SU1450051A1 - Single- to three-phase voltage converter - Google Patents

Abstract

The invention relates to electrical engineering and can be used 9 auxiliary electrofusion as a power source. The purpose of the invention is to obtain a nominal output voltage with a reduced input voltage, a decrease in energy consumption, weight and dimensions, and an increase in the reliability of starting an electric motor, when used as a load. The additionally introduced capacitor 13 is connected via switches 14, 10 in parallel with the resistive element 12 and the secondary winding of the differential transformer 8 and to the phases A and C of the load. The first primary winding of the transformer 8 and its secondary winding are connected to the input terminal 1. Resistive element 12 is non-linear. When the input voltage is lowered by switching the switches 10, 14, the autotransformer 4 and the above elements are controlled by adjusting the output voltage until the latter reaches its nominal value while reducing the capacitor 13 capacitance and eliminating the starting current in phase A of the load through the first primary transformer winding 8. 2 zp f-ly, 2 ill. (L 4a followed

Description

The invention relates to electrical equipment and can be used, for example, in the repair of a railway or as an auxiliary equipment on electric trains with AC power.

The purpose of the invention is to obtain a nominal output voltage at a lower input voltage, as well as a reduction in energy consumption, mass-size parameters and an increase in the reliability of starting an electric motor when used as a load.

FIG. 1 shows a circuit diagram of a converter; in fig. 2 is a vector diagram of voltages and currents at a reduced input voltage.

The converter (Fig. 1) contains input terminals 1 and 2, of which the second input terminal .2 is common with the second output terminal 3, Autotransformer 4, connected by its lowering terminal to terminal 3, has a intermediate terminal 5 and pin 6. Between pin 5 of the autotransformer and the first “1 input pin 1, a chain of a series-connected capacitor 7 and the first primary winding of the differential transformer 8 is turned on. The first primary winding is connected to the first input pin 1, the first output winding The output 9 via the first (modal) switch 10 can be connected to one of the terminals of the first primary winding of the differential transformer 8, the scorching terminal 6 of the autotransformer and the third output terminal 11 are connected via the second primary winding of the transformer 8. A resistor 12 is connected to the secondary winding of the transformer 8, and the additional capacitor 13 is also connected via a second (modal) switch 14, the common point of connection between the resistor 12 and the capacitor 13 is connected to the input port 1. The switch 14 can connect a free one terminal of the capacitor 13 or to the secondary winding of the differential transformer 8, or in the disconnected position, or to the output terminal 11 To the output terminals 3, 9 and 11, respectively, the phases B, A, C of the load 15 are connected.

The converter works as follows.

When combined with input switch 1 with output switch 10 with output output 9, and with switch 14 in an intermediate state, i.e. without connecting a capacitor 13, as in the known device, a single-phase voltage is converted into a three-phase voltage. In this case. Phases A and B of load 15 most of the energy is obtained directly from pins 1 and 2, connected

to the supply single-phase line. The input of the autotransformer 4 (between pins 5 and 3) in series with the capacitor 7 is also connected to. pins 1 and 2, and the autotransformer transmits the input power to the third phase of the load 15.

The load current of phase C, passing through both primary windings of the transformer 8, creates mutually compensating

therefore, only the revolutions caused by the magnetizing current of the autotransformer 4, which in the normal mode is 5-10% of the rated current, should be taken into account. Therefore, in normal mode, the voltage on the secondary winding of the differential transformer is close to zero.

five

The converter provides a three-phase symmetrical current in the load (electric motor) only with one selected value of the load. When the voltage on the autotransformer 4 rises above the nominal, then

 Due to the saturation of the magnetic circuit, the magnetizing current increases nonlinearly. At the same time, in the differential transformer 8, uncompensated amp revolutions increase,

The voltage on the secondary winding and the current through the resistor 12 are disconnected. Due to the flow of the current through the resistor 12, the current in the primary circuit is suppressed and the voltage on the autotransformer 4 decreases. In case of accidental disconnection of the load 15 from the converter, the differential transformer B s resistor 12 cannot eliminate the phenomenon of voltage resonance, but they reduce significant overvoltages and dangerous overheating, as long as the relay voltage (not shown) that a transformer connected to the secondary winding and 8, disables

0

14

circuit breaker on the input of the converter.

When the switches 10 and 14 are in the positions shown in FIG. 1, the converter at rated input voltage provides nominal output voltages. For these conditions in FIG. 2 shows a vector diagram under the assumption that the load angle 1 / ps of which the linear three-phase currents of the motor used as the load are symmetrical is 30, and the current vector is out of phase from the voltage vector Ugg, U., between the corresponding output of the motor and the conditional neutral point O in the center of the triangle of vectors

voltage, Ugc, Uc / t-

FIG. The 1 and 2 arrows indicate the direction of the current from the expected higher potential to the lower potential of the branch, the direction of the voltage arrows (not shown) is chosen along the arrow of the corresponding current, and FIG. 2, for each voltage vector, the arrowhead indicates which potential is taken to be higher (the index of the highest potential at voltage designation is written nepBbw). Current 1, passing through capacitor 7, is 90 ° ahead of the voltage across this capacitor. The current i (, from the output 6 of the autotransformer 4 to the load phase C (electric motor) 15 is connected with the current 1 by the following ampere-turn equation:

,, - Wjjt - Aw.o; .

where W; ,, Wj - turns between pins 5 and 3, respectively, pins 3 and 6 of the autotransformer; AWj are the amperages of magnetization of the autotransformer 4, which under conditions of load are very small and therefore approximately equal to zero. Since the diagram of FIG. 1 in the autotransformer 4, currents 1 and 1 are opposite, then in the vector diagram of FIG. 2 they coincide in phase. Circuit circuit output J - the first primary winding of the transformer 8 - capacitor 7 - autotransformer 4 - output 2. - power supply - output 1,

5 1

we obtain the following equations for voltages and currents (Fig. 1).

Ut. id5 g - 71 0; and, and, “;

i, (i.A + - i Wgfe / w.); i-, w. - i, Wo. AW,

-I "1

"AT

Q 5

0

5 about 5

0

0

five

five

where W., ffc is the number of turns of the first and respectively the second primary windings of the transformer 8;

AW jj is the total number of primary differential ampere turns in transformer 8 (excluding reactive current Ip); Z ,, - reduced to turns

- about

W..resistance of all

l

transformer 8 circuits (resistor 12, capacitor 13 and magnetization circuits of this transformer),

Suppose that for the differential transformer 8 the ideal condition AWgj 0 is fulfilled. Under such conditions, the voltage U, g depends only on the current 1d. If the capacitance of the capacitor 13 is chosen so that the resistance of the capacitor is approximately three times less than the resistance of the resistor 12, and the magnetizing current of the transformer 8 is relatively small, then we obtain a vector diagram in Fig. 2, from which it can be seen that each of the equal output voltage modules and JC is larger than the input voltage module Uj. Thus, the converter ensures the normal operation of the electric motor with a low voltage at the input of the converter.

one

In order to ensure this function occurs with a relatively small voltage module U, the bottom of the first primary winding of transformer B, two methods are possible: resistor 12 is non-linear, for example, by connecting a varistor parallel to it, whose resistance decreases with increasing voltage; transformer 8 has a total number of primary differential ampere turns AWn. choose slightly different from zero, observing the following inequality:

liiWj.hli.w

81

As can be seen from FIG. 2, the vector sum of the currents I and 1d passing through the first primary winding of the transformer 8 in the low voltage mode at the converter input is less than one current 1 flowing through the same winding in the normal voltage mode at the converter input ( switch 10 in Fig. 1 in a different position).

If, in the undervoltage mode at the converter input, an accidental motor shutdown occurs at the output of the converter, the differential transformer introduces into the primary circuit not only the conpoTHBjfeHHe resistor 12 brought to the primary turns and the parallel magnetization resistance, but also the parallel resistance of the capacitor 13 The circuit of the said parallel resistances may cause ferroresonance of the current, as a result of which the voltage on the local circuit increases abruptly, reducing the current and renapr ferroresonance voltage at voltages generally loop autotransformer consisting of a 4, a condenser 7 and a differential transformer 8 with its said load. Thus, in this mode, significant overvoltage is limited and: dangerous overheating in case of accidental occurrence of ferroresonance. With a reduced input voltage of a single-phase line, it is advisable to start an unloaded three-phase electric motor through this converter by performing the following preparation; switch 10 is set to the normal input voltage mode (to the other extreme position compared to Fig. 1); put switch 14 in the position in which capacitor 13 is connected between input terminal 1 and output terminal 11.

The first recommendation is introduced so that a large starting current in phase A does not pass through the first primary winding of the transformer 8, since this current may trigger the above-mentioned overvoltage relay connected to the secondary winding of the transformer 8 (not shown)

with the subsequent shutdown of the automatic switch on the converter input. The second recommendation is introduced to facilitate motor starting by using a capacitor 13, which can be used for the same purpose and under normal input voltage. With an increased input voltage, three-phase output voltages can be reduced by using switch 14 to turn off the free output of a capacitor 13 and put the switch 10 or as shown in FIG. 1, or in the middle position.

Claims (3)

1. Single-phase to three-phase voltage converter., Containing two input and three output pins, of which the second input and output pins are combined into a common autotransformer, the output pins of which are connected to the common output, the chain from the intermediate output and the first input output is included serially connected capacitor and the first primary winding of the differential transformer, and the step-up terminal of the autotransformer is connected to the second primary winding of the differential transformer A recurrent output terminal, a resistive element included in parallel with the secondary winding of the differential transformer, wherein in order to obtain a nominal output voltage at a lower input voltage, the free input of the first primary winding of the differential transformer of the specified chain is connected to the first input terminal and two are added switch and additional capacitor, and the first primary winding of the differential transformer is made with a tap, connecting with one of the terminals of the first switch, the first extreme terminal of which is connected to the common connection point of the capacitor and the primary winding of the differential transformer of the specified chain, the second extreme terminal is connected to the first input, and the middle constant used, the output of the first switch is connected to the first the output pin, one pin of the second lane is connected to one of the pins of the resistive element, its other pin to one of the plates of the additional capacitor, the other of the KOTOporq plate. connected to another output of the resistive element. 2. The converter according to claim 1, characterized in that, in order to reduce energy consumption and mass-size parameters, the resistive element is made non-linear. 0051 Q 3. Converter on PP. 1 and 2, characterized in that, in order to increase the reliability of starting the electric motor when using it as a load, one output of the secondary winding of the differential transformer is connected to the first input terminal, and the second switch is equipped with an additional output connected to the third output terminal.