JPH0366685B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an initial charging control device for a phase advance capacitor for phase modulation, which is turned on and connected as necessary to a load such as an electric power system. .

[Conventional technology]

FIG. 1 is a circuit diagram showing an example of a method for introducing a phase advancing capacitor to be connected to an electric power system. In the figure, 1 is a circuit breaker, 2 is a main transformer, 3 is a series reactor, 4 is a phase advance capacitor,
5 is a switch consisting of two thyristors connected in antiparallel. The series reactor 3 is used to prevent waveform distortion due to harmonics of the system P to which the phase advance capacitor 4 is connected, and to suppress transient phenomena when the capacitor 4 opens and closes for the system P. Generally, it has a reactance of about 6 to 14% of the capacitor reactance.

Now, in FIG. 1, when it is determined by means not shown that it is necessary to turn on the phase advance capacitor 4 to the power system P, the circuit breaker 1 is turned on and the power is connected to the primary side of the main transformer 2. Connect system P. Next, the capacitor 4 is connected to the power system P by sending an ignition pulse to the gate of the thyristor switch 5 to turn on the switch. In this way, the power system P of the capacitor 4
Even if the capacitor 4 is once connected to the system P, it goes without saying that the capacitor 4 will be disconnected from the system P or reconnected depending on the load condition of the system P after that, and this disconnection and reconnection (this (also referred to as opening and closing) is performed by on/off control of the thyristor switch 5.

In order to suppress the flow of inrush current when the capacitor 4 is connected to the system P, the point (phase) at which the voltage becomes zero in one cycle of the AC voltage applied across the thyristor switch 5 is generally determined. A method is adopted in which the thyristor switch 5 is selected and the thyristor switch 5 is turned on to close the capacitor 4 (hereinafter referred to as the zero voltage synchronous closing method).

FIG. 2 shows waveforms of signals of various parts when the circuit shown in FIG. 1 has already entered normal operation, not at the time of starting.

At the time of startup, the capacitor 4 is in an uncharged state, and therefore the operation starts from charging the capacitor 4. However, when normal operation begins, the capacitor 4 is already in a charged state. In this state, the thyristor switch 5 is turned on and off to open and close the capacitor 4.

In Fig. 2, A shows the waveform of the power supply voltage (for one phase), B shows the voltage waveform applied to both ends of the capacitor 4, C shows the waveform of the current flowing through the capacitor 4, and D shows the waveform of the thyristor switch 5. The voltage waveform applied to both ends is shown, and E is the thyristor switch 5.
The ignition signal applied to the gate of FIG.

Now, in FIG. 2, it is assumed that the thyristor switch 5 is turned on at time _t1 and turned off at time _t2 . Until time t ₁ , capacitor 4
The voltage B across the thyristor switch 5 is charged to -E volts (steady voltage, peak value of the power supply voltage), and therefore the voltage D across the thyristor switch 5 is also the same as the power supply voltage waveform A raised by E volts. It is shaped like a wave. At time t ₁ , thyristor switch 5
By igniting the capacitor using the zero-voltage synchronous closing method, the transient current contained in the capacitor current C can be extremely small, and the capacitor current C settles down to a steady current within a few cycles, allowing smooth capacitor closing. can. After turning off the thyristor switch 5 at time _t2 , the capacitor 4
In the illustrated case, the voltage across the thyristor switch 5 is charged to +E volts, and the voltage d across the thyristor switch 5 also has a waveform obtained by lowering the power supply voltage waveform a by E volts.

FIG. 3 shows the waveforms of the various signals when the circuit shown in FIG. 1 is at startup. In this case, as in the case of FIG. 2, it is assumed that the thyristor switch 5 is turned on at time _t1 and turned off at time _t2 .

In this case, since it is the time of starting, the capacitor 4 is in an uncharged state until time t _1. Therefore, the voltage across the capacitor 4 is in a zero volt state, and the thyristor switch 5 has no voltage from the power supply. Waveform A is applied as is. At time _t1 , if the thyristor switch 5 is turned on at the zero point of the power supply voltage waveform A using the zero voltage synchronization method, the current C flowing through the capacitor 4 will be as shown in the figure due to the resonance between the capacitor 4 and the series reactor 3. This results in a large transient current.

[Problem to be solved by the invention]

The magnitude of this transient current changes depending on the magnitude of the reactance of the series reactor 3. Normally, this series reactor is determined to have a reactance of about 6 to 14% of the capacitor capacity, as mentioned earlier, but if the series reactor has a reactance of 6%, the peak of the transient current that flows would be The value reaches approximately twice the steady current (peak value of rated current), and the transient current continues for several cycles, depending on the circuit constants. In this way, when the thyristor switch is turned on when the capacitor is not charged during startup, a much larger current flows than when the thyristor switch is turned on when the capacitor is already charged to a steady voltage. In order to withstand this large current, the current capacity of the thyristor switch is increased,
This had the disadvantage that it had to be designed with a margin, which ultimately led to an increase in costs.

The present invention has been made in order to eliminate the drawbacks of the prior art as described above, and an object of the present invention is to prevent large transient current from flowing even when the thyristor switch is turned on at the time of starting. Initial charging control automatically charges the capacitor gradually after the circuit breaker is turned on until the thyristor switch is turned on, and the capacitor is fully charged when the thyristor switch is turned on. The goal is to provide equipment.

[Means to solve the problem]

To achieve the above object, in the present invention, a series circuit consisting of a circuit breaker, a series reactor, a phase advance capacitor for adjusting the phase, and a thyristor switch consisting of a plurality of thyristors connected in anti-parallel is connected to the power system as a load. and, after closing the circuit breaker, the thyristor switch is turned on and off to turn on and disconnect the phase advance capacitor for phase adjustment in the phase adjustment equipment, wherein the phase advance capacitor for phase adjustment is connected to and disconnected from the load. The device includes: a time limit means, a signal holding means, a voltage monitoring means, a firing angle command means, an AND circuit, a charging means, and a charging voltage monitoring means.

[Effect]

The time limit means detects the closing of the circuit breaker and generates a time limit output after a certain period of time. When the signal holding means receives the time-limited output, it holds it and continues to output the first signal from then on. The voltage monitoring means monitors the voltage across the thyristor switch, and outputs the second signal only during a period when the periodically changing voltage is below a predetermined value. Further, the firing angle command means monitors a voltage waveform of the electric power system as the load, and outputs a third signal representing a predetermined firing phase angle in the waveform.

Then, the AND circuit calculates the AND of the first to third signals and outputs the result. When the charging means receives the AND output from the AND circuit, it turns on the thyristor switch for a predetermined period of time, charges the capacitor during that time, and then turns off the thyristor switch. When the charging means repeatedly charges the capacitor as the AND output from the AND circuit is intermittently output, and the charging voltage exceeds a predetermined limit,
The charging voltage monitoring means detects this, resets the signal holding means, and turns off the first signal, thereby completing the initial charging control of the phase advance capacitor.

〔Example〕

Next, an embodiment of the present invention will be described with reference to the drawings.

FIG. 4 is a block diagram showing one embodiment of the present invention. In the figure, 1 is a circuit breaker, 2 is a main transformer, 3 is a series reactor, 4 is a phase advance capacitor,
5 is a thyristor switch, 6 is a synchronous transformer, 9
is a circuit breaker closing command generator, 10 and 11 are each a voltage detector, 12 and 13 are each a comparator, 14 is a timer, 15 and 16 are each a flip-flop, 17 is an AND gate, 18 and 19 are each a monostable multivibrator, 20 is
21 is a firing angle regulator, and 22 is a pulse amplifier.

The voltage detector 10 is for detecting the capacitor voltage across the phase advance capacitor 4, and the comparator 12 monitors this detected voltage level, and detects when the level reaches a predetermined level. When it does, comparator 12 issues a reset signal and sends it to flip-flop 15.
Further, when a closing command signal for the circuit breaker 1 is issued from the command generator 9, the command signal is sent to the flip-flop 15 via the timer 14, and this flip-flop 15 is set. As long as flip-flop 15 is set, initial charging of capacitor 4 is possible (as long as other conditions are satisfied).

The voltage detector 11 is for detecting the thyristor switch voltage across the thyristor switch 5, and the comparator 13 monitors this detected voltage level and detects that the level is within a predetermined range. , the comparator 13 outputs a signal only for a period within that range.
Send to AND gate 17. Also, the firing angle adjuster 2
1, a (π-α) signal (α=90°) synchronized with the synchronous voltage waveform of the power supply voltage supplied via the synchronous transformer 6 is supplied to the AND gate 17.

Furthermore, a set output signal indicating that flip-flop 15 can be initially charged is sent to AND gate 17. When the AND condition of these three input signals is satisfied, the AND gate 17 generates an output. This output sets flip-flop 16 by driving monostable multivibrator 18,
This set output determines the firing phase of the thyristor switch 5 during initial charging. The output of the monostable multivibrator 18 is sent via the NOT gate 20 and the monostable multivibrator 19 to the reset terminal of the flip-flop 16, and by resetting the flip-flop 16, the end of the firing period of the thyristor is determined. The actual firing signal is supplied to each thyristor of the thyristor switch 5 via a pulse amplifier 22.

The partial functions of each part of the circuit should now be understood.

Next, the operation of the initial charging control device according to the present invention will be explained. Before that, let me explain again the meaning of initial charging.

In FIG. 4, the circuit breaker 1 is closed by a closing command from the circuit breaker closing command generator 9, and the power is turned on. Since it is the time of starting, the capacitor 4 is in an uncharged state. Therefore, the capacitor 4 is gradually charged while controlling the thyristor switch 5 to turn on and off. When charging of the capacitor 4 is completed, the thyristor switch 5 is turned off to wait for the next normal operation. This completes the initial charging, and from now on, by inputting the normal ON-OFF command to the flip-flop 16, the thyristor switch 5 is controlled to turn on and off, and the phase advance capacitor is opened and closed. . Next, the operation of the initial charging control device will be explained with reference to FIG.

FIG. 5 is a waveform diagram showing signals of various parts of the circuit of FIG. 4 during the initial charging operation.

In FIG. 5A, e is the power supply voltage, and i _c is the waveform of the charging current of the capacitor 4. In addition, B is the output of the voltage detector 10 (voltage waveform of the capacitor 4)
C is a waveform diagram showing changes over time until charging of capacitor 4 is completed; C is a waveform diagram showing temporal changes in the output of voltage detector 11 (voltage waveform across thyristor switch 5); is a waveform diagram of the closing command signal of the circuit breaker 1 outputted from the command generator 9, E is a waveform diagram showing the set output (initial chargeable period signal) of the flip-flop 15, and F is the output from the firing angle regulator 21. is a waveform diagram of the (π-α) signal (generally chosen to be α = 90°). A waveform diagram of the signal that is output only during that period,
H is a waveform diagram of the output of the monostable multivibrator 18 (on command signal of thyristor switch 5), R is a waveform diagram of the output of the monostable multivibrator 19 (OFF command signal of thyristor switch 5), and N is the output of the flip-flop 16. Waveform diagram of (firing signal of thyristor switch 5), le is comparator 1
Waveform diagram of output 2 (signal output when detecting that the voltage level of capacitor 4 has reached a predetermined charge completion level), O shows the waveform when the capacitor 4 is fully charged and the normal operation is resumed. , a waveform diagram of the ignition signal applied to the thyristor switch 5 to turn on the capacitor.

Now, at time t ₁ , circuit breaker 1 is
When the battery is turned on, the flip-flop 15 is set at time _t2 after the set time _T1 of the timer 14 has elapsed, and the initial charging mode is entered. The time T ₁ of the timer 14 may be set to about 5 seconds, which is the time from when the circuit breaker 1 is turned on until the transient phenomenon caused by the exciting current of the transformer 2 is almost completely stopped. The capacitor 4 is in an uncharged state until initial charging is started, and therefore, during this period, the voltage applied to the thyristor switch 5 has the same waveform as the power supply voltage.

After time t ₂ when the initial charging mode is reached, the (π-α) signal from the firing angle regulator 21 changes the electrical angle from 90° of the positive half wave of the power supply voltage e.
During 180°, the thyristor switch voltage reaches the detection level of the comparator 13 (for example, 20% of the peak value).
At time t ₃ (below), an output is generated from the AND gate 17 and an ON command for the thyristor switch 5 is sent from the monostable multivibrator 18 to the flip-flop 16. At this time _t3 , the flip-flop 16 is set, the ignition signal N is applied to the thyristor switch 5, and the thyristor switch 5 is turned on at the phase of time _t3 . As a result, a transient inrush current i _c (FIG. 5a) flows due to resonance between the capacitor 4 and the series reactor 3. The setting of the voltage detection level of the comparator 13 at this time is such that this inrush current is kept small, and the capacitor voltage (R) at the end of initial charging is equal to the peak value of the power supply voltage or within an appropriate allowable voltage range. Choose a value like this.

Normally, the voltage detection level of the comparator 13 is set within the range of 10 to 30% of the peak value of the power supply voltage.
When the detection voltage V _TH is below this level, the comparator 13 may output an output. Further, the inrush current _ic must be made to flow only during the positive half-wave period, and after that period, the thyristor switch 5 must be turned off so that it does not flow during the negative half-wave period. This is because if inrush current flows during the negative half-wave period, capacitor 4
This is because when the current flowing into the capacitor eventually becomes zero and the thyristor is turned off, the capacitor voltage returns to a value close to the initial non-charged state. So, after the ON command at time t ₃ , a predetermined time T ₂
In order to issue an off command after the elapse of T2, the monostable multivibrator 18 passes through the NOT gate 20 and the monostable multivibrator 19, and after the set time _T2 of the monostable multivibrator 18, the off command of the thyristor switch 5 is sent to the flip-flop 16.
The flip-flop 16 is thereby reset and the thyristor switch 5 is gate-blocked.

The pulse width of the ignition signal N during this initial charging, that is, the set time T ₂ of the monostable multivibrator 18 is:
It is determined from the resonance frequency of the capacitor 4 and the series reactor 3. Normally, the setting time T ₂ of the monostable multivibrator 18 may be selected to be about 1 ms to 2 ms.
As a result, an inrush current as shown by _ic in FIG. 5A flows, and the thyristor switch 5 is turned off at time _t4 when the current becomes zero. At this time, capacitor 4
is charged to a certain capacitor voltage by being charged from when the thyristor switch is turned on at phase _t3 until it is turned off at time _t4 . As shown in the figure, the thyristor switch voltage C has a waveform obtained by shifting the power supply voltage by the capacitor charging voltage.

After that, the capacitor charging control described above will be repeated, but the firing phase of the thyristor switch 5 will be determined by monitoring the thyristor switch voltage C.
The capacitor 4 is gradually charged, and when the capacitor voltage L reaches the voltage detection level of the comparator 12 (time _t5 ), a reset output signal is output from the comparator 12, thereby resetting the flip-flop 15. The initial chargeable motor is completed, and thereafter it becomes possible to shift to the normal operation mode. Normally, the voltage detection level of the comparator 12 may be set to the peak value of the power supply voltage (V _c ≈100%). Further, instead of directly detecting the capacitor voltage, it may be calculated indirectly from the thyristor switch voltage and the power supply voltage.

As a result, when controlling the opening/closing of a phase-advanced capacitor using a thyristor switch, it is no longer accompanied by an excessive transient current at startup unlike in the past, and the capacitor can be turned on smoothly with extremely small transient current. become able to.

〔Effect of the invention〕

When turning on the phase advance capacitor at startup,
In the past, the capacitor was charged without being charged, but according to this invention, the initial charging of the capacitor is automatically performed, and the capacitor is charged to the steady voltage (peak value of the power supply voltage). After that, the capacitor is inserted and the transition to normal operation is made possible, so there is no large transient current flowing through the capacitor at startup unlike in the conventional case, and the capacitor can be inserted smoothly. Since there is no need to prepare for the current, the overall device capacity can be reduced, which has the advantage of reducing costs.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an example of a method of inputting a phase advance capacitor to be input and connected to an electric power system.
Figure 2 is a waveform diagram showing the waveforms of the signals in each part when the circuit shown in Figure 1 is in normal operation, and Figure 3 is the waveform of the signals in each part when the circuit shown in Figure 1 is in the starting state. 4 is a block diagram showing one embodiment of the present invention; FIG. 5 is a waveform diagram showing signals of various parts of the circuit of FIG. 4 during initial charging operation;
It is. Symbol explanation, 1... Breaker, 2... Main transformer,
3...Series reactor, 4...Phase advance capacitor,
5... Thyristor switch, 6... Synchronous transformer, 9... Circuit breaker closing command generator, 10, 11...
...Voltage detector, 12, 13...Comparator, 1
4...Timer, 15, 16...Flip-flop, 17...AND gate, 18, 19...Monostable multivibrator, 20...NOT gate,
21... Firing angle adjuster, 22... Pulse amplifier.

Claims (1)

[Claims] 1. A series circuit consisting of a circuit breaker, a series reactor, a phase advancing capacitor for phase adjustment, and a thyristor switch consisting of a plurality of thyristors connected in anti-parallel is connected to a power system as a load, and the circuit is interrupted. In the initial charging control device for the phase advance capacitor in a phase modifier, the phase advance capacitor is connected to and disconnected from the load by turning on and off the thyristor switch after the thyristor switch is turned on. time limit means 14 that detects the closing of the circuit breaker and generates a time limit output after a certain period of time; and signal holding means that holds the time limit output when it is input and continues to output the first signal thereafter. 15, a voltage monitoring means 13 that monitors the voltage across the thyristor switch and outputs a second signal only during a period when the periodically changing voltage is below a predetermined value;
Monitoring the voltage waveform of the power system as the load,
a firing angle command means 21 for outputting a third signal representing a predetermined firing phase angle in the waveform; an AND circuit 17 for calculating and outputting the AND of the first to third signals; Charging means 18, 16, 20, 19 for turning on the thyristor switch for a predetermined period of time when the AND output from the product circuit is input, charging the capacitor during that time, and then turning off the thyristor switch. The charging means repeatedly charges the capacitor as the AND output from the AND circuit is intermittently output, and when the charging voltage exceeds a predetermined limit, this is detected. 1. An initial charge control device for a phase advance capacitor, comprising: charge voltage monitoring means 12 for resetting said signal holding means 15 and turning off said first signal.