SU1374327A1 - Arrangement for protecting electromagnetic voltage transformer from ferro-resonance damage in network with effectively earthed neutral - Google Patents

Abstract

The invention relates to power engineering and can be used to protect electromagnetic transformers from damage caused by ferroresonance in electric networks with an effectively grounded neutral. The purpose of the invention is to increase the sensitivity of the device to the detection of the ferro-resonance process. When it occurs (L

Description

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In the ferroresonance process, the high voltage winding 5 of the voltage transformer 2 and the primary winding 7 of the transformer 3 carry the current of the ferroresonance process, the voltage at the output of the rectifier 11 increases, and when it reaches the turn-on voltage of the threshold element 12, the power thyristor 10 turns on,

connected in parallel to the secondary winding 7 of the voltage transformer 2 through the diodes of the surge bridge 8, the ballast resistor 9, as a result of which the equivalent dynamic inductance of the voltage transformer 2 changes, which disrupts the ferroresonance process. 1 il.

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The invention relates to power engineering and can be used to protect electromagnetic transformers from damage caused by ferroresonance in electric networks with an effectively earthed neutral.

The purpose of the invention is to increase the sensitivity of the device to the detection of the ferroresonance process.

The drawing shows the principle single linear diagram of the device

The device 1, installed in the immediate vicinity of the voltage transformer 2, contains a transformer 3, the primary winding 4 of which is connected in series with the high-voltage winding 5 of the voltage transformer between its low potential potential and the ground 6. The phase transformer of the voltage transformer is connected to one of the phases of the bus system in the electrical network.

The terminals of one of the secondary windings 7 of the voltage transformer are connected to the outputs of a power rectifying bridge 8 through a ballast resistor 9, the positive pole of the bridge is connected to the anode of the power thyristor 10, and the negative one to the cathode of the latter, the control electrode of the thyristor is connected to the positive pole of the rectifier Mettel 11 through the threshold element 12. At the same time, its anode is connected to the control electrode of the thyristor 10, and the cathode is connected to the positive pole of the center — Metel 11, whose negative pole is connected to the cathode of the power thyristor 10 and the negative pole of the power rectifying bridge 8. At the output of rectifier 11, the smoothing

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A capacitor 13 is connected, and the input of this mittel is connected to the terminals of the secondary winding 14 of the input transformer 3 of the device.

To improve the rectangularity of the transfer characteristic of the threshold element, a current amplifier at transistor 15 (shown by a dotted line) can be introduced into the circuit, the load of which is the control transition of the power thyristor 10. The use of a current amplifier is advisable if necessary for the temperature stability of the switching voltage of the threshold element, as well as for large variations in the arcing current of the power thyristor 10. The resistor 16 serves to limit the current of the control electrode of the thyristor to an acceptable value.

A trimming resistor 17 (shown in phantom) serves to adjust the device triggering current by changing the demagnetizing flow of the secondary winding 14 of the transformer 3, which leads to a change in the DC voltage at the output of the rectifier 11, which is applied to the threshold element 12, the device drop current can be also adjust the selection of the threshold element with the necessary turn-on voltage.

Parallel to the smoothing capacitor 13, a discharge resistor 18 is connected, designed to discharge this capacitor when the ferro-resonance is disrupted and the device is restored to its initial state.

The device works as follows

In normal operation of a voltage transformer, through its high-voltage winding 5 and the primary winding 4 of the transformer 3 connected in series with it, a magnetizing current of the voltage transformer flows, caused by the appearance of alternating voltage on the terminals of the secondary winding 14, which is rectified by rectifier 11 is smoothed by the capacitor 13 and is applied to the threshold element 12. Since the voltage on the с smoothing capacitor is less than the turn-on voltage of the threshold element, the current through it is negligible, The voltage on the control electrode of the power thyristor 10 is practically absent, it is in the disconnected state, having no effect on the voltage transformer mode.

When a ferroresonance process occurs, the high-voltage winding 5 of the transformer 2 voltage and the primary winding 4 of the transformer 3 generate a magnetizing current of the voltage transformer and the current of the ferroresonant process, which pulls the level of the direct voltage at the output of the rectifier 11. When the current in the high-voltage winding reaches, equal to the current of its thermal stability, the voltage at the output of the thruster becomes equal to the turn-on voltage of the threshold element 12, the current through it rises sharply and turns on The power thyristor 10, connecting parallel to the secondary winding 7 through the diodes of the rectifying bridge 8, the ballast resistor 9. At the same time, the equivalent inductance of the voltage transformer changes, which causes the ferroresonance process, the voltage at the output of the rectifier 11 becomes less than the threshold for switching off the threshold element 12 , the current through it decreases sharply, the voltage on the control electrode of the power thyristor 10 becomes close to zero and the thyristor switches off at the first transition through zero current. Automatically restoring normal circuit transformer voltage mode 2.

The capacity of the smoothing capacitor 13 is chosen such that the constant of its charge time is several seconds and the inclusion of the threshold element 12 and the power thyristor 10 with a sharp increase in the current in the primary winding 4 of the transformer 3 and the voltage transformer 2 connected to it in series It occurred with a delay of several seconds with respect to the beginning of the increase in current. This is necessary to prevent the device from falsifying when the transformer is switched on by injecting a magnetising current in its high-voltage winding.

Claims (1)

Invention Formula A device for protecting an electromagnetic voltage transformer from damage during ferroresonance in a network with an effectively grounded neutral, equipped with code terminals for connection to one of the secondary windings of a voltage transformer and input terminals containing an emergency mode sensor, a power thyristor with a control unit, connected between positive and negative poles of a rectifying single-phase bridge, one AC output of which serves as an input terminal of the device, and the second output is connected to a ballast resistor, the second end of which serves as the second input terminal of the device, characterized in that, in order to increase the sensitivity of the device to the detection of the ferroresonance process, the emergency mode sensor is implemented in the form of a transformer, the primary windings of which serve as input terminals of the device connected in series with the primary winding between the voltage transformer of the same phase and the ground, and the secondary winding is connected to the input of the control unit, made in the form of the second rectifier The output bridge is shunted in parallel by a smoothing capacitor and a resistor, the negative pole of the second rectifying bridge is connected to the negative pole of the first temporal bridge, the positive pole is connected via a threshold element to the control electrode of the thyristor.