JP5396675B2 - Insulation monitoring device - Google Patents

Description

  The present invention relates to an insulation monitoring device, and more particularly, a resistance included in a zero-phase current input from a ground wire of a single-phase two-wire type, single-phase three-wire type, and three-phase three-wire type electric circuit via a zero-phase current sensor. The present invention relates to an apparatus for detecting an effective value of a ground fault current.

  An insulation monitoring device for monitoring the leakage current of an electric circuit is known. In particular, in recent years, it has been necessary to monitor the electric circuit in a live state in response to a request for 24 hours of uninterruptible power. The leakage current includes the ground fault current Igc due to the ground capacitance C0 and the ground fault current Igr due to the insulation resistance R0, but the cause of the leakage fire is a decrease in the insulation resistance. If the leakage current Igr caused by the current can be accurately detected, the insulation state of the electric circuit can be accurately grasped, and a catastrophe such as a leakage fire can be prevented.

  As a conventional insulation monitoring device, there is one that applies a low frequency signal for measurement from an injection transformer to an electric circuit and detects a leakage current I0 that is fed back through a ground capacitance C0 and an insulation resistance R0 with a zero-phase current transformer. (See Patent Document 1). However, since this insulation monitoring device requires an injection transformer and a power supply device for generating a low frequency signal for measurement, and the circuit scale increases, there is a recent need for a small insulation monitoring device that does not use an injection transformer. It is growing.

  As an insulation monitoring method that does not use an injection transformer, for example, a zero cross point of a zero phase current waveform input from a zero phase current sensor is obtained, a zero cross point of a voltage waveform input from a voltage probe or the like is obtained, and a triangular shape is obtained from the phase difference. A method of calculating an effective value of a ground fault current Igr caused by an insulation resistance by performing a calculation using a function (hereinafter referred to as “a method”) is known (see Patent Document 2). Also, the vector calculation is performed using the zero-phase current waveform input from the zero-phase current sensor and the ideal sine wave generated with reference to the zero-cross point of the voltage waveform input from the voltage probe, etc. There is known a method (hereinafter referred to as “b method”) for obtaining an effective value of the leakage current Igr (see Patent Document 3).

JP-A-10-90324 JP 2005-140532 A JP 2002-125313 A

  However, in the case of the a method shown in Patent Document 2, a circuit such as a comparator is required as means for obtaining the zero cross point of the zero phase current waveform input from the zero phase current sensor. In the a method, it is necessary to determine the phase difference between the two phases with high accuracy by comparing the zero-phase current and the zero-cross point of the line voltage, and a high-precision comparator is required to obtain the phase difference with high accuracy. Become. As a result, there arises a problem that the physical scale is increased and the cost is increased.

  Further, in the case of the b method shown in Patent Document 3, means for generating an ideal sine wave is necessary, and in the implementation of software, the quantum that has passed through the AD converter from the zero-phase current waveform input from the zero-phase current sensor. Since the calculation using the trigonometric function is performed on the digitized data and the idealized sine wave discretized data, there is a problem in that the measurement accuracy decreases due to an increase in error factors. In particular, since the ideal waveform formed as a simulation does not always match the actual voltage waveform, if the ideal waveform and the actual voltage waveform deviate, the measurement accuracy may be greatly deteriorated.

  The present invention solves the above problems, and the object of the present invention is to eliminate the need for means for obtaining the zero-cross point of the zero-phase current waveform and eliminate the need for means for generating an ideal sine wave to eliminate two errors. Another object of the present invention is to provide a reliable insulation monitoring apparatus that is reduced in size and improved in accuracy by performing simple operations such as addition, subtraction, and constant conversion.

In order to solve the above-described problems, an insulation monitoring apparatus according to the present invention includes a zero-phase current detecting means for detecting a zero-phase current Io from a ground line of a single-phase two-wire or single-phase three-wire circuit, and the zero-phase current. Zero-phase current capturing means for capturing the zero-phase current Io detected by the detecting means, and inter-circuit voltage phase capturing means for capturing phase information of the voltage between the circuit between the ground line and the non-ground line of the circuit When the phase of the voltage between the circuits is a reference phase, the time variable is t, and the period of the voltage between the circuits is T, the period of the voltage between the circuits is a unit, and when 0 ≦ t ≦ T / 2, the above zero The zero-phase current Io (t) value output from the phase current capturing means is cumulatively added. When T / 2 <t <T, the zero-phase current Io (t) value is cumulatively added. Addition / subtraction means for subtracting one of the cumulative addition values from the other, and a predetermined calculation for the value output from the addition / subtraction means By applying it is characterized a calculating means for calculating an effective value igr resistive ground fault current, in that it comprises. The electrical circuit voltage phase capturing means outputs the detection timing of the zero cross point in the voltage waveform of the captured electrical circuit voltage as phase information, and the adding and subtracting means is an arbitrary zero cross point output from the electrical circuit voltage phase capturing means. The calculation means may include constant multiple conversion means for converting the value output from the addition / subtraction means by a constant multiple to obtain the effective value igr of the resistive ground fault current.

In addition, the insulation monitoring apparatus according to the present invention captures the zero-phase current Io detected by the zero-phase current detection means and the zero-phase current detection means for detecting the zero-phase current Io from the ground line of the three-phase three-wire electric circuit. Zero-phase current capturing means, inter- circuit voltage phase capturing means for capturing phase information of the inter-circuit voltage between the first non-ground line and the second non-ground line of the electrical circuit, and phase information of the inter- circuit voltage Phase shift means for converting phase information moved by 90 °, phase information output from the phase shift means as a reference phase, time variable as t, and period between voltage paths as T. The cumulative value of the zero-phase current Io (t) at 0 ≤ t ≤ T / 2 is cumulatively added, and the value of the zero-phase current Io (t) at T / 2 <t <T is cumulatively added. Addition / subtraction means for subtracting the other from one of the cumulative addition values, and the value output from the addition / subtraction means And a calculation means for obtaining an effective value igr of the resistive ground fault current by performing a predetermined calculation. The electric circuit voltage phase capturing means outputs, as phase information, the detection timing of the zero cross point in the voltage waveform of the acquired electric circuit voltage to the phase moving means, and the phase moving means outputs the zero cross point timing to 90 ° of the reference phase. The value is output to the adder / subtractor by moving by the amount. There may be included a constant multiple conversion means for converting and obtaining the effective value igr of the resistive ground fault current.

The insulation monitoring device according to the present invention includes a device power supply for supplying power to the insulation monitoring device, a phase of a power supply voltage taken in by the device power supply from an arbitrary electric circuit, and a reference phase output from an inter-circuit voltage phase capturing means. obtains a phase difference by comparing, further comprising a phase comparator storing means for storing the phase difference, the phase comparator storage means, generates a reference phase based on the phase and the phase difference between the supply voltage taken from a predetermined path May be.

In the present invention, the phase comparison storage means inputs a zero-phase current Io having a resistance ground fault current component of zero to the zero-phase current detection means, and the resistance ground fault current component obtained at this time becomes zero. It is preferable to include a phase difference adjusting means for adjusting the phase difference.

  In the present invention, the constant multiple conversion means inputs a zero-phase current Io having a predetermined effective value to the zero-phase current detection means, and the effective value of the zero-phase current obtained at this time is the same as the predetermined effective value. It is preferable to include an amplitude value adjusting means for adjusting the value of the constant multiple so as to be a value.

  According to the present invention, the time t = 0 of the reference phase is determined based on the zero cross point of the phase of the voltage waveform between the electric circuits input from the voltage detection means such as a voltage probe, and when 0 ≦ t ≦ T / 2, The value of Io (t) is added, and when T / 2 <t <T, the value of Io (t) is subtracted. Since it is a constant multiple of the effective value igr of the ripple current, there is no need for means for obtaining the phase of the zero-phase current waveform input from the zero-phase current sensor, and the voltage phase input from the voltage detection means such as a voltage probe is used. The means for generating the ideal sine wave is also unnecessary. Therefore, the circuit scale can be reduced. Since it is not necessary to calculate the phase difference itself between the zero-phase current and Igr in order to obtain Igr, the measurement accuracy of the insulation resistance can be increased.

It is a block diagram which shows the structure of the insulation monitoring apparatus by 1st Embodiment. It is a block diagram which shows the structure of the insulation monitoring apparatus by 2nd Embodiment. It is a vector diagram which shows the electric current component of the zero phase current in a single phase 3 wire system and a single phase 2 wire system. It is a figure which shows the relationship between the voltage between electrical circuits, and a zero phase current. It is a block diagram which shows the structure of the insulation monitoring apparatus by 3rd Embodiment. It is a block diagram which shows the structure of the insulation monitoring apparatus by 4th Embodiment. It is a block diagram which shows the structure of the insulation monitoring apparatus by 5th Embodiment. It is a vector diagram which shows the electric current component of the zero phase current in a three-phase three-wire system. FIG. 3 is a block diagram showing a configuration of an insulation monitoring device in the case of capturing a phase of a three-phase three-wire electric circuit in two phases of one non-ground phase and a ground phase and another non-ground phase and a ground phase. is there. It is a graph which shows the simulation result at the time of giving an Io phase error. It is a graph which shows the simulation result at the time of giving Io RMS value error. It is a graph which shows the simulation result when not giving an error. It is a graph which shows the simulation result at the time of increasing the sampling number of 1 period. It is a schematic diagram for demonstrating the method of calculating | requiring igr by setting t = 0 as the time of about β from the zero crossing point of the electric circuit voltage. It is a schematic diagram for demonstrating the method of calculating | requiring igr by making t = 0 the time of being late | slow by (pi) / 2 from the zero crossing point of the voltage between electrical circuits.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a block diagram showing a configuration of an insulation monitoring apparatus according to the first embodiment of the present invention.

  As shown in FIG. 1, the insulation monitoring apparatus 1A according to the present embodiment is a phase capture type insulation monitoring apparatus that monitors a single-phase three-wire electric circuit 20 and extends from a ground line (ground phase) 20o. Zero-phase current sensor (zero-phase current detection means) 2 attached to the ground line 3o, zero-phase current capturing means 4 comprising an amplifier circuit, LPF, etc., and non-grounded via a voltage probe (voltage detection means) 3a The voltage phase adjustment between the electric circuits connected to one of the wires (non-ground phase) 20a and 20b (here, the non-ground wire 20a) and connected to the ground wire 20o via the voltage probe (voltage detection means) 3b. Loading means 5, zero-phase current capturing means 4, addition / subtraction means 6 connected to circuit voltage phase capturing means 5, constant multiple conversion means 7 connected to addition / subtraction means 6, and constant multiple conversion means 7 And connected notification means 8.

  The zero-phase current capturing means 4 captures the zero-phase current detected by the zero-phase current sensor 2 and extracts the zero-phase current waveform Io (t) (t is a time variable). On the other hand, the inter-circuit voltage phase capturing means 5 captures the inter-circuit voltage between the ground line 20o and the non-ground line 20a and obtains the zero cross point of the inter-circuit voltage. The difference between the zero cross point P1 where the zero phase current crosses from minus to plus and the zero cross point P2 where the zero phase current crosses from minus to plus becomes the cycle T of the zero phase current. The adder / subtractor 6 sets the detection time of the zero-cross point P1, which is the reference phase, to t = 0, the time of one cycle as T, and the zero-phase current when the first half of the cycle is 0 ≦ t ≦ T / 2. The value of Io (t) is added, and when T / 2 <t <T, which is the half cycle of the latter half, the value of Io (t) is subtracted. The constant multiple conversion means 7 multiplies the addition / subtraction value by a conversion constant to obtain an effective value igr of the resistive ground fault current. The notification means 8 monitors the effective value igr of the resistive ground fault current, and notifies that the lamp is turned on or the value is displayed when the effective value reaches the alarm value.

  FIG. 2 is a block diagram showing a configuration of an insulation monitoring apparatus according to the second embodiment of the present invention.

The insulation monitoring device 1B shown in FIG. 2 is different from the insulation monitoring device 1A of FIG. 1 in that the single-phase two-wire electric circuit 30 is monitored, but the device configuration is substantially the same, and is for phase acquisition. The lead wires are the same in that one is connected to the non-ground line 30a and the other is connected to the ground line 3o extending from the ground line 30o . For this reason, the same components are denoted by the same reference numerals, and detailed description of the insulation monitoring device 1B is omitted.

  Next, a method for obtaining the effective value igr of the resistive ground fault current will be described in detail.

  FIG. 3 is a vector diagram showing current components of the zero-phase current in the single-phase three-wire system and the single-phase two-wire system.

  As shown in FIG. 3, the zero-phase current Io is a combination of the capacitive ground fault current Ic and the resistive ground fault current Igr. In the single-phase three-wire and single-phase two-wire electric circuits, The phases of the fault current Ic and the resistive ground fault current Igr are shifted by 90 °. α is a phase angle between the zero-phase current Io and the resistive ground fault current Igr. Therefore, when the magnitude of the resistive ground fault current Igr is expressed by the zero-phase current Io, the following equation (1) is obtained. That is, if the magnitude of the zero-phase current Io and the phase angle α are obtained, the magnitude of the resistive ground fault current Igr can be obtained.

  Next, consider the zero-phase current waveform Io (t). With t as a time variable, the time at the zero crossing point, which is the reference phase output from the inter-circuit voltage phase capturing means 5, is t = 0, and the phase difference between the reference phase and the zero-phase current waveform, that is, Igr (t) and Io When the phase difference of (t) is α, the amplitude value of the zero-phase current waveform is Io, the angular frequency is ω, the frequency is f, and the time of one cycle of the circuit frequency is T, the single-phase three-wire system and the single-phase 2 In the linear system, the zero-phase current waveform Io (t) output from the zero-phase current capturing means 4 to the adding / subtracting means 6 can be expressed as shown in Expression (2).

  FIG. 4 is a diagram illustrating the relationship between the voltage between the electric circuits and the zero-phase current. The phase shift between the electric circuit voltage (reference phase) and the zero-phase current corresponds to the phase angle α shown in Equation (2). Of course, the cycle of the voltage between the electric circuits and the cycle of the zero-phase current are the same. As shown in FIG. 4, when 0 ≦ t ≦ T / 2, zero-phase current Io (t) is cumulatively added, and when T / 2 <t <T, the value of Io (t) is cumulatively subtracted. The result is asIo. asIo is as shown in Equation (3) (Igr in the equation is the amplitude value of the resistive ground fault current). By applying the relationship of equation (1), the phase angle α is removed from equation (3).

  Therefore, the amplitude value Igr of the resistive ground fault current is as shown in the formula (4). When the effective value of the resistive ground fault current to be obtained is igr, the formula (5) is considered in consideration that igr is positive. ) To express igr. Based on the known value asIo, igr can be obtained without calculating the phase angle α.

  In the design for software implementation, k is a time variable for one-period sampling, and the zero-phase current waveform output from the zero-phase current capturing means 4 is output from the Io (k) and the inter-circuit voltage phase capturing means 5. The time of the zero cross point of the reference phase is k = 0, the phase difference between the reference phase and the zero-phase current waveform is α, the amplitude value of the zero-phase current waveform is Io, and the number of samplings of one cycle of the circuit frequency is N (N is 2) Io (k) can be expressed as in Equation (6).

  Here, r is an offset value at the time of input to the AD converter and can be known in design, but it may be obtained every cycle. When 0 ≤ k ≤ N / 2, the value of Io (k) is added. When N / 2 <k <N, the value of Io (k) is subtracted, and the result is asIo. (7) (Igr is the amplitude value of the resistive ground fault current). By applying the relationship of equation (1), the phase angle α is removed from equation (7).

  Therefore, the amplitude value Igr of the resistive ground fault current is as shown in Formula (8). If the effective value of the resistive ground fault current to be obtained is igr, the formula (9) is taken into account that igr is positive. It becomes.

  However, the conversion based on the number of bits and the range of the AD converter is not considered here because the constant of the constant multiple conversion means 7 changes. A median or the like may be used as a measure for avoiding multiple interrupts.

  As described above, the insulation monitoring apparatus 1 according to the present embodiment determines the time t = 0 of the reference phase based on the zero cross point of the phase of the voltage waveform between the electric circuits input from the voltage probe, and 0 ≦ t ≦ T / 2 Io (t) value is added at the time of I, and Io (t) value is subtracted when T / 2 <t <T, and the result of adding / subtracting one period is multiplied by a constant. Thus, the effective value igr of the resistive ground fault current can be obtained. If the relationship of Formula (1) is applied to Formula (3) or Formula (7), the phase angle α can be removed from the formula. That is, Igr and igr can be obtained without taking the effort to find α itself. Therefore, a means for obtaining the phase of the zero-phase current waveform input from the zero-phase current sensor becomes unnecessary, and a means for generating an ideal sine wave based on the voltage phase becomes unnecessary. Since the two are not required, the scale can be reduced, and the measurement accuracy of the insulation resistance can be improved because there is no error based on the calculation of the phase angle α and the calculation of the ideal sine wave.

  FIG. 5 is a block diagram showing a configuration of an insulation monitoring apparatus according to the third embodiment of the present invention.

  As shown in FIG. 5, the insulation monitoring device 1C according to the present embodiment is characterized by using the device power supply 10 of the insulation monitoring device 1C and determining the time t = 0 of the reference phase based on the zero cross point of the power supply voltage waveform. There is in point to do. The device power supply 10 is necessary for operating the insulation monitoring device 1C itself, and is composed of a transformer circuit, LPF, or the like. Furthermore, the insulation monitoring device 1C is provided with a phase comparison storage means 11 which is the original reference output from the phase of the power supply voltage provided from the apparatus power supply 10 and the voltage phase capturing means 5 between the electric circuits. The phase difference d obtained by comparing with the phase is stored. During operation of the insulation monitoring device 1C, the phase difference d held by the phase comparison storage means 11 is added to the phase from the device power supply 10, and the effective value igr of the resistive ground fault current is obtained using the result as a reference phase. .

  Therefore, if the phase of the voltage waveform of the electric circuit is first acquired by using the voltage probes 3a and 3b, even if the signal acquisition means 3a and 3b of the inter-circuit voltage phase acquisition means 5 are removed thereafter, the apparatus The effective value igr of the resistive ground fault current can be obtained by adding the phase difference d held by the phase comparison storage unit 11 to the phase from the power supply 10 and using the added result as a reference phase. Therefore, it is very convenient in a situation where it is difficult to always install the voltage probe, and the cost can be reduced.

  The reason why the voltage probes 3a and 3b are used in the initial setting is that the phase of the power supply voltage acquired from the apparatus power supply 10 does not always coincide with the phase of the original electric circuit position to be acquired using the voltage probes 3a and 3b. Is due to.

  Although it is desirable to monitor the insulation state of the electric circuit 20 on a 24-hour basis, there are situations where it is difficult to always connect the voltage probes 3a and 3b. According to the third embodiment, since igr can be calculated based on the voltage waveform of the apparatus power supply 10, it is possible to monitor insulation for 24 hours without always connecting a voltage probe. However, the operating power of the apparatus power supply 10 may be supplied from another electric circuit that is transformer-coupled to the electric circuit 20. Even if the operating power of the apparatus power supply 10 is supplied from the electric circuit 20, the voltage waveform supplied to the apparatus power supply 10 and the electric circuit 20 are provided by the delay in the apparatus power supply 10 and the transmission delay from the electric circuit 20 to the apparatus power supply 10. The phase of the voltage waveform is not always in phase. For this reason, although the voltage waveform of the electric circuit 20 and the voltage waveform of the apparatus power supply 10 are synchronized, some phase difference d (phase lag) is generated between the two. If the phase difference d is measured when the apparatus is installed, thereafter, the phase of the voltage waveform of the electric circuit 20 is obtained by adding the phase difference d to the phase of the voltage waveform provided to the apparatus power supply 10. Can do. Therefore, the insulation can be monitored without always connecting the voltage probes 3a and 3b.

  As described above, according to the present embodiment, since the reference phase is generated based on the voltage phase from the apparatus power supply 10 during the operation of the insulation monitoring apparatus 1C, it is not necessary to always connect the voltage probes 3a and 3b. Therefore, the configuration can be very advantageous in terms of reliability and cost. That is, when the voltage probes 3a and 3b are always connected to the electric circuit, the voltage probe itself may cause a ground fault, which may be a source of trouble. Further, in order to make the voltage probe compatible with the constant connection, it is necessary to make the voltage probe more durable and reliable, and the cost becomes high. However, if the voltage probe is used only at the time of installation of the insulation monitoring device and the voltage probe is removed after the phase is first taken in, it is advantageous in terms of cost because a simple voltage probe can be reused. .

  FIG. 6 is a block diagram showing a configuration of an insulation monitoring apparatus according to the fourth embodiment of the present invention.

  As shown in FIG. 6, the feature of the insulation monitoring device 1D according to the present embodiment is to adjust in advance the phase shift of the effective value igr of the resistive ground fault current due to variations in the characteristics of the zero-phase current sensor 2 and the board mounted components. It has a function. As shown in FIG. 3, when the zero-phase current Io consists only of the capacitive ground fault current Ic and the resistive ground fault current Igr is zero, the effective value igr of the resistive ground fault current is theoretically zero. However, in practice, the effective value igr of the resistive ground fault current is not always detected as 0 by the phase delay element included in the zero-phase current capturing unit 4 or the inter-circuit voltage phase capturing unit 5. . Therefore, a pseudo electric circuit 21 through which only the capacitive ground fault current Ic can flow is prepared, the voltage of the apparatus power supply 10 is taken from the pseudo electric circuit 21, and the effective value igr of the resistive ground fault current is obtained by the constant multiple conversion means 7. Then, the phase difference held by the phase comparison storage unit 11 is adjusted so that the effective value igr of the resistive ground fault current converges to 0, and the adjusted phase difference is stored in the phase comparison storage unit 11. The effective value igr of the resistive ground fault current adjusted in phase can be obtained. Such adjustment work is performed before the insulation monitoring device 1D is installed on the electric circuit (more specifically, before product shipment).

  In addition, the insulation monitoring device 1D according to the present embodiment can also adjust in advance the amplitude deviation of the effective value igr of the resistive ground fault current due to variations in the characteristics of the zero-phase current sensor 2 and the board-mounted components. For such adjustment, a means for obtaining the effective value of the zero-phase current Io is provided, and the effective value igr of the resistive ground fault current is obtained by the constant multiple conversion means 7 so that the capacitive ground fault current is flowing. The conversion value of the constant multiple conversion means 7 may be changed.

  For example, at the time of shipment from the factory, a zero-phase current Io having only a capacitance component having an effective value of Ic of ic = 500 mA and an effective value of Igr of igr = 0 mA is experimentally passed. It is assumed that the constant multiple conversion means detects non-negative igr due to a delay element or the like inside the insulation monitoring device 1D. When igr = 1mA is detected when a trial zero-phase current Io with ic = 500mA and igr = 0mA is applied, 1/500 of the zero-phase current Io is detected as igr by a device-specific element. It turns out that it will be. By registering such a value as a correction value, the delay factor inside the apparatus can be removed from the igr detected during insulation monitoring, so that the measurement accuracy can be further improved. Actually, when a non-negative igr is detected when a zero-phase current Io having only a capacitance component is supplied, the original phase angle α = Adjust to zero. This adjustment becomes a correction value.

  The same applies to not only the phase but also the amplitude adjustment. For example, it is assumed that when the zero-phase current Io having only a resistance component satisfying ic = 500 mA and igr = 0 is flowed experimentally at the time of shipment from the factory, the amplitude of the detected Io is 499 mA. In this case, the actual amplitude of Io can be obtained by multiplying the detected amplitude of Io by a multiplier k = 500/499.

  As described above, according to the present embodiment, the phase error and the amplitude error inherent to the device can be corrected before the insulation monitoring device 1C is installed in the electric circuit, and the resistance ground fault current with higher accuracy can be corrected. Detection is possible.

  FIG. 7 is a block diagram showing a configuration of an insulation monitoring apparatus according to the fifth embodiment of the present invention.

As shown in FIG. 7, the insulation monitoring apparatus 1E according to the present embodiment is a phase capture type insulation monitoring apparatus that monitors a three-phase three-wire electric circuit 20 and includes a phase shift means 9. It is a feature. That is, the insulation monitoring device 1E includes a zero-phase current sensor (zero-phase current detection means) 2 attached to a ground line 3o extending from the ground line (ground phase) 20o, and a zero-phase current capturing unit including an amplifier circuit and an LPF. Between the circuit 4 and the electric circuit connected to one non-ground line (non-ground phase) 20a via the voltage probe 3a and connected to the other non-ground line (non-ground phase) 20b via the voltage probe 3b Voltage phase capturing means 5, phase shift means 9 connected to the inter-circuit voltage phase capture means 5, zero-phase current capture means 4, addition / subtraction means 6 connected to the phase shift means 9, and addition / subtraction means 6 And a constant multiple conversion means 7 connected to, and a notification means 8 connected to the constant multiple conversion means 7.

  The zero-phase current capturing means 4 takes in the zero-phase current detected by the zero-phase current sensor 2 and extracts the zero-phase current waveform Io (t) (t is a time variable). On the other hand, the inter-circuit voltage phase capturing means 5 captures the inter-circuit voltage between the non-ground line 20a and the non-ground line 20b, and the phase of the inter-circuit voltage waveform is obtained. Is shifted, and this shifted phase is set as the reference phase. The adder / subtractor 6 sets the time of the zero cross point of the reference phase to t = 0, the time of one cycle of the reference phase as T, and zero phase current when the first half of the cycle is 0 ≦ t ≦ T / 2 The value of Io (t) is cumulatively added. When T / 2 <t <T, which is the latter half of the cycle, the value of Io (t) is cumulatively subtracted. The constant multiple conversion means 7 multiplies the addition / subtraction value by a conversion constant to obtain an effective value igr of the resistive ground fault current. The notification means 8 monitors the effective value igr of the resistive ground fault current, and notifies that the lamp is turned on or the value is displayed when the effective value reaches the alarm value.

  Next, a method for obtaining the effective value igr of the resistive ground fault current will be described in detail.

  FIG. 8 is a vector diagram showing the current component of the zero-phase current in the three-phase three-wire system.

The zero-phase current Io shown in FIG. 8 is a combination of the capacitive ground fault current Ic and the resistive ground fault current Igr in the circuit oa. In the three-phase three-wire circuit, the capacitive ground fault current Ic and the resistance The phase of the ground fault current Igr is shifted by 120 °. α is a phase angle between the zero-phase current Io and the reference phase Igrm. Therefore, when the absolute value of the resistive ground fault current Igr is expressed by the zero-phase current Io, the following equation 10 is obtained.

 That is, if the magnitude of the zero-phase current Io and the phase angle α can be obtained, the magnitude of the resistive ground fault current Igr can be obtained. The current ioa in the electric circuit oa, the current iab in the electric circuit ab, and the current iob in the electric circuit ob are out of phase by 60 °. Here, the capacity component ica of the ground fault current for the current ioa advances by 90 ° with respect to the current ioa. Similarly, the capacitance component icb of the ground fault current for the current iob advances by 90 ° with respect to the current iob. Since the capacitance component of the ground fault current for the current iab is sufficiently small, it is not considered here. By combining ica and icb, the capacitance component Ic as the entire ground fault current is obtained. The phase of Ic and the phase of Igr are shifted by 120 °. A phase delayed by 90 ° from the capacitance component Ic is defined as a reference phase Igrm. The phase difference between Igrm and Io is α. Since the phase of Igr is in phase with the current ioa, the phase difference between Igrm and Igr is 30 °. When Igr and Ic are combined, it becomes Io. However, at this stage, the sizes of Igr and Io are unknown. Thus, the relationship of Expression (10) is established. Igr can be obtained by substituting this relationship into equations (3) and (7).

  Next, consider the zero-phase current waveform Io (t). For the addition / subtraction means 6, in the case of a three-phase three-wire system, t is a time variable, the zero-phase current waveform output from the zero-phase current detection means 4 is Io (t), and the reference phase output from the phase shift means 9 The time of zero cross point of t = 0, the phase difference between the reference phase and the zero-phase current waveform is α, the amplitude value of the zero-phase current waveform is Io, the angular frequency is ω, the frequency is f, and the time of one cycle of the circuit frequency Assuming T, even in the three-phase three-wire system, the zero-phase current waveform Io (t) output from the zero-phase current detection means 4 to the addition / subtraction means 6 can be expressed as shown in Expression (2).

  When 0 ≤ t ≤ T / 2, the value of Io (t) is added. When T / 2 <t <T, the value of Io (t) is subtracted, and the result is asIo. (11) where Igr is the amplitude value of the resistive ground fault current.

  Therefore, the amplitude value Igr of the resistive ground fault current is as shown in the formula (12), and the effective value igr of the resistive ground fault current to be obtained is given as the formula (13) in consideration that igr is positive. .

  In the design for software implementation, k is a time variable for one-period sampling, the zero-phase current waveform output from the zero-phase current detection means 4 is Io (k), and the zero cross of the reference phase output from the phase shift means 9 The point time is k = 0, the phase difference between the reference phase and the zero-phase current waveform is α, the amplitude value of the zero-phase current waveform is Io, and the number of samplings of one cycle of the circuit frequency is N (N is an even number greater than 2) ), Io (k) can be expressed as in equation (6).

  Here, r is an offset value at the time of AD converter input, which can be known in design, but may be obtained every cycle. When 0 ≤ k ≤ N / 2, the value of Io (k) is added. When N / 2 <k <N, the value of Io (k) is subtracted, and the result is asIo. (14) (Igr is the amplitude value of the resistive ground fault current).

ゆえに、抵抗性地絡電流の振幅値Igrは式（１５）のようになり、求める抵抗性地絡電流の実効値をigrとすると、igrが正であることを考慮して、式（１６）になる。

Therefore, the amplitude value Igr of the resistive ground fault current is as shown in Expression (15). If the effective value of the resistive ground fault current to be obtained is igr, then considering that igr is positive, Expression (16) become.

  However, the conversion based on the number of bits and the range of the AD converter is not considered here because the constant of the constant multiple conversion means 7 changes. A median or the like may be used as a measure for avoiding multiple interrupts.

  By the way, in the case of capturing the phase of the three-phase three-wire electric circuit in two steps, that is, one non-ground phase and the ground phase, and the other non-ground phase and the ground phase, as shown in FIG. If the phase acquired at the second time is stored in the phase comparison storage means 11 and the median value of the phase acquired at the second time and the stored phase is taken, the phase becomes Igrm as shown in FIG. The result is the same as the result when the phase is moved by 90 °.

  As described above, the insulation monitoring apparatus 1 according to the present embodiment determines the time t = 0 of the reference phase based on the zero cross point of the phase of the voltage waveform between the electric circuits input from the voltage probe, and 0 ≦ t ≦ T / 2 Io (t) value is added at the time of, and Io (t) value is subtracted when T / 2 <t <T, and the result of adding / subtracting one period is multiplied by a constant. Thus, the effective value igr of the resistive ground fault current can be obtained. Therefore, a means for obtaining the phase of the zero-phase current waveform input from the zero-phase current sensor becomes unnecessary, and a means for generating an ideal sine wave based on the voltage phase becomes unnecessary. Since the two are unnecessary, the scale is reduced, and the error based on the calculation of the phase difference and the ideal sine wave is eliminated, so that the measurement accuracy of the insulation resistance can be improved.

  A simulation of resistive ground fault current measurement was performed comparing the present invention with a conventional b system.

  In the simulation, input parameters shown in FIGS. Here, “Frequency” is the frequency of the circuit, “Io RMS” is the effective value of the zero-phase current, and “Number of samplings per cycle” is the current value of the zero-phase current waveform sampled at regular intervals during one cycle of the circuit frequency. “AD converter bit number” is the number of AD converter bits provided in the zero phase current detection means, and “AD converter input range” is twice the maximum zero phase current amplitude value corresponding to the maximum bit of the AD converter. The “ideal sine wave amplitude value” is the amplitude value of the ideal sine wave by the b method, the “Io effective value error” is the error of the zero phase current effective value, and the “Io phase error” is the phase error of the zero phase current waveform. .

  In the simulation results shown in each figure, the horizontal axis is the phase difference of Io, the vertical axis is the error from the true value of the effective value igr of the resistive ground fault current output by the input parameter, and the b method, theoretical error, and The case of the present invention is shown in comparison. The theoretical error is assumed not to be a quantization error of the AD converter. For the ideal sine wave used in the b method, 3600 data were prepared at intervals of 0.1 °.

  The input parameters for the simulation shown in each figure are: frequency: 50 Hz, Io effective value: 1000 mA, 1 period sampling number: 32, AD converter bit number: 12 bit, ideal sine wave amplitude value: 1000 mA. Io RMS error and Io phase error are changed. FIG. 10 shows a simulation result when Io effective value error: 0 mA and Io phase error: −0.1 °. As shown in FIG. 10, when the Io phase error is given by −0.1 °, there is an error of the present invention so as to match the theoretical error which is an error due to a clean sine wave, and the error of the b method is separated from the theoretical error. became. The sawtooth waveform is an influence due to a quantization error by the AD converter. The b method includes a discretization error due to an ideal sine wave.

  FIG. 11 shows the simulation results when the Io effective value error is 1 mA and the Io phase error is 0 °. As shown in FIG. 11, when the Io effective value error is given 1 mA, the error of the present invention is matched with the theoretical error which is a beautiful half-wave rectification, and the error of the b method is shifted away from the theoretical error. .

  FIG. 12 shows a simulation result when Io effective value error: 0 mA and Io phase error: 0 °. As shown in FIG. 12, when no error is given, the theoretical error is 0 regardless of the Io phase difference, the error of the present invention is in the vicinity of 0, and the error of the b method is far from the theoretical error.

  FIG. 13 shows a simulation result when Io effective value error: 0 mA and Io phase error: −0.1 °. However, here, the number of samples in one cycle is set to 128. As shown in FIG. 13, when the Io phase error is −0.1 ° and the number of samplings per period is 128, it can be seen that the b method approaches the ideal error.

  In the case of the a method, when a phase error occurs, as shown in the ideal error graph of FIG. 13, when the Io phase error is -0.1 °, the error of the effective value igr of the resistive ground fault current is about 1.7 mA at the maximum. It can be said that the influence of is great.

  The b method may approach or improve the theoretical error under certain conditions by changing the number of samplings or changing the rounding, rounding, or rounding up of each value of the ideal sine wave, but the phase adjustment value, Io phase error, Io As the RMS value error changes, the error does not approach the ideal error and becomes unstable as a result. Moreover, it can be said that if the number of samplings is increased, the error becomes closer to the ideal error because the discretization error disappears.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. Needless to say, it is included in the range.

  For example, in each of the above embodiments, a zero-phase current sensor is used as the zero-phase current detection means, and a voltage probe is used as the inter-circuit voltage detection means. However, the present invention is limited to such an acquisition means. Instead, various current / voltage capturing means can be employed. Further, in each of the above embodiments, cumulative addition is performed in the first half cycle and cumulative subtraction is performed in the second half cycle in units of one cycle of the circuit voltage. However, this is reversed and cumulative subtraction and cumulative addition are performed. Addition / subtraction may be performed in this order. This is based on the fact that igr, which is the effective value of the resistive ground fault current, is “positive”, and the calculation based on the absolute value is performed as shown in equations (5), (9), (13), and (16). Because. Furthermore, in each of the above embodiments, addition / subtraction is performed with the zero crossing point of the electric circuit voltage set to t = 0. For example, as shown in FIGS. 14 and 15, timing shifted from the zero crossing point of the electric circuit voltage Even if the addition / subtraction processing is performed for the period of the voltage between the circuit with t = 0, it is possible to calculate the resistive ground fault current although the subsequent calculation is somewhat complicated.

  FIG. 14 is a schematic diagram for explaining a method of obtaining igr, where t = 0 is a time point before and after the zero crossing point of the voltage between the electric circuits by β. Assume that asIo, which is determined as t = 0 when the time is delayed by β from the zero cross point, is referred to as A1, and asIo which is determined as t = 0, which is advanced from the zero cross point as β, is referred to as A2. A1 is calculated | required by the following formula | equation (17).

また、Ａ２は以下の式（１８）により求められる。

Moreover, A2 is calculated | required by the following formula | equation (18).

Ａ１とＡ２を加算すると式（１９）となる。

βがゼロでないとすると、抵抗性地絡電流の実効値igrは、式（１）に基づく以下の式（２０）により求めることができる。

こうして、igrからαを消去できるため、βが既知であれば、Ａ１、Ａ２からigrを求めることができる。

When A1 and A2 are added, Expression (19) is obtained.

If β is not zero, the effective value igr of the resistive ground fault current can be obtained by the following equation (20) based on the equation (1).

In this way, α can be deleted from igr. Therefore, if β is known, igr can be obtained from A1 and A2.

FIG. 15 is a schematic diagram for explaining a method of obtaining igr, where t = 0 is a time point delayed by π / 2 from the zero crossing point of the voltage between the electric circuits. In this case, asIo is obtained by equation (21).

であるから、Igrは、以下の式（２５）により求められる。

ゆえに、実効値igrは、以下の式（２６）により求められる。

Therefore, Igr is obtained by the following equation (25).

Therefore, the effective value igr is obtained by the following equation (26).

1A to 1F Insulation monitoring device 2 Zero phase current sensor (Zero phase current detection means)
3 Voltage probe (voltage detection means)
4 Zero-phase current capture means 5 Inter-circuit voltage phase capture means 6 Addition / subtraction means 7 Constant multiple conversion means 8 Notification means 9 Phase shift means 10 Device power supply input means 11 Phase comparison storage means

Claims (8)

A zero-phase current detecting means for detecting a zero-phase current Io from a ground wire of a single-phase two-wire or single-phase three-wire circuit;
Zero phase current capturing means for capturing the zero phase current Io detected by the zero phase current detecting means;
An inter-circuit voltage phase capturing means for capturing phase information of an inter-circuit voltage between a ground line and a non-ground line of the electrical circuit;
When the phase of the voltage between the circuits is the reference phase, the time variable is t, and the period of the voltage between the circuits is T, the period of the voltage between the circuits is a unit, and when 0 ≤ t ≤ T / 2, the zero-phase current Cumulative addition of the value of the zero-phase current Io (t) output from the capture means. When T / 2 <t <T, the value of the zero-phase current Io (t) is cumulatively added. Addition / subtraction means for subtracting the other from one of the values;
An insulation monitoring apparatus comprising: an operation unit that obtains an effective value igr of the resistive ground fault current by performing a predetermined operation on the value output from the addition / subtraction unit. The circuit voltage phase capturing means outputs the detection timing of the zero cross point in the voltage waveform of the captured circuit voltage as the phase information,
The addition / subtraction means sets the timing of an arbitrary zero cross point output from the inter-circuit voltage phase capturing means as t = 0,
2. The insulation monitoring apparatus according to claim 1, wherein the calculation unit includes a constant multiple conversion unit that converts the value output from the addition / subtraction unit to a constant multiple to obtain an effective value igr of the resistive ground fault current. . Zero-phase current detecting means for detecting zero-phase current Io from a ground wire of a three-phase three-wire circuit;
Zero phase current capturing means for capturing the zero phase current Io detected by the zero phase current detecting means;
An inter- circuit voltage phase capturing means for capturing phase information of an inter-circuit voltage between the first non-ground line and the second non-ground line of the electrical circuit;
Phase shift means for converting the phase information of the voltage between the electric circuits into phase information shifted by 90 °;
When the phase information output from the phase shifting means is a reference phase, the time variable is t, and the period of the inter-circuit voltage is T, the unit of one period of the inter-circuit voltage is 0 ≦ t ≦ T / 2 Addition / subtraction of cumulatively adding the zero-phase current Io (t) value, cumulatively adding the zero-phase current Io (t) value at T / 2 <t <T, and subtracting the other from one of the cumulative addition values Means,
An insulation monitoring apparatus comprising: an operation unit that obtains an effective value igr of the resistive ground fault current by performing a predetermined operation on the value output from the addition / subtraction unit. The inter-circuit voltage phase capturing means outputs, as the phase information, the detection timing of the zero cross point in the voltage waveform of the captured inter-circuit voltage to the phase moving means,
The phase shift means shifts the timing of the zero cross point by 90 ° of a reference phase and outputs it to the addition / subtraction means,
The addition / subtraction means sets the timing of an arbitrary zero cross point output from the phase shift means as t = 0,
4. The insulation monitoring apparatus according to claim 3, wherein the arithmetic means includes constant multiple conversion means for converting a value output from the addition / subtraction means to a constant multiple to obtain an effective value igr of the resistive ground fault current. . A device power supply for supplying power to the insulation monitoring device, a phase of a power supply voltage taken in by the device power supply from an arbitrary electric circuit, and a reference phase output from the inter-circuit voltage phase capturing means are compared. A phase comparison storage means for obtaining a phase difference and storing the phase difference;
5. The insulation monitoring apparatus according to claim 1, wherein the phase comparison storage unit generates a reference phase based on a phase of a power supply voltage taken in from the predetermined electric circuit and the phase difference. . The phase comparison storage means inputs a zero-phase current Io having a zero resistance ground fault current component to the zero phase current detection means, and the phase difference so that the resistance ground fault current component obtained at this time becomes zero. 6. The insulation monitoring apparatus according to claim 5, further comprising a phase difference adjusting unit that adjusts. The constant multiple conversion means inputs a zero-phase current Io having a predetermined effective value to the zero-phase current detection means so that the effective value of the zero-phase current obtained at this time becomes the same value as the predetermined effective value. 5. The insulation monitoring apparatus according to claim 2 , further comprising an amplitude value adjusting means for adjusting the value of the constant multiple.   The information processing device according to any one of claims 1 to 7, further comprising notification means for notifying that when an effective value igr of the resistive ground fault current obtained by the calculation means is equal to or greater than a predetermined threshold value. The insulation monitoring device described in 1.

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