SU936179A2 - Device for thermal protection of induction electric motor - Google Patents

Description

The invention relates to devices for protecting electric motors from emergency operation. According to the main author. St. No. 3576, a device is known, comprising, e, a power source, thermal sensors mounted on the windings of an electric motor and connected to the input of a control unit made in the form of an electronic key on two transistors, output connected to an actuator (thyristor) and disconnecting device Cl 1. Disadvantage The known device consists of 3 that in the rotor stop mode when the stator is included in the network, which takes place when the electric motor is tilted or the rotor is jammed from cold or hot conditions, as well as If the phase loses during start-up or phase loss and the rotor stops, the device triggers with a significant time delay, which leads to the maximum allowable heating of the winding and rapid aging of the motor insulation. The purpose of the invention is to increase the speed in the rotor stop mode when the stator is connected to the network. This goal is achieved by adding a capacitor, a time relay and a magnetically controlled contact located in the area of the frontal parts of the motor winding to the device for temperature protection of the asynchronous motor, and the time relay is connected to the power source through the closing contact of the device’s disconnecting unit and the magnetically controlled the contact is connected in series with the time relay contact that closes with a time delay and is connected to the input of the control unit of the device to which it is connected ndensator. 39 In FIG. 1 is a schematic diagram of the protection device; in fig. 2 shows a variant of fastening a magnetically controlled contact in the area of the frontal parts of an electric motor winding; in fig. 3 a phase diagram of the two-layer winding of a two-pole electric motor and the distribution of the magnetic field of dispersion along the phase zones of the winding in normal operation, when the rotor of the electric motor and the stator connected to the network, with a break in phase A, B, C and a stationary rotor are deployed. The protection device (Fig. 1) includes a power supply unit 1, a control unit 2 that turns off the protection device 3, a time relay A, thermal sensors, a magnetically controlled contact 8, a power, an 8th contactor 9, and control buttons 10 and 11. The power contactor 9 is connected in series with the closing contact 12 of the tripping device 3 and the time relay is switched on via the second closing contact 13 of the same tripping device. The magnetically controlled contact 8 is connected via the grounding contact H of the relay 4 to the input of the control unit, i.e. parallel to thermal sensors. A capacitor 15 is also connected to the input of the control unit. The magnetically controlled contact 8 is located in the zone of the frontal parts of the motor winding. It can be mounted on the electric motor bearing shield or directly on the winding. FIG. 2 shows the fastening of a magnetically controlled contact between the motor case 16 and the winding 17. The magnetically controlled contact is placed in a non-magnetic shell 18 and pressed against the housing 1b by a strip 19, tightened with screws 20 and 21. Thermal sensors 5-7 are placed in the winding (not shown). One wire from the thermal sensors is connected to the magnetoresistant contact and three wires from all protection sensors are brought into the terminal box of the electric motor. In the protection device, the time relay t can be of any design. It is an obligatory requirement to provide an adjustable time delay for the closing contact to operate. Neither connect it via the closing contact 13 of the tripping protection device. 3 The protection device operates as follows. When the button 10 is pressed, the voltage goes to the protection device, and if the engine temperature is below acceptable and the device is in good condition, the contact 12 of the opening device 3 is closed and the contactor 9 and the electric motor are turned on. At the same time, contact 13 is closed, and the time relay is connected to the network and periodically with a frequency of 100 Hz it closes and opens the magnetically controlled contact 8 from the magnetic field dissipating the starting currents of the motor. Time relay k is set to a delay time slightly longer than the motor start time (3 normal conditions. Pointer during normal start, contact C closes when magnetic control contact 8 ceases to operate due to a decrease in motor current. In case of emergency start, when the rotor is stationary for a time longer than the start-up time of the electric motor during normal starting, contact 14 is closed during the switching mode of the magnetically controlled contact 8 and the input of the control unit 2 and is shunted by this contact. A capacitor 15 connected in parallel with the input is also periodically shunted to reduce the voltage at the input of the dongle for a time sufficient to disconnect device 3. Its contact 12 will break the circuit of the power contactor 9 and the motor will shut off from the mains. In normal operation of the electric motor, the magnetically controlled contact 8 is open and the time relay contact k is closed. If in emergency cases the rotor stops when the stator is on, the magnetic Oleen scattering of the engine in the area of the winding frontal parts increases sharply (line 22-25 in FIG. 3). The magnetically controlled contact switches the input of the control unit, the protection device disconnects the motor from the mains with a short time delay of 0.13-0.17 seconds, which provides a detuning from the current surges at near short circuits in the supply mains. When heated, the motor winding is above the permissible temperature of the device

59

triggered by thermal sensors regardless of the state of the magnetically controlled contact.

The magnetic field of the dissipation of the motor winding when the rotor stops and the stator is turned on is distributed along the phase winding zones evenly (line 22 in Fig. 3). s with stationary rotor and broken phase A, B or C - uneven, has zones of maximum and minimum floor (line 2325 in FIG. 3) - However, along the phase zones of the winding in the region of the frontal parts there are zones where at any phase break and stationary rotor magnetic field of dispersion is greater than magnetic field. MK, causing the triggering of the magnetically controlled contact 8. In FIG. 3, these zones are indicated by dashed lines. The magnetic contact is located in one of these zones.

In order to allow the movement of the mapping contact 8, during adjustment, release the screws 20 and 21 (Fig. 2) and move the magnetically controlled contact in the axial direction. Gaskets (not shown) are used to move it in the radial direction.

Introduction to a time relay device, a capacitor, and a magneto-controlled contact allows the device to combine all the advantages of temperature protection and turn it off in practice.

In an instant when the emergency rotor stop occurs when the stator is connected to the network, the motor winding can be heated to maximum permissible temperatures, which increases the service life of the motor winding insulation.

Claims (1)

1. USSR author's certificate No. 3576, cl. H 02 H 7/08, H 02 H 5/04, 1971. YY t FIG. I