JPH03293922A - Protective relay - Google Patents

Abstract

PURPOSE:To remove unnecessary operation in inrush currents by changing over a phase judgement system by discriminating inrush currents and currents in other quadrants. CONSTITUTION:The magnitude of currents is judged at every phase in the sections of judging means 11-13 for the magnitude of electric waves in the processing of the AND of three phase, phase is judged at every phase in the sections of phase judging means 14-16, the ANDs of the results of the judgements of currents and phase are taken at every phase, and the AND of three phase of the result is taken and output. A three-phase AND system is adopted as a changeover means 22 when the currents of either phase are larger than a set current value, and a three-phase synthetic method is adopted when the currents of either phase are not larger than that. Since the inrush currents of a load transformer are larger than reverse excitation currents, both can be discriminated by bringing the set current value of changeover to 10-20%.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a digital protective relay for protecting a power system.

[Conventional technology]

Figure 2 is a block diagram of the conventional processing method, showing (1) to (3)
) is a means of calculating the magnitude of the current in each phase, (4) to (6
) is a means for calculating the power of each phase, (7) is a means for adding and synthesizing the three-phase currents, (9) is a means for determining the magnitude of the combined current, and (8) is a means for calculating the three-phase current. A means for adding and synthesizing the powers, α-tou, is a means for determining the phase using the combined powers.

Next, the operation will be explained. This element is caused by the fact that even if the power transmission from the electric power company stops on one line, voltage will be generated on the transmission line from other lines, as shown in Figure 3.
To prevent this, a circuit breaker (24) at the network power receiving point
At that time, the network transformer (23) is reversely excited and ti appears to be flowing out, so the reverse power is detected. FIG. 4 shows the phase characteristics of the reverse power elements of the spot network relay. If the capacitor capacity of the cable of the transmission 1i line is small, the phase of the outflowing current will be only the reverse excitation current of the network transformer, and since a lagging current flows in the outflow direction, the phase will be in the third quadrant of Figure 4, and the phase of the cable capacitor will be When the capacitance is large, a leading current flows in the outflow direction, resulting in the fourth quadrant of FIG. If the load contains a capacitor for power factor correction and the load power becomes very small, a leading current flows in the receiving direction, resulting in
Although this is a quadrant, the phase characteristics are designed to have a margin of 3° so that the reverse power element does not operate even if a current with an advance of 90° flows. The phase of the reverse excitation current of the network transformer in the third quadrant of Figure 4 is delayed by about 80 degrees on average for three phases, but there is a delay of 90 degrees by one phase due to the transformer.
''.In order for the reverse power element to operate even in such a case, the decision is made using the combined three-phase power.

Therefore, the processing of the relay is to calculate the magnitude of the current of each phase in the calculation means (11 to (3)), add and synthesize the three phases in the composition means (7), and set the setting value in the determination means (9). Then, calculating means (4) to (6) calculate the power of each phase, combining means (8) adds and combines the three phases, and determining means 01 calculates the magnitude of the power of each phase. It determines whether it is in the operating phase or not, and outputs the operating output based on the AND condition of current and phase.

[ts, n that the invention seeks to solve]

Since the conventional spot network relay is configured as described above, there is a problem in that it may operate when an inrush current flows when the load transformer is turned on. The reason is that the inrush current of the load transformer has a delayed current in the power receiving direction, which is in the first quadrant of Figure 4, but the inrush current contains a lot of second harmonic current, and when three phases are combined, the second harmonic current is As shown in PAVll in Figure 5, the result is a repeating operation and return, so since digital relays perform processing at a constant cycle, only the operation judgment part may be displayed. It is from.

Note that FIG. 5 shows the results of calculating the power in the relay from the actual inrush waveform.

This invention was made to solve the above-mentioned problems, and aims to obtain a relay characteristic that does not operate even when an inrush current of a load transformer flows, while retaining the conventional relay characteristics.

[Means to solve the problem]

The method according to the present invention has two characteristics: the 11 flow value is large, which is a characteristic of the inrush II flow, and the phase is different for each phase, and when looking at each phase, there are operating phase and non-operating phase. The phase determination method is switched depending on the magnitude of the current, so that the inrush does not operate with current.

[Effect]

Switching of the phase determination method in the present invention is performed and processed by distinguishing the inrush current from currents in other quadrants.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, Q is the same three-phase synthesis processing means as before, (21) is the three-phase AND processing means, and O
L1 to 0 are magnitude determination means for determining the magnitude of the current of each phase, 041-Q19 is a phase determination means for determining the phase of each phase, and (22) is a three-phase synthesis processing means am and a three-phase AND This is a switching means for switching the processing of the processing means (21).

Next, the operation will be explained. First, the 3-phase synthesis process is exactly the same as the conventional 0-order 3-phase AND process, in which the current size determination means 0D-0 determines the current size for each phase, and the phase is determined. The phase is determined for each phase in the section between the means and OQ, the current and phase determination results are ANDed for each phase, and the three phases are ANDed and output. The switching means (22) switches between the three-phase combination method and the three-phase AND method depending on the magnitude of the current; if the current of any phase is larger than the set current value, the three-phase AND method is used; If not, use the three-phase synthesis method. The three-phase combination method and the three-phase AND method will give the same result if the current in each phase changes in the same way. Since the capacitor capacitance of is balanced for the three phases, there is no problem with either method. As mentioned above, the reverse excitation current of the network transformer in the third quadrant is unbalanced, but this reverse excitation current is 0.00% of the rated current.
Since the inrush current of the load transformer is very small at 1% to 7% and larger, it is possible to distinguish between the two by setting the switching current value to 10 to 20%. As can be seen in Figure 5, when looking at the inrush current for each phase, one phase has an inactive phase, and none of the three phases are in an active phase, so when looking at the AND condition for each phase, It will definitely become inoperable.

In the above embodiment, the in-rush current was determined based only on the magnitude of the current, but the content ratio of the second harmonic current, which is largely included in the in-rush current, may also be determined.

〔Effect of the invention〕

As described above, according to the present invention, the relay characteristics are equivalent to those of the conventional relay only by switching the processing method, and furthermore, the relay characteristics can be obtained without unnecessary operation due to the inrush current of the load transformer.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a block diagram showing a conventional protective relay, Fig. 3 is a skeleton diagram of spot network power reception, and Fig. 4 is a phase characteristic diagram of a reverse power element. , FIG. 5 is a diagram showing the waveform of the inrush current and the result of power calculation within the relay. In the figure, (to) is the three-phase synthesis processing means, and (21) is the three-phase synthesis processing means.
The phase AND processing means (21) is a switching means. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] A protective relay that receives power from multiple lines and protects spot network power reception that realizes uninterruptible power reception, uses a 3-phase combination method to process small current areas, and a 3-phase AND method to process large current areas, and when power transmission is stopped. A protective relay that is characterized by issuing a command to open a circuit breaker to prevent interference from other lines.