JPH08314559A - Rush current suppressor for transformer - Google Patents

Abstract

PURPOSE: To obtain a rush current suppressor for a transformer which protects a power system from the transformer rush current by suppressing voltage fluctuation made by the transformer rush current which is generated by supplying the transformer of the power system. CONSTITUTION: The suppressor suppressing the transformer rush current (i), which is generated at the time of supplying the transformer 12 to the system bus 3, is provided with SVC 6 with TCR 4 of a thyristor 8 and a reactor 7, an SVC control circuit 10 phase-controlling the thyristor 8 for ignition, and an instantaneous compensation circuit 30 provided with a switching switch 31 operating the SVC circuit 10 only at the time of supplying the transformer. A multiplier 18 and a pulse generation circuit 20 in the SVC control circuit 10 are connected to each other by the switching switch 31 only during a fixed time after the supply of the transformer. Thus, the instantaneous reactive power (q) of the rush current (i) is outputted to the pulse generation circuit 20 from the multiplier 18 to ignite the thyristor 8 with an ignition pulse corresponding to the sudden instantaneous reactive power (q). Then the compensation reactive power (q) compensating the rush current (i) is generated at TCR 4 to suppress voltage fluctuation accompanied by the rush current (i) of the system bus 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transformer inrush current suppressing device effective for a power system in which a transformer is frequently turned on in a substation or a power consumer.

[0002]

2. Description of the Related Art In a power system having a general load or a fluctuating load which is supplied with power when a transformer is turned on, measures against the inrush current of the transformer when the transformer is turned on (described later) are taken. Further, in a power system having a fluctuating load such as an arc furnace, a thyristor control reactor type reactive power compensator (hereinafter referred to as SVC) is installed for the purpose of suppressing a voltage fluctuation of a system bus due to a load fluctuation. 3, a thyristor control reactor (hereinafter referred to as TCR) 4 and a filter (hereinafter referred to as FL) 5 are connected in parallel to the system bus 3 to form an SVC 6.

A substation power supply 1 is connected to a system bus 3 via a power system reactance 2, and a load 11 is connected to the system bus 3 via a step-down transformer 12 and a circuit breaker 13. The load 11 is connected to the power source 1 by turning on the circuit breaker 13 by a transformer closing command signal from the outside. The reactive power generated by the fluctuation of the load 11 is detected by the SVC control circuit 10, the SVC 6 is controlled by the SVC control circuit 10, and the reactive power for compensation for canceling the load reactive power is applied from the SVC 6 to the system bus 3 to apply power to the system. Voltage fluctuations on the bus bar 3 are suppressed.

The TCR 4 of the SVC 6 is a series circuit of a reactor 7 such as a high-impedance transformer and an antiparallel connection thyristor 8, and the thyristor 8 is phase-controlled by a roll call pulse P from the SVC control circuit 10 to cause a delay in the TCR 4. Reactive power is applied to the system bus 1. The FL 5 is provided with a phase advancing capacitor 9, and supplies the reactive power generated thereby to the system bus 1. The delayed reactive power and the advanced reactive power suppress the voltage fluctuation of the system bus 1.

The SVC control circuit 10 detects the instantaneous value q of the load reactive power from the load current I detected by the current transformer 14 and the bus voltage E detected by the transformer 15.
And a low-pass filter (hereinafter referred to as LPF) that detects the load reactive power Q from the average value of the output values of the multiplier 18
9 and a pulse generation circuit 20 for generating a roll call pulse P for phase-controlling the thyristor 8 of the TCR 4 from the load reactive power Q.
Is provided. The load current I is phase-converted by the phase conversion circuit 16 and output to the multiplier 18, and the bus voltage E is converted by the voltage phase shifter 17 into a voltage V whose phase is delayed by 90 ° and output to the multiplier 18. . The multiplier 18 outputs the load reactive power instantaneous value q obtained by multiplying the load current I and the bus voltage V delayed by 90 °, and the average value of this instantaneous value q is obtained by the LPF 19 to output the load reactive power Q to the pulse generation circuit. It is output to 20.

The pulse generation circuit 20 generates an ignition pulse P at the timing of the cross point of the load reactive power Q and the sawtooth wave reference signal Vf from the pulse generation reference signal forming circuit 21 to phase control the thyristor 8 of the TCR 4. And fire it. By controlling the phase of the thyristor 8, the load reactive power Q is applied to the TCR 4.
The compensating reactive power that cancels out is generated, and the voltage fluctuation due to the load fluctuation of the system bus 3 is suppressed.

[0007]

When the circuit breaker 13 is turned on and the transformer 12 is turned on in the power system shown in FIG. 3, for example, a sudden and intermittent inrush current (shown by the current waveform A in FIG. 4) is generated. Some excitation currents i flow to the system bus 3 for a short time of about several seconds. This inrush current i appears on either the plus side or the minus side, and the first one is the maximum, and the second one is gradually reduced from the second one. The magnitude of the initial inrush current i is not constant according to the residual magnetic flux value of the transformer 12 when the transformer is turned on, but is large and becomes 3 to 5 times the transformer capacity. When such a large rush current i flows through the system bus 3, it causes an instantaneous voltage drop in the system bus 3 and adversely affects other loads (motors, fans, lighting equipment, etc.) connected to the system bus 3 (rotation speed). Deterioration, flicker of lighting, etc.), and if worse, system cutoff may occur.

The voltage fluctuation of the system bus 3 due to the inrush current i when the transformer is turned on cannot be suppressed by the SVC 6. That is, the instantaneous value of the load reactive power obtained by multiplying the sudden and intermittent inrush current i and the bus voltage is used as the LPF 21.
When the load reactive power is detected through the power supply, the load reactive power has a waveform as shown in the power waveform B of FIG. 4, that is, a rise and fall of an average of several sudden and intermittent inrush currents i. Appears as a gentle waveform. The load reactive power of this waveform B does not correspond to the actual inrush current i, and this load reactive power is output to the pulse generation circuit 20 to generate an ignition pulse at the timing of crossing with the sawtooth wave reference signal Vf. Even if the thyristor 8 of the TCR 4 is phase-controlled, the voltage fluctuation of the system bus 3 may not be suppressed and the voltage fluctuation may be amplified, which may have an adverse effect.

Therefore, as a countermeasure against the transformer rush current in the power system, the residual magnetic flux of the transformer is canceled before the transformer is turned on so that the rush current is not generated. However, since the number and types of transformers and loads installed in the power system are various, there is a problem that it is difficult to take the above countermeasures for each transformer.

Further, as a measure against transformer inrush current in a power system in which an SVC 6 as shown in FIG. 3 is installed, the pulse generation circuit 20 is cut off only when the transformer is turned on to interrupt the ignition pulse generation. There is. In this case, the voltage fluctuation amplification of the system bus 3 when the transformer is turned on is eliminated,
At present, the problem of voltage fluctuation due to transformer inrush current remains.

An object of the present invention is to provide a transformer inrush current suppressing device which directly suppresses a voltage fluctuation due to a transformer inrush current generated when a transformer of a power system is turned on, thereby protecting the power system. It is in.

[0012]

DISCLOSURE OF THE INVENTION The present invention is a device for suppressing inrush current when a transformer is turned on in a system bus.
An SVC having a TCR in which a series circuit of an anti-parallel connection thyristor and a reactor is connected to a system bus, and a multiplier for detecting the instantaneous reactive power of the inrush current when the transformer is turned on by multiplying the bus voltage at the system bus and the load current. , An SVC control circuit having a pulse generation circuit for generating an ignition pulse for phase-controlling a thyristor of a TCR according to the instantaneous reactive power output value of the multiplier, and inputting a transformer to a system bus From the time point, the output of the multiplier is input to the pulse generating circuit for a certain period of time when an inrush current is generated, and after this certain period of time, the instantaneous compensation circuit includes a changeover switch that shuts off the input of the multiplier output to the pulse generating circuit. The above-mentioned object is achieved by a configuration including.

[0013]

Function: The bus voltage at the system bus is multiplied by the load current to detect the instantaneous reactive power of the inrush current when the transformer is turned on by the multiplier, and the detected instantaneous reactive power output is used to directly phase the TCR thyristor. When the delayed reactive power generated by the control for the instantaneous reactive power compensation is applied to the system bus, the compensation reactive power corresponding to each of the sudden and intermittent transformer inrush currents is given to the system bus, and the transformer inrush current is applied. The voltage fluctuation of the system bus line due to Also, after a certain period of time when the transformer inrush current is generated, the input of the multiplier output to the pulse generation circuit is cut off by the changeover switch, so that the SVC is opened and the normal operation of the power system after the transformer is turned on can be achieved. Reserved.

[0014]

Embodiments of the present invention will be described below with reference to FIGS.

The transformer inrush current suppressing device shown in FIG. 1 is applied to the power system shown in FIG. 3, and the SVC 6 shown in FIG.
And SVC 6 and S having substantially the same structure as the SVC control circuit 10.
The VC control circuit 10 includes an instantaneous compensation circuit 3 which is a feature of the present invention.
It is a structure with 0 added. The same as in FIG. 3 of FIG. 1, or
Corresponding parts will be assigned the same reference numerals and explanations thereof will be omitted.

The SVC 6 shown in FIG. 1 has the same structure as the SVC 6 shown in FIG. 3, and is constructed by connecting a TCR 4 and a FL 5 in parallel to a system bus 3. The SVC control circuit 10 shown in FIG.
This corresponds to a circuit in which the low pass 19 of the C control circuit 10 is omitted and the changeover switch 31 of the instantaneous compensation circuit 30 is arranged instead.

The instant compensation circuit 30 is provided with a CB closing command circuit 32 which operates by a transformer closing command signal m from the outside to turn on the circuit breaker 13 and at the same time switches the changeover switch 31. The changeover switch 31 is a contact switch or a non-contact switch of a semiconductor switching element. The change-over switch 31 cuts off the output from the multiplier 18 to the pulse generating circuit 20 and the circuit connection terminal 35 for inputting the output of the multiplier 18 to the pulse generating circuit 20, and the pulse generating circuit 2
Switching between a break ground terminal 36 which grounds the 0 input terminal.

When the CB closing command circuit 32 is activated by the transformer closing command signal m, for example, the CB closing circuit 33 is activated to turn on the circuit breaker 13, and at the same time, the CB closing determination circuit 34 is activated to cut off the changeover switch 31. The ground terminal 36 is switched to the circuit connection terminal 35. When the change-over switch 31 is switched to the circuit connecting terminal 35, the state is maintained for a certain period of time when the transformer inrush current i is generated, and after this certain period of time, the circuit connecting terminal 35 is automatically switched to the breaking earth terminal 36. . Such automatic switching of the changeover switch 31 after a predetermined time has elapsed is controlled by a built-in CB closing determination circuit 34 or a special timer circuit (not shown).

The instantaneous compensation circuit 30 operates for a certain period of time after the breaker 13 is turned on and the transformer 12 is turned on to the system bus 3, and the SVC control circuit 10 and the SVC 6 are supplied to the system bus 3 by the transformer inrush current i. The operation of suppressing the voltage fluctuation of is performed. This voltage fluctuation suppressing operation is shown in FIG.
This will be described with reference to the waveform diagram of (d).

When the circuit breaker 13 is turned on by the CB closing command signal m and the transformer 12 is closed to the system bus 3, the system bus 3
An inrush current i of the transformer flows. This inrush current i is a reactive power whose phase is delayed by 90 ° with respect to the bus voltage E, and its magnitude changes depending on the voltage phase when the transformer is turned on and the transformer residual magnetic flux. In FIG. 2A, the inrush current i that differs in three steps of large, medium, and small is indicated by the symbol. The inrush current i is abrupt and is generated intermittently as the magnitude gradually decreases within a few seconds after the transformer is turned on.

When the inrush current i of the system bus 3 is detected by the current transformer 14 and output to the multiplier 18, the multiplier 18 multiplies the inrush current i by the bus voltage V from the voltage phase shifter 17,
The instantaneous reactive power q shown in FIG. 2 (b) is calculated. Figure 2
The three-stage instantaneous reactive power q shown in (b) and having different magnitudes corresponds to the inrush current i in () of FIG. The instantaneous reactive power q is the same sudden power as the inrush current i, and is generated intermittently for a fixed time of about several seconds.

At the same time when the transformer is closed by the CB closing command signal m, the instantaneous compensating circuit 30 switches the changeover switch 31 to the circuit connecting terminal 35. Therefore, the instantaneous reactive power q calculated by the multiplier 18 is output. The value is directly input to the pulse generation circuit 20. The pulse generation circuit 20 is shown in FIG.
As shown in (c), the ignition pulse P is generated at the timing of the cross point of the instantaneous reactive power q and the sawtooth wave reference signal Vf from the pulse generation reference signal forming circuit 21, and the thyristor 8 of the TCR 4 is phase-controlled. To fire.

Large, medium and small instantaneous reactive power q due to inrush current i
And the pulse phase β at the crossing point of the reference signal Vf is shown in FIG.
As shown in (c) and, different from large, medium and small. That is, the instantaneous reactive power q and the pulse phase β in FIG.
, And the pulse phase β increases as the instantaneous reactive power q increases, and the pulse phase β decreases as the instantaneous reactive power q decreases. Such a pulse phase β
The thyristor current i _Th flowing through the TCR 4 when the thyristor 8 is phase-controlled and ignited by the ignition pulse P
Is shown in FIG.

As is apparent from FIG. 2 (d), the instantaneous reactive voltage is
Thyristor current i when force q is large _ThBecomes small and instant
Thyristor current i when reactive power q is small_ThIs big
It Such a thyristor current i_ThFlows to system bus 3
As a result, the TCR 4 causes the inrush current i of the system bus 3 to be intermittent.
The system operates by making each phase independent and canceling them sequentially.
Voltage fluctuations associated with inrush current i of bus bar 3 are suppressed.

The above-described inrush current suppressing operation is performed only for a fixed time of several seconds after the transformer is turned on and no inrush current is generated. When this fixed time has elapsed, the instant compensation circuit 30 switches the changeover switch 31 from the circuit connection terminal 35 to the cutoff ground terminal 36 by timer control. After that, the output of the multiplier 18 is cut off, the pulse generation circuit 20 is stopped, and the SVC6
Is stopped, and the influence of the SVC 6 on the system bus 3 side is avoided.

Although the transformer inrush current shown in FIG. 1 has been described as being generated on the plus side, the inrush current may be generated on the minus side. Applicable.

The load shown in FIG. 1 is not limited to the variable load, and the transformer for supplying the transformer inrush current to the power system is not limited to the load input transformer, but may be a transformer for supplying AC power to the system bus. May be

[0028]

According to the present invention, the multiplier detects the instantaneous reactive power of the inrush current that suddenly flows in the system bus when the transformer is turned on, and the detected instantaneous reactive power directly affects the thyristor of the thyristor control reactor. By applying the delayed reactive power for instantaneous reactive power compensation generated by controlling the phase to the system bus, compensation reactive power corresponding to each of the sudden and intermittent transformer inrush currents is given to the system bus, Voltage fluctuations on the system busbar due to transformer inrush current are suppressed. Therefore, it is possible to reduce various troubles on the power system such as load malfunction and damage due to transformer inrush current.

Further, after a lapse of a certain time when the transformer inrush current is generated, the input of the multiplier output to the pulse generating circuit is cut off by the changeover switch to open the SVC, so that the power system after the transformer is turned on. The normal operation of is secured.

Further, since the existing SVC can be applied as it is to the SVC installed on the system bus, and the SVC control circuit can be applied only by replacing a part of the existing SVC control circuit with a changeover switch, the existing equipment can be installed in a large size. It is possible to provide a transformer inrush current suppressing device that can be used partially, which is advantageous in terms of capital investment.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a transformer inrush current suppressing device and a power system showing an embodiment of the present invention.

2 (a) to (d) are voltage / current waveform diagrams at various points for explaining the operation of the transformer inrush current suppressing device of FIG.

FIG. 3 is a circuit diagram of a power system including an SVC.

FIG. 4 is a waveform diagram of transformer inrush current and its reactive current generated in the power system of FIG.

[Explanation of symbols]

 3 System Bus 4 Thyristor Control Reactor (TCR) 6 Reactive Power Compensator (SVC) 8 Thyristor 10 Reactive Power Compensator Control Circuit 11 Load 12 Transformer 18 Multiplier 20 Pulse Generation Circuit 30 Instantaneous Compensation Circuit 31 Changeover Switch i Transformer Inrush Current q Instantaneous reactive power P Firing pulse

Claims (1)

[Claims] 1. A reactive power compensator for suppressing inrush current when a transformer is turned on in a system busbar, the reactive power compensating device having a thyristor control reactor in which a series circuit of an antiparallel connection thyristor and a reactor is connected to a system busbar. A multiplier that multiplies the bus voltage on the bus and the load current to detect the instantaneous reactive power of the inrush current when the transformer is turned on, and controls the phase of the thyristor according to the instantaneous reactive power output value of this multiplier. A reactive power compensator control circuit having a pulse generation circuit for generating an ignition pulse to be ignited, and the output of the multiplier only for a certain period of time when the transformer inrush current is generated from the time of inputting the transformer to the system bus. An instantaneous compensation circuit having a changeover switch for inputting to the pulse generation circuit and cutting off the input of the multiplier output to the pulse generation circuit after a certain period of time. Transformer inrush current suppression apparatus according to symptoms.