SU784043A1 - Ac contact-free switch - Google Patents

Description

The invention relates to automation and can be used for switching AC circuits in nominal and emergency modes, in particular for disconnecting short-circuit currents.

Known AC switches containing thyristors, diodes, capacitors and control unit G1).

The disadvantage of this device is its low reliability, due to the complexity of the control circuit, the lack of redundancy of switching capacitors and the application of high voltage to thyristors in 1S all operating modes.

Non-contact alternating current switches are also known, containing main thyristors, a capacitor with a charge circuit, bridge circuits, protection and control units [2].

This device has insufficiently high reliability and large dimensions. 25

In order to increase reliability and reduce the size of a non-contact ”alternating current switch containing main anti-parallel main thyristors with reactors 30, a capacitor with a charge value, connected through the corresponding resistors in the diagonal of the first and second bridge circuits, the shoulders of each which are formed by diodes and switching thyristors, protection and control units connected respectively to the cathode of one of the main thyristors and the cathodes of the diode and switching thyristor of one arm of the first bridge circuit and with a power supply bus, another bus of which is connected to the cathode of the other main thyristor and the cathodes of the diode and the switching thyristor of the other arms of the first bridge circuit, a transformer is introduced, and the anodes of the main thyristors are connected through the corresponding primary windings of the transformer to the anodes of the diodes and switching thyristors of the corresponding arms of the second bridge circuit, while the anodes and cathodes of the diodes, respectively, of the first and second bridge circuits through the corresponding secondary winding. transformer ki are connected to the terminals of the corresponding resistors.

The drawing shows a circuit diagram of the proposed switch.

eristors 1, 2, included sequence, 4, condensation, resistors 10,11, 12, switching protection tiblock 17, unit

R

The switch contains the main ones with reactors 3 torr 5, diodes 6-9, the charging circuit of the control transistors 13-16, 18, primary windings 19, 20 and secondary windings 21-24 of the transistor, and a power supply 25.

The principle of operation of the switch is as follows.

If a short stutter occurs (for example, at the moment when the thyristor 1 conducts), the switching capacitor 5 is connected to the thyristor 1 using thyristors 13 and 14 with a voltage polarity that locks the thyristor 1. Due to the magnetic connection of the winding 20 with the windings 21 and 23, the total current I flowing from the reactor 3 is divided into three currents: the current through the capacitor, the current through the resistor 11, the winding 21 and the diode 9 and the current through the diode 7, the winding 23 and the resistor 10. If we assume that the number of turns of the windings 19, 20 is equal, the windings 21, 22 and 23, 24 'is equal to W ^, then the relationship between the quantities the currents are determined based on the law of the total current (excluding the magnetization current), as follows:

® 4 q * i c - c

Since the I-L + 2L · locking the voltage applied to the thyristor 1 is equal to _'t and s _from -5 ,, where - EMF across the winding 20 of the transformer.

From the voltage balance equation for the circuit, the capacitor 5 - resistor 11-winding 21 implies that the EMF on it is equal to ll _c + RI c.

Then

·. b ' ¹ since U - U - - \,' · ^{s 0 s} о I where V _o is the initial voltage, then finally

For circuit breaker without additional current transformer about

Thus, with the introduction of the transformer, the initial voltage decreases, but the equivalent capacity increases

With EK8

to

IS $ 0 '40

As the analysis of the Transition Processes shows, there is an optimal ratio W ^ / W ^, which provides an increase in the thyristor closing time for a given value of the locking time.

The cross section of the magnetic circuit of the current transformer is selected from the condition of its saturation after changing the polarity of the voltage of the capacitor 5.

When the voltage across the capacitor 5 increases, resistors 10 and 11 are connected in parallel through it through diodes 7 and 9. At the same time, the thyristors 13 and 14 remain on, but due to shunting of the capacitor 5, the resistors in the circuit are abruptly damped in parallel and, therefore, overvoltage reduction. The resistance values of resistors 10, 11 are selected according to the maximum allowable current of thyristors and diodes. After the natural transition of the current through zero when the polarity of the mains voltage changes, the thyristors 13, 14 are locked, since the control signal is no longer supplied from the blocks 17, 18.

In the next half-period, with thyristors 13, 14 locked, happen! accelerated charge of the capacitor 5 through the resistors 10 and 11 and the diodes 6 and 8. Therefore, the repeated switch-on time does not exceed half the period of the network frequency.

The charging circuit 12 is only necessary for charging the capacitor 5 in the absence of voltage on the switch or to compensate for its discharge currents through the leakage resistance of thyristors and diodes.

Claims (2)

1. Author's certificate of the USSR 396829, cl. H 03 K 17/56, 08.13.71. 2. USSR author's certificate No. 481134, cl. H 03 K 17/56, 02/06/73.