JPH0412484B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a reactive power compensator installed in a substation or the like.

FIG. 1 shows a conventional example of this type of reactive power compensator. 1, 1 is the generator of the power plant, 2, 2 is the two-circuit transmission line of the power system, 3, 3 is the disconnector for disconnecting the faulty line, and 4 is the middle point of the power plant, that is, the middle point of the system ( 5 is a reactive power compensator. 6
1 is a power capacitor, 7 is a reactor, and 8 is a current controller, and these three components constitute the main circuit of the reactive power compensator 5. The current controller 8 consists of phase-controlled antiparallel thyristors 8a and 8b, and is connected in series to the reactor 7. 9 is a voltage transformer, and 10 is a voltage detector. The voltage detector 10 outputs a voltage signal (DC) V having a magnitude corresponding to the voltage (effective value) at the intermediate point 4. 11 is an adder which adds the voltage signal V and the voltage reference signal Vref to the indicated polarity, and generates a voltage deviation signal ΔV=Vref−V
is supplied to the phase controller 12. The phase controller 12 has a characteristic expressed by a transfer function of K/1+TS, and outputs the voltage deviation signal ΔV multiplied by K. Here, K is a gain and T is a time constant. A gate signal generator 13 generates gate signals for the thyristors 8a and 8b at the phase of the system voltage corresponding to the phase control signals K and ΔV output from the phase controller 12.

That is, the firing phase of the thyristors 8a and 8b is such that the voltage at the midpoint 4 is equal to the voltage reference signal, as shown in FIG.
V=Vref with a size corresponding to the level of Vref
In this case, the leading reactive power Q _C taken by the power capacitor 6 and the lagging reactive power Q _R taken by the reactor 7 are equal, and the reactive power flowing into the main circuit of the reactive power compensator 5 Q _S =Q _C +Q _R is controlled to be zero, and when V > Vref, Q _R > Q _C and reactive power Q _S is controlled to become lagging reactive power, and conversely, when V < Vref If Q _C > Q _R
Thus, the reactive power Q _S is controlled to become the phase-advanced reactive power.

Now, assuming that a three-phase short circuit accident occurs at point F of the two-line power transmission line 2 at time t1 shown in Figure ₃ a and b, the voltage at the intermediate point 4 is about to drop, so
As the phase control signal K・△V increases, the delayed reactive power flowing to the reactor 7 decreases, and the leading reactive power flowing to the power capacitor 6 increases, so that the reactive power Q _S taken by the main circuit becomes The phase advance region shown in FIG. 2 is reached, the voltage drop at the intermediate point 4 is suppressed, and the system is operated stably. On the other hand, the above-mentioned short circuit fault is immediately detected by a protective relay (not shown), and at time t ₂ after several cycles of the grid frequency, the short circuit breakers 3, 3 operate and the faulty line is removed, and the fault line is removed from the intermediate point 4. voltage begins to recover. For this reason, the large phase-advanced reactive power Q _S flowing in the main circuit
= Q _C follows the reactive power Q _O required by the power system, oscillates and decreases, and reaches a relatively low steady-state value.

However, in this conventional device, a power capacitor 6 with a capacity large enough to cope with the maximum power system disturbance that may occur in the power system is prepared, and this is always connected to the power system. Both the reactor 7 and the current controller 8 must have a large capacity equal to the capacity of the power capacitor 6, and since they are also operated in the slow phase region shown in Figure 2, the capacitance is increased accordingly. Since it is necessary to increase the size of Since it is necessary to take lagging phase reactive power corresponding to this leading phase reactive power, there is a drawback that electrical loss is large.

This invention was made to eliminate the above-mentioned conventional drawbacks, and includes a first main circuit that can continuously control reactive power and is always connected to the power grid, and a first main circuit that can control reactive power in stages. When the amount of reactive power required by the power system exceeds the compensation capacity of the first main circuit, the power system is divided into a second main circuit that is turned on, and in the case of overcompensation, the second main circuit is switched on for a certain period of time. The purpose of the present invention is to provide a reactive power compensator that can greatly reduce the cost of the main circuit and the electrical loss during steady state compared to the conventional system by having a configuration in which the power is released in stages as the time passes. shall be.

An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 4, 20 is a first main circuit, and 30 is a second main circuit, both of which are inserted in parallel to the intermediate point 4 of the power system explained in FIG. The first main circuit 20 has a configuration in which a power capacitor 23 is connected in parallel to a circuit including a reactor 21 and a current controller 22 for controlling the current flowing therein. It shares 1/4 of the total compensation capacity ±Qsmax imposed on the compensation device (however, the + and - signs represent the leading and lagging components of the reactive power, respectively). For this reason, the maximum capacity of the power capacitor 23 is selected to be +0.25Qsmax. The current controller 22 sets the current range corresponding to -0.25Qsmax (continuous rating) of the slow phase capacity of the reactor 21 as the control range (steady state control range) during continuous rating, and sets the current range corresponding to -0.25Qsmax (continuous rating) of the slow phase capacity of the reactor 21 as the control range (steady state control range) for short time ratings.
It has the characteristic that it can be controlled up to the current range corresponding to Qsmax (short-time rating).

The second main circuit 30 is a capacitor bank comprising power capacitors 31, 32 and 33 whose maximum capacity is equal to that of the power capacitor 23, each capacitor 31, 32 and 33 connected to a switch 34, 35 and 33, respectively. It is possible to connect to the intermediate point 4 via.

41 is a dead band circuit device, and the current controller 2
The dead band width is set to the value V _D of the phase control signal K・△V which gives the upper limit value of the steady state control range of No. 2.
>V _D , the excess signal ε=K・△V−V _D
Output. 42 is an integrator and the excess signal ε
is integrated and sent to the comparator 43. The comparator 43 outputs an output when the input integral value ∫εdt reaches a predetermined value E, and the output is input to the controller 44 and simultaneously supplied to the integrator 42 as a reset signal. The controller 44 of this embodiment is composed of a shift register, and the output of the comparator 43 is inputted to the UP terminal of the controller 44. Each time the input is received, the output is shifted up by one step and the output terminals A ₁ , A ₁₀ and Capacitor input signals S ₃₁ , S ₃₂ and S ₃₃ are sequentially output from A ₁₀₀ .
The switches 34, 35 and 36 are closed by the capacitor input signals S ₃₁ , S ₃₂ and S ₃₃ , respectively. 41~
44 constitutes a control circuit of the second main circuit. 51
is a current transformer that detects the current flowing through the reactor 21 and inputs it to the overload detector 52. Overload detector 52 receives the output of current transformer 51,
When the output is other than the continuous rated current value of the thyristors 22a and 22b, a capacitor closing release signal Soff is outputted at predetermined intervals. This signal Soff is input to the down terminal of the controller 44, which is a shift register. The controller 44 is a capacitor closing signal.
Soff causes the shift down one step at a time, and the outputs of the output terminals A ₁ , A ₁₀ and A ₁₀₀ are sequentially reduced. 51
52 constitute a control amount monitoring circuit. In addition, the first
The main circuit is composed of 9 to 13.

It is continuously controlled by a control circuit in the same manner as described with respect to FIG.

Next, the operation of this device will be explained with reference to FIGS. 5a and 5b.

While the voltage at the intermediate point 4 is the voltage V corresponding to the voltage reference value Vref (state before time t ₁ ), the reactor 21 and capacitor 23 each have Q _R =
A lagging reactive power of 0.25Qsmax and a leading reactive power of Q _C =0.25Qsmax flow, and the overall reactive power Q _S is zero. Furthermore, for voltage fluctuations at the intermediate point 4 in the range of V _D > △V (however, Vref < V), the magnitude of the excess signal ε is zero, so the reactive power of the first main circuit is controlled by the first control circuits 9 to 13 in the range of 0 to +0.25Qsmax in accordance with the magnitude of the phase control signal K·ΔV, and the intermediate point 4
maintain the voltage constant. In other words, in response to voltage fluctuations caused by minute disturbances in the power grid, the capacitor bank of the second main circuit is not input to the power grid;
The problem is dealt with using only the first main circuit.

At time _t1 , the three-phase short circuit described above occurs, and in order to suppress voltage fluctuations caused by this large-scale disturbance in the power system, the power system requires phase-advanced reactive power Q _O shown by the dotted line in Figure 5a. Assume that Due to this systematic disturbance, the magnitude of the phase control signal K·ΔV exceeds the dead band width VD at time _t2 , and an excess signal ε is output.

When the output ∫εdt of the integrator 28 reaches the set value E at time _t2 , that is, when the reactive power flowing to the first main circuit reaches +0.25Qsmax, the controller 44 outputs the capacitor closing signal _S31 . , the switch 34 is closed and the capacitor 31 is connected to the intermediate point 4. Even if the capacitor 31 is connected to the intermediate point 4, since the excess signal ε exists, the capacitor input signal is subsequently
_S32 is output and the capacitor 32 is connected to the power system at time _t3 , and for the same reason, the capacitor input signal S33 is output and the capacitor ₃₃ is connected to the power system at time _t4.
is connected to intermediate point 4. In this way, the reactive power Q _O (phase advance) required by the power system to maintain the voltage at the intermediate point 4 is compensated by the capacitors 23, 31 to 33 of the first main circuit and the second main circuit.
On the other hand, the three-phase short circuit described above is immediately detected by a protective relay (not shown). Assuming that the disconnectors 3, 3 open as described above at time _t5 and the faulty line is removed, the voltage at the intermediate point 4 begins to recover from time _t5 . For this reason, the reactive power Q _O (phase advance) decreases oscillatingly and settles down to a relatively low normal value as shown in FIG. 5a.

Even if the reactive power Q _O starts to decrease, the second main circuit 30 remains connected to the intermediate point 4, so that the phase-advanced reactive power of Qsmax−Q _O becomes surplus, so this surplus is canceled out. Therefore, as shown in FIG. 5b, the circuit of the reactor 21 and the current controller 22 receives a delayed phase reactive power exceeding the rated value, resulting in an overload state, but the overload state is detected by the overload detector 52. The capacitor closing signal Soff is input to the controller 44 at time _t6 , which is a predetermined time _T0 after time _t5 .

As a result, the capacitor input signal S ₃₃ disappears, the switch 36 opens, and the capacitor 33 connects to the intermediate point 4.
be separated from Thereafter, in the same manner, the excess capacitor of the second main circuit 30 is disconnected every predetermined period of time _TO until an overload condition does not occur, and the reactor 21 and current controller 22 are released from the overload condition. Ru.

The current controller 22 controls the delay phase reactive power from 0 to -
The period of the overload state during which it is necessary to control the current in the range corresponding to the range of Qsmax is only the period when the second main circuit 30 is connected to the power system, and this period is generally short. Second main circuit 3
During steady state when 0 is not turned on, current controller 2
Since the control range of No. 2 is a current range corresponding to the range of slow phase reactive power from 0 to 0.25Qsmax, the current controller 22 and reactor 21 are set as continuous ratings.
It is sufficient to have a current capacity corresponding to a slow phase reactive power of 0.25Qsmax, and a current capacity corresponding to a slow phase reactive power of Qsmax as a short-time rating. In addition, since the second main circuit is connected to the intermediate point 4 for a short time as described above, the reactor 21
The period during which the delayed phase reactive power of Qsmax is taken is short, and the reactive power taken during steady state is 0.25Qsmax, so the electrical loss is small.

In this embodiment, even if the second main circuit 30 is connected to the power grid and the reactive power Q _O required by the power grid starts to decrease, the switches 34 to 36 are switched on according to the subsequent attenuation of the reactive power Q _O. Avoid opening and closing, and deal with the attenuation fluctuation by overload operation control of the current controller 22, and release of the second main circuit 30 is caused by the overload state of the circuit between the reactor 21 and the current controller 22. Since this is carried out while monitoring the power system, the effect of suppressing disturbances in the power system is high, and as in the conventional case where the entire compensation range is continuously controlled by the current controller 22, it is possible to reduce the oscillation of the reactive power _QO . On the other hand, a compensation effect that responds smoothly and quickly can be obtained. In this way, the second
The main circuit 30 is not released following fluctuations in the reactive power _QO , but is released when the reactive power _QO begins to settle down to a steady value, so the switches 34 to 36 Since it is sufficient that the circuit closes at a high speed and the circuit opening speed may be low, the response time is severely restricted, and a lower cost can be used.

In the above embodiment, the reactive power compensation amount of the first main circuit 20 is controlled by the thyristors 22a and 22b inserted on the reactor 21 side, but as shown in FIG. Alternatively, a current controller 24 consisting of thyristors 24a and 24b may be inserted so that both current controllers 22 and 24 control the compensation amount.

Further, the control amount monitoring circuit may be any circuit as long as it has a function of detecting the accumulation state of the control amount of the current controller 22.

As described above, according to the present invention, in addition to the first main circuit that includes a reactor and a power capacitor, is capable of continuously controlling reactive power from a slow phase region to a fast phase region, and is always connected to the power system. , a second main circuit is provided which is composed of a plurality of power capacitors and can be turned on and released from the power system in stages, and when the second main circuit is turned on, the reactive power required by the power system is met. By configuring this to be carried out when the compensation range of the first main circuit is exceeded, the first main circuit that is always connected to the power system has the maximum compensation capacity necessary to stabilize the power system. It is only necessary to share the fractional capacity, and the reactor and current controller only need to have a short-time overload rating that corresponds to the maximum compensation capacity above, so the reactor and current controller have a smaller capacity than before. In addition to significantly reducing the electrical loss during steady state, the attenuation fluctuations in reactive power are dealt with by overload operation of the current controller. Excellent turbulence control effect can be obtained.

[Brief explanation of drawings]

Figure 1 is a block diagram of a conventional reactive power compensator, Figure 2 is a compensation characteristic diagram of the reactive power compensator, and Figures 3A and 3B illustrate the operation of the conventional device during power system disturbances. Diagram 4 to explain
The figure is a block configuration diagram of an embodiment of the reactive power compensator according to the present invention, FIGS. 5a to 5b are diagrams for explaining the operation of the above embodiment, and FIG. FIG. In the figure, 9... voltage transformer, 10... voltage detector, 11... adder, 12... phase controller,
13... Gate signal generator, 20... First main circuit, 21... Reactor, 22, 24... Current controller, 22a, 22b, 24a, 24b... Thyristor, 23... Power capacitor, 30 ...Second main circuit, 31-32...Power capacitor,
34-36... Switch, 41... Dead band circuit device, 42... Integral value, 43... Comparator, 44...
Controller, 51...Current transformer, 52...Overload detector. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A first main circuit that includes a power capacitor, an overload rated reactor, and a current controller and is always connected to the power grid, and a first main circuit that includes one or more power capacitors and that is connected to the power grid via a switch. a second main circuit that can be turned on automatically, a first control circuit that controls the current controller according to the amount of fluctuation in the grid voltage, and a second main circuit that can be turned on when the amount of fluctuation in the grid voltage exceeds a set level; a second control circuit that sends a capacitor closing signal to each corresponding switch of the switch for closing the power capacitor of the second main circuit each time the integral value of the circuit reaches a set value; a controlled variable monitoring circuit that sends a capacitor closing release signal to the second control circuit to gradually release the second main circuit until the current flowing through the current controller falls within the steady state control range of the current controller; A reactive power compensator, wherein the set level corresponds to a steady-state compensation capacity of the first main circuit.