JPH04325824A - Ground fault detector - Google Patents

Abstract

PURPOSE:To prevent erroneous detection of grounding direction by employing a detection signal subjected to vector operation if the zero-phase voltage or current in a distribution line is lower than a set level otherwise employing a detection signal not subjected to vector operation. CONSTITUTION:Zero-phase voltage and current detected from a distribution line are fed through a lowpass filter 1 and an A/D converter 2 to a first level deciding section 3. The first level deciding section 3 compares the detected zero-phase voltage and current with set levels and feeds them through a bandpass filter 4 to a vector operating section 5 if they are lower than the set levels. A subtractor 54 outputs zero-phase voltage and current, from which residual components are removed, to a second level deciding section 6. The second level deciding section 6 outputs the zero-phase voltage and current to an output section 9 if they are lower than set levels otherwise outputs a prestored detection signal, prior to ground fault, through a tap switch 53 to the subtractor 54 and directly to a duration deciding section 7.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ground fault detection device for power distribution lines.

0002

[Prior Art] A conventional ground fault detection device detects a zero-sequence current by adding the currents detected by current transformers installed in each phase of a distribution line, and capacitively couples the ground voltage of each phase. The zero-sequence voltage is detected by taking out the voltage using a capacitor voltage divider and adding each ground voltage using the low-voltage side capacitor. These zero-sequence currents and zero-sequence voltages are input to the zero-sequence current level determination section and the zero-sequence voltage level determination section, and it is determined whether each level is above the threshold level. At some point, an input signal is input to an AND circuit, and a duration determining section detects whether or not the output is longer than a preset time, and when the output is longer than a preset time, it is determined that a ground fault has occurred. In addition, when a ground fault occurs, the phase determination section determines whether the ground fault point is on the load side or the power supply side by checking the phase difference between the zero-sequence current and zero-sequence voltage. was.

0003

[Problems to be Solved by the Invention] Conventional ground fault detection devices produce a slight zero-sequence voltage, so-called residual voltage, due to variations in ground capacitance among the three phases even when no ground fault has occurred on the distribution line. is occurring, and a zero-sequence current, so-called residual current, is also occurring. Residual voltage and residual current due to variations in the characteristics of the three phases of the current transformer and capacitor voltage divider that measure the amount of electricity on the distribution line are added vectorially to the residual amount on the distribution line and are detected. An error had occurred. For this reason, the amount of electricity detected from the distribution line is sampled at a predetermined period, and the sample value detected before the current time and stored in the storage unit is compared with the sample value at the current time, and the remaining Some devices are designed to detect zero-sequence current and zero-sequence voltage that are not affected by components, but when the zero-sequence current and zero-sequence voltage become large, overrange occurs at the input section when converted by the A/D converter. Therefore, a measurement error in the phase angle is caused, and the ground fault direction is likely to be erroneously detected. In addition, when the zero-sequence current and zero-sequence voltage gradually increase, that is, when the value obtained by subtracting the stored sample value from the sample value at the current time is smaller than a predetermined value, as the absolute value increases, However, it could not be detected using conventional methods.

0004

[Means for solving the problem] A detection signal at the current time detected by a zero-sequence voltage detection means and a zero-sequence current detection means provided on the distribution line is detected before the current time, and is stored in a temporary storage unit. In a ground fault detection device that detects a ground fault from a signal obtained by subtracting a detection signal, the magnitude of the zero-sequence voltage and zero-sequence current detected by the zero-sequence voltage detection means and the zero-sequence current detection means and a first level determination section that compares the detection signal stored in the storage section that was detected before the current time from the detection signal at the current time when the first level determination section is below the set value. a vector calculation unit that outputs the obtained signal and outputs a detection signal at the current time when the signal is equal to or greater than a set value; a second level determination unit that compares the output of the vector calculation unit with the set value; A duration determination section that does not output the output when the value is below the set value, measures the duration when the set value is exceeded, and outputs the output when the set time is exceeded; The phase difference is calculated and outputted to the output section.

[0005]

[Function] Therefore, if the zero-sequence voltage or zero-sequence current of the power distribution line is less than the set value, the detection signal that has been subjected to vector calculation is used, and if it is greater than the set value, the detection signal that is not subjected to vector calculation is used to The voltage, zero-sequence current, and phase difference are calculated.

[0006]

[Embodiment] The present invention will be described below with reference to an embodiment shown in FIG. 1 is a low-pass filter that allows only frequency components below 1/2 of the sampling frequency f to pass; 2
3 is an A/D converter that converts the analog signal passed through the low-pass filter 1 into a digital signal. 1 is a level determination unit, 4 is a band pass filter that passes only the fundamental wave component of the signal, 5 is a vector calculation unit that calculates changes in the zero-sequence voltage and zero-sequence current, and 6 is a vector calculation unit that calculates changes in the zero-sequence voltage and zero-sequence current. a second level determination unit that calculates the output using a predetermined algorithm and compares it with a set value; 7 is a duration determination unit that detects the time period in which the second level determination unit 6 exceeds the set value; 8 is zero; A phase difference calculation section 9 calculates the phase difference between the phase voltage and the zero-phase current, and 9 is an output section that outputs the calculation result. The vector calculation unit 5 includes a delay circuit 51, a delay circuit 52, a tap change switch 53, and a subtracter 54. Next, the operation will be explained. Zero-sequence voltage V detected from the distribution line by zero-sequence voltage detection means and zero-sequence current detection means (not shown)
After passing through the low-pass filter 1 , the zero-phase current IO 2 is converted into a digital value by the A/D converter 2 and output to the first level determination section 3 . The first level determination section 3 compares the results calculated by a predetermined algorithm with the set zero-sequence voltage VO2 and zero-sequence current IO2. It is output to each delay circuit 51, 52. The delay circuit 51 of the vector calculation section outputs the zero-sequence voltage and zero-sequence current detected before the current time to the tap change switch 53, and outputs the output of the tap change switch and the output of the first level determination section to the bandpass filter 4. The signal is output to the subtracter 54 through the subtracter 54. The subtracter 54 outputs the zero-sequence voltage and zero-sequence current from which residual components have been removed to the second level determination section 6. The second level determination section determines the zero-sequence voltage, the zero-sequence voltage VO1 set by the zero-sequence current,
When the zero-sequence current is smaller than IO1, it is output to the output section 9,
Do not output the calculation result. When the zero-sequence voltage V0 and the zero-sequence current I0 are larger than the set zero-sequence voltage VO1 and zero-sequence current IO1 in the second level determination section 6, switching is made to the delay circuit 51, the shift register of the delay circuit 52 is stopped, The stored detection signal before the ground fault is output from the tap change switch 53 to the subtracter 54 and also to the duration determination section 7. When the zero-sequence voltage and zero-sequence current continue longer than the set time, the duration determination section 7 outputs the zero-sequence voltage and zero-sequence current to the phase difference calculation section 8,
calculates the phase from the input zero-sequence voltage and zero-sequence current, and outputs the phase, zero-sequence voltage, and zero-sequence current to the output section 9. This state is shown in area A of FIG. That is, zero-sequence voltage V0
is larger than the set zero-sequence voltage VO1 and smaller than VO2, and the zero-sequence current is larger than the set zero-sequence current IO1 and smaller than IO2. Next, the zero-sequence voltage VO and zero-sequence current IO detected from the power distribution line are determined to be the zero-sequence voltage VO2 and zero-sequence current IO2 set in the first level determination section 3.
When it is larger, the subtracter 5 passes from the first level determination section 3 to the tap change switch 51 of the vector calculation section 5.
Output to 4. The subtracter 54 outputs the output of the first level determining section 3 as is to the second level determining section 6. Second
The level determination unit compares the set zero-sequence voltage VO1 and zero-sequence current IO1 with the zero-sequence voltage VO and zero-sequence current IO from the subtracter 54, and maintains the zero-sequence voltage and zero-sequence current from the subtracter. It is output to the time determination section, and when the zero-sequence voltage and zero-sequence current continue for a certain period of time, it is output to the phase difference calculation circuit. The phase difference calculation circuit calculates a phase difference from the zero-sequence voltage and zero-sequence current, and outputs this phase difference, the zero-sequence voltage, and the zero-sequence current to an output section. This state is shown in region B of FIG. That is, this is a case where the zero-sequence voltage VO is larger than the set zero-sequence voltage VO2, and the zero-sequence current IO is larger than the set zero-sequence current IO2. next,
If the zero-sequence voltage VO detected from the distribution line is greater than the set zero-sequence voltage VO1 and smaller than VO2, the zero-sequence current IO
When is larger than the set zero-sequence current IO2, the zero-sequence voltage VO is subjected to vector calculation, and the zero-sequence current IO is outputted to the output section without performing vector calculation. This state is shown in area C of FIG. When the zero-sequence voltage VO is larger than the set zero-sequence voltage VO2 and the zero-sequence current IO is larger than the set zero-sequence current IO1 and smaller than IO2, the zero-sequence voltage VO is not subjected to vector calculation, and the zero-sequence current IO is Performs vector operations and outputs to the output section. The situation is shown in Figure 2.
It is shown in area D of .

[0007]

Effects of the Invention The present invention enables highly reliable detection without erroneous detection over a region where the zero-sequence voltage or zero-sequence voltage of a power distribution line is small to large. Furthermore, if the set values VO2 and IO2 of the first level determination section are set to be higher than the residual zero-sequence voltage and residual zero-sequence current of all distribution lines,
High-sensitivity detection is possible on all feeder poles.

[Brief explanation of drawings]

[Fig. 1] Circuit diagram showing an embodiment of the present invention

[Fig. 2] Diagram for explaining the embodiment of Fig. 1

[Explanation of symbols]

1 Low pass filter 2 A/D converter 3 First level determination section 4 Bandpass filter 5 Vector calculation section 51 Delay circuit 52 Delay circuit 53 Tap change switch 54 Subtractor 6 Second level determination section 7 Duration determination section 8 Phase difference calculation section 9 Output section

Claims (1)

[Claims] [Claim 1] Subtracting a detection signal detected before the current time and stored in a temporary storage unit from a detection signal at the current time detected by a zero-sequence voltage detection means and a zero-sequence current detection means provided on the distribution line. In a ground fault detection device that detects a ground fault from a signal obtained by A signal obtained by subtracting a detection signal stored in the storage unit detected before the current time from the detection signal at the current time when the level judgment unit 1 and the first level judgment unit are below the set value. a vector calculation unit that outputs a detection signal at the current time when it is equal to or greater than a set value; a second level determination unit that compares the output of the vector calculation unit with a set value; A duration determination section that controls the level determination section so as not to output to the output section when the level is below a set value, measures the duration when the level is equal to or greater than the set value, and outputs the output when the set time is exceeded; A ground fault detection device that calculates the phase difference from the phase voltage and zero-sequence current and outputs the phase difference to the output section.