SU1753568A1 - Method of starting sync engine provided with start unit - Google Patents

Abstract

Use: The invention is used to start synchronous motors. The essence of the invention: the start of the synchronous motor 1 is that its stator is connected to the network, and the excitation winding 3 is connected to the series-connected starting resistor 4 and the capacitive compensation unit 5 with the same-name EMF and rotor current. When the opposite polarity of the emf and rotor current with a key 6 shunt the capacitive compensation unit 5. 2 hp f-ly, 1 ill. ate about 00

Description

The invention relates to electrical engineering, and more specifically to methods for starting synchronous machines with electromagnetic excitation and can be used to start synchronous motors.

The aim of the invention is to increase the reliability of starting a synchronous motor by increasing the average starting torque generated by the field winding.

The goal is achieved by the fact that in the start-up method of a synchronous motor with a start-up unit made in the form of series-connected starting resistor and a capacitive compensation unit, at which the stator is connected to the mains and close the excitation winding to the starting unit, the polarity of the EMF and the rotor current and at their different polarities, a capacitive compensation unit is shunted.

In addition, the goal is achieved by the fact that when shunting the capacitive compensation unit further increases the multiplicity of the starting resistor.

This goal is also achieved by additionally controlling the amount of slip and the specified shunting, carried out when the rotor reaches a specified amount of slip.

In the asynchronous start mode of the synchronous motor, due to the phase shift between the EMF and the excitation winding current (0V), due to the nature of the load, the motor moment develops only at time intervals when the polarity of the EMF and current are the same. In the time intervals corresponding to the opposite polarity of the EMF and current, the field winding creates a braking torque. Since the average starting torque due to the excitation winding, in one rotation of the rotor of a synchronous motor, is composed of accelerating (motor) and braking torques, the accelerating current is forced to affect the amplitude and phase of the excitation winding by turning on and off the capacitive current block. and reduce braking moments, which ultimately leads to an increase in the average starting torque.

The initial phase of the emf of the excitation winding is zero;

  Sin Sot, (1)

where Efm is the amplitude value of EMF 0V;

So is the fixed value of the slip;

t is the current time.

The current in the field winding lags behind the EMF by an angle of $ 2 (1):

 sin (Sot-Vfc), where lfm- - Efm

v (i + Kp) 2 + (So ta

peak value of current; rt is the active resistance of the field winding;

Kn - the multiplicity of the starting resistor;

T - transition time constant along the longitudinal axis of the poles of a synchronous motor.

arc sft € S

When a capacitive compensation unit is introduced, the transition time constant is determined by the expression:

Xf-Xc / S2 (.

rf st

where Xf, Xc are respectively the inductive co-resistance of the field winding and the reduced value of the capacitance at the mains frequency.

Changing the value of the capacitance compensation unit as a slip function reduces the transient time constant, increases the amplitude of the rotor current with a simultaneous decrease in its phase with the same polarity of the EMF and current 0V. At opposite polarities of the indicated values, the capacitive compensation unit is shunted, the transient time constant is increased, the current amplitude 0V is reduced with a simultaneous increase in its phase. In addition, by increasing the multiplicity of the starting resistor, the field winding additionally reduces the amplitude of the current.

The drawing shows a functional diagram of the device for implementing the method of starting a synchronous motor.

The device contains a synchronous motor 1 with a rotor EMF sensor 2 and with an excitation winding 3, in parallel with which a starting resistor 4 connected in series with each other and a capacitive compensation unit 5 shunted by a control key 6 of bilateral conductivity, controlled by a pathogen 7, a slip block 8 The output is connected to the capacitive compensation unit 5, and successively connected to the excitation winding 3 of the rotor current sensor 9. The signals from the EMF 2 and current 9 sensors are received respectively by comparators 10 and 11, the outputs of which are connected to the inputs of element I 12 and the inputs of two elements HE 13 and 14. The output signals of element HE 13 and 14 arrive at the input of element 15.

The outputs of the elements 12 and 15 are connected to the input of the element OR NOT 16, the output of which through the amplifier 17 is connected to the input of the controlled switch 6 of two-sided conductivity.

The starting method of the synchronous motor is as follows.

Asynchronous start of the synchronous motor 1 begins after connecting it to the AC network. In this case, the excitation winding 3 is closed to the starting resistor 4 and the capacitive compensation unit 5, the control key 6 of double-sided conduction is open, and the controlled exciter 7 is disconnected (for example, by removing the control pulses from the thyristors). In this case, capacitive compensation of the inductance of the excitation circuit occurs, as a result of which the amplitude of the excitation winding current increases and its phase shift decreases with respect to the EMF of the excitation winding. With a positive value of emf and current, the polarity of which is determined by sensors 2 and 9, a logic level 1 appears at the output of comparators 10 and 11, as a result of which the output of element I 12 also results in a level of logic G, and at the output of elements NOT 13 and NOT 14 - the logical level O. The signal of the logical level G from the AND 12 element is fed to one of the inputs of the element ORI 16, transforming at the output to the logical level O, as a result of which the control key 6 of two-sided conductivity remains open at the same name polarity of emf and current p torus.

When the EMF of the rotor changes (the opposite polarity of the EMF and current) at the output of the comparator 10 a logic level of 0 appears, and the output of the comparator 11 remains a logic level of 1, resulting in the output of the AND 12 element of logic 0, and at the output of the element OR-NOT 16, the level of the logical G, which leads to the activation of the control key 6 through the amplifier 17. As a result, the current in the field winding decreases and its phase changes, which leads to a decrease in the braking moment created by the field winding.

 By changing the polarity of the excitation winding current (the same name as the polarity of the emf and rotor current) at the output of the comparators 10 and 11 there appear levels of logic O, at the output of elements HE 13, 14 and 15 there are levels of logical G, and at the output of element OR- NOT 16 is a logic level O, as a result of which the controlled key 6 of two-sided conductivity is switched off and compensation of the inductance of the excitation winding 3 occurs. When this occurs, the rotor current increases with a simultaneous decrease in its phase, and the motor torque created by the winding

arousal increases. When the polarity is changed, the cycle of operation of the device is repeated. In the ideal case, the inductance is fully compensated, the current coincides in phase with the EMF and the excitation winding for each rotor turns only on the motor moment. When the inductance is partially compensated, a phase shift appears between the EMF and the rotor current, however, the motor moments will be greater and the braking moment less. compared with the known methods of starting a synchronous motor.

As the sensor 2 for the EMF of the field winding, an additional winding consisting of one

0 or several turns laid over the main field winding. The connection of the EMF sensor 2 with the comparator 10 in brushless systems is direct, and in statistical systems of independent excitation, this connection is provided by the use of two contact rings and a brushing device.

Unit 5 capacitive compensation can be made in the form of capacitive rods,

0 laid in the slots of the rotor of a synchronous motor and electrically interconnected. In this case, the slip block is not needed, since the capacitance automatically changes as a function of frequency.

5 EMF of the rotor or slip due to the effect of current displacement in capacitive rods.

In addition, the block 5 capacitive compensation can be made of capacitive

0 elements (capacitors), which are connected in parallel to each other in a sliding function by controlled two-way conduction keys according to the signal of the sliding unit 8. In this case, the latter can be performed, for example, according to a well-known scheme and must be supplemented by executive outputs for switching on the controlled keys of double-sided conductivity.

0 The method of starting a synchronous motor may have modifications. For example, to reduce the rotor current with opposite polarity of the EMF and current, the control key 6 can switch the unit 5 capacitive

5 compensation through the additionally entered resistor of the required multiplicity.

If it is necessary to increase the average electromagnetic moment created by the excitation winding, in the required part of the asynchronous characteristic, the capacitive compensation of the inductance of the excitation circuit is carried out starting from a certain predetermined slip value. In this case, from the slip block 8, an additional signal is used to turn on the key b until the rotor reaches a predetermined slip value, after which the signal including the key b is removed.

Claims (3)

The application of the proposed method makes it possible to increase the reliability of the asynchronous start mode of a synchronous motor by increasing the average moment created by the field winding. Claim 1. Method for starting a synchronous motor with a start-up unit made in the form of serially connected starting resi five the capacitor and capacitor compensation unit, in which the stator is connected to the mains and close the field winding to the starting block, characterized in that, in order to increase the starting reliability by increasing the average starting torque, the polarity of the EMF and rotor current is determined and, if they differ, they are shunted capacitive compensation unit. 2. A method according to claim 1, characterized in that, by shunting the capacitive compensation unit, the multiplicity of the starting resistor is further increased. 3. A method according to claim 1, characterized in that it additionally controls the amount of slip and said shunting is carried out when the rotor reaches a predetermined amount of slip.