JP2008020322A - Device and method for detecting short-circuit of electrical installation - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately determine short-circuit of an electrical installation even when a phase advance capacitor installation for improving power factor is installed in the electrical installation. <P>SOLUTION: This device applies an alternating voltage of variable frequency generated in an alternating voltage generator 14 from a detection probe 13 to two phases of the electrical installation and detects current flowing into the electrical installation by applying of the alternating voltage of variable frequency. An impedance display part 16 calculates and displays impedance of the electrical installation from the current flowing into the electrical installation and the applied alternating voltage. A checker changes the frequency of the alternating current generated in the alternating voltage generator 14 so that the impedance of the electrical installation should be maximum with a frequency variable device 15, and determines whether or not the electrical installation might be short-circuited based on the maximum value of the impedance. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a short circuit detection device and method for detecting a short circuit of an electrical facility in a power receiving / distributing facility, for example.

  The ground fault state of the electrical equipment in the power distribution facility can be easily detected by a commercially available “insulation resistance meter”. In an insulation resistance meter, a DC voltage is applied to electrical equipment to measure the flowing current, and the applied DC voltage is divided by the measured current to measure the insulation resistance of the electrical equipment. Such an insulation resistance meter cannot detect the short-circuit state of the electrical equipment. This is because the insulation resistance meter detects a direct current by applying a direct current voltage to detect an insulation resistance of the electrical equipment.

  That is, in order to detect the short-circuit state between the phases of the electrical equipment, since the transformer and the coil of the measuring instrument are connected between the phases, the AC impedance ωL is detected. However, in DC, ω = 0. This is because the impedance ωL between the phases is almost zero even if the electrical equipment is not in a short-circuited state and is detected as a short-circuited state. Here, ω is the angular frequency of the alternating current, and L is the inductance of the coil.

Therefore, in order to detect the short-circuit state of the electrical equipment, power is applied to the electrical equipment using a withstand voltage test apparatus capable of generating an alternating current of commercial frequency. As an AC electrical circuit short-circuit detection device suitable for circuit inspection work in power receiving and distribution equipment and AC electrical circuits with a large number of feeders, it has an impedance used for short-circuit detection and an indicator lamp (or buzzer) with a rectifier. Connect the power supply to the AC electrical circuit as a power supply for short circuit detection, connect the indicator lamp with rectifier in parallel with the AC electrical circuit, and if the AC circuit is not short-circuited, the voltage is applied to the rectifier and the indicator lamp lights up. In the case of short-circuiting, there is one in which the voltage is not applied to the rectifier and the indicator lamp is turned off, and the presence or absence of a short-circuit can be determined through this indicator lamp (for example, see Patent Document 1).
JP-A-9-218234

  However, the pressure test apparatus requires a power supply of commercial frequency, and the apparatus is heavy and not easy to carry in. Further, the power supply of commercial frequency is required even in the case of Patent Document 1. Furthermore, when a phase advance capacitor equipment for power factor improvement is installed in the electrical equipment, the impedance ωL of the coil is canceled out and the impedance of the electrical equipment becomes a low value. Detection becomes difficult.

  For example, a phase-advancing capacitor facility for power factor improvement has a capacitor capacity of about 15% of the power receiving capacity. Therefore, in an electric facility with a power receiving capacity of 1000 kVA, a low value of 0.7 kΩ is detected as the impedance of the phase-advancing capacitor. The It is difficult to determine whether this value indicates a short circuit state.

For example, when the short circuit resistance value on the low voltage side of the light transformer is about 1Ω, the resistance value seen from the high voltage side of the light transformer is the square of the voltage ratio ({(6600) / 210} ² = 990 Magnifying power) is 990Ω. In addition, when the two phases on the low voltage side of the power transformer are short-circuited, the detected impedance value varies greatly depending on the power receiving capacity and the short-circuit resistance value of the electrical equipment.

  In reality, even if the two phases on the low-voltage side of the power transformer are completely short-circuited, two phases (for example, between ab and bc phases) of the three phases (a, b, and c) on the high-voltage side ) Is 0.5 to 10 kΩ, and the remaining one phase (for example, between a and c phases) fluctuates significantly as 1 to 30 kΩ, and whether the detected value represents the impedance of a healthy phase advance capacitor, It is impossible to judge whether a two-phase short circuit is indicated on the low-pressure side.

  An object of the present invention is to provide an electrical equipment short-circuit detection device and method that can accurately determine a short circuit of an electrical equipment even when a phase advance capacitor equipment for power factor improvement is installed in the electrical equipment. is there.

  The short-circuit detection device for electrical equipment according to the invention of claim 1 imposes an alternating voltage generator for generating an alternating voltage of variable frequency and an alternating voltage of a variable frequency generated by the alternating voltage generator on two phases of the electrical equipment. And a detection probe for detecting a current flowing through the electrical equipment by applying a variable frequency alternating voltage, and a current flowing through the electrical equipment by applying a variable frequency alternating voltage applied from the detection probe. An impedance display unit that calculates and displays the impedance of the electrical equipment from the supplied AC voltage, and a variable frequency for changing the frequency of the AC voltage generated by the AC voltage generator so that the impedance of the electrical equipment is maximized And an apparatus.

  According to a second aspect of the present invention, there is provided a method for detecting a short circuit in an electrical equipment, wherein an AC voltage having a variable frequency is applied to two phases of the electrical equipment, and an electric current applied to the electrical equipment is applied by applying an AC voltage having a variable frequency. Calculate the impedance of the electrical equipment from the AC voltage, change the frequency of the AC voltage so that the calculated impedance of the electrical equipment is maximized, obtain the maximum value of the impedance of the electrical equipment, and obtain the electrical equipment A short circuit of the electrical equipment is detected based on a maximum value of the impedance.

  According to the present invention, the presence or absence of a short circuit in an electrical facility can be detected quickly and easily before energization.・ We can prevent damage. In particular, there is a high possibility of a short circuit occurring in an electrical facility after a large earthquake, and the present invention is indispensable for detecting the occurrence of the short circuit when energizing the electrical facility after the earthquake.

  FIG. 1 is a configuration diagram of a short-circuit detection apparatus for electrical equipment according to an embodiment of the present invention. The short-circuit detection device includes a detection device main body 11, a DC power supply device 12 that supplies measurement power to the detection device main body 11, and a detection probe 13 for measuring the impedance between each phase of the electrical equipment. And the detection apparatus main body 11 displays the alternating voltage generator 14 which generate | occur | produces alternating voltage based on the power supply for measurement from the direct current power supply 12, the frequency variable apparatus 15 which changes the frequency of alternating voltage, and the impedance of electrical equipment. The impedance display unit 16 is configured to include a frequency adjustment knob 17 for continuously changing the frequency, and a display magnification adjustment knob 18 for changing the magnification of the impedance display.

  The AC voltage generator 14 receives the DC voltage from the DC power supply device 12 and generates an AC voltage having a frequency specified by the frequency variable device 15. As the DC power supply device 12, a dry cell or a small battery is used in consideration of portability. The variable frequency AC voltage generated by the AC voltage generator 14 is applied to two phases of the electrical equipment from the detection probe 13 via the impedance display unit 16. Then, the detection probe 13 detects a current flowing through the electrical equipment by applying an AC voltage having a variable frequency and inputs the current to the impedance display unit 16.

  The impedance display unit 16 calculates and displays the impedance of the electrical equipment from the current flowing through the electrical equipment detected by the detection probe 13 and the applied AC voltage. The impedance displayed on the impedance display section 16 can be adjusted in display magnification by a display magnification knob 18, and the frequency of the frequency variable device 15 is adjusted by a frequency change knob 17 to be applied to electric equipment. The frequency of AC voltage can be adjusted. In the embodiment of the present invention, the frequency change knob 17 is operated so that the impedance displayed on the impedance display unit 16 is maximized, and whether or not a short circuit has occurred in the electrical equipment based on the maximum impedance value. Will be judged.

  FIG. 2 is an equivalent circuit diagram of an electrical facility having a phase advance capacitor facility. In FIG. 2, C is the capacity of the phase advance capacitor equipment of the electrical equipment (capacity between the two phases of the electrical equipment), and L is the inductance on the voltage application side of the transformer (usually the voltage on the high voltage side is applied from the high voltage side). , R is an equivalent insulation resistance. In FIG. 2, the ground capacitance such as a cable is ignored. This is because the capacitance to ground such as a cable is generally smaller than the capacitance C of the phase advance capacitor.

  For such electrical equipment, the current I flowing when the AC voltage V is applied from the short-circuit detection device is represented by the following equation, when the phase-advancing capacitor current IC, the inductance current IL, and the insulation resistance current IR are: It is shown by the formula (1).

I = IC + IL + LR = (jωC + 1 / jωL + 1 / R) V
= {1 / R + (1 −ω ² LC) / jωL} V (1)
Here, at the complete resonance frequency ω (ω ² = 1 / LC), the equation (1) becomes V / I = R, and only the insulation resistance R of the electrical equipment can be detected. In other words, the impedance of the electrical equipment is maximized at the complete resonance frequency ω (ω ² = 1 / LC), and is not affected by the capacitance C of the phase advance capacitor equipment and the inductance L of the transformer coil or the like. Accordingly, since the current flowing through the insulation resistance R can be measured when the impedance is maximum, it can be accurately determined whether or not a short circuit has occurred.

  FIG. 3 is a flowchart showing an example of the steps of the electrical equipment short-circuit detection method according to the embodiment of the present invention. First, the detection probe is connected to any two phases on the high voltage side of the electrical equipment to be inspected (S1), and an AC voltage with a variable frequency is applied (S2). A current flowing through the electrical equipment is detected by applying an AC voltage having a variable frequency (S3), and the impedance of the electrical equipment is calculated and displayed from the detected current and the applied AC voltage (S4). The inspector obtains the maximum impedance value of the electrical equipment by changing the frequency of the AC voltage so that the displayed impedance is maximized (S5), and the electrical equipment is based on the obtained maximum impedance value of the electrical equipment. Is detected (S6).

Next, Table 1 shows an example of a test result obtained by performing a short circuit detection by simulating a short circuit with actual electrical equipment using the short circuit detection device according to the embodiment of the present invention. Table 1 shows the test results of a 675 kVA A building electrical installation with a phase advance capacitor.

  As a short circuit simulation, there is no short circuit (No. 1), two phase short circuit on the high voltage side of the transformer (No. 2), short circuit on the low voltage side of the light transformer (No. 3), two phases on the low voltage side of the power transformer (Blue red) Short circuit (No. 4) was performed in four ways, and the detection phase was measured on the high voltage side of the transformer.

  First, in the case of no short circuit (No. 1), the maximum impedance between the blue-white two phases on the high-voltage side is 10 kΩ when the frequency is 10 Hz, and each of blue-red and red-white two on the high-voltage side. The maximum impedance between the phases was 8 kΩ. Since the electric equipment has the phase advance capacitor, it can be determined that the frequency 10 Hz is a resonance frequency between the capacitance C of the phase advance capacitor and the inductance L of the coil such as a transformer. The maximum impedance 10 kΩ between the blue-white two phases is the insulation resistance value between the blue-white two phases. Similarly, the maximum impedance 8 kΩ between the two phases blue-red and red-white is blue-red, red. -It can be judged that it is the insulation resistance value between each two phases of white. Since all the insulation resistance values are large values, it can be determined that no short circuit has occurred.

  Next, in the case of a two-phase short circuit (No. 2) on the high voltage side of the transformer, the maximum impedance between the blue-red two phases is 0Ω regardless of the frequency value. From this, it can be determined that the insulation resistance value between the blue-red two phases is zero, and the blue-red two phases are short-circuited. On the other hand, since the maximum impedance between the blue-white two phases is 7 kΩ and the insulation resistance value between the blue-white two phases is a large value, it can be determined that no short circuit has occurred between the blue-white two phases. .

  In the case of the short circuit on the low voltage side of the light transformer (No. 3), the maximum impedance between the blue and red phases at the short circuit point (No. 2) is the same as in the case of the two phase short circuit on the high voltage side of the transformer (No. 2) The insulation resistance value is 0Ω, and it can be determined that the two phases of blue and red are short-circuited. On the other hand, since the maximum impedance between the blue-white two phases is 7 kΩ and the insulation resistance value between the blue-white two phases is a large value, it can be determined that no short circuit has occurred between the blue-white two phases. . Here, in the case of the short circuit of the light transformer (No. 3), the same characteristic as the two-phase short circuit (No. 2) on the high voltage side of the transformer is the single phase three-wire type on the low voltage side of the light transformer. It can be determined that this is the case.

  The two-phase (blue-red, blue-white) maximum impedance of the three phases (blue, red, white) of the high-voltage side is connected to the two-phase (blue-red) short circuit (No. 4) on the low-voltage side of the power transformer. Is 2.5 kΩ, and the remaining one phase (red-white) is 8 kΩ. In the case of a blue-red two-phase short circuit on the low-voltage side, the maximum impedance of the two phases on the high-voltage side (blue-red, blue-white) decreases. In the case of a power transformer, the high-voltage side is Y-connected. Since the low pressure side is a Δ connection, it is considered that the influence appears in the two phases on the high pressure side. In any case, when a short circuit occurs in any two phases on the low voltage side of the transformer, the maximum impedance of two phases (blue-red, blue-white) of the three phases on the high voltage side (blue, red, white) Since the remaining one phase (red-white) maintains a large value, a short circuit can be determined from this maximum impedance relationship.

As described above, in the embodiment of the present invention, the frequency of the alternating voltage to be applied is not fixed to one value such as 50 Hz, but the frequency is variable. A value close to the insulation resistance of the electrical equipment can be detected without the influence. In particular, when a phase advance capacitor is installed, the capacitance C of the phase advance capacitor resonates with an inductance L of a transformer or the like at each frequency ω of ω ² = 1 / LC, and from the impedance display of the short circuit detection device. Since the influence of L and C is eliminated, a value close to the insulation resistance of the electrical equipment can be detected.

  Similarly, even when two phases are short-circuited on the low-voltage side of the power transformer, the frequency is varied and detection is performed at a frequency at which the display impedance of the short-circuit detection device is maximized. In this case, if the two detected values v1 and v2 are substantially the same among the three interphase detected values on the high pressure side and the other detected value v3 is about three times the value of v1 and v2, the low pressure side It can be determined as a two-phase short circuit. If the three detected values are substantially the same and are about 2 kΩ or more, it can be determined that there is no short circuit between the two phases.

  In addition, in the short circuit on the high voltage side, the short circuit on the low voltage side of the light transformer, and the three-phase short circuit on the low voltage side of the power transformer, the indication of the short circuit detection device is almost 0Ω, and the short circuit condition can be clearly detected. On the other hand, it is not necessary to use a short-circuit detection device because a ground fault detection of an electrical facility and a short circuit between a high voltage side and a low voltage side can be detected quickly by a conventional insulation resistance meter.

  According to the embodiment of the present invention, an AC voltage whose frequency can be varied is applied to two phases of the electrical equipment, and the ratio of the current flowing out of the short-circuit detection device and the applied voltage {(applied voltage) / ( (Outflow current) = impedance}, the influence of the inductance L and the capacitance C is eliminated from the obtained impedance, and a value close to the insulation resistance of the electrical equipment can be detected. Therefore, it is possible to accurately determine a short circuit of the electrical equipment.

The block diagram of the short circuit detection apparatus of the electrical installation concerning embodiment of this invention. The equivalent circuit diagram of the electrical equipment which has the phase advance capacitor equipment. The flowchart which shows an example of the process of the short circuit detection method of the electrical equipment concerning embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Detection apparatus main body, 12 ... DC power supply device, 13 ... Detection probe, 14 ... AC voltage generator, 15 ... Frequency variable device, 16 ... Impedance display part, 17 ... Frequency adjustment knob, 18 ... Display magnification adjustment knob

Claims (2)

An AC voltage generator for generating an AC voltage of variable frequency;
A detection probe for applying a variable frequency AC voltage generated by the AC voltage generator to two phases of the electrical equipment and detecting a current flowing through the electrical equipment by applying a variable frequency AC voltage;
An impedance display unit that calculates and displays the impedance of the electrical equipment from the current flowing through the electrical equipment and the applied alternating voltage by applying an alternating voltage of a variable frequency applied from the detection probe;
A frequency variable device for changing the frequency of the AC voltage generated by the AC voltage generator so that the impedance of the electrical equipment is maximized;
A short-circuit detection device for electrical equipment, comprising: A variable frequency AC voltage is applied to the two phases of the electrical equipment,
Calculate the impedance of the electrical equipment from the current flowing through the electrical equipment and the applied alternating voltage by applying an alternating voltage of variable frequency,
Change the frequency of the AC voltage so that the calculated impedance of the electrical equipment is maximized to obtain the maximum value of the impedance of the electrical equipment,
A method for detecting a short circuit in an electrical facility, comprising: detecting a short circuit in the electrical facility based on the obtained maximum impedance value of the electrical facility.

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