive feature of the device is the lack of power consumption in standby mode, low weight and dimensions. The absence of auxiliary contacts of the magnetic starter in the circuit of the actuating element (relay) and a lower voltage on key elements (photothyristors of optocouplers) increases the reliability of the device, facilitates its installation and commissioning, and therefore, the reliability of turning off the electric motor in emergency modes is higher, which determines the technical - the economic effect of the device, expressed in the cost of the saved electric motor.

References:

1. Grundulis A.O. Protection of electric motors in agriculture. - M.: Agropromizdat, 1988. - P.12.
2. Kolomoytsev K.V. Protection of electric motors from non-full-phase modes of operation//Radioamator. - 1994. - No. 2. - P.10.
3. Author's certificate of the USSR No. 1451795. Cl. NO2N 7/08, 1989.
4. Kolomoitsev K.V. Device for protecting a three-phase asynchronous motor in the event of a fuse failure // Elektrik. 2003. - No. 4. - P.7-8.

Authors: K.V. Kolomoitsev, R.M. Kolomoitsev

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