Alternating electric path short-circuit determination device and method for determining short-circuit in alternating electric path

Abstract

To provide an alternating electric path short-circuit determination device and a method for determining a short-circuit in an alternating electric path which allow identification of the short-circuit in the electric path.SOLUTION: The alternating electric path short-circuit determination device includes: a current source circuit for generating a current with a current value according to the amplitude value of a three-phase alternating signal of a test frequency on a phase-by-phase basis and flowing the generated current in each phase of a test target electric path in a voltage-free state before a determination test is started; and a determination unit for detecting a voltage generated in the test target electric path, while the generated current is being flown from the current source circuit to the test target electric path and determining the magnitude of the voltage with respect to a predetermined threshold value.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to an AC electric circuit short-circuit determination device and an AC electric circuit short-circuit determination method. [Background technology]

[0002] An overcurrent breaker installed in an electric circuit to which three-phase AC power is supplied breaks the overcurrent caused by a short circuit on the load side. This causes a power outage on the load side of the overcurrent breaker. Before restoring power, it is necessary to confirm that there is no factor causing an overcurrent on the load side of the overcurrent breaker. By the way, there are cases where a transformer is provided in the electric circuit on the load side of the overcurrent circuit breaker, and cases where it is not provided. There has been a demand for a method to easily identify short circuits in the electric circuit (three-phase short circuits, line-to-line short circuits) regardless of the presence or absence of a transformer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 53-2765 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the windings of a transformer conduct electricity between the phases of a three-phase AC. Therefore, it is difficult for detection methods that use direct current, such as insulation testers, to distinguish between electricity caused by a winding and electricity caused by a short circuit. In the case of an electric circuit that includes a transformer, it can be difficult to distinguish between a short circuit in the electric circuit (three-phase short circuit, line-to-line short circuit) and electricity caused by the windings of the transformer.

[0005] The present invention has been made in consideration of the above circumstances, and has an object to provide an AC electric circuit short-circuit determination device and an AC electric circuit short-circuit determination method that are capable of identifying a short circuit in an electric circuit. [Means for solving the problem]

[0006] (1) One aspect of the present invention for solving the above problem is an AC circuit short-circuit determination device that includes a current source circuit that generates a current for each phase, the current value of which corresponds to the amplitude value of a three-phase AC signal at a test frequency, and flows the generated current through each phase of a test target electric circuit that is in a voltage-free state before a determination test is started, and a determiner that detects a voltage generated in the test target electric circuit while the generated current is flowing from the current source circuit to the test target electric circuit, and determines the magnitude of the voltage relative to a predetermined threshold value. (2) The above AC electric circuit short circuit determination device includes a signal generator that sets either a first frequency or a second frequency as the test frequency and generates a three-phase AC signal of the test frequency. When an insulating transformer is provided in the electric circuit under test, the signal generator passes the generated current through each phase of the electric circuit under test on the secondary side of the transformer, and the determiner detects a voltage generated in each phase of the electric circuit under test on the secondary side of the transformer and determines the magnitude of the voltage. (3) The AC electric circuit short circuit determination device includes a signal generator that generates a three-phase AC signal of a test frequency, the test frequency being either a first frequency or a second frequency, the first frequency being lower than a lower limit frequency of an allowable fluctuation range of a rated AC frequency of the transformer, and the second frequency being higher than the first frequency and lower than an upper limit frequency of the allowable fluctuation range. (4) The signal generator in the above-described AC electric circuit short-circuit determination device includes an oscillator that outputs a signal of the test frequency, and a three-phase signal generator that converts the signal of the test frequency into a three-phase AC signal of the test frequency. (5) The test frequency signal in the above-mentioned AC electrical circuit short-circuit determination device is a single-phase AC signal, and the three-phase AC signal of the test frequency includes a first phase signal having a phase based on the phase of the single-phase AC signal, a second phase signal having a phase that is advanced from the phase of the single-phase AC signal, and a third phase signal having a phase that is delayed from the phase of the single-phase AC signal. (6) The three-phase signal generator of the above-mentioned AC electric circuit short-circuit determination device generates a three-phase AC signal having the test frequency, the three-phase AC signal including a first phase based on a reference phase of the single-phase AC signal, a second phase advanced in phase from the reference phase of the single-phase AC signal, and a third phase delayed in phase from the reference phase of the single-phase AC signal. (7) The three-phase signal generator of the above-mentioned AC electric circuit short-circuit determination device includes a first phase adjustment unit that generates a second-phase signal by inverting a phase that is advanced by a first angle from the phase of the single-phase AC signal at a reference frequency, and a second phase adjustment unit that generates a third-phase signal having a phase that is advanced by a second angle from the phase that is advanced by the first angle at the reference frequency. (8) In the above-described AC electric circuit short-circuit determination device, the signal generator includes an inverter that generates a three-phase AC signal of the test frequency. (9) The current source circuit in the above-described AC electric circuit short-circuit determination device includes a rotating electric machine that generates a three-phase AC signal of the test frequency. (10) The determiner in the AC circuit short circuit determination device determines the magnitude of the voltage generated between phases on the secondary side of the transformer while the current source circuit is causing the generated current to flow to the secondary side of the transformer. The voltage generated between the phases on the primary side may be set to a measurable magnitude. (11) The determiner in the above-mentioned AC circuit short circuit determination device identifies the possibility of a line-to-line short circuit on the secondary or primary side of the transformer when the magnitude of the voltage generated between the phases on the secondary side of the transformer is close to zero while the current source circuit is flowing the generated current to the secondary side of the transformer. (12) The oscillator of the signal generator in the above-described AC electric circuit short-circuit determination device is configured to be able to change the test frequency. (13) The oscillator of the signal generator in the above-described AC electric circuit short-circuit determination device is configured to be able to change the test frequency in response to an operation. (14) One aspect of the present invention is a method for determining a short circuit in an AC circuit, comprising: generating a current for each phase, the current value of which corresponds to an amplitude value of a three-phase AC signal having a test frequency; causing a current source circuit to supply the generated current to each phase of a test target electric circuit that is in a voltage-free state before a determination test is started; detecting a voltage generated in the test target electric circuit while the generated current is being supplied from the current source circuit to the test target electric circuit; and determining a magnitude of the voltage relative to a predetermined threshold value. Effect of the Invention

[0007] According to the present invention, it is possible to provide an AC electric circuit short circuit determination device and an AC electric circuit short circuit determination method that are capable of identifying a short circuit in an electric circuit. [Brief description of the drawings]

[0008] [Figure 1] 1 is a configuration diagram of a measurement target to which an AC electric circuit short circuit determination device according to an embodiment is applied; [Diagram 2] 1 is a diagram for explaining an application example of an AC electric circuit short circuit determination device according to an embodiment; [Diagram 3] 1 is a configuration diagram of an AC electric circuit short circuit determination device according to an embodiment; [Figure 4] FIG. 2 is a diagram for explaining the relationship between the frequency characteristics of the transformer of the embodiment and the test frequency. [Diagram 5] 1 is a diagram for explaining a difference between a current source and a voltage source in determining whether an AC circuit is short-circuited according to an embodiment. FIG. [Figure 6] FIG. 2 is a schematic diagram of a three-phase AC current source according to an embodiment. [Figure 7A] FIG. 2 is a more specific configuration diagram of a three-phase AC current source. [Figure 7B] FIG. 2 is a functional explanatory diagram of each circuit block of a three-phase AC current source. [Figure 8] FIG. 4 is a more specific configuration diagram of a determination unit. [Figure 9] FIG. 4 is a diagram for explaining an example of a line voltage according to the embodiment. [Figure 10A] FIG. 13 is a diagram for explaining the frequency response of a measurement system appearing in a transformer output voltage. [Figure 10B] 10A and 10B are diagrams for explaining the frequency response of a measurement system that appears in a transformer output voltage in the embodiment. [Figure 11] 10A and 10B are diagrams for explaining determination of a line voltage according to a test target electric circuit in the embodiment. [Figure 12] 1 is a configuration diagram of an AC electric circuit short circuit determination system according to an embodiment; [Figure 13] 1 is a configuration diagram of an AC electric circuit short circuit determination device according to an embodiment; [Figure 14] 1 is a configuration diagram of an AC electric circuit short circuit determination device according to an embodiment; [Figure 15A] FIG. 1 is a configuration diagram of a voltage source circuit with a drooping characteristic function according to an embodiment. [Figure 15B] FIG. 1 is a configuration diagram of a voltage source circuit with a drooping characteristic function according to an embodiment. [Figure 16] FIG. 2 is a configuration diagram of a three-phase signal generator according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. (First embodiment) FIG. 1 is a configuration diagram of a measurement target to which an AC electric circuit short circuit determination device according to an embodiment of the present invention is applied. Fig. 2 is a diagram for explaining an application example of the AC electric circuit short circuit determination device according to the embodiment, and Fig. 3 is a configuration diagram of the AC electric circuit short circuit determination device according to the embodiment.

[0010] The AC system under measurement receives three-phase AC power, converts it from high voltage to low voltage using a transformer, and supplies the three-phase AC power to a low voltage load. For example, a circuit breaker CB, a transformer, and a distribution circuit breaker MCCB are installed for overcurrent protection in the order listed from the power source side of this AC system. The circuit breaker CB and the distribution circuit breaker MCCB cut off the overcurrent when it flows to the load side. The transformer has, for example, a Y-connected primary winding and a D-connected secondary winding. In the following description, the three phases on the primary side of the transformer are referred to as R1S1T1 phases, and the three phases on the secondary side are referred to as RST phases. When carrying out the tests described below on an electric circuit in which a leading-phase capacitor SC is connected to the secondary circuit of a transformer via a disconnector LBS, the test shall be carried out after opening the disconnector LBS to disconnect the leading-phase capacitor SC from the electric circuit.

[0011] For example, a test probe of the AC electric circuit short circuit determination device 1 is connected to an electric circuit on the secondary side of a transformer.

[0012] The AC electric circuit short circuit determining device 1 includes a current source circuit 4 and a determining unit 5. A current source circuit 4 of the AC electric circuit short circuit determination device 1 supplies a three-phase AC test signal to the electric circuit on the secondary side of the transformer.

[0013] The current source circuit 4 generates a current for each phase, the current value of which corresponds to the amplitude value of the three-phase AC signal of the test frequency. The current source circuit 4 passes the generated current through each phase of the test target electric circuit, which is in a voltage-free state before the start of the judgment test. The current source circuit 4 is an example of an AC constant current source.

[0014] The determination unit 5 of the AC electric circuit short-circuit determination device 1 detects and determines the voltage of the electric circuit on the secondary side of the transformer. The judgment unit 5 detects a voltage generated in the test target electric circuit while a current generated by the current source circuit 4 is flowing from the current source circuit to the test target electric circuit, and judges the magnitude of the voltage relative to a predetermined threshold value.

[0015] The AC electric circuit short circuit determination device 1 of the embodiment further includes a signal generator 2. The signal generator 2 sets either the first frequency or the second frequency as the test frequency and generates a three-phase AC signal of the test frequency. The signal generator 2 is configured to generate three-phase AC signals of at least both the first frequency and the second frequency. For example, the signal generator 2 is configured to generate three-phase AC signals of at least both the first frequency and the second frequency.

[0016] The first frequency is lower than the lower limit frequency of the allowable fluctuation range of the rated AC frequency of the transformer. The second frequency is higher than the first frequency, lower than the upper limit frequency of the allowable fluctuation range of the rated AC frequency, and higher than the lower limit frequency.

[0017] The signal generator 2 includes an oscillator 2A and a three-phase signal generator 2B. The oscillator 2A outputs a signal of the test frequency. For example, the test frequency may be selected from among several preset frequencies, or may be a frequency determined by operation. The three-phase signal generator 2B converts the signal of the test frequency into a three-phase AC signal of the test frequency.

[0018] The oscillator 2A and the three-phase signal generator 2B of the signal generator 2 may be configured as analog circuits.

[0019] The load of the AC circuit short circuit determination device 1 is the test circuit as described above. This impedance is Z L As shown in Fig.

[0020] FIG. 4 is a diagram for explaining the relationship between the frequency characteristics of the transformer of the embodiment and the test frequency. The graph in Figure 4 shows the impedance Z of a model that simply equates a transformer to an inductor. L 4 shows an example of a frequency characteristic showing a change in

[0021] Impedance Z L is calculated from the inductance L of the inductor and the frequency f.

[0022] Z L =jωL, ω=2πf

[0023] Thus, for an inductor with ideal characteristics, this graph would be a straight line.

[0024] The frequency range assigned to the horizontal axis of this graph includes the standard frequency of the commercial power supply and its conditionally acceptable range, which may be, for example, a management target for the frequency fluctuation of the commercial power supply.

[0025] 4 is set to 50 Hz, and the upper limit of the fluctuation range (f0+β) is set to 50.2 Hz, etc. This beta value is just an example, and may be determined as appropriate without being limited to this. The frequency range from 0 Hz to the "upper limit of the fluctuation range (f0+β)" is divided into two, a low frequency band FZ1 and a high frequency band FZ2. The first representative frequency f1 is determined from the low frequency band FZ1, and the second representative frequency f2 is determined from the high frequency band FZ2. The impedance value at the first representative frequency f1 is smaller than the impedance value at the second representative frequency f2.

[0026] As described above, the magnitude of the impedance is determined by the frequency. For example, the range of frequencies in which the impedance increases as the frequency increases may be set as the range for extracting the first representative frequency f1 and the second representative frequency f2. By selecting the first representative frequency f1 and the second representative frequency f2 from within this range, it is guaranteed that the frequency and the impedance change monotonically. The first representative frequency f1 and the second representative frequency f2 are examples of the first frequency and the second frequency.

[0027] As a specific example of the setting, the boundary between the low frequency band FZ1 and the high frequency band FZ2 may be set at 20 Hz and the second representative frequency f2 may be determined from 32 Hz to 40 Hz. (See FIG. 10A.) The boundary between the low frequency band FZ1 and the high frequency band FZ2 and the second representative frequency f2 may be determined according to the frequency characteristics of the transformer. For example, the second representative frequency f2 may be set to a frequency lower than the frequency at which the gain of the frequency characteristics of the transformer peaks. The frequency at which this peak appears is often close to the rated frequency of the AC.

[0028] The difference between the current source and the voltage source in determining whether or not an AC circuit is short-circuited according to the embodiment will be described with reference to Fig. 5. Fig. 5 is a diagram for explaining the difference between the current source and the voltage source in determining whether or not an AC circuit is short-circuited according to the embodiment. FIG. 5(a) shows a configuration in which an AC current source is connected between the RS phases on the secondary side of a transformer. FIG. 5(b) shows a configuration in which an AC voltage source is connected between the RS phases on the secondary side of the transformer. The table in Figure 5(c) shows how the line voltage is generated.

[0029] For example, Figures 5(a) and 5(b) both show a state in which a short circuit occurs between phases S1 and T1 on the primary side. In the configuration shown in FIG. 5(a), for example, the voltage between the RS phases to which a test device including an AC current source is connected may become 0V. When such an event occurs, the RS phases are short-circuited. On the other hand, if a short circuit occurs other than between the RS phases (for example, between the S1-T1 phases), the voltage between the RS phases to which the test device is connected will not become 0V. As a result, by determining whether the voltage between the RS phases to which the test device is connected becomes 0V, it can be determined whether a short circuit has occurred between the RS phases to which the test device is connected or in the RS phase to which the test device is connected. In addition, the condition between each phase on the secondary side can be tested by changing the connection destination of the test equipment and performing the same test.

[0030] In the case of the AC voltage source shown in Figure 5(b), if a short circuit occurs between any of the phases (phase-to-phase short circuit), the RS phase-to-phase voltage will be 0V. Therefore, all phase-to-phase voltages will be 0V. Because each phase-to-phase voltage is 0V, it can be identified that there is a high possibility that a short circuit has occurred, but it is not possible to identify the location of the short circuit. Furthermore, if a short circuit occurs on the load side of the AC voltage source, the test voltage used in this test will be lost. This will result in a state where the test cannot be performed.

[0031] As shown in Figure 5(c) in the case of an AC current source (see Figure 5(a)), if a short circuit (phase-to-phase short circuit) occurs between any of the phases (indicated as "Short circuit present" in the figure), the phase-to-phase voltage of the phase pair where the phase-to-phase short circuit occurs will be 0V, and a voltage of several volts (V) will be generated between the other phase pairs where no phase-to-phase short circuit occurs. The magnitude of this voltage depends on the turns ratio of the transformer and the magnitude of the output current. If a short circuit (0V) occurs between the phases to which the test equipment is connected, it is advisable to test the other phases in the same way. If no short circuit (phase-to-phase short circuit) occurs between any of the phases (indicated as "No short circuit" in the figure), the phase-to-phase voltages of none of the phase pairs will be 0V, and a small voltage or a voltage of several volts will be generated. In contrast, in the case of an AC voltage source (see Figure 5(b)), if a short circuit occurs between any of the phases (phase-to-phase short circuit), the voltage between each phase becomes 0 V, which is the same as if the output of the AC voltage source was short-circuited, making measurement impossible.

[0032] With reference to FIG. 6, a schematic configuration of a three-phase AC current source will be described. FIG. 6 is a schematic diagram of a three-phase AC current source according to an embodiment. 1 shows an example of a three-phase AC current source including a signal generator 2 and a current source circuit 4 of an AC electric circuit short circuit determination device 1.

[0033] The output of the oscillator 2A (OSC) is connected to the input of the three-phase signal generator 2B. The oscillator 2A (OSC) generates a single-phase AC signal with an adjustable frequency. The oscillator 2A (OSC) is an example of an AC signal source.

[0034] The three-phase signal generator 2B generates a three-phase AC signal (voltage waveform) from a single-phase AC signal by using a combination circuit including first and second phase shift circuits (reference shift angle 60 degrees) of the single-phase AC signal, a buffer circuit, an inverting amplifier circuit, a non-inverting amplifier circuit, etc.

[0035] The input of the three-phase signal generator 2B is internally split into two. The first branch destination is connected to the R-phase circuit of the current source circuit 4 in the subsequent stage. The second branch is connected to the input of the first phase shift circuit.

[0036] The output of the first phase shift circuit is branched into two via a buffer circuit. The first branch is connected to the input of an inverting amplifier circuit that also has an attenuation compensation function, and the output of the inverting amplifier circuit is connected to the S-phase circuit of the current source circuit 4 in the subsequent stage. The second branch is connected to the input of a second phase shift circuit, its output is connected to the input of a non-inverting circuit that also has the function of attenuation compensation, and its output is connected to the T-phase circuit of the subsequent current source circuit 4.

[0037] The functions relating to phase adjustment of each circuit block in FIG. 6 are shown in vector diagrams attached to each circuit block.

[0038] A more specific example of the configuration of the three-phase AC current source will be described with reference to FIGS. 7A and 7B. Fig. 7A is a more specific configuration diagram of a three-phase AC current source, and Fig. 7B is a functional explanatory diagram of each circuit block of the three-phase AC current source.

[0039] The input of the R-phase circuit of the current source circuit 4 is connected to the output of the oscillator 2A via a coupling capacitor C1 in order to block the DC component.

[0040] The first phase shift circuit includes a first-order lead circuit made of a capacitor C2 and a resistor R7. The lead angle of the reference frequency by the first phase shift circuit is set to approximately 60 degrees. The above configuration attenuates the signal. For example, the attenuation rate is configured to be 0.44 times. This attenuation amount is compensated for by the gain of the inverting amplifier circuit in the subsequent stage. The buffer circuit amplifies the output signal of the first phase shift circuit by a factor of 1 and supplies the amplified signal to the input of the inverting amplifier circuit. The inverting amplifier circuit inverts the phase of the output of the buffer circuit and amplifies it with a predetermined gain, which is preferably set so as to compensate for the attenuation rate of 0.44 in the first phase shift circuit described above. The input of the S-phase circuit of the current source circuit 4 is connected to the output of the inverting amplifier circuit.

[0041] The second phase shift circuit includes a first-order lead circuit made of a capacitor C3 and a resistor R17. The lead angle of the reference frequency by the second phase shift circuit is set to approximately 60 degrees. The above configuration attenuates the signal. This attenuation is compensated for by the gain of the non-inverting amplifier circuit in the subsequent stage. The non-inverting amplifier circuit amplifies the output of the second phase shift circuit by a predetermined gain. The predetermined gain is an attenuation factor of 0.44 in both the first phase shift circuit and the second phase shift circuit. 2 It is advisable to set it to compensate twice as much. The input of the T-phase circuit of the current source circuit 4 is connected to the output of the non-inverting amplifier circuit.

[0042] The R-phase circuit, S-phase circuit, and T-phase circuit of the current source circuit 4 each include a common circuit configuration and are configured independently of one another. Therefore, the R-phase circuit will be described as an example.

[0043] The R-phase circuit is a constant current circuit including one operational amplifier stage that uses resistor R6 as a resistor for adjusting the output current. Resistor R1 is used to adjust the input impedance. Resistor R1 supplies ground potential to the non-inverting input of the operational amplifier. In the R-phase circuit, the cutoff band of the high-pass filter is determined by the filter characteristics determined by the combined impedance of resistors R1, R2, and R4, and the capacitance of capacitor C1. For example, resistor R1 can be considered to be in parallel with the series circuit of resistors R2 and R4. The capacitance of capacitor C1 should be determined according to the combined impedance of resistors R1, R2, and R4. Resistors R2, R3, R4, and R5 are resistors used for gain adjustment. Capacitor C4 is a capacitor used as a noise filter. Resistor R31 is a dummy resistor used to compensate for operation when the load is released. The output of the R-phase circuit is connected to the output terminal for the R-phase circuit.

[0044] The S-phase circuit and the T-phase circuit are configured with a phase shift circuit and a circuit that performs gain compensation in the subsequent stages. The S-phase circuit differs from the above in that a high-pass filter is configured using the above-mentioned first phase shift circuit and that gain compensation is performed in the subsequent stages independently of the current source circuit 4, but the filter characteristics are the same as the R-phase circuit. The T-phase circuit differs from the above in that a high-pass filter is configured using the above-mentioned first phase shift circuit and second phase shift circuit and that gain compensation is performed in the subsequent stages independently of the current source circuit 4, but the filter characteristics are the same as the R-phase circuit.

[0045] A more specific example of the configuration of the determination unit will be described with reference to FIG. FIG. 8 is a more specific configuration diagram of the determination unit 5.

[0046] The R-phase to S-phase circuit, the S-phase to T-phase circuit, and the T-phase to R-phase circuit of the determination unit 5 each include a common circuit configuration and are configured independently of each other. Therefore, the R-phase to S-phase circuit will be described as an example.

[0047] Resistors R30 and R31 form a voltage divider circuit for the input signal. The resistors R30 and R32 are configured to have the same value, and the resistors R31 and R33 are configured to have the same value, and the operational amplifier is used as a differential amplifier. For example, when the difference between the input voltages of the operational amplifier, that is, the two phase voltages, is smaller than a predetermined value, and the output voltage of the operational amplifier is not sufficient even when amplified with a predetermined gain, the LED1 provided at the output of the operational amplifier will be turned off. This "when the output voltage of the operational amplifier is not sufficient" corresponds to the case where the output voltage of the operational amplifier is not sufficient for the forward bias voltage of LED1. The cathode of LED1 in this circuit is connected to the output of the operational amplifier, and the current limiting resistor R34 connected in series with LED1 is connected to the neutral point N. LED1 lights up when the operational amplifier outputs a negative voltage larger than the forward bias voltage of LED1. If a potential difference large enough to output such a large voltage occurs between the two phase voltages, it can be seen that there is no short circuit. The diode connected in reverse to LED1 is a protection circuit for suppressing reverse bias of LED1.

[0048] FIG. 9 is a diagram for explaining an example of a line voltage according to the embodiment. The upper part of FIG. 9(a) shows the line voltage of the RS phase, and the lower part shows the line voltage of the ST phase. The upper part of FIG. 9(b) shows the line voltage of the ST phase, and the lower part shows the line voltage of the TR phase. The line voltage of the RS phase shown in the upper part of Figure 9(a) is 2.8V. P-P For example, this voltage is the voltage generated between two lines when the impedance of resistor R31, which is a dummy resistor provided in the AC electric circuit short-circuit determination device 1, is set to 100Ω. Each line voltage has an amplitude equivalent to this. As shown in the lower part, the period of the line voltage of each phase is 25 ms and the frequency is 40 Hz. This period and frequency are examples of test frequencies, and the specific values ​​may be changed.

[0049] Fig. 10A is a diagram for explaining the frequency response of a measurement system that appears in the output voltage of the AC electric circuit short-circuit detection device 1. This measurement system is when the AC electric circuit short-circuit detection device 1 is connected to the secondary side of a transformer and the primary side of the transformer is opened to create an unloaded state, and the only current flowing through the transformer is the excitation current. The frequency characteristics shown here are due to the voltage observed on the secondary side of the transformer in an unloaded state using the above measurement system. The same applies below. The impedance of the transformer in a no-load state is considered to be roughly proportional to the AC frequency. The frequency response of this measurement system includes a tendency that depends on the frequency characteristics of the circuits such as the signal generator 2 of the AC circuit short circuit detection device 1. The first-order lead circuit exhibits gain characteristics equivalent to a high-pass filter. Therefore, if the phase shift circuit of the three-phase signal generator 2B of the signal generator 2 is configured with a first-order lead circuit, the gain will decrease in the region below the cutoff frequency.

[0050] By passing the output current of the AC electric circuit short circuit detection device 1 through a transformer, it is possible to obtain a frequency response that includes a tendency toward high-pass characteristics. As a result, the amplitude of signals in the lower frequency range is reduced.

[0051] Incidentally, the theoretical impedance value of a reactor (inductor) increases in proportion to the frequency. Therefore, in the case of a comparative example in which the magnitude of the constant current controlled current is not frequency dependent, the higher the frequency of the signal passed through the reactor, the larger the amplitude of the signal will be. When this is judged using a predetermined threshold, the higher the frequency, the smaller the margin for the threshold becomes. The same tendency is observed in the case of a transformer.

[0052] Therefore, the AC electric circuit short circuit determination device 1 reduces the amplitude of the signal in the lower frequency range, so that even if the frequency of the signal output from the AC electric circuit short circuit determination device 1 increases, the signal is not converted to a large amplitude, and even if the frequency increases, the margin relative to the threshold value is not reduced.

[0053] The AC circuit short circuit determination device 1 is provided with LEDs 1, 2, and 3 for displaying the determination result. For example, when it is determined that no short circuit has occurred as a result of the R-phase-S-phase determination (normal state), LED 1 is turned on, and when it is determined that a short circuit has occurred (short circuit state), LED 1 is turned off. Similarly, LEDs 2 and 3 are turned on in accordance with the S-phase-T phase determination result and the T-phase-R phase determination result. In this way, even when the determination uses the bias of an LED that has no frequency dependency, if the amplitude of the signal in the lower frequency range is low, it is possible to reduce the change in signal amplitude due to differences in frequency.

[0054] Referring to FIG. 10B, the frequency response of the measurement system appearing in the transformer output voltage of the embodiment will be described. FIG. 10B is a diagram for explaining the frequency response of the measurement system appearing in the transformer output voltage of the embodiment. 10B(a), (b), and (c) are voltage waveforms observed when the test frequency was set to 10 Hz, 40 Hz, and 53 Hz, respectively, in a situation where there was no short circuit in the tested electric circuit. The upper row of each shows the waveform of the output signal (single-phase AC signal) of oscillator 2A (OSC), and the lower row shows the RS line voltage when AC electric circuit short circuit determination device 1 is connected to the R phase and S phase and an excitation current is passed through the transformer.

[0055] In this test, the initial frequency is set to a sufficiently low frequency, and the frequency is gradually or stepwise increased while observing the voltage waveform (lower part) at each frequency. The amplitude of the input voltage waveform of the current source circuit 4 shown in the upper part of each frequency is approximately 6.5V. P-P In contrast, the amplitude of the line voltage waveforms shown in the lower row is 8.5 mV in the order of (a), (b), and (c). P-P , 105mV P-P , 75mV P-P From this result, the impedance Z of the circuit including this transformer can be estimated to be 0.09 Ω, 1.16 Ω, and 0.83 Ω, respectively.

[0056] The above is the voltage waveform when there is no short circuit in the circuit under test. However, if a short circuit occurs between the RS lines, the amplitude of the observed voltage waveform will be 0V. The above measurement system is configured as a single-phase circuit.

[0057] With reference to FIG. 11, the determination of the line voltage according to the electric circuit under test in the embodiment will be described. 11 is a diagram for explaining the determination of the line voltage according to the electric circuit under test in the embodiment. The measurement system shown here is a three-phase circuit.

[0058] The waveforms shown in Figures 11(a), (b), and (c) are voltage waveforms observed when the state of the tested electric circuit is changed. The judgment unit 5 judges these voltage waveforms. Figure 11(a) shows each (line) voltage waveform in a normal state when no short circuit occurs (for example, when the impedance is 1 Ω), (b) shows each (line) voltage waveform in the event of a three-phase short circuit, and (c) shows each line voltage waveform in the event of a line-to-line short circuit. As shown in Figure 11(a), when the impedance is 1Ω, 8V is applied between each line. P-P For example, if the impedance is to be determined as "not shorted" when it is half that, i.e., 0.5Ω or more, then the threshold voltage of the determination circuit should be set to 4V. P-P It is recommended to do so. As shown in Figure 11(b), when a three-phase short circuit occurs, the voltage between each line is 0.8 to 1.2 V. P-P A voltage waveform of 0.1Ω is observed. Comparing with the result of FIG. 11(a) above, the impedance can be estimated to be about 0.1Ω. In the case of the embodiment, since a current source is used, the amplitude of the voltage waveform may not become 0 due to the impedance of the wiring even in the case of a three-phase short circuit. Therefore, even if such a voltage occurs between each line, it is necessary to judge this as "a short circuit". As shown in Figure 11(c), when the TR lines are shorted, 0.8 V is applied between the TR lines. P-P A voltage waveform of about 8V is observed between the ST lines in a healthy state. P-P In this manner, the location of the line short circuit can be determined based on the amplitude of the observed voltage waveform.

[0059] (Display of judgment result) The determination unit 5 identifies the magnitude of each line voltage using the determination criteria defined as above. When the TR lines are shorted and the R-S lines and the ST lines are healthy, the line-to-line potential between the TR lines becomes approximately 0. The determination unit 5 detects this and turns off the LED 2 associated with the TR lines. On the other hand, if the short circuit between the TR lines is eliminated, the line-to-line potential between the TR lines is no longer substantially 0. The determination unit 5 detects this and turns on the LED 2 associated with the TR lines.

[0060] When a three-phase short circuit occurs, the potential between each line becomes approximately 0. The determination unit 5 detects this and turns off all of the LEDs.

[0061] According to the above embodiment, the AC electric circuit short-circuit determination device 1 includes a current source circuit 4 that generates a current for each phase, the current value of which corresponds to the amplitude value of a three-phase AC signal at a test frequency, and flows the generated current through each phase of the test target electric circuit that is in a voltage-free state before the start of a determination test, and a determination unit 5 that detects a voltage generated in the test target electric circuit while the generated current is flowing from the current source circuit to the test target electric circuit, and determines the magnitude of the voltage relative to a predetermined threshold value. This makes it possible to identify a short circuit in the electric circuit.

[0062] The AC electric circuit short circuit determination device 1 includes a signal generator 2 that sets either a first frequency or a second frequency as the test frequency and generates a three-phase AC signal of the test frequency, thereby facilitating testing of an electric circuit in which an insulating transformer is provided in a test target electric circuit. For example, in this case, the signal generator 2 passes the generated current through each phase of the test target electric circuit on the secondary side of the transformer. The determination unit 5 may detect a voltage generated in each phase of the test target electric circuit on the secondary side of the transformer and determine the magnitude of the voltage.

[0063] The above first and second frequencies may be set as follows. For example, the first frequency is lower than a lower limit frequency of an allowable fluctuation range of a rated AC frequency of the transformer, and the second frequency is higher than the first frequency and lower than an upper limit frequency of the allowable fluctuation range.

[0064] The signal generator 2 includes an oscillator 2A that outputs a signal of the test frequency, and a three-phase signal generator 2B that converts the signal of the test frequency into a three-phase AC signal of the test frequency. With this configuration, the three-phase signal generator 2B can generate a three-phase AC signal of the test frequency from a single-phase AC signal of the test frequency. The three-phase AC signal of the test frequency may include a first phase signal having a phase based on the phase of the single-phase AC signal, a second phase signal having a phase advanced from the phase of the single-phase AC signal, and a third phase signal having a phase delayed from the phase of the single-phase AC signal.

[0065] The three-phase signal generator 2B may generate a three-phase AC signal having the test frequency, the three-phase AC signal including a first phase based on a reference phase of the single-phase AC signal, a second phase whose phase is advanced from the reference phase of the single-phase AC signal, and a third phase whose phase is delayed from the reference phase of the single-phase AC signal.

[0066] The above-mentioned three-phase signal generator 2B may include a first phase adjustment unit that inverts a phase that is advanced by a first angle from the phase of the single-phase AC signal at a reference frequency to generate a second-phase signal, and a second phase adjustment unit that generates a third-phase signal having a phase that is advanced by a second angle from the phase that is advanced by the first angle at the reference frequency.

[0067] The determination unit 5 may determine the magnitude of the voltage generated between the phases on the secondary side of the transformer while the current source circuit 4 is causing the generated current to flow through the secondary side of the transformer.

[0068] The judgment unit 5 may identify that there is a possibility of a line-to-line short circuit on the secondary side or primary side of the transformer when the magnitude of the voltage generated between phases on the secondary side or primary side of the transformer is close to zero while the current source circuit is flowing the generated current to the secondary side of the transformer.

[0069] (Variation 1) The oscillator 2A of the signal generator 2 may be configured to be able to change the test frequency. For example, the oscillator 2A of the signal generator 2 may be configured to be able to change the test frequency continuously or intermittently in response to an operation. Here, an example of a case where the test frequency is determined to be gradually increased continuously will be described. If the frequency is within the range of FZ1, the LED will turn off regardless of whether there is a short circuit or not. By gradually increasing the frequency and reaching a frequency within the range of FZ2, if there is a short circuit the LED will turn off, and if there is no short circuit the LED will turn on. In this way, after it has been confirmed that all LEDs are turned off at a frequency within the range of FZ1 (by increasing the frequency and increasing the amplitude of the signal so that it passes the threshold), the presence or absence of a short circuit is displayed on the LED, thereby increasing the reliability of the judgment result. By checking in advance that the LED is not lit due to a malfunction of the measurement system or poor contact in the measurement lead wires, it is possible to prevent a mistaken determination that a short circuit exists. In addition, when changing intermittently, this can be achieved by preparing multiple predetermined test frequencies, one or more for each of the FZ1 range and the FZ2 range, and switching to a desired frequency selected from among them.

[0070] (Variation 2) In the above embodiment, a case has been described in which an electric circuit provided with a transformer is the test object.A case has been described in which an electric circuit provided with a transformer is the test object. A transformer may not be provided in the electric circuit to be tested, and the AC electric circuit short circuit determination device 1 may be applied to an electric circuit that does not have a transformer. In the case of an electric circuit not provided with a transformer, it is advisable to provide a reactor (inductor) in series with the output terminal between the output terminal of the AC electric circuit short-circuit determination device 1 and the electric circuit under test. The AC circuit short circuit determination device 1 may be configured with the reactor (inductor) built in, and further, a switch may be provided in series with the reactor (inductor). In this case, it is preferable to close the switch to open the reactor (inductor) and open the switch to connect the reactor (inductor) in parallel with the load.

[0071] (Variation 3) In the above embodiment, the gain characteristic and phase characteristic of the primary lead circuit constituting the phase shift circuit of the three-phase signal generator 2B are determined using a specific frequency. Even when test signals of different frequencies are used, the gain characteristic and phase characteristic determined using the specific frequency are used regardless of the frequency of the test signal used. Instead, in this modification, a case will be described in which, when test signals of different frequencies are used, phase shift circuits corresponding to the respective frequencies are used.

[0072] As described above, the gain and phase characteristics of the first-order lead circuit are frequency dependent. Therefore, when testing using multiple frequencies, an error occurs with respect to the ideal phase shift amount depending on the frequency, but this effect can be reduced by using a three-phase signal generator 2B suitable for each frequency of the test signal. This will be explained below.

[0073] FIG. 16 is a configuration diagram of a three-phase signal generator 2C according to an embodiment. The three-phase signal generator 2C includes three-phase signal generators 2B-10 and 2B-40, and switches SW21 and 22. The switches SW21 and 22 are preferably linked switches. Similar to the above-described three-phase signal generator 2B, the three-phase signal generator 2C has an oscillator 2A provided in the preceding stage and a current source circuit 4 provided in the succeeding stage. The relationship between the oscillator 2A and the current source circuit 4 in the three-phase signal generator 2C is similar to that in the above-described three-phase signal generator 2B. The current source circuit 4 generates a constant current controlled three-phase AC by using the signal generated by the three-phase signal generator 2C.

[0074] The three-phase signal generator 2B-40 is configured similarly to the three-phase signal generator 2B described above, and the frequency characteristics and phase characteristics of its phase shift circuit may be similar to those of the phase shift circuit of the three-phase signal generator 2B. The reference frequency of the phase shift circuit of the three-phase signal generator 2B is set to, for example, 40 Hz. When the three-phase signal generator 2B-40 side is selected by the switches SW21 and SW22 and the three-phase signal generator 2B-40 receives a 40 Hz single-phase AC voltage (1Φ40Hz OSC output) of a predetermined amplitude from the oscillator 2A (OSC), the amplitude (three-phase AC voltage) of the signal (40Hz 3Φ output) output from the three-phase signal generator 2B-40 is configured to be equal to the amplitude of the output of the three-phase signal generator 2B-10.

[0075] The three-phase signal generator 2B-10 is configured similarly to the three-phase signal generator 2B (2B-40) described above, but the phase shift circuit of the three-phase signal generator 2B-10 has frequency characteristics and phase characteristics different from those of the phase shift circuit of the three-phase signal generator 2B. For example, the reference frequency of the phase shift circuit of the three-phase signal generator 2B-10 is set to, for example, 10 Hz. When the three-phase signal generator 2B-10 side is selected by the switches SW21 and SW22 and the three-phase signal generator 2B-10 receives a 10 Hz single-phase AC voltage (1Φ10Hz OSC output) of a predetermined amplitude from the oscillator 2A (OSC), the amplitude (three-phase AC voltage) of the signal (10Hz 3Φ output) output from the three-phase signal generator 2B-10 is configured to be equal to the amplitude of the output of the three-phase signal generator 2B-40. A three-phase AC signal is supplied to the current source circuit 4 from either the three-phase signal generator 2B-40 or the three-phase signal generator 2B-10 depending on the setting of the switch SW22.

[0076] In this way, by providing the frequency characteristics and amplitude characteristics according to the frequency of the test signal by each high-pass filter, it is possible to reduce the phase error caused by changing the frequency.

[0077] Second Embodiment A second embodiment will now be described. In the first embodiment, a description has been given of detection of a short circuit using the AC electric circuit short circuit determination device 1. In the present embodiment, an example in which the detection accuracy is improved by further using a voltage detector 6 will be shown and described.

[0078] FIG. 12 is a configuration diagram of an AC electric circuit short circuit determination system 1A according to an embodiment. The AC electric circuit short-circuit determination system 1A includes a voltage detector 6 in addition to the AC electric circuit short-circuit determination device 1. The voltage detector 6 detects, for example, each line voltage of R1S1T1 phase. For example, the voltage detector 6 detects each line voltage connected to the voltmeters 61, 62, and 63. A tester may be used as the voltage detector 6. The transformer shown in the figure is an isolation transformer that steps down the high voltage (6600V) on the primary side to a low voltage (210V).

[0079] As in the first embodiment, the voltage detector 6 detects the line voltage of the R1S1T1 phase during a test using the AC electric circuit short-circuit determination device 1. If the condition is healthy, the voltage detector 6 can detect a voltage of several volts. In contrast, if a short circuit occurs on the primary side of the transformer, approximately 0 V is detected in the shorted line voltage of R1S1T1 phase.

[0080] According to the above embodiment, in addition to providing the same effects as the first embodiment described above, it becomes easier to identify the state of the primary side of the transformer.

[0081] (Third embodiment) A third embodiment will now be described. In the first embodiment, an example in which an operational amplifier is used to configure the signal generator 2 is shown and exemplified. Instead, in the present embodiment, an example in which a digital type signal generator 2D is used is shown and the differences from the first embodiment are mainly described.

[0082] FIG. 13 is a configuration diagram of an AC electric circuit short circuit determination device according to an embodiment. The AC electric circuit short-circuit determination device shown in Fig. 13 includes a digital signal generator 2D. The signal generator 2D includes an inverter 3 that is mainly configured with a digital circuit. The inverter 3 generates a three-phase AC voltage by voltage frequency control (Vf control) or the like. The inverter 3 may be configured as a power converter that converts DC power into AC power. Note that the inverter 3 of this embodiment can output any magnitude of output power as long as it outputs an AC voltage waveform. The AC voltage waveform should preferably be a sine wave.

[0083] The current source circuit 4 receives the three-phase AC voltage generated by the inverter 3 and converts it to generate a current of a desired current value. The current source circuit 4 passes the generated current through the electric circuit under test.

[0084] For example, by configuring the signal generator 2D to include an inverter 3 that generates a three-phase AC signal at a test frequency, it is possible to identify a short circuit in an electric circuit in the same manner as in the first embodiment. In addition, the inverter 3 can manage the signal phase and signal amplitude for each phase independently, which makes it easy to manage the signal phase and signal amplitude when changing the test frequency, such as by adjusting the signal frequency within a specified range while setting the phase difference between each phase to 120 degrees and the signal amplitude to be constant.

[0085] (Fourth embodiment) A fourth embodiment will now be described. In the first to third embodiments, examples using a current source circuit 4 formed by an electronic circuit have been shown and described. Instead, in the present embodiment, an example using a rotating electric machine 4M as the current source circuit 4 will be shown and described focusing on the differences from the first embodiment.

[0086] FIG. 14 is a configuration diagram of an AC electric circuit short circuit determination device according to an embodiment. The AC electric circuit short circuit determination device shown in FIG. The rotating electric machine 4M is an example of a three-phase AC generator. The rotating electric machine 4M generates a three-phase AC current by rotating the shaft of the rotating electric machine 4M at a predetermined speed using an electric motor (not shown) or the like. The rotating electric machine 4M passes this three-phase AC current through an electric circuit to be tested.

[0087] For example, the inverter 3 can be used to control the motor to control the speed of the rotating electric machine 4M. The inverter 3 can output a three-phase AC current of a test frequency from the rotating electric machine 4M by increasing the speed of the motor in a stepwise or gradually manner.

[0088] As described above, the current source circuit 4 includes the rotating electric machine 4M that generates a three-phase AC current. Even if the rotating electric machine 4M is used as the current source circuit 4, a short circuit in an electric circuit can be identified in the same manner as in the first embodiment.

[0089] Fifth embodiment A fifth embodiment will now be described. In the first to third embodiments, an example in which a current source circuit 4 is used has been shown and described. In the fourth embodiment, an example in which a rotating electric machine 4M is used has been shown and described. In these examples, the current to be supplied to the electric circuit under test is supplied from a current source. Instead, in this embodiment, an example in which current buffer circuits 4B and 4C are used is shown and described, focusing on the differences from the first embodiment.

[0090] An example of a voltage source circuit with a drooping characteristic function will be described with reference to FIGS. 15A and 15B. 15A and 15B are configuration diagrams of a voltage source circuit with a drooping characteristic function according to an embodiment. A current buffer circuit 4B shown in FIG. 15A and a current buffer circuit 4C shown in FIG. 15B are examples of a voltage source circuit with a drooping characteristic function. The drooping characteristic function of the current buffer circuit 4B and the current buffer circuit 4C also serves as an overcurrent protection function. Although one phase is shown in this figure, similar circuits are applied to the other two phases.

[0091] For example, the current buffer circuit 4B is a buffer circuit using an operational amplifier with a gain of 1. A resistor (called a current detection resistor) is connected in series to the output of this operational amplifier to detect the magnitude of the output current. When a short circuit occurs at the output of the current buffer circuit 4B, a potential difference occurs between the output voltage of the operational amplifier and the output voltage of the current buffer circuit 4B, causing a voltage drop in the current detection resistor. The current flowing through this current detection resistor is limited to a current value determined by the power supply voltage of the operational amplifier (or the maximum value of the output voltage of the operational amplifier) ​​and the impedance of the current detection resistor. This limits the output current of the current buffer circuit 4B to the above current value. As a result, the voltage output by the current buffer circuit 4B drops due to a drooping characteristic with a predetermined current as the upper limit.

[0092] Similarly to the above, by providing a current buffer circuit 4C using transistors at each output of the signal generator 2, the above requirement can be met. The current buffer circuit 4C is a transistor-based amplifier configured as a push-pull type. A resistor (called an emitter resistor) is connected in series with the emitter of the transistor to detect the magnitude of the emitter current. In this configuration, the emitter current is roughly equal to the output current of the current buffer circuit 4C. When the voltage generated in the emitter resistor becomes larger than the threshold voltage of a transistor (called an overcurrent protection transistor) provided for the overcurrent protection circuit, the overcurrent protection transistor turns ON, reducing the output current of the current buffer circuit 4C and resolving the overcurrent state. As a result, the voltage output by the current buffer circuit 4C drops due to the drooping characteristic with a certain current as the upper limit.

[0093] Such a current buffer circuit 4B or 4C is connected to the electric path under test to apply a voltage to the electric path. If a short circuit occurs in that circuit, the voltage will drop due to the droop characteristic in response to an overcurrent. If no short circuit occurs in the electrical path, the overcurrent protection circuit will not respond and the output voltage will be at the desired level.

[0094] As described above, even if the current buffer circuit 4B or 4C is used instead of the current source circuit 4, a short circuit in an electric path can be identified in the same manner as in the first embodiment.

[0095] According to the AC electric circuit short-circuit determination device shown in any of the above-described embodiments, it becomes possible to identify a short circuit in an electric circuit by including a current source circuit that generates a current for each phase with a current value corresponding to the amplitude value of a three-phase AC signal at a test frequency and flows the generated current to each phase of a test target electric circuit that is in a voltage-free state before the start of a determination test, and a determiner that detects a voltage generated in the test target electric circuit while the generated current is flowing from the current source circuit to the test target electric circuit and determines the magnitude of the voltage relative to a predetermined threshold value.

[0096] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope of the invention and its equivalents described in the claims, as well as in the scope and spirit of the invention. [Explanation of symbols]

[0097] 1 AC circuit short circuit determination device 2. Signal Generator 3 Inverter 4 Current source circuit 5 Judgment section

Claims

1. a current source circuit that generates a current for each phase, the current value of which corresponds to the amplitude value of a three-phase AC signal having a test frequency, and causes the generated current to flow through each phase of a test target electric circuit that is in a no-voltage state before a judgment test is started; a determiner that detects a voltage generated in the test target electric circuit while the generated current is flowing from the current source circuit to the test target electric circuit, and determines a magnitude of the voltage relative to a predetermined threshold value; An AC circuit short circuit determination device comprising:

2. a signal generator that sets one of a first frequency and a second frequency as the test frequency and generates a three-phase AC signal of the test frequency; Equipped with When the test circuit is provided with an isolation transformer, The signal generator causes the generated current to flow through each phase of the test target electric circuit on the secondary side of the transformer; The determiner detects a voltage generated in each phase of the test target electric circuit on the secondary side of the transformer and determines the magnitude of the voltage. The AC electric circuit short circuit determination device according to claim 1 .

3. a signal generator that sets one of a first frequency and a second frequency as the test frequency and generates a three-phase AC signal of the test frequency; Equipped with The first frequency is a frequency lower than a lower limit frequency of an allowable fluctuation range of a rated AC frequency of the transformer, The second frequency is higher than the first frequency and lower than an upper limit frequency of the allowable fluctuation range. The AC electric circuit short circuit determination device according to claim 2 .

4. The signal generator includes: an oscillator that outputs a signal of the test frequency; a three-phase signal generator for converting the signal at the test frequency into a three-phase AC signal at the test frequency; Including, The AC circuit short circuit determination device according to claim 2 .

5. the test frequency signal is a single-phase AC signal; The three-phase AC signal of the test frequency is a first phase signal having a phase based on the phase of the single-phase AC signal; A second phase signal having a phase advanced from the phase of the single-phase AC signal; and a third phase signal having a phase delayed from the phase of the single-phase AC signal. The AC circuit short circuit determining device according to claim 4.

6. The three-phase signal generator includes: a first phase based on a reference phase of the single-phase AC signal; a second phase that is advanced from a reference phase of the single-phase AC signal; and a third phase whose phase is delayed from a reference phase of the single-phase AC signal, as the three-phase AC signal of the test frequency. The AC electric circuit short circuit determining device according to claim 5.

7. The three-phase signal generator includes: a first phase adjustment unit that inverts a phase of the single-phase AC signal at a reference frequency, the phase being advanced by a first angle from the phase of the single-phase AC signal, to generate a second phase signal; a second phase adjustment unit that generates a third-phase signal having a phase advanced by a second angle from the phase advanced by the first angle at the reference frequency; The AC electric circuit short circuit determination device according to claim 5 .

8. The signal generator includes: an inverter for generating a three-phase AC signal at said test frequency; The AC circuit short circuit determination device according to claim 2 .

9. The current source circuit comprises: A rotating electric machine that generates a three-phase AC signal of the test frequency. The AC electric circuit short circuit determination device according to claim 1 .

10. The determiner is The magnitude of the voltage generated between the phases on the secondary side of the transformer is determined while the current source circuit is causing the generated current to flow on the secondary side of the transformer. The AC circuit short circuit determination device according to claim 2 .

11. The determiner is When the magnitude of the voltage generated between the phases on the secondary side of the transformer is a value close to 0 in a state where the current source circuit is flowing the generated current to the secondary side of the transformer, it is determined that there is a possibility of a line-to-line short circuit on the secondary side or the primary side of the transformer. The AC electric circuit short circuit determination device according to claim 10.

12. The oscillator of the signal generator is configured to be able to change the test frequency. The AC circuit short circuit determining device according to claim 4.

13. The oscillator of the signal generator is configured to be able to change the test frequency by receiving an operation. The AC circuit short circuit determining device according to claim 4.

14. generating a current having a current value corresponding to an amplitude value of a three-phase AC signal having a test frequency for each phase, and causing the generated current to flow from a current source circuit to each phase of a test target electric circuit that is in a no-voltage state before starting a judgment test; detecting a voltage generated in the test target electric circuit while the generated current is flowing from the current source circuit to the test target electric circuit, and determining a magnitude of the voltage relative to a predetermined threshold value; A method for determining whether an AC circuit is short-circuited, comprising:

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