RU2214641C1 - Magnetic starter - Google Patents

Abstract

FIELD: electrical engineering; low-voltage metal-clad switchgear. SUBSTANCE: magnetic starter designed for power distribution among ac motors of important drives running continuously has short-circuit protective gear of three fuses connected to terminals of first, second, and third phases, phase-failure protective gear incorporating three phase-failure relays with one contact at each relay, power contacts connected in series with fuses, overload protective gear, and control circuit; newly introduced in phase-failure protective gear are phase- shifting capacitors, each of them being connected between adjacent phases through respective contact of phase-failure relay; the latter has making contacts. EFFECT: enhanced effectiveness of starter phase-failure protection due to affording no-break operation of motor. 1 cl, 1 dwg

Description

 The invention relates to the field of electrical engineering and can be used as a magnetic starter in low-voltage complete devices for distributing electricity between AC motors of critical electric drives with continuous operation.

 Known magnetic starter containing a device for protection against short circuit currents, consisting of three phase fuses, a control circuit consisting of a start and stop button, coil, block contacts and contacts of thermal relays, two thermal relays included in the extreme phases [1]. This starter is widely used in general-purpose electric drives, however, it does not have protection against phase failure, so if the voltage drops in any of the wires in the network, the drive is inoperative.

 The closest in technical essence to the claimed invention is a magnetic starter containing a device for protecting against short circuit currents, consisting of three phase fuses, a phase failure protection device, consisting of three phase failure relays, bypassing these fuses, each of which is equipped with one NC contact , power contacts, a motor protection device against overload currents, consisting of two thermal relays included in the extreme phases, and a control circuit, consisting of s start and stop buttons, reels, contacts the thermal relay and connected in parallel with start button and contact block of series-connected phase failure relay NC contacts [2]. This magnetic starter is characterized by the presence of three different motor protection devices, however, the protection against phase failure is relatively low, since when any phase is broken, the engine stops, which is unacceptable for technological reasons.

 The technical result of the invention is to increase the efficiency of the protection device against phase loss of the magnetic starter by ensuring uninterrupted operation of the engine.

 The technical result achieved is achieved by the fact that in a magnetic starter containing a short circuit protection device, consisting of three fuses connected by one terminal to terminals for connecting the corresponding phases of the network, a phase failure protection device, consisting of three maximum voltage relays with make contacts, at the same time, the windings of the maximum voltage relays are connected in parallel with the corresponding fuses, a switch with a control coil and three closing power contacts, vk connected in series with the corresponding fuses, a block contact in the form of a make contact, in addition, a device for protection against overload currents, consisting of the first and second thermal relays with NC contacts, and the other terminals of the first and second power contacts are connected to the first and second terminals for connection the motor through the heating elements of the respective thermal relays, and the other terminal of the third power contact is connected to the third terminal for connecting the motor directly, and the control circuit connected between the connection point of the first fuse with the first power contact and the connection point of the second power contact with the second thermal relay and containing the stop button opening contact, the contact bridged contact closing start button contact, the control coil of the switch and the opening contacts of the first and second thermal relays, three phase-shifting capacitors are introduced, each of which is connected between the corresponding pair of terminals of adjacent phases through the make contact maximum voltage relay.

 The drawing shows a circuit diagram of a magnetic starter with three types of motor protection: protection against short circuit currents, protection against overload currents and advanced protection against phase failure.

 The magnetic starter contains a short circuit protection device 1, consisting of three fuses 2, 3 and 4 connected to the terminals for connecting the first A, second B and third C phases, a phase-loss protection device 5, consisting of three maximum relays 6, 7 and 8 voltages with make contacts 9, 10 and 11, respectively. Between the output terminals of the neighboring phase fuses, series circuits are included from the corresponding mentioned making contacts 9, 10 and 11 and the corresponding phase-shifting capacitors 12, 13 and 14. Each of the maximum voltage relays 6, 7 and 8 is connected in parallel to the corresponding fuse 2, 3 and 4. Device also contains a switch with a control coil 26 and power contacts 15-1, 15-3 and 15-2, connected in series with the corresponding fuses 2, 3 and 4, a device 16 for protecting against overload currents, consisting of two fishing relays 17 and 18 with NC contacts 19 and 20, the first 15-1 and second 15-2 power contacts included in the extreme phases are connected respectively to the first and second terminals for connecting the motor 21 through the heating elements of the corresponding thermal relays 17 and 18 and the third power contact 15-3 is connected to the third terminal for connecting the motor 21 directly, and the control circuit 22 connected between the inputs of the first 15-1 and second 15-2 power contacts and consisting of serially connected stop buttons 23, start buttons 24, shunted second auxiliary contact 25, coil control switch 26 and contacts 19 and 20, thermal relay.

 The device operates as follows.

 In static mode, when the start button 24 is not pressed, the magnetic starter is de-energized and the motor 21 does not work, in the presence of mains voltage, the power contacts 15 are energized, but not closed.

If there is a voltage of the network A, B, C and pressing the start button 24, the coil 26 will work and the power contacts 15-1, 15-2 and 15-3 will be closed, supplying electricity to the motor 21 and it will start to work, while the block contact 25 also it closes by shunting the start button 24. When a short circuit current occurs, for example, in phase A, the fuse 2 of the short circuit current protection device 1 blows and the maximum voltage relay 6 of the phase 5 open circuit breaker trips and closes its contact 9, thus creating a circuit charge phase-shifting capacitor 12, last whose charge voltage on phase A is restored. The voltage recovery time in any of the phases is determined by the time constant:
τ = rС,
where r is the phase resistance;
C is the capacity of the phase-shifting capacitor,
and the process of voltage recovery in each phase is identical to that described, while only the state of the elements in these modes changes in accordance with the table. The engine 21 continues to work, since it is an inertial device and does not have time to react to phase failure and voltage recovery. The status of the magnetic starter and the state of the network in it are signaled by the contacts of the triggered maximum voltage relays 6, 7 and 8, which are not shown in the diagram. With prolonged action of the overload currents, thermal relays 17 (18) are activated and, breaking the contacts 19 (20), break the power supply circuit of the coil 26, the latter is disconnected, breaking the power contacts 15-1, 15-2 and 15-3, from which the motor 21 stops . The engine is stopped using the 23 stop button.

 Thus, the loss of voltage in any of the phases of the network does not stop the motor 21, which leads to the continuity of the process; this ensures the achievement of a technical result.

Sources of information
1. Low voltage devices. Magnetic starters, control buttons. Consolidated Directory. - M.: VNIIEM, 1965, Fig. 173, p. 92;
2. Electrical reference book. T. 3, book. 1. / Ed. V.G. Gerasimova. - M.: Energoatomizdat, 1988, Fig. 44.43, p. 640.

Claims (1)

 A magnetic starter comprising a short circuit protection device consisting of three fuses connected by one terminal to terminals for connecting the corresponding phases of the network, a phase failure protection device consisting of three maximum voltage relays with make contacts, while the windings of the maximum voltage relays are connected in parallel corresponding fuses, a circuit breaker with a control coil and three closing power contacts connected in series with the corresponding fuses li, a block contact in the form of a make contact, in addition, a device for protection against overload currents, consisting of the first and second thermal relays with opening contacts, and the other terminals of the first and second power contacts are connected to the first and second terminals for connecting the motor through heating elements the corresponding thermal relay, and the other terminal of the third power contact is connected to the third terminal for connecting the motor directly, and the control circuit connected between the connection point of the first is protected For the first power contact and the connection point of the second power contact with the second thermal relay and containing the stop button opening contact, the contact bridged by the start button closing contact, the control coil of the switch and the opening contacts of the first and second thermal relays, characterized in that three phase-shifting capacitors, each of which is connected between the corresponding pair of terminals of adjacent phases through the make contact of the corresponding maximum voltage relay.

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