RU2849439C1 - Method for changing the transformation coefficient of a power transformer - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: invention relates to the field of electrical power engineering, in particular to transformer transformation ratio regulators (TRR). The technical result is achieved by a method for changing the transformation ratio of a power transformer, in which all transformer taps are connected to the power supply network via power electronic switches and vacuum contactors, one of which is kept in the on state by a control unit. To change the transformation ratio, current-limiting resistors are connected in series to the electronic switches. Using the control unit , the electronic switch of the operating tap, shunted together with the resistance connected by the vacuum contactor, is opened, the vacuum contactor of the operating tap is disconnected, open the electronic switch of the selected tap, close the electronic switch of the operating tap, switch on the vacuum contactor of the selected tap, and close the electronic switch of the selected tap.

EFFECT: simplification and increased reliability in the method for changing the transformation ratio of a power transformer.

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Description

The invention relates to electrical engineering and power engineering, specifically to transformer ratio controllers (TRCs). The use of TRCs in electrical networks allows for maintaining the required voltage level at the connection point by varying the power transformer's ratio and the number of turns in the high-voltage (HV) winding.

A known method for controlling transformer voltage under load by switching taps on a power transformer winding using bidirectional triac electronic switches [RU patent for utility model No. 158346, published December 27, 2015] is used to set the power transformer transformation ratio and switch taps on the high-voltage winding connected to the power grid using triac electronic switches, enabling stepwise changes in the transformation ratio and, consequently, changes in the voltage on the low-voltage (LV) secondary winding. To synchronize control of the triac electronic switches, the input voltage is monitored.

The disadvantages of this method are the need to use synchronization of the control of the triac electronic keys based on information about the input voltage, which leads to a more complex control circuit for the keys.

A method is known for controlling the voltage of a transformer under load by switching the branches of the windings of a power transformer using bidirectional thyristor switches [RU patent No. 2274945, published 20.04.2006], according to which the transformation ratio is set by switching the branches of a sectioned high-voltage winding using bidirectional thyristor switches using measurements of the supply network voltage and the currents of the thyristor switches, while the switching of the thyristor switches is carried out by a control unit taking into account that after the current passes through zero, the input voltage level is measured and valve-by-valve control of the thyristors is carried out depending on the time remaining until the change in voltage polarity.

The disadvantages of this method are: the need to use current sensors in each branch of bidirectional thyristor switches, as well as the use of valve-by-valve control of bidirectional thyristor switches (as opposed to key-by-key control), which together reduces the reliability of operation and complicates the device implementing the method.

A method is known for controlling the voltage of a transformer under load, including monitoring the voltage of the supply network (RU Patent No. 2711589, published on 17.01.2020 Bulletin No. 2), in which, using a control unit, control pulses are supplied to bidirectional thyristor switches, each of which contains two anti-parallel connected thyristors connected in the branch circuits of the transformer windings using current monitoring, the current in the supply network is monitored and the time intervals are recorded at which the voltage and current of the supply network have the same and different signs, the phase shift between the current and voltage of the supply network is measured and, depending on the requirements for controlling the voltage at the transformer output and the phase shift between the current and voltage of the supply network, the corresponding bidirectional thyristor switches are controlled at the corresponding fixed time intervals,

The disadvantages of the method are that they monitor the current in the power supply network and record the time intervals at which the voltage and current of the power supply network have the same and different signs, measure the phase shift between the current and voltage of the power supply network and, depending on the requirements for controlling the voltage at the transformer output and the phase shift between the current and voltage of the power supply network, control the corresponding bidirectional thyristor keys at the corresponding fixed time intervals, which in combination reduces the reliability of operation and complicates the device implementing the method.

A known method for changing the transformation ratio of a power transformer (RU Patent No. 2752000, published July 21, 2021, Bulletin No. 21) is adopted as a prototype. In this method, all transformer taps are connected to the power grid via power electronic switches, one of which is maintained open by a control unit. To change the transformation ratio, a control circuit for the power electronic switches is first created in the control unit using two solid-state relays, one with normally closed contacts, and the other with normally open contacts for the taps being connected and disconnected. Next, power is simultaneously applied to the solid-state relays, the contact of one of which opens the power electronic switch and connects the tap of the transformer winding to the power grid, and the contact of the other closes the power electronic switch of the tap being disconnected and disconnects the tap being disconnected from the power grid.

The disadvantages of this method are the need to use synchronization of electronic key control using solid-state relays, which leads to a more complex key control circuit and does not eliminate the possibility of a short-circuit between two taps.

The technical objective of the proposed invention is to simplify and increase the reliability of the method for changing the transformation ratio of a power transformer.

The technical result is that in the proposed method, switching of taps is performed using electronic keys, with which current-limiting resistors are connected in series, and the constantly operating tap is connected to the power supply network through a closed contact of a vacuum contactor.

The technical result in the method for changing the transformation ratio of a power transformer, in which all taps of the transformer are connected to the power supply network through power electronic keys, the electronic keys are opened on one tap and closed on the other tap, is achieved by the fact that current-limiting resistances are included in series with the electronic keys, the electronic key of the operating tap is opened with the help of a control unit, shunted together with the resistance by the closed contact of the switched-on vacuum contactor, the vacuum contactor is switched off, thereby opening the contact of the vacuum contactor, the electronic key of the selected tap is opened, the electronic key of the operating tap is closed, the vacuum contactor of the selected tap is switched on, thereby closing the contact of the switch, and the electronic key of the selected tap is closed.

Explanations: an open contact of a contactor means a break between the contacts, i.e. it means the absence of an electrical connection between the contacts, and an open electronic switch means minimal resistance between the input and output of the switch, i.e. an open path for electric current.

The essence of the proposed method for changing the transformation ratio of a power transformer is explained in the drawing Fig. 1, which shows a diagram of a power transformer with taps and a device for controlling the switching of transformer taps under load.

In the diagram in Fig. 1, the voltage on the secondary winding of the LV is changed by changing the number of turns of the primary winding of the HV due to additional turns, which are connected to the power supply network by electronic keys (VS1 - VSm). Electronic keys with optical isolation are opened/closed by control signals from the control unit UB. Contacts (KV1 - KVm) of the vacuum contactors are closed/opened by control actions on the vacuum contactors from the control unit UB. Current-limiting resistors (R1 - Rm) are connected in series with the electronic keys. The open/closed state of the electronic keys is monitored by devices (KA1 - KAm) connected to current transformers (TA1 - TAm). The diagram in Fig. 1 shows tap 1 of the primary winding of the HV in operation, connected by the closed contact (KV1) of the contactor to the power supply network (A/B/C - X/Y/Z). The contacts of the remaining contactors (KV1 - KVm) are open.

The method is implemented as follows:

For example, initially, tap 1 of the HV primary winding is in operation, connected to the power supply via the closed contact KV1 of the contactor. The tap to which switching is required is selected (e.g., tap 2), with switches VS1 and VS2 closed. Switches VSn and VSm are not involved in the switching.

Before switching, immediately after selecting tap 2 manually or automatically by program using the UB control unit, open the electronic switch VS1 of the operating tap 1, shunted together with the resistor R1 by the closed contact KV1 of the vacuum contactor, open the contact KV1 of the vacuum contactor, open the electronic switch VS2 of the selected tap 2, close the electronic switch VS1 of the operating tap 1, close the contact KV2 of the vacuum contactor of the selected tap 2, and close the electronic switch VS2 of the selected tap. Switching is complete. After this, tap 2 remains connected to the power supply network via the closed contact KV2. The progress of the switching is monitored using the readings of the KA1 and KA2 devices. Switching from any tap to any other can be performed in a similar manner.

Thus, the method of changing the transformation ratio of a power transformer allows for reliable switching of the power supply network from one tap to another without current surges and without overvoltages due to current-limiting resistances, without unwanted transient processes of the electrical mode during switching.

Claims (1)

A method for changing the transformation ratio of a power transformer, in which all taps of the transformer are connected to the supply network through power electronic keys, the electronic keys are opened on one tap and closed on another tap, characterized in that current-limiting resistances are installed in series with the electronic keys, the electronic key of the operating tap is opened with the help of a control unit, shunted together with the resistance by the closed contact of the switched-on vacuum contactor, the vacuum contactor of the operating tap is switched off, thereby opening the contact of the vacuum contactor, the electronic key of the selected tap is opened, the electronic key of the operating tap is closed, the vacuum contactor of the selected tap is switched on, thereby closing the contact of the switch, and the electronic key of the selected tap is closed.