JPH0670446A - Digital ground fault phase selection relay - Google Patents

Abstract

(57) [Abstract] [Purpose] In a digital ground fault phase selection relay, prevent a normal phase malfunction when eliminating an accident without delaying the operation time. [Structure] An undervoltage detection element (| Vm that detects a ground fault phase that has occurred in the power system when the three-phase voltage of the power system is introduced and the magnitude of the voltage is below a predetermined level for each phase.
.Vertline..ltoreq.Vk) and an overvoltage detection element (.vertline.Vm-n.vertline..gtoreq.K.VN) that determines that the phase voltage of the undervoltage detection element is equal to or higher than a predetermined level before a predetermined time, and is a sound phase When the overvoltage detecting element is in operation, the operation output of the undervoltage detecting element is invalidated for a certain period.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital ground fault phase selection relay which is applied to a ground fault phase selection for a single phase trip by detecting a voltage drop at the time of an accident occurring in a power system.

[0002]

2. Description of the Related Art In consideration of single-phase reclosing, one-line ground fault, the circuit breaker is tripped only in the fault phase. In the so-called single-phase reclosing system, an undervoltage relay is provided as a ground fault phase selection relay, and one line At the time of a ground fault, the three-phase trip circuit is locked. Therefore, the undervoltage relay as the ground fault phase selection relay is required to detect at high speed with respect to other relays.

The configuration of the digital undervoltage relay uses a sample hold circuit, an A / D conversion circuit, a digital processor, etc., as shown in "Protective Relay Engineering" P-101 published by the Institute of Electrical Engineers of Japan. It is a relay that calculates the amplitude of the voltage by using the voltage data as the sampled digital amount and outputs the operation when the calculated value is equal to or lower than the set value level. The configuration of the digital relay, the voltage calculation method, and the like are well known in the art, and are not the main object of the present invention, and will not be described further.

[0004]

When an undervoltage relay is applied as a phase selection relay for a single-phase trip of a resistance grounding system, a single-phase reclosing is successful and a sudden phase change occurs when the accident is eliminated, resulting in a single-phase reclosing. Nevertheless, the undervoltage relay of the sound phase may malfunction. The three-phase voltage vector at the time of one-line ground fault in the resistance grounding system is shown in "Protective relay engineering" P-43 published by the Institute of Electrical Engineers of Japan, as shown in P-43. ), The phase changes from before the accident because it is lifted by the zero-phase voltage. Therefore, when the accident is eliminated and the original phase relationship is restored, a sudden phase change occurs. This is shown in FIG. 4 as a voltage waveform.

When such a voltage waveform is input to the relay, the output of the analog filter has a reduced amplitude of the voltage immediately after the accident is removed as shown in FIG. 5 (part A in the same figure), and simply detects an undervoltage. In the undervoltage relay according to the related art, the undervoltage relay malfunctions for a moment despite the sound phase, and it is determined to be the accident phase. At this time, if the main relay related to the trip is not restored, the circuit breaker will be tripped due to the malfunction of the undervoltage relay of the sound phase. One of the means to prevent the malfunction of this undervoltage relay is to carry out the operation verification multiple times.
According to this method, there is a drawback that the operation time becomes slow and it becomes impossible to satisfy the above-mentioned required specifications of high-speed operation.

The present invention has been made in order to solve the above problems, and provides a digital ground fault phase selection relay capable of preventing a malfunction of a sound phase when eliminating an accident without delaying an operation time. It is an object.

[0007]

In order to achieve the above object, according to the present invention, the voltage of the power system is sampled at a constant cycle, the sampling value is converted from analog to digital, and then generated in the power system using this digital data. In a digital ground fault phase selection relay applied as a phase selection for a ground fault, the undervoltage relay of a sound phase at the time of fault removal is detected by detecting that the voltage amplitude value of the sound phase during the accident is larger than a predetermined level. It is configured to prevent the malfunction of.

[0008]

Since the voltage amplitude value during an accident is detected, the sound phase malfunction can be prevented when the accident is eliminated without delaying the operation time.

[0009]

Embodiments will be described below with reference to the drawings. Figure 1
FIG. 3 is a block diagram showing an embodiment of the present invention. FIG. 1 is constructed for each phase. In this figure, | Vm | ≦ Vk ………………………………………… (1) is determined by the conventional technique. The operation formula of the undervoltage relay is shown. Vk is a settling value, and | Vm | is an amplitude value of the voltage at the latest sampling time. Moreover, | Vm-n | ≧ K · VN ………………………………………………………………………………………………………………………………………………………………………………………………………… （……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………. That is, the rise of the healthy phase voltage at the time of a one-line ground fault in the resistance grounding system is detected. here,
.Vertline.Vm-n.vertline. Indicates a voltage amplitude value n samplings before the latest sampling time, K indicates a constant, and VN indicates a rated voltage level. K should be set to 1.2, for example, as long as it can detect an increase in the sound phase voltage at the time of a one-line ground fault.

According to this configuration, when an accident occurs, the accident phase is
It does not hold because the left side of equation (2) is the rated voltage level,
The operation is output according to the equation (1). On the other hand, the healthy phase is (1)
The expression itself does not work. Also, since the sound phase voltage during an accident at the time of a one-line ground fault is higher than the rated voltage, formula (2) is established, and the malfunction of formula (1) at the time of eliminating the accident is blocked by formula (2). There is no erroneous output of the sound phase.
During a two-wire short-circuit or a two-wire ground fault, the phase of the healthy phase voltage does not change much, and the sudden phase change at the time of eliminating the accident is slight (1).
The formula does not malfunction.

In this embodiment, since it is configured to determine whether the voltage amplitude value of the undervoltage relay in the same phase as the relevant phase during the accident is larger than a predetermined value, the operation time performance at the time of occurrence of the accident is improved. While maintaining the same level as before, it is possible to prevent the malfunction of the undervoltage relay of the sound phase due to the sudden phase change at the time of eliminating the accident.

In the first embodiment, it is judged whether or not the voltage amplitude value of the undervoltage relay in phase with the relevant phase during the accident is larger than a predetermined value. However, the second embodiment shown below is as follows: It is configured to determine whether the voltage amplitude value of the other phase is larger than a predetermined value with respect to the relevant phase of the undervoltage relay. A block diagram of the first embodiment is shown in FIG. In FIG. 2, | Vam | ≦ Vk …………………………………… (3) shows the operation formula of the A-phase undervoltage relay determined by the prior art. Where Vk is the set value and | Vam | is the amplitude value of the A-phase voltage at the latest sampling time. Also, | Vbm-n | ≧ K ・ VN ………………………………………… (4) | Vcm-n ｜ ≧ K ・ VN …………………………………… (5) is an equation for determining whether or not the B-phase and C-phase voltage amplitude values during the accident are above a predetermined level. Here, A
Although the phases are described, the same applies to the B and C phases.
The accidental A and C phase voltages are used for the B phase, and the accidental A and B phase voltages are used for the C phase.

In this configuration, when an accident occurs, the accident phase is
Similar to the first embodiment, the operation output is performed according to the equation (3). However, since the equation (4) or (5) is satisfied and the operation output is restored when n samplings have elapsed from the occurrence of the accident, an off-delay timer is provided. This off-delay timer may not be set if it is unnecessary. With regard to the sound phase at the time of eliminating the accident, the same effect as that of the first embodiment is obtained.

In the above first and second embodiments,
Each phase voltage is used as the voltage during an accident and is set to 10. However, in the third embodiment, it is configured to determine whether or not the level of the zero phase voltage is equal to or higher than a predetermined level. A block diagram of the third embodiment is shown in FIG. In FIG. 3, | V0m-n | ≧ Vk …………………………………… (6) is an equation for detecting the zero-phase voltage level during an accident. As described in the first embodiment, since the malfunction of the undervoltage relay of the sound phase at the time of eliminating the accident becomes a problem at the time of the one-line ground fault, the one-line ground fault is detected by the equation (6). The reason for setting the off-delay timer is the same as in the second embodiment. Also in the third embodiment, the same effect as that of the first embodiment can be expected. In addition, in the above embodiment, the undervoltage relay in the case where only the voltage is input is shown, but the current compensation type may have the same configuration.

[0015]

As described above, according to the present invention, in a digital undervoltage relay applied as a phase selection relay for a single-phase trip, it is confirmed that the voltage amplitude value during an accident is larger than a predetermined level. Since the detection is performed, it is possible to prevent the malfunction of the undervoltage relay of the sound phase at the time of eliminating the accident without delaying the operation time.

[Brief description of drawings]

FIG. 1 is a block diagram of an undervoltage relay according to the present invention.

FIG. 2 is a block diagram for realizing a second embodiment.

FIG. 3 is a block diagram for realizing a third embodiment.

FIG. 4 is a voltage waveform of a sound phase at the time of a one-line ground fault and at the time of eliminating the accident.

5 is a diagram showing an analog filter output waveform to which the voltage waveform of FIG. 4 is input.

[Explanation of symbols]

Vm Amplitude value of voltage at the latest sampling point Vk Voltage settling value at the latest sampling point Vm-n Amplitude value of voltage before n sampling from the latest sampling point Vam Amplitude value of phase A voltage at the latest sampling point

Claims (1)

[Claims] 1. An undervoltage detection element for detecting a ground fault phase that has occurred in a power system when a three-phase voltage of the power system is introduced and the magnitude of the voltage is less than a predetermined level for each phase. The undervoltage detection element has an overvoltage detection element that operates at a predetermined level or more before a predetermined time of the undervoltage detection element and determines that it is in a healthy phase, and detects the undervoltage for a certain period when the overvoltage detection element is operating. A digital ground fault phase selection relay characterized by nullifying the operation output of an element.