JP5535880B2 - Ungrounded AC circuit ground fault detector - Google Patents

Description

  The present invention includes a commercial frequency circuit in which a plurality of feeders are branched from a bus, and an ungrounded AC circuit in which an inverter circuit is connected to each feeder. The present invention relates to a ground fault detection device for an ungrounded AC circuit capable of detecting both ground faults.

  There has been proposed a ground fault detection circuit for detecting a ground fault in a non-grounded line and determining whether the ground fault is a one-wire ground fault or a two-wire ground fault (for example, see Patent Document 1). This ground fault detection circuit detects the zero-phase current of the single-phase AC line on the load side from the ground impedance that grounds each line of the non-grounded single-phase AC line, and generates a power frequency signal corresponding to the zero-phase current. A determination circuit for determining the two-wire grounding of the single-phase AC line based on the output of the output zero-phase current sensor is provided.

  Conventionally, such a non-grounded AC circuit 1 includes a commercial frequency circuit 2 in which a plurality of feeders L1 to Ln are branched from a bus L0 as shown in FIG. In this system, an inverter circuit 3 is connected to each of the feeders L1 to Ln of the non-grounded AC circuit 1. In this inverter circuit 3, inverters INV1 to INVn are connected to the load side of each of the feeders L1 to Ln of the ungrounded AC circuit 1, and variable speed motor loads M1 to Mn are connected to the output side of the inverters INV1 to INVn. The structure is provided.

  The bus L0 of the non-grounded AC circuit 1 is provided with a zero-phase transformer EVT for detecting a ground fault of the entire non-grounded AC circuit, and a zero-phase current transformer ZCT0 is connected to the ground line of the zero-phase transformer EVT. Is provided. In addition, each of the feeders L1 to Ln of the non-grounded AC circuit 1 is provided with zero-phase current transformers ZCT1 to ZCTn for detecting ground faults of the feeders L1 to Ln. Ground fault detection circuits CT0 to CTn are connected to the zero phase current transformer ZCT0 provided on the ground line of the zero phase transformer EVT and the zero phase current transformers ZCT1 to ZCTn provided to the feeders L1 to Ln, respectively. Has been. In addition, the code | symbol CB0-CBn in a figure is a circuit breaker provided in bus L0 and each feeder L1-Ln.

  In the ground fault detection circuits CT0 to CTn, when a ground fault occurs in the feeders L1 to Ln of the ungrounded AC circuit 1, a commercial low-pass filter (LPF) is used to detect a ground fault current at the commercial frequency. A frequency component higher than the frequency is cut. In the ground fault detection circuits CT0 to CTn, only the ground fault current at the commercial frequency is detected by this low-pass filter.

Japanese Patent Laid-Open No. 9-163584

  By the way, in the ground fault detection apparatus of the non-grounded AC circuit 1 described above, for the purpose of detecting a ground fault in the commercial frequency circuit 2, a ground fault detection circuit CT0 to CTn having a built-in low-pass filter is provided. It has become. On the other hand, in the inverter circuit 3, since the variable speed motor loads M1 to Mn are operated while controlling the speed, the output frequency is, for example, about 0 to 400 Hz.

  Therefore, when a ground fault occurs in the inverter circuit 3, the ground fault detection circuits CT0 to CTn described above cannot detect the ground fault. That is, the output frequency of the inverter circuit 3 may be higher than the commercial frequency, and the ground fault detection circuits CT0 to CTn cut the frequency component higher than the commercial frequency by the low-pass filter. However, the current situation is that it is impossible to detect the ground fault current at the output frequency of the inverter circuit 3 which is too high.

  In some cases, a ground fault detection circuit capable of detecting a ground fault in the inverter circuit 3 is built in the inverters INV1 to INVn. In that case, the inverter itself becomes larger and the cost of the inverters INV1 to INVn increases. It becomes an expensive ground fault detection device. Furthermore, when a ground fault occurs in the inverter circuit 3 when the inverters INV1 to INVn are started or stopped, the output frequency of the inverter circuit 3 is in the low frequency region, so that it is provided on the ground line of the zero-phase transformer EVT. There is a problem that the ground fault current cannot be detected by the zero phase current transformer ZCT0, and the iron core of the zero phase transformer EVT is demagnetized due to the ground fault current in the low frequency region. there were.

  Therefore, the present invention has been proposed in view of the above-described problems, and the object of the present invention is to provide both low-cost ground faults occurring in commercial frequency circuits and ground faults occurring in inverter circuits. An object of the present invention is to provide a ground fault detection device for a non-grounded AC circuit that can detect a fault.

As a technical means for achieving the above-described object, the ground fault detection device for an ungrounded AC circuit according to the present invention branches a plurality of feeders from a bus provided with a ground fault detection zero-phase transformer, A non-grounded AC circuit having a commercial frequency circuit provided with a zero-phase current transformer for detecting a ground fault in a feeder, and an inverter circuit connected to each feeder, the ground wire on the primary side of the zero-phase transformer has its A resistor for detecting a ground fault current flowing in the ground line is provided, and a ground fault detection circuit connected to the zero-phase current transformer and the resistor includes a ground fault current at a commercial frequency, a frequency component higher than the commercial frequency, and It is possible to detect a ground fault current at an output frequency of an inverter in a low frequency region .

  In the present invention, the ground fault current flowing through the ground line is detected by the ground fault detection circuit by monitoring the voltage across the resistor provided on the ground line of the zero-phase transformer. In the ground fault detection circuit, it is possible to detect the ground fault current at both the commercial frequency and the inverter output frequency without cutting a frequency component higher than the commercial frequency without incorporating a low-pass filter as in the past. This makes it possible to detect a ground fault that has occurred in the inverter circuit. As a result, it is not necessary to incorporate a ground fault detection circuit that can detect a ground fault in the inverter circuit into the inverter, so that it is possible to reduce the cost of a ground fault occurring in a commercial frequency circuit and a ground fault occurring in the inverter circuit. Both accidents can be detected.

  In addition, the resistor that functions as a ground fault current detection resistor also functions as a limiting resistor. In other words, when a ground fault occurs in the inverter circuit when the inverter is started or stopped, even if the output frequency of the inverter circuit is in the low frequency region, the ground fault current in the low frequency region causes the zero-phase transformer to The ground fault current can be reliably detected without the iron core being demagnetized.

  It is desirable that the ground fault detection circuit according to the present invention compares the phase of the ground fault current flowing through the resistor with the phase of the current flowing through each feeder, and identifies the ground fault feeder based on the phase comparison. The ground fault feeder can be easily identified by the phase comparison of the ground fault current.

  It is desirable that the ground fault detection circuit according to the present invention detects the magnitude of the current flowing through each feeder and specifies the ground fault feeder based on the comparison of the current values. It becomes possible to specify the ground fault feeder easily by comparing the current values of the ground fault current.

  The ground fault detection circuit in the present invention detects the carrier frequency component of the inverter circuit included in the ground fault current flowing in the ground fault feeder, and the ground fault point is the commercial frequency circuit or the inverter circuit depending on the presence or absence of the carrier frequency component. It is desirable to determine whether or not. It becomes easy to determine whether the ground fault point is a commercial frequency circuit or an inverter circuit based on the presence or absence of the carrier frequency component of the inverter circuit.

  The resistance in the present invention is preferably set to a value that does not saturate the iron core of the zero-phase transformer due to the low-frequency ground fault current that occurs when the inverter is started and stopped. In this way, when a ground fault occurs in the inverter circuit when the inverter is started and stopped, it is possible to prevent the core of the zero-phase transformer from being demagnetized by the ground fault current in the low frequency region. Burnout of the zero-phase transformer due to current generation can be prevented beforehand.

  According to the present invention, it is possible to detect a ground fault current at both the commercial frequency and the output frequency of the inverter without cutting a frequency component higher than the commercial frequency without incorporating a low-pass filter as in the prior art. Thus, it becomes possible to detect a ground fault occurring in the inverter circuit. As a result, it is not necessary to incorporate a ground fault detection circuit that can detect a ground fault in the inverter circuit into the inverter, so that it is possible to reduce the cost of a ground fault occurring in a commercial frequency circuit and a ground fault occurring in the inverter circuit. Both accidents can be detected.

1 is a schematic configuration circuit diagram showing a ground fault detection device for an ungrounded AC circuit in an embodiment of the present invention. It is a schematic structure circuit diagram which shows the prior art example of the ground fault detection apparatus of a non-grounded AC circuit.

  An embodiment of a ground fault detection device for an ungrounded AC circuit according to the present invention will be described in detail below with reference to the drawings. In FIG. 1, the same parts as those in FIG.

  The ungrounded AC circuit 1 in this embodiment includes a commercial frequency circuit 2 that branches a plurality of feeders L1 to Ln from a bus L0 as shown in FIG. 1, and an inverter is connected to each feeder L1 to Ln of the commercial frequency circuit 2 Circuit 3 is connected. In this inverter circuit 3, inverters INV1 to INVn are connected to the load side of each feeder L1 to Ln of the commercial frequency circuit 2, and variable speed motor loads M1 to Mn are connected to the output side of the inverters INV1 to INVn. It has a configuration. In addition, the code | symbol CB0-CBn in a figure is a circuit breaker provided in bus L0 and each feeder L1-Ln.

  The bus L0 of the non-grounded AC circuit 1 is provided with a zero-phase transformer EVT for detecting a ground fault of the entire non-grounded AC circuit, and a resistance Rs is provided on the ground line of the zero-phase transformer EVT. Yes. In addition, each of the feeders L1 to Ln of the non-grounded AC circuit 1 is provided with zero-phase current transformers ZCT1 to ZCTn for detecting ground faults of the feeders L1 to Ln. Ground fault detection circuits RT0 to RTn are connected to the resistor Rs provided on the ground line of the zero phase transformer EVT and the zero phase current transformers ZCT1 to ZCTn provided to the feeders L1 to Ln, respectively.

  Here, the difference between the ground fault detection device of the conventional non-grounded AC circuit 1 shown in FIG. 2 and the ground fault detection device of the non-grounded AC circuit 1 of the embodiment shown in FIG. The zero-phase current transformer ZCT0 is provided in the ground line of the transformer EVT, and the ground fault detection circuits CT0 to CTn are provided with the low-pass filter. In this embodiment, the resistor Rs is connected to the ground line of the zero-phase transformer EVT. And the ground fault detection circuits RT0 to RTn are not provided with a low-pass filter.

  Note that the resistor Rs of this embodiment functions as a resistance for detecting a ground fault current, and also functions as a limiting resistor for preventing the core deviation of the zero-phase transformer. The ground fault detection circuits RT0 to RTn also have a current phase discrimination function and a carrier frequency component discrimination function of the inverter circuit 3, as will be described later.

  In the non-grounded AC circuit 1, the ground fault current flowing in the ground line is detected by the ground fault detection circuit RT0 by monitoring the voltage across the resistor Rs provided in the ground line of the zero-phase transformer EVT. By detecting the ground fault current, the ground fault resistance value can be determined. The ground fault detection circuits RT0 to RTn do not incorporate a low-pass filter as in the prior art, do not cut a frequency component higher than the commercial frequency, and have a ground fault current at both the commercial frequency and the output frequency of the inverters INV1 to INVn. It is possible to detect a ground fault that has occurred in the inverter circuit 3. As a result, it is not necessary to incorporate in the inverters INV1 to INVn a ground fault detection circuit capable of detecting a ground fault in the inverter circuit 3, so that the ground fault and inverter circuit generated in the commercial frequency circuit 2 can be produced at low cost. Both of the ground faults that occurred in 3 can be detected.

  Here, when a ground fault occurs in the inverter circuit 3 when the inverters INV1 to INVn are started or stopped, conventionally, a ground fault current is generated by the zero phase current transformer ZCT0 provided on the ground line of the zero phase transformer EVT. (See FIG. 2), since the output frequency of the inverter circuit 3 is in a low frequency region when the inverters INV1 to INVn are started or stopped, the ground fault current is detected by the zero-phase current transformer ZCT0. Moreover, the iron core of the zero-phase transformer EVT is demagnetized due to a ground fault current in a low frequency region, and an overcurrent is generated.

  On the other hand, as in this embodiment, by monitoring the voltage across the resistor Rs provided on the ground line of the zero-phase transformer EVT, the output of the inverter circuit 3 when the inverters INV1 to INVn are started or stopped Even when the frequency is in the low frequency region, the ground fault current can be detected, and the resistor Rs that functions as a detection resistor for the ground fault current also functions as a limiting resistor. The iron core of the zero-phase transformer EVT is not demagnetized by the current, and no overcurrent is generated.

  Identification of feeders L1 to Ln (hereinafter referred to as ground fault feeders) in which a ground fault has occurred in the ungrounded AC circuit 1 is performed in the following manner based on the phase of the current flowing through the feeders L1 to Ln.

  In the ground fault detection circuits RT0 to RTn, the phase of the ground fault current flowing through the resistor Rs and the current flowing through each of the feeders L1 to Ln are compared. For example, when a ground fault occurs in the feeder L2 as illustrated, a ground fault current Igi having the same phase as the ground fault current Igs flowing through the resistor Rs flows through the ground fault feeder L2. On the other hand, a current Ic having a phase opposite to that of the ground fault current Igs flowing through the resistor Rs flows to the feeder L1 (hereinafter referred to as a healthy feeder) in which a ground fault has not occurred due to the capacitance C to the ground. Therefore, the feeder L2 through which the ground fault current Igi having the same phase as the ground fault current Igs flowing through the resistor Rs can be specified as the ground fault feeder. The ground fault feeder can be easily identified by the phase comparison of the ground fault current. As for the other feeders L3 to Ln in which no ground fault has occurred, a current having a phase opposite to that of the ground fault current Igs flowing through the resistor Rs flows due to the ground capacitance, similarly to the feeder L1 described above.

  The ground fault feeder in the non-grounded AC circuit 1 can be specified based on the magnitude of the current flowing through the feeders L1 to Ln.

  That is, the ground fault detection circuits RT0 to RTn detect the magnitudes of currents flowing through the feeders L1 to Ln. For example, when a ground fault occurs in the feeder L2 as shown in the figure, the current Ic from the other feeder L1 flows into the ground fault feeder L2 together with the ground fault current Igi. The maximum value obtained by adding the current Ic from the feeder L1 is flowed. From this, it is possible to specify the ground fault feeder L2 through which the maximum current flows. By detecting the maximum value of such a ground fault current, it becomes possible to easily specify the ground fault feeder. In addition, a current flows into the ground fault feeder L2 from the other feeders L3 to Ln in which no ground fault has occurred as in the above-described feeder L1.

  Next, for example, when a ground fault occurs in the feeder L2 as shown in the figure, whether the ground fault point in the ground fault feeder L2 is the commercial frequency circuit 2 or the inverter circuit 3 is as follows. So identify. That is, since the control signal of the inverter circuit 3 includes a carrier frequency component of about 1 kHz, for example, the ground fault point can be specified based on the presence or absence of this carrier frequency component.

  The ground fault detection circuits RT0 to RTn specify that the ground fault point is the inverter circuit 3 when the carrier frequency component of the inverter circuit 3 is included in the ground fault current Igi flowing through the ground fault feeder L2. If the carrier frequency component is not included in the ground fault current Igi, the ground fault point can be specified as the commercial frequency circuit 2. It becomes easy to determine whether the ground fault point is the commercial frequency circuit 2 or the inverter circuit 3 based on the presence or absence of the carrier frequency component of the inverter circuit 3.

  The resistance Rs connected to the ground line of the zero-phase transformer EVT is a value that does not saturate the iron core of the zero-phase transformer EVT due to the low-frequency ground fault current generated when the inverters INV1 to INVn are started and stopped, for example, It is set to 100 to 300Ω. In this way, when a ground fault occurs in the inverter circuit 3 when the inverters INV1 to INVn are started and stopped, the iron core of the zero-phase transformer EVT is demagnetized by the ground fault current in the low frequency region. Can be prevented, and burning of the zero-phase transformer EVT due to overcurrent can be prevented.

  In a system with a large ground capacitance in each of the feeders L1 to Ln, since the ground fault current flowing through the feeders L1 to Ln becomes large, in the ground fault detection circuits RT0 to RTn, when the ground fault current exceeds a predetermined threshold value The ungrounded AC circuit 1 may be protected by disconnecting the ground fault feeder L2 from another feeder by the circuit breaker CB2.

  The present invention is not limited to the above-described embodiments, and can of course be implemented in various forms without departing from the gist of the present invention. It includes the equivalent meanings recited in the claims and the equivalents recited in the claims, and all modifications within the scope.

DESCRIPTION OF SYMBOLS 1 Ungrounded AC circuit 2 Commercial frequency circuit 3 Inverter circuit EVT Zero phase transformer INV1-INVn Inverter L0 Bus L1-Ln Feeder Rs Resistance RT0-RTn Ground fault detection circuit ZCT0-ZCTn Zero phase current transformer

Claims (5)

Multiple feeders are branched from the bus with a zero-phase transformer for ground fault detection, each feeder is equipped with a commercial frequency circuit with a zero-phase current transformer for ground fault detection, and an inverter circuit is connected to each feeder In the non-grounded AC circuit, a resistance for detecting a ground fault current flowing in the ground line is provided on the ground line on the primary side of the zero-phase transformer, and a ground connected to the zero-phase current transformer and the resistor is provided. The fault detection circuit is capable of detecting a ground fault current of a commercial frequency, a frequency component higher than the commercial frequency, and a ground fault current of an output frequency of an inverter in a low frequency region. Fault detector.   2. The ground fault detection circuit according to claim 1, wherein the ground fault detection circuit compares the phase of the ground fault current flowing through the resistor with the phase of the current flowing through each feeder, and identifies the ground fault feeder based on the phase comparison. Fault detector.   2. The ground fault detection device for an ungrounded AC circuit according to claim 1, wherein the ground fault detection circuit detects the magnitude of a current flowing through each feeder and identifies the ground fault feeder based on a comparison of the current values.   The ground fault detection circuit detects a carrier frequency component of an inverter circuit included in a ground fault current flowing in the ground fault feeder, and determines whether a ground fault point is a commercial frequency circuit or an inverter circuit with or without the carrier frequency component. The ground fault detection apparatus of the non-grounded AC circuit according to any one of claims 1 to 3.   The non-grounding according to any one of claims 1 to 4, wherein the resistor is set to a value that does not saturate the iron core of the zero-phase transformer due to a low-frequency ground fault current that occurs when the inverter is started and stopped. AC circuit ground fault detector.

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