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INVENTION
Patent of the Russian Federation RU2074472
DEVICE FOR CONSUMER PROTECTION FROM OVERLOADS
IN AC NICKS

Name of the applicant: Kresyak Vitaliy Nikolaevich
The name of the inventor: Vitaly Kresyak
The name of the patent holder: Kresyak Vitaliy Nikolaevich
Address for correspondence:
Date of commencement of the patent: 1995.07.20

Usage: in electrical engineering, in particular in AC electric networks, where overvoltages can occur during normal operation of the power supply system or as a result of an accident.

SUMMARY OF THE INVENTION: The device comprises a threshold element and an actuating element connected thereto, which is simultaneously a protective device. The executive body consists of a diode bridge with a power thyristor, whose control circuit includes a field-effect transistor. The drain of the field effect transistor is connected to the thyristor anode, the source to the control electrode, and the gate to the voltage divider across the resistors and the rectifier of the mains voltage, which consists of a diode with a storage capacitor and a threshold element connected in parallel between the gate of the transistor and the thyristor anode. The device achieves increased reliability and overload capacity in terms of voltage, minimum power loss on the consumer, protection against overvoltage at the initial start-up.

DESCRIPTION OF THE INVENTION

The invention relates to electrical engineering, in particular to AC electrical networks, in which overvoltages can occur during normal operation of the power supply system or as a result of an accident, and is used to protect the consumer from overvoltages.

Devices for protecting the consumer against overvoltages are known , containing a threshold element and an actuating element connected to it, made on two counter-parallelly connected thyristors, which shunt the consumer in case of overvoltage, and a short-circuit in the mains, resulting in short-circuit protection devices Closure ( author of the St. N 630695 ).

To restore the device, it is necessary to replace the fuses or to switch on the circuit breaker. As a result, there is a significant loss of information.

The closest in terms of technical essence and achieved effect to the proposed device is a device for protecting an electric consumer from overvoltages , containing a threshold element and an actuating element connected to it, made up of two counter-connected thyristors, having a transformer, matching thyristors and protective counter-parallelly connected thyristors , Included in series with the consumer of electricity.

As the voltage in the mains reaches a maximum value, a signal is output from the output of the threshold element to the control electrodes of the thyristors, which unlock and shunt the secondary winding of the transformer. In this case, the voltage coming to the control electrodes of the matching thyristors is reduced, which is locked, and, consequently, the protective thyristors are blocked, and the voltage in the consumer's power supply network drops to zero. After reducing the supply voltage, the user's working capacity is automatically restored.

Disadvantages of such a device are the presence of a transformer that operates when the protection is activated in the maximum load mode, which reduces reliability and limits the ability of the device to operate if the mains voltage is repeatedly exceeded. The supply of the control thyristor control circuits with a reduced mains voltage from the transformer reduces the rate of current rise on the control electrodes, which leads to some delay in the switching of the thyristors in each half-cycle of the mains voltage, and this leads to loss of power on the consumer. At initial connection to a network with an increased voltage, at least one half-period of the increased voltage of the network is delivered to the consumer, since the threshold element is triggered when a specified voltage value is reached, while the protective thyristors are already opened by the control current, and this can lead to an exit from The building of the consumer with significant network overvoltages.

The technical goal of the invention is to increase reliability, overload capacity for voltage, reduce power losses on the consumer and protect it when initially connected to a network with increased voltage.

The problem is solved by the fact that in a device for protecting a consumer from overvoltages in AC networks containing a threshold element and an actuating element connected to it, the new is that the actuator serves simultaneously as a protective device and consists of a diode bridge with a power thyristor, into a control circuit Which includes a field effect transistor whose drain is connected to the anode of the thyristor and the source to the control electrode, and the gate through the voltage divider on the resistors is connected to the rectifier of the mains voltage on the diode, the threshold element and the storage capacitor being connected in parallel between the gate of the transistor and the cathode of the thyristor.

The increased reliability and overload capacity is achieved due to the lack of a transformer operating in the maximum load mode at an increased mains voltage, the minimum power loss on the consumer due to the high rate of increase in the power thyristor control current by applying the full rectified network voltage between its cathode and anode. Protection against overvoltage at the initial connection to the network with increased voltage is realized due to the excess of the time of charge of the storage capacitor over the opening time of the thyristor at each half-cycle of the mains voltage.

The figure shows the electrical circuit of the proposed device.

The device for protecting the consumer from overvoltages in AC networks comprises an electric power consumer 1, an executive body that is simultaneously a protective device consisting of a diode bridge with diodes 2, 3, 4, 5 and a power thyristor 6, whose control circuit includes a high-power high-voltage field-effect transistor 7, the drain of which is connected to the thyristor anode, and the source to the control electrode. The gate of this transistor through the voltage divider on the resistors 8 and 9 is connected to the rectifier of the mains voltage on the diode 10. The storage capacitor 11 and the threshold element 12 are connected in parallel between the gate of the transistor 7 and the cathode of the thyristor 6.

The device operates in the following way: at a mains voltage less than the limiting value, the power thyristor 6 is opened during each half-period due to the control current flowing through the permanently open field-effect transistor 7 and the control electrode, when a positive diode bridge rectified by 2, 3, 4, Voltage of the network applied between the cathode and the anode of the thyristor, and the consumer 1 is connected to the supply network, since the positive half-cycle passes through the diode 2, the thyristor 6 and the diode 5, and the negative through the diode 4, the thyristor 6 and the diode 3. At the same time, the rate of current rise The control is maximal, since before the opening of the thyristor 6 between the anode and the cathode, at the beginning of each half-period the total network voltage is applied, and the cathode-control electrode of the thyristor 6 and the drain-source transition of the field-effect transistor 7 are small in the open state, which leads to a minimum of the thyristor switching time in The beginning of each half-period of the network, and, consequently, to the minimum power losses at the consumer close to the theoretically possible. When the thyristor 6 is opened, the control current drops practically to zero, since the voltage between the cathode and the anode is very slight. The field-effect transistor 7 is continuously opened by a positive voltage on the storage capacitor 11 charged through the voltage divider on the resistors 8 and 9 by a portion of the mains voltage rectified by the diode 10. [ As the network voltage rises above the threshold, the threshold element 12 discharges the storage capacitor 11 to zero, which causes the transistor 7 and the power thyristor 6 to close, and the consumer 1 is disconnected from the mains, the voltage limit can repeatedly exceed the rated voltage of the network and is limited by the breakdown voltage of the power Thyristor 6, field effect transistor 7 and diodes 2, 3, 4, 5.

With the initial connection to the high voltage network, the power thyristor 6 is closed, since the charging time of the storage capacitor 11, and consequently the opening of the field effect transistor 7, is many times greater than the response time of the threshold element 12, while the threshold element 12 discharges the capacitor 11, and the consumer 1 Protected from overvoltage.

When using this device, higher reliability and overvoltage capacity are achieved, minimum power losses on the consumer (up to 1% in prototypes), overvoltage protection at the initial inclusion.

CLAIM

A device for protecting a consumer against overvoltages in alternating current networks, comprising a threshold element and an actuating element connected thereto, characterized in that the actuating element, which is simultaneously a protective device, consists of a diode bridge with a power thyristor whose control circuit includes a field effect transistor, a drain Which is connected to the anode of the thyristor, the source to the control electrode, and the gate of this transistor through the voltage divider on the resistors is connected to the rectifier of the mains voltage on the diode with a storage capacitor and a threshold element connected in parallel between the gate of the transistor and the cathode of the thyristor.

print version
Date of publication 25.11.2006гг

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