SU699648A1 - Device for limiting magnetizing current of electric machine - Google Patents

Description

to decrease the setting of the ARV voltage. Upon reaching the limit of the limitation zone for the operation of the relay, the capacitor is connected in parallel with the relay. A disadvantage of the known device is the lack of a quick return of the indicated delay element to the initial state (absence of a fast discharge circuit of a capacitor) when the operating point moves away from the boundary of the limiting region. As a result, with the periodic nature of the working point departure (for example, asynchronous operation in the power system), the time adjustment from the frequency and voltage fluctuations will not occur, i.e. The device has low noise immunity and selectivity.

A disadvantage of the known device is also the dependence of the characteristic of the magnetisation of the throttles on the external magnetic fields, temperature, and natural aging, which leads to a decrease in the density.

The aim of the invention is to increase accuracy, noise immunity and selectivity.

For this purpose, the device for limiting the current magnetization of electric machines is equipped with a series connected by a pulse comparator and a pulse expander, the input of the pulse comparator is connected to the output of the measuring element, and the output of the pulse extender is connected to the input of the relay element. connected to the measured voltage through a resistor whose resistance is chosen not less than the order of greater resistance of the capacitor in a given frequency range.

The measured parameter is the voltage across the capacitor, which is directly proportional to the magnitude of the voltage being measured and inversely proportional to the frequency. The magnitude of this voltage, equal to the opening voltage of the unijunction transistor, corresponds to the characteristic of the limitation of the magnetization cable in the coordinates of the frequency-voltage. Since the opening of the single junction transistor of the limiting region occurs once in a period, the return coefficient of the device increases, which also contributes to an increase in the accuracy of operation. Increased selectivity is achieved by using a comparator in the delay element, at the input of which an RC circuit with an additional diode is installed, having a constant charge time of the capacitor

the required amount of delay, and providing a quick discharge of the capacitor when the delay element returns to its original state.

FIG. 1 shows the proposed device, a block diagram; in fig. 2 - circuit diagram in principle.

A device for limiting the current. Magnetization of electric machines contains a measuring element 1 connected in series with one another, a pulse comparator 2, an expander 3 ,. pulses, delay element 4 and relay element 5, the output of which is connected to the input of the voltage regulator setpoint lowering unit.

The measuring element 1 (Fig. 1) is connected to the secondary winding of the isolation transformer 6 (Fig. 2). The measured voltage is fed to the input of the CS circuit formed by the resistor 7 and the capacitor 8. From the output of the measuring element, the voltage is connected in parallel to each other the resistor 9 and the capacitor 10 are supplied to the emitter of the unijunction transistor 11, the first base of which is connected to the minus of the power source through the resistor 12, and the second base is connected to the positive source through the series-connected resistors 13 and 14 ika: Power. Between the common connection point of resistors 13 and 14 and the minus Zener diode 15 is turned on, these elements form a parametric stabilization. The torus that serves to eliminate the effect of changes in the supply voltage and the ambient temperature on the characteristics of a pulse comparator 2.

The pulse expander 3 is provided on two single vibrators 16 and 17. The single vibrator 16 is formed by transistors 18 and 19, and the single vibrator 17 by transistors 20 and 21. To obtain the desired output characteristic, the base of transistor 18 is connected via diode 22 to the collector of transistor 20 the base of the transistor 21 through the capacitor 23. The delay element 4 is formed by a comparator 24, which includes an operational amplifier 25, the non-inverting input of which through a resistor 26 is connected to the minus of the supply source a, and through a resistor 27 a master circuit time consisting of a resistor 28, a diode 29 and a capacitor 30 is connected to the output. The input time of the master circuit is connected to the output of the 3 pulse extender. The output of the operational amplifier 25 is connected to the input of the relay element 5. The relay element 5 is formed by a transistor 31, the base circuit of which is connected via a resistor 32 to the output of the delay element 4, and a relay 33 connected by the diode 34 is connected to the collector circuit of transistor 31. The output of the relay element is normally open contacts 35, which are connected to the set-down block of the field control setpoint.

The device works as follows.

To the input of the limiting device Through a measuring transformer. The voltage of an electrical machine, such as a power transformer of a power plant, is applied. When the limit of the limit of the output of the pulse comparator 3 is reached, a pulse is generated through the capacitor 22 to the base of the transistor 21. The dwell time of the single vibrator 17 is chosen to be approximately half the period of the measured voltage so that the single vibrator is in the initial state. The duration of the shutdown of the single vibrator 16 is chosen to be approximately one and a half periods of the measured voltage in order to prevent the delay element 4 from being reset from period to period. The one-shot 17 is triggered by closing the transistor 21 with a falling edge at the output of comparator 2.

The transistor 20 opens and the transistor 18 closes through the diode 22, and a voltage appears at the output of the expander 3 pulses. At the moment of closing of the transistor 20, the operating cycle of the one-shot 16 begins, which ends with the opening of the transistor 18 and the disappearance of the voltage at the output of the expander 3 pulses, if the operating point of the electric machine in the frequency-voltage coordinates is, the output will go off .

The delay time of the element 4 is determined by the time constant of the charge circuit of the capacitor 30 from the moment the transistor 18 closes. Opening the transistor 18 causes the capacitor 30 to quickly discharge through the diode 29 and thereby return the delay element 4 to its original state.

The transistor 31 opens when a delay element 4 is triggered, the relay 33 acts to lower the set point of the excitation controller of the electric machine.

The use of a capacitor in the device as a measuring element in combination with a single junction transistor allows an increase in accuracy and noise immunity, and the use of an impedance extender

0 times with a delay element - device selectivity.

As a result, it becomes possible to more severely limit the magnetizing current and additional

5 reducing losses in electric machines, in particular, power transformers of power plants.

Claims (3)

1. US patent 3521148, cl. 322-28, 1970. 2. Patent ClJA 3617856, cl. 322-24, 1971. 3.Research Report Theoretical and experimental research and development of equipment for regulating, managing and improving sustainability, topic director VG Lyubarsky, state registration number No. 70000448, 1971, p. 4-5, fig. 1-1. .28 I 7 i