RU2774920C2 - Device for control of speed of synchronous engine and its protection from asynchronous mode - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: invention relates to electrical engineering, in particular to devices for control of an electric drive. A diode is included in an armature winding circuit of a machine exciter as a sensor for control of engine speed. A variable resistor is connected in parallel with the diode, from which a negative half-wave is taken and supplied to control winding of positive feedback by a variable voltage component on engine excitation winding. The device controls the speed of rotation of the engine, provides for resynchronization in case if it runs out of synchronism, and does not allow long-term operation in an asynchronous mode.

EFFECT: increase in the reliability of protection of a synchronous machine from an asynchronous mode.

1 cl, 1 dwg

Description

The invention relates to electrical engineering, in particular to relay protection. The purpose of the invention is to improve the reliability of the protection of the synchronous machine from the asynchronous mode.

The drawing shows a block diagram of the proposed device. The device contains: 1. R - disconnector; 2. K - high voltage contactor; 3. SD - synchronous motor; 4. VK - diode; 5. VM - machine exciter; 6. UE - universal switch; 7. TP - thyristor converter; 8. D5 - diode; 9. OVMV - excitation winding of the machine exciter; 10. MU - magnetic amplifier; 11. 1n-1k - positive feedback winding on the motor stator current; 12. 2n-2k - negative connection winding for mains voltage; 13. 3n-3k - winding for forcing the excitation of the engine; 14. 4n-4k - positive feedback winding on the variable voltage component on the motor excitation winding; 15. 6n-6k - winding of negative feedback on excitation of the exciter; 16. РВ1 - time relay; 17. РВ2 - time relay; 18. RF - boost relay; 19. RPT - starting current relay; 20. PV - excitation starter; 21. RPO - starting relay, leading to the shutdown of a synchronous motor in case of unsuccessful resynchronization.

Below is a diagram of the control of a synchronous electric drive (see drawing). The motor stator 3 SD is powered by a 6 kV network through a disconnector 1 R and a high-voltage contactor 2 K. The excitation winding 3 SD is powered by a 5 VM exciter, which is driven by the motor shaft. The excitation of the exciter is independent of the thyristor converter 7 TP.

In the initial position of the circuit, the universal switch 6 UP is set to zero, the boost relay 18 RF is pulled in, the rest of the devices are turned off.

The purpose of the control windings of the magnetic amplifier 10 MU: 11 1n-1k - positive feedback on the stator current, 12 2n-2k - negative feedback on the mains voltage, 13 3n-3k - excitation forcing winding, 14 4n-4k - positive feedback on the variable component of the voltage on the motor excitation winding, 15 6n-6k - negative feedback on the excitation current of the exciter.

To start the engine, switch 6 UE turns to the right and then returns to the zero position, while the contactor 20 PV turns on and shunts contact 6 UP with its closing contact; contactor 2 K connects the motor to the mains. The relay 19 RPT is activated from the starting current and opens the excitation starter 20 PV with its opening contact. At a subsynchronous speed, the inrush current relay 19 RPT disappears and, with its NC contact, supplies voltage to the PV coil 20, which connects the converter 7 TP to the power source. At the same time, its closing contact shunts the RPT relay 19, preventing the excitation from being turned off in the event of a short-term increase in motor current. After connecting 7 TP to the network, a voltage appears at its input, causing the excitation of the machine exciter 5 VM, which in turn leads to a rapid increase in the excitation current 3 SD and drawing it into synchronism. To turn off the engine, the handle 6 UE turns to the left and returns to the zero position, while the contactor 20 PV is turned off, the motor excitation current decreases and the latter goes into asynchronous mode. At the same time, the time relay coil 16 PB1 is de-energized, which opens its normally open contact with a time delay, and the 2 K contactor disconnects the motor from the network.

When the mains voltage drops by 20-25% of the nominal value, the forcing relay 18 RF is switched off and closes the circuit of the excitation forcing winding 13 3n-3k, due to which the excitation current increases to the maximum value

When the voltage is restored, the relay 18 RF turns on again and turns off the winding 13 3n-3k.

Protection of a synchronous motor from a long-term asynchronous operation is based on monitoring the variable voltage component that occurs in the rotor winding in an asynchronous mode, and a 4 VK diode connected in series in the armature winding of the machine exciter 5 VM is used as a voltage sensor. Parallel to the diode, resistance P12 is connected, from which the negative half-wave of the alternating voltage is removed and fed to the winding 14 4n-4k of the magnetic amplifier. With an increase in the alternating voltage on the excitation winding of the motor, the winding 14 4n-4k acts in such a way that the excitation current of the exciter, and, consequently, the motor, grows. The feedback coefficient is chosen in such a way that when the motor rotation speed deviates from the synchronous one by 15-20%, the excitation current reaches the maximum allowable value. This forcing allows resynchronization of the synchronous motor. With successful resynchronization of the motor, the excitation current will decrease to a certain value, the value of which is determined by the resulting ampere-turns of the MU control windings.

In the asynchronous mode of operation of the synchronous motor, along with the excitation forcing, 21 RPO is activated, which, with its opening contact, turns on the time relay 17 RV2. If the resynchronization was unsuccessful (relay contact 21 RPO is open), time relay 17 РВ2 with a time delay of 15-20 s will open its normally open contact in the circuit of coils 16 РВ1 and 20 ПВ, which will turn off the engine.

Relay 21 RPO will also work during start-up and if the acceleration time of the engine for any reason exceeds 15-20 s, the engine will be turned off.

"Device for monitoring the speed of a synchronous motor and protecting it from asynchronous mode" (application No. 2020108087) improves the reliability of this device and reduces the cost and operating costs.

Claims (1)

A device for controlling the speed of a synchronous motor and protecting it from an asynchronous mode, in which the stator of the synchronous motor is connected to a 6 kV power supply network through a disconnector and a high-voltage contactor, the excitation winding located on the rotor of the synchronous motor is powered by a machine exciter, which is driven from the synchronous shaft motor, while the excitation winding of the machine exciter is powered by a thyristor converter, which is connected to a 380 V power supply network through an excitation starter, and its control circuits are connected to the outputs of a magnetic amplifier, which includes a positive feedback control winding for the stator current, a negative control winding voltage feedback control winding, excitation forcing winding, positive feedback control winding for the variable voltage component on the motor excitation winding and negative feedback control winding for excitation excitation current, different due to the fact that a diode is included in the armature winding circuit of the machine exciter as a sensor to control the motor speed, a variable resistor is connected in parallel with the diode, from which a negative half-wave is removed and fed to the positive feedback control winding on the variable component of the voltage on the motor excitation winding.

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