JPH0777485B2 - Protective relay - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Field of Industrial Application) The present invention relates to a protective relay device for protecting a power system and equipment.

(Prior Art) Various types of AC switches are used in which thyristor elements are connected in anti-parallel to control gate signals of the elements. An example in which the magnitude of the current flowing through the inductive load is controlled by this type of AC switch will be briefly described below.

FIG. 3 is a circuit diagram for controlling the current of the single-phase load (reactor) by the AC switch, and the magnitude of the current is controlled by controlling the control angle α of the thyristor. The relationship between the control angle α and the current waveform at this time is as shown in FIG. 4 when α90 °.

As shown in the figure, when α = 90 °, the waveform is almost a sine wave, and the effective current value is the largest, and as α becomes greater than 90 °, the effective value decreases and the magnitude of the current can be controlled. At α90 °, the waveform of i _L has the same positive and negative magnitude and does not include the DC component. Therefore, the magnitudes of the currents flowing through the thyristors T _A and T _B in FIG. 3 are also the same.

Next, the protection of the circuit of FIG. 3 will be described. The protection of this kind of circuit is to detect the magnitude of the current i _L flowing in the reactor L via a current transformer, and if this is an overcurrent, open a breaker (not shown) to cut off the current i _L. It is generally based on current protection. That is, damage to the reactor L or the thyristors T _A and T _B due to overcurrent can be prevented.

(Problems to be Solved by the Invention) As described above, this AC switch is used at a control angle α of 90 °.
i _L continuously becomes the same as in the uncontrolled state, and a transient DC component is generated.

FIG. 5 shows this example, and shows that the magnitudes of the positive and negative wave currents are different. In an extreme case, the waveform shifts to one polarity. In this case, since the currents flowing through the two thyristors T _A and T _B are determined by the polarity of the current i _L , the thyristor T _A is in an overcurrent state more than the thyristor T _B at the current including such a direct current component. .

For example, in the severest case, the average current A flowing in the thyristor T _A when the waveform has one polarity is expressed by the following equation.

However, I _AC : AC effective value On the other hand, the average current B when α = 90 ° is expressed by the following equation.

And the ratio is Therefore, due to the superposition of the direct current component, the average current can be three times or more that in normal operation. However, the magnitude of the alternating current of current i _L has not changed. Therefore, an overcurrent protection relay that responds to the magnitude of an alternating current that is generally used cannot operate and therefore cannot protect the thyristor T _{A from} an overcurrent.

The present invention has been made in view of the above circumstances, and when the control of the AC switch becomes abnormal and one of the thyristors that are antiparallel is overloaded, the current of each thyristor is applied to the protection device. It is an object of the present invention to provide a protective relay device capable of protecting a thyristor by detecting it by the current of a reactor as in the conventional case without introducing it.

[Structure of Invention]

(Means for Solving the Problems) Explaining the configuration for achieving the above object, in the present invention, in a protective relay device for protecting an AC switch, a means for introducing a current flowing through the AC switch, and a positive current of this current. Each time limit overcurrent element responding to each magnitude of the wave and the negative wave, and means for sending a protection output for cutting off the current of the AC switch when any one of these time limit overcurrent elements operates. And consisted of

(Operation) If the control of the AC switch is normal and the control angle α is α90 °, the DC component is not superimposed on the load current, so the average currents of the positive and negative waves are equal. Therefore, if the sensitivity of each anti-time limit overcurrent element that detects a positive wave and a negative wave is set to a predetermined value, each of the anti-time limit overcurrent elements will not operate unnecessarily.

On the other hand, if the control of the AC switch becomes defective for some reason and the control angle α becomes α <90 °, the DC component is superimposed on the load current. Therefore, when the positive DC component is superimposed or the negative DC component is superimposed, the corresponding anti-time limit overcurrent element operates to derive the protection output.

(Examples) Examples will be described below with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of a protective relay device according to the present invention. The AC switch portion in FIG. 1 is the same as that in FIG.

In the figure, CT is an AC device for detecting the current i _{L of the} reactor L and introducing it into a protective relay device R _y (hereinafter referred to as relay R _y ), ACT is an auxiliary current transformer, and the current transformer CT Introduce secondary current to relay R _y . DP and DN are half-wave rectification circuits that take the output of ACT as input and derive the positive wave I _p and negative wave I _n of the secondary current of CT respectively. OCR1 and OCR2 are anti-time-overcurrent elements of the same kind, and each responds to the magnitude of the positive wave I _p and the negative wave I _n . OR is an OR circuit that receives the outputs of OCR1 and OCR2 as input and sends the output (protection output) of relay R _y when one of them operates, opening the circuit breaker (not shown) or thyristor T _A , T _B The gate is blocked to cut off the current flowing through the AC switch.

Next, the operation will be described.

First, the control of the AC switch is normal and the control angle α is α90.
If the load current i _L is DC, the DC component is not superimposed, and as a result, the average currents of the positive wave I _p and the negative wave I _n are equal. Therefore, the response of each overtime element OCR1 and OCR2 is equal. When the operating current is α = 90 °, the effective current value is maximum. The magnitude of the average current at this time And then, by setting a greater extent than the sensitivity of the OCR1 and OCR2 the B _N slightly than it can prevent unnecessary operation of the OCR1, OCR2 during normal operation.

Next, when the control of the AC switch becomes defective for some reason and the control angle α becomes α <90 °, the DC component is superimposed on the load current i _L as described above. For example, when a positive DC component is superposed, the average value current of the positive wave I _p increases, and its magnitude depends on the relationship with the current phase when control failure occurs,
May be greater than B _N.

In this case, the larger the magnitude of the average value current Seinami I _p, a overload for thyristor T _A, requires a rapid protection, responsive to the average value current Seinami I _p The reverse current overcurrent element OCR1 operates faster as the average current increases.
Cut off the current flowing through the AC switch.

Similarly, if a negative DC component is superposed and it is B _N or more in the average value current of the negative wave I _n , the reverse time limit overcurrent element OCR2 operates contrary to the above, and cuts off the current flowing through the AC switch. To do. Here thyristors T _A and T _B of the overload resistance curve (I
-T curve) is known, the currents flowing through the AC switches can be cut off before the thyristors T _A and T _B are damaged by properly selecting the OCR1 and OCR2 anti-time curves so that they can be coordinated. it can.

FIG. 2 is a diagram showing an application example of the protective relay device according to the present invention, which is a case where the protective relay device is used for protection of an AC switch of a reactive power compensator (SVC).

In FIG, BUS power bus, CB is breakers, C is the compensation capacitor, T is trans, L _C compensation reactor, SW AC switch, CT is a current transformer, the R _y is a protective relay device. The reactive power compensator (SVC) controls the reactive power in order to keep the power supply bus voltage constant, but in the example shown in the figure, the magnitude of the current in the compensation reactor L _C is controlled by the AC switch SW.

Also in this case, as in the case of FIG. 1, there is an abnormality in the control angle of the thyristor that constitutes the AC switch SW, and when α <90 °, a DC component current flows in the AC switch, resulting in an antiparallel connection. One of the existing thyristors may be overloaded. Therefore, the current flowing through the compensation reactor L _C is taken into the relay R _y via CT, and the breaker CB is cut off by the protection output similar to that in the case of FIG.

The relay R _y is configured to detect an overcurrent independently for each of the positive wave and the negative wave of the input current. Therefore, for example, even when the effective value of the fundamental wave of the current flowing through the AC switch SW is about the rated current, if the positive or negative current (average current value) becomes large due to the superposition of a large DC component, the protection output CB as shown in the figure
Since the current that flows in the AC switch SW is cut off by opening the relay, if the relay is settled so that protection coordination of the relay and thyristor element can be taken, even in such a case,
It does not damage the thyristors that make up the AC switch.

〔The invention's effect〕

As described above, according to the present invention, the load current through the AC switch is detected, and this is introduced into the anti-time limit overcurrent element that responds to the positive wave and the anti-time limit overcurrent element that responds to the negative wave, Since any one of them operates to judge the control failure of the AC switch to shut off the power supply, the thyristor constituting the AC switch can be protected only by detecting the load current.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of a protective relay device according to the present invention, FIG. 2 is a diagram showing an application example of the protective relay device according to the present invention, and FIG. 3 is a diagram showing an AC switch controlling the current of a reactor. FIG. 4 is a circuit diagram, and FIG. 4 is a diagram for explaining a reactor current when the control angle is α90 °, and FIG. 5 is a diagram for explaining a reactor current when the control angle is α <90 °. T _A , T _B …… Thyristor element, L …… Reactor ACT …… Auxiliary current transformer, DP, DN …… Half-wave rectification circuit OCR1, OCR2 …… Reverse time overcurrent element RT …… Protective relay

Claims (1)

[Claims] 1. A protective relay device for protecting an alternating current switch, in which thyristor elements are connected in antiparallel, from an overcurrent,
Means for introducing a load current flowing in the load connected to the AC switch, a pair of half-wave rectification means for deriving a positive wave current and a negative wave current of the load current, and a pair of half-wave rectification means respectively Reverse current overcurrents that operate when the positive and negative wave currents are input and the load current when the control angle of the AC switch is 90 ° is greater than the set value that exceeds the magnitude of the positive and negative wave currents. A protective relay device comprising: an element; and a means for sending a protective output for cutting off the current of the AC switch when any one of the anti-time-overcurrent elements operates.