JPH05115127A - Active filter - Google Patents

Abstract

PURPOSE:To suppress the excitation throw-in current regardless of the throw-in timing of a breaker by exciting the winding of a receiving transformer from secondary side with an active filter before throwing in the breaker on the power source side of the receiving transformer, and generating a magnetic flux having phase lag of 90 deg. behind system voltage in an iron core. CONSTITUTION:When a receiving transformer 1 is thrown in, the DC capacitor of an active filter 2 is charged first, and then a breaker 2A is closed, and the active filter 2 is connected to the secondary side of the receiving transformer 1. On the other hand, system voltage Vs is detected with a voltage detector 3, and is taken in a control circuit 2B, and the voltage VACF of the same phase as the system voltage is generated in the active filter 2, and is applied to the secondary side of the receiving transformer 1, and a magnetic flux having phase lag of 90 deg. behind the system voltage is generated in the iron core. Next, the agreement of the phases between the system voltage Vs and the voltage VACF of the active filter 2 is detected with a phase comparator 6, and a throw-in permission signal is given to the breaker 1A.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active filter connected to a secondary side bus bar of a power receiving transformer, and more particularly to an active filter which can be used for suppressing an exciting inrush current of the power receiving transformer.

[0002]

2. Description of the Related Art When a transformer is turned on in a system, if a transformer is turned on near the zero point of the system voltage, a large exciting inrush current may transiently flow. As a method of suppressing the excitation inrush current, a circuit has been proposed which monitors the system voltage phase and turns on the power source side circuit breaker of the transformer at the timing when the excitation inrush current does not occur.

[0003]

By the way, since the exciting inrush current of the transformer reaches several times the rated current, malfunction of the protective relay, influence of the lowering of the bus voltage on the equipment and the like occur.

If the phase of the system voltage is detected and the transformer is turned on during the voltage peak, an excessive inrush current can be suppressed, but it is difficult to control the closing timing of the breaker.

Therefore, an object of the present invention is to provide an active filter capable of suppressing an inrush current of excitation by utilizing an active filter connected to the secondary side of a transformer.

[0006]

In order to achieve the above-mentioned object, the present invention has a configuration as shown in FIG. 1, in which the system voltage on the primary side of the power receiving transformer 1 whose excitation inrush current is to be suppressed. A voltage detector 3 such as PT that detects Vs, and a control circuit 2B that causes the active filter 2 to generate a voltage VACF having the same phase as the system voltage obtained by the voltage detector 3, the system voltage Vs, and the active filter. 2 output voltage VAC
It is characterized in that a phase comparison circuit 6 for sending a closing command to the power source side circuit breaker 1A of the power receiving transformer 1 is provided on the condition that Fs match.

[0007]

With the above-described structure, the power receiving transformer 1 is turned on before the power source side breaker 1A of the power receiving transformer 1 is turned on.
The winding of is excited by the active filter 2 from the secondary side,
A magnetic flux delayed by 90 ° from the system voltage is forcibly generated in the iron core of the power receiving transformer 1. If the magnetic flux having such a phase is present in the iron core, the magnetizing inrush current can be suppressed regardless of the closing timing of the breaker 1A.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a waveform diagram for explaining the operation of FIG. 1, and FIG. 3 is a flow chart for explaining the operation of FIG.

In FIG. 1, 1 is a power receiving transformer, 1A is a power source side breaker of the power receiving transformer 1, 2 is an active filter, 2A is a power source side breaker of an active filter 2, 2
B is a control circuit for controlling the active filter 2, 2C is a DC capacitor of the active filter 2, 3 is a voltage detector such as PT for detecting the system voltage Vs, 4 is a load, 4A is a power source side breaker of the load 4, 5 Is a voltage detector, and 6 is a power source circuit breaker 1A of the power receiving transformer 1 under the condition that the output voltage VACF of the active filter 2 and the system voltage Vs are in phase.
3 shows a phase comparison circuit that sends a closing permission signal to the. In the above configuration, the power source side circuit breaker 1A of the power receiving transformer 1 is open, the circuit breaker 2A of the active filter 2 is open, and the circuit breaker 4A of the load 4 is open.

When the power receiving transformer 1 is put into the system, as described above, if the breaker 1A is closed, an excessive magnetizing inrush current may flow. Therefore, before closing the breaker 1A, the active filter 2 is closed. After charging the DC capacitor 2C of No. 2 and making it operable, firstly the breaker 2A is closed and the active filter 2 is connected to the secondary side of the power receiving transformer 1. On the other hand, the system voltage Vs on the power supply side of the power receiving transformer 1
Is detected by the voltage detector 3, and the detected value is detected by the control circuit 2B.
Take in. The control circuit 2B causes the active filter 2 to generate a voltage VACF that is in phase with the system voltage Vs. Thus, by applying the voltage VACF having the same phase as the system voltage Vs to the secondary side of the power receiving transformer 1 before being turned on, the exciting current i0 flows, and the magnetic flux Φ with a phase delay of 90 ° from VACF is generated in the iron core. become. FIG. 2 shows this state. As described above, since VACF has the same phase as the system voltage Vs, the iron core magnetic flux Φ is delayed by 90 ° from the system voltage Vs. When this state is reached, the breaker 1A can be turned on.

As shown in FIG. 2, when exciting the power receiving transformer 1 with the active filter 2, the voltage VACF of the active filter 2 is gradually increased,
It is necessary to prevent the inrush current of excitation by the active filter 2. The normal active filter 2 operates while charging the DC capacitor 2C through the main circuit. However, before the power receiving transformer 1 is turned on, energy is not received from the system side, so the DC capacitor 2C is always supplied to the DC capacitor 2C by the separate power supply 7. I have to give it power. (However, since it is only the excitation energy of the power receiving transformer 1, the energy does not become so large.)

When the comparator 6 detects a match between the system voltage Vs and the voltage VACF of the active filter 2, the breaker 1
A closing permission signal is given to A. When the logical product of this signal and the circuit breaker ON command signal becomes "1", the circuit breaker 1A is turned on. After the breaker 1A is turned on, the active filter 2 switches to normal filter operation such as suppression of harmonics generated from the load 4, fluctuation of bus voltage, and suppression of flicker. The flowchart of FIG. 3 summarizes the series of driving operations described above.

According to the present invention, by adding a control circuit and a detection circuit without changing the main circuit configuration of the active filter which is normally used for the fault current generated from the load 4,
It is intended to prevent an inrush current of the power receiving transformer 1.

[0014]

INDUSTRIAL APPLICABILITY As described above, the present invention utilizes the active filter installed on the secondary side of the power receiving transformer, and before the power source side breaker of the power receiving transformer is turned on, the power receiving transformer. By controlling the iron core magnetic flux to an appropriate phase by exciting the coil from the secondary winding side, the breaker on the power supply side of the power receiving transformer can be turned on regardless of the system voltage phase, and highly reliable inrush current suppression Can be realized.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a waveform diagram for explaining the operation of FIG.

FIG. 3 is a flowchart showing the operation of FIG.

[Explanation of symbols]

1 ... Power receiving transformer 1A ... Breaker 2 ... Active filter 2A ... Breaker 3 ... Voltage detector 4 ... Load 4A ... Breaker 5 ... Voltage detector 6 ... Phase comparison circuit 7 ... DC power supply

Claims (1)

[Claims] 1. An active filter connected to a secondary side bus of a power receiving transformer, a voltage detector for detecting a primary side system voltage of the power receiving transformer, and the active filter and the voltage detector. And a control circuit that generates a voltage in the same phase as the system voltage obtained in step 1, and a phase comparison that sends a closing permission signal to the breaker of the power receiving transformer on condition that the phases of the system voltage and the active filter output voltage match. An active filter having a circuit.