SU244478A1 - DEVICE FOR ELECTRIC MOTOR PROTECTION - Google Patents

Description

The known motor protection devices include current transformers, a magnetic starter, a switching element, and capacitors.

The proposed device differs from the known ones in that the magnetic starter winding, connected to the power source through a capacitor, is shunted by a switching element, for example, a cold cathode tiratron, whose control circuit is connected via dividing diodes integrating an RCR circuit and a voltage divider supplied from the secondary Windings two current transformers connected in series with stator motor windings.

This simplifies the device and improves its reliability in the operation of providing comprehensive current protection.

FIG. 1 shows the basic (electrical) scheme of the device proposed, FIG. 2 is a diagram with a composite thyratron and thermal protection.

The device has two current transformers Tpi and Tr.2, rectifying diodes / d and D, filter capacitor C, separating diodes Dz, D forming together with resistors RU and independent for a regular AND discharge circuit of the integrating RCR circuit, divider the current cutoff R, 2, the circuit To: De, limiting the resistors R,

RT, switching element T (cold cathode tiratron), rectifying d, iodine Dv, anodic time s – adage circuit R ,, Сз, D and magnetic actuator MP. The device works as follows. . When the start button and the actuator magnetic circuit are open, the entire voltage of the source of the titanium falls on capacitor C as the inductive resistance of the magnetic actuator winding when the magnetic circuit is open is several times less than when closed, and the capacitor capacitance is determined by partially compensating the inductance of the winding with

closed magnetic circuit so that the voltage across the winding is equal to the nominal one.

When a capacitor is shunted by the start-up button, a nominal voltage is applied to the electromagnet winding and it is turned on. As a result of the magnetic circuit closure, the inductive resistance of the winding increases sharply and after the start button is opened, the capacitor capacitance of the capacitor is compensated for by the active resistance of the winding, the resistance of the circuit decreases sharply and the voltage on the winding remains nominal. The voltage on the secondary windings of transz is higher than the ignition voltage of the thyratron at the starting currents of the electric motor. The constant charge time of the RCR circuit is chosen by the IB several times longer than the constant acceleration time of the mechanism. Therefore, during the start-up, the voltage across the capacitor € -2 of the integrating RCR circuit does not reach the ignition voltage of the thyratron.

If the motor overload duration exceeds the acceleration time of the mechanism, then after a certain time interval determined by the RCRC charge constant time circuit, the voltage on the capacitor Ca reaches the voltage of the thyratron ignition source T. The last, shunt the winding of the magnetic starter, causes it to turn off.

The charging and discharging devices are integrated, its RCR circuits are separated by D and D diodes, which at the same time, and their values are resistive In RS and 4, they increase the selectivity of protection and generate a voltage on the capacitor of –2, proportional to the thermal effect of the electric motor current a certain time interval during periodic overloads.

The device has a current cut-off. If a short circuit occurs, the voltage removed from the voltage divider emitted on the resistors K and unlocks the diode Dz causes the thyratron to ignite and the motor to turn off without time delay. In order to maintain the thyratron in the lighted state for the time required to turn off the magnetic starter, a time reference circuit is used, Cs HI diode Dm.

In those cases when it is necessary to build up from long-term overloads of small multiplicity, temperature-sensitive elements (thermal stresses) Tpi, Tr2, Tps are built into the stator windings of the electric motor. These elements form voltage dividers with resistors Ra, Ra, Ky, the midpoints of which are connected to the control, the electrode of the thyratron, via an addition circuit made on the diodes Dd,, Yes. The power of the dividers is dried; it is derived from a ferroresonant voltage stabilizer Art. By selecting the ratio of the shoulders of these voltage dividers, a temperature response temperature of the thermal protection is established. When the temperature of any of the motor windings above the preset is exceeded, one of the Dd, Dy, Dy diodes is opened, the thyratron T is ignited and the engine is turned off.

In the case of using magnetic starters whose nominal voltage exceeds the maximum allowable anode voltage of a thyratron, a composite thyratron TI, TZ is used. At the same time to reduce the residual stress. on the magnetic winding

the actuator after disconnection in parallel, the coil of the relay is connected to the capacitor C, the capacitance of which is selected

from the condition of current resonance.

The described device provides integrated protection of electric motors from short-circuit currents, overloads, phase failure and, if necessary, thermal one. from long overloads. The virtues of the device are its non-contact

n work switching elements in them; pulse mode, which allows an increase in the switching power and reliability of the device as a whole.

PREEMO invention

A device for protection of an electric motor against abnormal operating conditions, which contains current transformers, a magnetic starter, a switching element and capacitors, which, with a gap to simplify and improve reliability of operation while providing integrated current protection, the magnetic starter winding connected to the power source through a capacitor, shunted by a switching element, for example, a thyratron with a HOLO. ONE cathode, the control circuit of which is connected via dividing diodes to an integrating RCR circuit and divide eh voltages fed by secondary

windings of two current transformers connected in series with the stator motor windings.

-A 8 С О

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