RU2432658C1 - METHOD TO INCREASE RELIABILITY OF STEP-DOWN TRANSFORMER SUBSTATION OPERATION IN DISTRIBUTION GRIDS 6( 10 )/0,4 kV - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: method is designed for use in distribution grids 6(10)-0.4 kV, comprising a step-down transformer 6(10)/0.4 kV, three-phase lines 0.4 kV, a microcontroller, current sensors, installed at buses of the step-down transformer and at outgoing load cables, switches with drives installed at low voltage side of the transformer. Connection and disconnection of single-phase loads is done with the microcontroller. Switching elements are modules of IGBT-transistors. The moment of time to supply a control pulse from a microcontroller to disconnect loads is determined on the basis of the condition of zero current at outgoing cables of loads, to connect loads - on the basis of the condition of zero current at buses of the step-down transformer.

EFFECT: increased reliability of a step-down transformer substation operation.

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Description

The invention relates to the field of electrical engineering, in particular to power supply, and can be used in distribution networks 6 (10) / 0.4 kV, containing a step-down transformer 6 (10) / 0.4 kV, three-phase lines 0.4 kV associated with tires of the step-down transformer and transmitting electrical energy from the step-down transformer to single-phase loads.

A known method of reducing losses (US Pat. No. 2351049, published March 27, 2009), which consists in reducing the current asymmetry coefficient in a step-down transformer and in a three-phase power line supplying a step-down transformer substation having single-phase loads of different capacities, characterized in that the reduction the asymmetry coefficient of the currents in the phases of the three-phase supply line and the transformer windings is carried out by switching single-phase loads connected to the buses of the step-down transformer using switches, which are controlled by a microcontroller, the analog inputs of which receive AC signals from the sensors on the low voltage side of the transformer, while the microcontroller controls the switches that transfer loads from one phase to another on the buses of the step-down transformer substation, based on the condition of minimizing the current asymmetry coefficient, moreover, if the total values of currents in phases differ from the average current value, then part of the loads from the phase having a larger current is disconnected from e and included in a phase having a lower current, and specific loads to be switched are determined by the microcontroller of the condition that the total currents in the phases of their mean value.

The disadvantage of this method is the low reliability due to:

- the presence of switches that are unable to provide quick inclusion and disconnection of phase loads from the buses of the step-down transformer;

- high values of transient currents when switching loads on and off due to the impossibility of accurately determining the moment when loads are connected to the buses of the step-down transformer and disconnected from the buses of the step-down transformer;

- the impossibility of monitoring the state of the switches, leading to the simultaneous inclusion of switches of different phases on a single-phase load - the occurrence of interphase short circuit.

The objective of the proposed method is to increase the reliability of the step-down transformer substation 6 (10) /0.4 kV.

The technical result achieved in the process of solving the problem is to increase the reliability of the lowering substation by reducing the maximum transient current when switching loads on and off, as well as to protect the transformer 6 (10) / 0.4 kV and semiconductor modules from phase to phase short circuits and increase the service life of the transformer and semiconductor elements.

The specified technical result is achieved by a method of increasing the reliability of a step-down transformer substation in distribution networks of 6 (10) / 0.4 kV, containing a step-down transformer of 6 (10) / 0.4 kV, three-phase lines of 0.4 kV connected to the buses of the step-down transformer and transmitting electrical energy from a step-down transformer to single-phase loads, a microcontroller that controls the connection of single-phase loads to the buses and their disconnection from the busbars of the transformer of the step-down transformer substation, the signals at which current switches installed on cables connecting single-phase loads to the step-down transformer buses and current sensors installed on the step-down transformer tires, actuators mounted on the high-voltage side of the step-down transformer, which reduce the transient currents when switching loads on and off, and prevention of interphase short circuit, while as devices connecting single-phase loads to the buses and disconnecting them from the buses lowering transformation semiconductor modules on IGBT transistors are used, the state of which is controlled by a microcontroller, and the time moment for applying a control pulse from a microcontroller to turn off transistors of semiconductor modules on IGBT transistors is determined from the condition that the current in the outgoing load cables is equal to zero, the time moment for supplying a control pulse from a microcontroller to turn on transistors of semiconductor modules on IGBT transistors is determined from the condition that the bus current is zero ah step-down transformer.

The method is implemented as follows: the drawing shows a connection diagram of a step-down transformer between a supply line of 6 (10) kV and single-phase loads, which consists of a step-down transformer 1, a supply of a three-phase line 2, single-phase loads 3 connected to the buses of a step-down transformer 4, by means of semiconductor modules 7 on IGBT transistors controlled by a microcontroller 6, to which signals from current sensors 5 are installed, installed on the outgoing cables connecting the loads to the buses of the step-down transformer and with current sensors 9 installed on the buses of the step-down transformer and supplying signals to the analog inputs of the microcontroller, switches 8 with actuators connecting the transformer to a three-phase line of 6 (10) kV.

The need to switch loads from one phase to another is determined by signals from current sensors 5 and 9. The switching speed can be provided by semiconductor transistor modules 7. When the current sensor 5 fixes the value of zero current and the need to switch the load, the microcontroller sends a control pulse to the corresponding transistor module.

This happens as follows: the current sensor 5 captures the current value equal to zero and sends an analog signal to the microcontroller 6, the microcontroller through its analog outputs, after a lag time equal to the current change period, sends a control signal to the transistors of modules 7, which disconnect the load from a more loaded phase and then connect it to a less loaded phase after a signal delay time equal to the current change period, when the current sensor 9 fixes zero current on the transformer buses. The position of all the transistors and circuit breakers is constantly monitored by the microcontroller by the signals received from the current sensors 5 in its analog inputs. In the event of a malfunction of one of the semiconductor modules 7, the microcontroller gives a lock signal to the transistors of the modules of the other phases when the transistor of a module of any phase does not turn off. In the event of a short circuit on the buses of the step-down transformer, the signal on the bus currents is fed to the analog inputs of the microcontroller, the microcontroller, in case of exceeding the permissible current with a time delay, sends a signal to disconnect the transformer from the three-phase 6 (10) kV line to switches 8 through its analog outputs.

Thus, it is achieved:

- reduction of transient currents when switching loads on and off by using modules containing IGBT transistors and turning on the transistors when the current on the buses of the step-down transformer is equal to zero and when the current on the outgoing cables connecting the loads to the buses of the step-down transformer is equal to zero;

- elimination of interphase short circuit due to blocking the short circuit of transistors of modules of other phases when the transistor of a module of any phase is turned on.

Claims (1)

A method for improving the reliability of a step-down transformer substation in 6 (10) / 0.4 kV distribution networks, which consists in reducing transient currents when switching loads on and off and eliminating interphase short circuit in 6 (10) / 0.4 kV distribution networks containing step-down transformer 6 (10) / 0.4 kV, three-phase 0.4 kV lines connected to the buses of the step-down transformer and transmitting electrical energy from the step-down transformer to single-phase loads, a microcontroller that controls the connection of single-phase loads to the buses and disconnecting them from the busbars of the transformer of the step-down transformer substation, the signals to which come from current sensors installed on cables connecting single-phase loads to the buses of the step-down transformer and current sensors installed on the buses of the step-down transformer and on the outgoing load cables, circuit breakers with drives mounted on the high voltage side of the step-down transformer, characterized in that as devices connecting single-phase loads to the buses and disconnecting and from the buses of the step-down transformer, semiconductor modules based on IGBT transistors are used, the switching of which is controlled by a microcontroller, and the time moment for supplying a control pulse from a microcontroller to disconnect transistors of semiconductor modules on IGBT transistors is determined from the condition that the current in the outgoing load cables is equal to zero, time for supplying a control pulse from a microcontroller to turn on transistors of semiconductor modules on IGBT transistors is determined from the condition that the current on the tires of the step-down transformer is equal to zero.