SU1638758A1 - Three-phase motor protection for unbalanced and open- phase conditions - Google Patents

Description

The invention relates to electrical engineering, to relay protection of a three-phase electric motor. The purpose of the invention is the expansion

functionality by using a phase-shifting element to increase the power factor of an electric drive operating with a symmetrical system of applied voltages. In the event of a decrease in current in phase C, contact 15 of the third current relay 7 closes, the third contactor 3 trips, its open contacts: first 21, second 37, fourth 42 open, closing contacts: first 27, second 30, third 33, fourth 41 are closed, which provides an artificial phase failure C, the parallel connection of three capacitors 22-24, the transfer of energy from phase B to phase C of the electric motor through choke 4, and from phase A through three capacitors 22-24 and full use of the power of the protected motor. 1 il.

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The invention relates to electrical engineering, in particular to relay protection of three-phase electric motors.

The purpose of the invention is the extension of functionality by using a phase-shifting element to increase the power factor of an electric drive operating with a symmetric system of applied voltages.

'The drawing shows a diagram of the proposed device.

The device includes three contactor 13, the phase-shifting element of the inductor 4, three current relays 5-7, included in the motor power supply circuit, an active-capacitive negative sequence filter 8, to the output of which is connected a reverse sequence voltage control coil 9 with a zener diode 10 included in the diagonal rectifier bridge 11 through the ballast. 12, disconnecting contacts of current relays; contact 13 of the first relay 5, contact 14 of the second relay 6 and contact 15 of the third relay 7, closing contacts 16-18 of the relay 9 of the voltage control of the negative sequence are included in the supply circuit of the contactors, the first opening contacts of which are: contact 19 of the first contactor 1, contact 20 of the second contactor 2 and the contact 21 of the third contactor 3, are included in the motor power supply circuit, three identical capacitance capacitors 22-24, the total capacity of which, when turned on in parallel, is equal to the calculated capacitance of the phase-shifting element. One output of the choke is connected to phase A via the first make contact 25 of the first contactor 1 ,. with phase B through the first closing contact 26 of contactor 2, with phase C through the first closing contact 27 of contactor 3. The other output of the choke 4 is connected to phase C through the second closing contact 28 of contactor 1, with phase A through the second closing contact 29 of the third contactor 3, the first output of the second capacitor 23 is connected directly to the first output of the first capacitor 22, and to the first output of the third capacitor 24 via the third normally-open contacts 30-32 of contactors 1-3, respectively, and to phase C through the second disconnecting contact 33 of contactor 1, the second output of the second capacitor 23 is connected to the first output of the third capacitor 24 via a third disconnecting contact 34-36 of contactors 1-3 connected to each other and a contact of the contactor 1 and the third disconnecting to the motor phase A 34 35 and the fourth 37 contacts of the contactor 2, the second output of the first capacitor 22 is connected to the second output of the third capacitor directly, with the second output of the second capacitor 23 through parallel connected between each fourth make 38-40 contacts of the contactor 1-3, respectively, and with phase B through the fourth opening 41 contact of the contactor 3.

A device for protecting a three-phase electric motor from asymmetrical and incomplete-phase modes operates as follows.

If there is no voltage at the input of the device to protect a three-phase electric motor from asymmetrical and non-full-phase modes, there is no current in the motor power supply circuit and the negative sequence voltage, the reverse sequence voltage relay 9, contactors 1–3 and phase-shifting elements do not work.

When a symmetric voltage is applied to the motor, it turns on and works normally, current relays 5-7 are triggered and contacts 13-15 open in the supply circuit of contactors 1-3, the negative sequence voltage is absent, the reverse sequence voltage control relay 9 does not work, its contacts 16-18 are open, the phase-shifting element (choke) is disconnected, and the capacitors 2'2,23 and 24 are connected to the line voltage respectively: VS through the second 33 and fourth contacts 41 of the contactors 1 and 3; AC - through the second and third 33, 34 and fourth and third disconnecting contacts 37, 35 contactors 1 and 2; AB through the fourth disconnecting contact 37 of contactor 2, the third and fourth disconnecting contacts 36, 41 of contactor 3. The electric motor operates with simultaneous compensation of reactive power, and consequently, with a high power factor.

When asymmetry of the supplied voltages is higher than the allowable voltage, the negative sequence reaches the value at which the negative voltage control relay 9 operates and closes the contacts 16-18 in the coil circuit of contactors 1-3, the current in one of the phases (for example, A) decreases to which contact 13 of the first current relay 5 cannot remain in the open state, it closes, the contactor 1 is activated, its first, second and third disconnecting contacts 19, 33, 34 open, and the closing first, second, third

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and the fourth contacts 25, 28, 30 and 38 are closed, thus providing an artificial break in the phase A of the network, switching on the capacitors of the first, second, third 22-24 in parallel, transfer of energy from phase B through the phase shifting element to the capacitors 22-24, and from phase C through the phase-shifting element of the throttle 4, the full use of the power of the protected motor.

If as a result of asymmetry of the supplied voltage, the current decreases in phase B, then contact 14 of the second current relay 6 closes, contactor 2 trips, its first, second, third 20, 35 and 37 open contacts open, and the first, second, third, and fourth short circuit 26 , 42, 31 and 39 are closed, which provides an artificial phase failure In the network, the inclusion of the phase-shifting elements of the inductor 4 and the capacitors 22-24 and the full use of the power of the protected motor,

In the case of a decrease in current in phase C, contact 15 of the third current relay 7 closes, the third contactor 3 trips, its first, second and fourth 21, 36 and 41 open contacts open, the first, second, third and fourth contacts 27, 29, 32 and 40 are closed, which provides an artificial phase failure C, parallel connection of three capacitors 22-24, energy transfer from phase B to phase C of the electric motor through choke 4, and from phase A through three capacitors 22-24 and full use of the power of the protected motor.

When one of the network phases (for example, A) breaks, the voltage on the coil of the reverse sequence voltage control relay 9 is maintained within the required value by the Zener diode 11, the reverse sequence voltage control relay closes its contacts 16-18, the current relay coil 5 de-energizes, its opening contact 13 closes, the contactor .1 operates, its opening contacts first, second and third 19, 33 and 34 open, and the closing contacts first, second, third, 25, 28, 30 and 38 close, and the A phase failure duplicated network. Three capacitors 22-24 are connected in parallel, energy is transferred to phase A of the motor from phase B through the phase shifting element, capacitors 22-24, and from phase C through the phase shifting element of the inductor 4 and full use of the power of the protected motor.

When starting the motor with a disconnected network phase (for example, A), the voltage on the coil of the reverse sequence voltage control relay 9 is maintained within the required value by the Zener diode 11, the reverse sequence voltage control relay closes its contacts 16–18, the current through the coil of the first current relay 5 does not leak, its opening contact 13 remains in the closed state, the contactor 1 is triggered, while the opening contact 19 opens, duplicating an open phase A, its contacts 33, 34 second and third also opening first, second, third, and fourth 25, 28, 30, and 38 are closed, and the phase-shifting elements of the choke 4, first, second, and third capacitors 22-24 are connected, thereby starting up the engine and making full use of its power in steady state. Break of two phases is equivalent to disconnection from the network.

When eliminating the unbalance of the supplied voltages or the loss of the phase of the network, the device for protecting the motor from asymmetrical and non-full-phase modes returns to its original state.

The proposed device allows to increase the efficiency of using phase-shifting elements by using capacitors of a phase-shifting element to compensate for reactive power and, thus, increase the power factor of an electric drive operating with a symmetric system of applied voltages.

Claims (1)

Claim A device for protection of a three-phase electric motor from asymmetrical and non-phase-phase modes, containing three contactors, the power contacts of each of which are intended to be connected in series to the phase wire supplying the three-phase electric motor, the first terminals of the control coils of the contactors are intended to be connected to the neutral wire of the network, three current relays, terminals the coils of which are connected in series with the power contacts of the contactors and with the terminals for connection to the mains, the inductive-capacitive phase shifting rd element, the negative sequence voltage relay, filter inverse sequence voltage, its three inputs connected to terminals for connection to the mains supply, the two outputs which through bal1638758 7 The flaring resistor is connected in parallel with the inputs of the rectifier bridge and the coil of the negative-sequence voltage control relay, a zener diode connected in parallel to the output of the rectifier bridge, the second coil of the first contactor being connected through the first closed contact of the reverse-voltage control relay and the first 10 current contact the relay is connected to the terminal for connection with the second phase of the network, the second output of the coil of the second contactor through the second contact a negative-sequence voltage control relay and 15 in series; a disconnected contact of the second current relay is connected to the terminal for connection to the third phase of the network; the second coil output of the third contactor is connected through the third closing contact of the negative sequence voltage relay and the disconnecting contact of the third current relay is connected to the terminal for connection to the first phase of the network, which is intended to extend the functionality by using capacitively To increase the phase-shifting element to increase the power factor of the electric drive operating 30 with a symmetric system of applied voltages, the capacity of the phase-shifting element is made in the form of three capacitors, the capacity of which, when connected in parallel, is equal to the calculated capacitance of the phase-shifting element, one output of the choke is connected to the terminals for connecting to the first second and third eight the phase terminals of the motor through the first closing contacts of the first, second and third contactors, the second terminal of the inductor is connected to the terminal for connection to the first, second and third phase terminals of the motor through the second closing contacts of the second, third and first contactors, respectively, the first terminal of the second capacitor is connected to the first the output of the first capacitor directly, and with the first output of the third capacitor - through the third contact contacts of each of the contactors and with a terminal for connection to the third phase output of the electric motor — through the second disconnecting contact of the first contactor, the second output of the second capacitor through the third disconnecting contacts of the first, second and third contactors connected in series with the first output of the third capacitor, the common point of the third disconnecting contacts the second and third 25 of its contactor through the fourth disconnecting contact of the second contactor connected to the terminal for connection with the first phase output of the electric motor The second terminal of the third capacitor is connected directly to the second terminal of the second capacitor through the fourth make contacts of each contactor connected in parallel, and to the terminal for connection to the second motor phase through the fourth contact of the third contactor. 40