JPS6215009B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a device for detecting disconnection of a three-phase line in a power system. In the so-called power supply end detection method for detecting disconnections in this type of three-phase line at a substation, there have already been proposals for a method that detects changes in phase current or line current before and after the disconnection, and determines a disconnection accident based on this. According to this, a disconnection can be detected because the current flowing in the disconnected phase is lower than that in the healthy phase, but after conducting various experiments, we found that the current decreases even when the disconnection occurs. Therefore, it has been found that it is not possible to accurately determine a disconnection accident just by knowing the change in current. That is, when a current with a poor power factor flows, such as when starting a motor, the pen oscilloscope record of the absolute value of each phase current shows a phenomenon in which the current instantaneously decreases in only one phase. When such an instantaneous decrease phenomenon occurs, there is a possibility that the relay will be determined to be disconnected, and in order to avoid such erroneous determinations, it is necessary to set the relay sensitivity to the worst value of this phenomenon. . As another example, when a transformer, motor, etc. is turned on, a phenomenon occurs in which the current in one phase decreases and the current in the other two phases increases. Such phenomena are difficult to predict and require actual measurements of instantaneous load fluctuation patterns at various substations. The present invention aims to prevent erroneous detection due to instantaneous load fluctuations when detecting a disconnection from current fluctuations in a substation. In this invention, while the active power seen from the power supply side decreases when one wire is disconnected, the active power decreases during instantaneous load fluctuations, such as when the load increases due to turning on a transformer, when excitation rush current is applied, or when turning on an induction machine load. Knowing that the current is increasing, we constantly measure the power change on the power supply side, and when the change in active power increases, we lock the device that determines the disconnection according to the change in current, causing the disconnection. This is characterized in that the occurrence is not determined. Now, on a three-phase line, when a transformer excitation rush flows as an instantaneous load fluctuation, the phase-to-phase voltage between phases a and b (transformer secondary voltage value) Vab, the line current of phases a to c (current transformer When the waveforms of the secondary current values (Ia to Ic) were analyzed, the following results were obtained. In each table below, A is the value before the instantaneous load fluctuation occurs, B is the value during one cycle from when this fluctuation occurred, and C is the value between the 1st cycle and the 2nd cycle. The values are shown respectively. Further, the order indicates a harmonic order, and O indicates a direct current component. Furthermore, the percentage is based on the fundamental wave component being 100.

【table】

【table】

【table】

【table】

【table】

【table】

【table】

【table】

【table】

【table】

【table】

【table】

【table】

【table】

【table】

【table】

【table】

[Table] In general, the active power Pa per cycle is determined by Pa=1/ ^T∫T _O P dt, where P is the instantaneous power and T is one period. Then, each DC component of voltage and current is
Eo, Io, voltage and current of rth harmonic, Er, Ir,
If the phase difference is r, It is expressed as The three-phase active power is obtained from the sum of the active powers of each phase obtained as described above. From the above-mentioned viewpoint, the increase in the transformer secondary power after the instantaneous load fluctuation is calculated from the table above and is approximately 53 W, which clearly shows a tendency for the power to increase. Therefore, when detecting the occurrence of a wire breakage accident from a change in line current, if the change in active power is detected at the same time as the change in current occurs, it will be possible to determine whether the current has changed due to the wire breakage. Alternatively, it becomes possible to determine whether the change is due to instantaneous load fluctuations. Therefore, when the current changes, if the active power decreases at the same time, it is assumed that a disconnection accident has occurred, and the determination device operates, and if it increases, the determination operation of the determination device is locked and the determination result is determined. All you have to do is make sure that it doesn't come out. Embodiments of the invention will be described with reference to the drawings. 1 is a three-phase power supply bus, 2 is a circuit disconnector, 3 is a three-phase distribution line, 4 is a current transformer, 5 is an auxiliary current transformer, 6 is a filter, 7 is a setting circuit, 9 is the absolute value of current a detection circuit for detecting; 10 a detection circuit for detecting current change;
11 is a memory circuit, 12 is a time limit circuit, 13 is an output relay, 14 is its contact, 15 is a trip command circuit for a breaker that disconnects the distribution line 3, and 16 is a circuit when this breaker is opened. This is an auxiliary contact that is closed in conjunction with the The above configuration is for detecting disconnection of the power distribution line 3 from a change in line current. The line current of the distribution line 3 is detected by a current transformer 4,
The current is input to a filter 6 via an auxiliary current transformer 5, where it is converted into the required direct current. Next, the setting circuit 7 sets the line current to a required value, and the detection circuit 9 detects the absolute value of the line current. Then, the detection circuit 10 detects a change from this detected value. When this variation exceeds a preset value, an output is output and the memory circuit 11 is set.
The output produced by this set is the time limit circuit 12
The output relay 13 is operated through the contact 14
Close. The trip command circuit 15 is now completed and the breaker opens the distribution line 3. When the breakdown is tripped, contact 16 is closed and memory circuit 11 is reset. Any method can be used to determine wire breakage based on changes in line current, but as an example, the following determination formula can be used. In other words, the changes in the line currents of phases a, b, and c after disconnection are expressed as △Ia, △Ib, and △, respectively.
Assuming Ic, △Ia/△Ib+△Ic>1 (in the case of a phase disconnection) △Ib/△Ia+△Ic>1 (in the case of b phase disconnection) △Ic/△Ia+△Ib>1 (in the case of c phase disconnection) ). By detecting these relationships, it becomes possible to detect the occurrence of a disconnection. However, according to the invention, in order to detect the change in active power, a ground voltage transformer 21 is inserted into the power supply bus 1, and the output of this transformer is further passed through an auxiliary voltage transformer 22 to detect the absolute change in active power. It is input together with the output of the auxiliary current transformer 5 to a detection circuit 23 that detects the value. The absolute value of the active power detected here is inputted via the setting circuit 24 to the detection circuit 25 that detects a change in power. When the power change detected here exceeds a predetermined value, an output is issued, and this output provides a reset signal to the memory circuit 11. Note that the measurement of active power shown in the figure is based on the two-power meter method based on Blondel's theorem. In the above configuration, if an instantaneous load change occurs on the distribution line 3, and any of the above-mentioned conditions is satisfied due to the change in the line current, the memory circuit 11 is set. However, in this case, since no wire breakage has occurred, the active power increases, so the memory circuit 11 outputs an output from the detection circuit 25 and the memory circuit
will be reset. This prevents the output relay 13 from operating at all. Next, if a disconnection occurs in any phase of the distribution line 3, the active power decreases, so no output is output from the detection circuit 25. Therefore, the detection circuit 10 detects the change in line current due to the disconnection. Even if an output is output from the memory circuit 11 and the memory circuit 11 is set by this,
No reset is performed, the trip command circuit 15 is completed, and the power distribution line 3 is opened. In the above explanation, when the disconnection determination conditions are satisfied and the active power decreases at the same time, a disconnection is determined as if a disconnection accident has occurred.On the other hand, when the active power increases, the determination operation is locked and the determination result is In the previous article, we talked about a configuration in which the disconnection detection function is always locked, and when the disconnection determination conditions are met and at the same time the active power decreases, the lock of the determination operation is released. You may also do so. For that purpose, the detection circuit 1
An AND gate is prepared which receives the outputs of 0 and 25, and the memory circuit 1 is connected to the output of this AND gate.
It may be configured to set the value to 1. As detailed above, according to the present invention, when determining the occurrence of a wire breakage from a change in the current flowing through a line, it is possible to determine whether the change in current is due to a wire breakage or an instantaneous load fluctuation due to a change in active power. Since it is determined whether the wire is connected or not, the occurrence of a wire breakage can be determined without error.

[Brief explanation of the drawing]

The figure is a circuit diagram showing an embodiment of the invention. 3...Three-phase distribution line, 10...Detection circuit for detecting current change, 11...Storage circuit, 23...Detection circuit for detecting the absolute value of active power.

Claims (1)

[Claims] 1. A device for detecting a disconnection based on a change in the current flowing in a power line, a device for detecting an increase in the active power of the power line, and a device for detecting an increase in the active power when the increase in the active power exceeds a certain value. , and a device for stopping a disconnection detection operation. 2. A device that detects a disconnection based on changes in the current flowing in a power line, a device that permanently stops the disconnection detection operation of the device, a device that detects active power of the power line, and an active power detected by the device that is constant. A disconnection detection device for a power line, comprising a device for releasing the stoppage of the disconnection detection operation when the disconnection detection operation decreases beyond a certain value.