JP2015108618A - High pressure insulation monitor method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide high pressure insulation monitor method and device capable of monitoring an insulation deterioration state of a high pressure electric circuit in a building at low cost in a hot line condition with simple means.SOLUTION: When a fluctuation portion ΔIof a zero-phase current Iis approximate to 0, an admittance Y between ground in-building is calculated by a relation expression of -Y={(I-If)/I}.Yor -Y={(I-I)/I}.Y, therefore an inverse 1/Yr of a real part Yr of the admittance Y between ground in-building is measured as an earth resistance Rg in a provisional mode. When the fluctuation portion ΔIof the zero-phase current Ibecomes larger than 0 after start of measurement, the admittance Y between ground in-building is calculated by a relation expression of -Y=(ΔI/ΔI).Y, and thereby the inverse 1/Yr of the real part Yr of the admittance Y between ground in-building is measured as an earth resistance Rg in a determined mode.

Description

  The present invention detects the zero-phase current generated in the campus high-voltage circuit connected to the non-grounded electrical circuit due to the ground fault occurring in the non-grounded system circuit, thereby reducing the ground fault resistance for the insulation degradation state of the campus high-voltage circuit. The present invention relates to a high voltage insulation monitoring method and a high voltage insulation monitoring apparatus which are monitored by measuring.

  Various electrical equipment (for example, transformers, phase-advancing capacitors, instrument transformers, current transformers, etc.) is connected to the high-voltage circuit connected to the non-grounded circuit, and installed on the high-voltage circuit. In addition, the zero-phase current transformer ZCT detects the zero-phase current flowing in the campus high-voltage path when a ground fault occurs, thereby monitoring the insulation deterioration state of the campus high-voltage path. In general, the load side from the power receiving point, which is a connection point with the high piezoelectric path, is referred to as a premise, and the protection range is referred to, and the system side from the power receiving point is referred to as the premise, and is outside the protection range.

  In this way, by detecting the zero-phase current flowing in the campus high piezoelectric path at the time of occurrence of the ground fault with the zero-phase current transformer ZCT, it is determined whether or not the ground fault is a campus ground fault. The insulation deterioration state of the campus high piezoelectric path is monitored. Conventionally, for example, a device disclosed in Patent Document 1 has been proposed as a means for monitoring an insulation deterioration state of a campus high piezoelectric path.

  This Patent Document 1 is based on a line constant measuring device that measures the line constant of an ungrounded electric circuit in a live line state and accurately grasps the insulation state of the electric circuit from the line constant, and the line constant measured thereby. This discloses a ground fault monitoring device for a non-grounded electric circuit capable of accurately obtaining the ground fault current from the zero-phase current calculated in this manner.

  That is, the line constant measuring device disclosed in Patent Document 1 includes a zero-phase current detection unit that detects a zero-phase current flowing in a non-grounded circuit, and a zero-phase voltage detection that detects a zero-phase voltage of the non-grounded circuit. Means, a reference voltage generating means for detecting a voltage of a part of the electric circuit and generating a reference voltage excluding the zero phase, and storing and detecting the zero phase current and the zero phase voltage at the start of the line constant measurement. When the zero-phase voltage is changed from the stored value by a predetermined value or more, the electric line change detecting means for storing the detected zero-phase current and the zero-phase voltage, and the vector sum of the ground admittance of each phase as the first line constant And the zero-phase voltage and zero-phase current memorized by the circuit change detecting means when the ground admittance in the equation representing the zero-phase current flowing by the unbalanced portion of the ground admittance of each phase as a reference voltage is the second line constant Based on the two By solving the standing vector equation, in which a line constant computing means for calculating a first line constant and a second line constants.

  Moreover, the ground fault monitoring apparatus disclosed in Patent Document 1 has the above-described line constant measurement device, and uses the first line constant and the second line constant calculated by this device, and the zero-phase current, zero-phase A ground fault current calculating means for inputting a voltage and a reference voltage as a vector quantity and performing a vector calculation based on a predetermined calculation formula to calculate a ground fault current is provided.

Japanese Patent No. 2999615

  By the way, in patent document 1, the zero phase voltage which appeared on the electric circuit is detected by the zero phase voltage detecting means. This zero-phase voltage detecting means has a configuration in which a voltage dividing capacitor is connected between the center connection point of three capacitors star-connected to the electric circuit and the ground, and the voltage across the voltage dividing capacitor is taken out via a transformer. is there. In this case, the transformer itself is expensive, and it takes time to install and remove the transformer when measuring the ground fault current, and the power circuit must be interrupted when installing and removing the transformer. There was a point left to do.

  In addition, as means for monitoring the insulation deterioration state of the campus high piezoelectric road, the ground fault relay (GR / DGR) which is generally spread as defined in JISC4601, 4609 and the applicant previously proposed. There is a high voltage insulation monitoring device (Japanese Patent Laid-Open No. 11-271384).

  However, the former ground fault relay does not have a function of detecting a ground fault in a high voltage road on the premises where the zero phase current is about 100 mA or less. In addition, since the latter high-voltage insulation monitoring device does not have means for measuring the phase of each phase voltage (ground voltage) of the premises high-voltage piezoelectric path, the ground fault current obtained by the calculation is a resistive ground fault, inductive ground. Whether it is a fault or a capacitive ground fault cannot be specified. Furthermore, this high voltage insulation monitoring device does not have a function of detecting a micro ground fault with a zero-phase current of 20 mA or less.

  Therefore, the present invention has been proposed in view of the above-described improvements, and the object of the present invention is to provide a high voltage insulation monitor that can monitor the insulation deterioration state of the campus high piezoelectric path at a low cost by a simple means. It is to provide a method and a high voltage insulation monitoring device.

The present invention provides a zero-phase current I ₀ that flows through a high voltage path on a campus connected to a non-grounded circuit when a ground fault occurs on a non-grounded circuit, and a shield line of a power cable installed on the high voltage path on the campus. through the zero-phase current I _0S is detected by current transformer, the zero-phase current I ₀ flowing through the premises pressure path, high insulation monitoring to measure the ground fault resistance based on the zero-phase current I _0S flowing through the shield wire of the power cable Method and high voltage insulation monitoring device.

As a technical means for achieving the above-described object, the high voltage insulation monitoring method according to the present invention sets the premises-to-ground admittance Y to -Y when the variation ΔI ₀ of the zero-phase current I ₀ approximates ₀ at the start of measurement. = {(I _{02 −If} ) / I _0S2 } · Y _0S or −Y = {(I ₀₂ −I ₀₁ ) / I _0S2 } · Y _0S , by calculating the relational yard-to-ground admittance Y Is measured as the ground fault resistance Rg in the provisional mode, and the fluctuation ΔI ₀ of the zero-phase current I ₀ becomes larger than ₀ after the measurement is started, the premises-to-ground admittance Y is By calculating with the relational expression of −Y = (ΔI ₀ / ΔI _0S ) · Y _0S , the reciprocal 1 / Yr of the real part Yr of the premises-to-ground admittance Y is measured as the ground fault resistance Rg in the definite mode. It is characterized by that.

In the high voltage insulation monitoring method of the present invention, the zero-phase current I _0S flowing through the shield wire of the power cable at the time of occurrence of a ground fault is detected by a current transformer, so that a live means can be used in a live state by a simple means. An inexpensive device can be realized that monitors the grounding resistance by measuring the ground fault resistance. Further, when the variation ΔI ₀ of the zero-phase current I ₀ approximates to ₀ at the start of measurement, the premises-to-ground admittance Y is set to −Y = {(I _{02 −If} ) / I _0S2 } · Y _0S or −Y = { By calculating with the relational expression of (I ₀₂ −I ₀₁ ) / I _0S2 } · Y _0S , the reciprocal 1 / Yr of the real part Yr of the premises premises admittance Y is measured as the ground fault resistance Rg in the provisional mode. be able to. In this way, by measuring the ground fault resistance Rg in the provisional mode, it is possible to accurately determine the insulation deterioration state of the campus high piezoelectric path at the start of measurement.

Further, when the variation ΔI ₀ of the zero-phase current I ₀ becomes larger than ₀ after the measurement is started, the premises-to-ground admittance Y is calculated by a relational expression of −Y = (ΔI ₀ / ΔI _0S ) · Y _0S. Thus, the reciprocal 1 / Yr of the real part Yr of the premises-to-ground admittance Y can be measured as the ground fault resistance Rg in the definite mode. Thus, by measuring the ground fault resistance Rg in the definite mode, it is possible to accurately determine the insulation deterioration state of the campus high piezoelectric path after the measurement is started. In the present invention, the ground capacitance C on the campus can be measured by dividing the imaginary part Yi of the ground-to-ground admittance Y by the angular velocity ω of the power supply frequency.

In the high voltage insulation monitoring method of the present invention, it is possible to detect the zero phase current I ₀ flowing in the campus high piezoelectric path when a ground fault occurs by the zero phase current transformer ZCT installed in the campus high piezoelectric path. As another means, it is desirable to connect a current transformer to the secondary side of the zero-phase current transformer ZCT, and to detect the zero-phase current I ₀ flowing through the campus high piezoelectric path when a ground fault occurs. . In this way, insulation monitoring can be performed simply by attaching a current transformer to the secondary side of the zero-phase current transformer ZCT already installed for ground fault protection relays. Even if an overvoltage such as a surge is applied, insulation is performed by the zero-phase current transformer ZCT, so that the protection against the overvoltage is ensured and reliability can be improved.

Further, the high voltage insulation monitoring apparatus of the present invention has a yard-to-ground admittance Y ₀ when the premises high piezoelectric road is healthy as a relational expression of −Y ₀ = (I ₀₂ −I ₀₁ ) _{ωC 0S} / (I _0S2 −I _0S1 ). In addition to the calculation, the premises-to-ground admittance Y when the campus high-piezoelectric road is healthy and when there is a ground fault is -Y = (I ₀ -I ₀₁ ) _{ωC 0S} / (I _0S -I _0S1 ) or -Y = (I ₀ -I ₀₂ ) The ground calculated from the relational expression of _{ωC 0S} / (I _0S −I _0S2 ) and calculated from the real part Yr of the campus-to-ground admittance Y, which is the difference between the campus-to-ground admittance Y and the campus-to-ground admittance Y ₀ The ground current Iga, Igb, Igc is calculated with respect to the ground voltage Ig using the ground voltage as a reference phase, and the cube root (ΣIg ³ ) ^{1 /} of the cube sum ΣIg ³ of each phase ground fault current Iga, Igb, Igc ³ is calculated as the resistance ground fault current Igr. An arithmetic unit for measuring resistance is provided.

Thus, each phase ground fault current Iga, Igb, Igc is calculated using the ground voltage as a reference phase, and the cube root (ΣIg ³ ) ^1/3 of the cube sum ΣIg ³ of each phase ground fault current Iga, Igb, Igc. By measuring the ground fault resistance by calculating the resistance ground fault current Igr, it is possible to accurately detect the ground fault accident even if the ground fault occurred in the ungrounded circuit is a micro ground fault Can do.

In the present invention, each phase ground fault current Iga, Igb, by correcting the inverse number times the maximum value n of the cube sum ShigumaIg ³ of Igc, the true value of the cube sum ShigumaIg ³ a (ΣIg ³⁾ / n The cube root {(ΣIg ³ ) / n} ^1/3 of the true value (ΣIg ³ ) / n of the cube sum ΣIg ³ is preferably calculated as the resistive ground fault current Igr. In this way, a ground fault can be detected more accurately.

In the present invention, it is desirable to normalize the cube sum ΣIg ³ of each phase ground fault current Iga, Igb, Igc at the monitoring level and calculate the square root of the normalized cube sum a plurality of times. In this way, the phase detection angle can be widened, and the resistive ground fault current can be accurately calculated.

In the present invention, it is desirable to offset the cube sum ΣIg ³ of each phase ground fault current Iga, Igb, Igc by a DC bias. In this way, the correction of the resistive ground fault current and the correction of the phase angle can be easily realized.

According to the present invention, by detecting the zero-phase current I _0S flowing through the shield line of the power cable at the time of the occurrence of the ground fault with the current transformer, the insulation deterioration state of the high voltage road on the premises is kept in a live state by a simple means. It is possible to realize an inexpensive device for monitoring by measuring the ground fault resistance. Further, when the variation ΔI ₀ of the zero-phase current I ₀ approximates to ₀ at the start of measurement, the premises-to-ground admittance Y is set to −Y = {(I _{02 −If} ) / I _0S2 } · Y _0S or −Y = { By calculating with the relational expression of (I ₀₂ −I ₀₁ ) / I _0S2 } · Y _0S , the reciprocal 1 / Yr of the real part Yr of the premises premises admittance Y is measured as the ground fault resistance Rg in the provisional mode. be able to.

Further, when the variation ΔI ₀ of the zero-phase current I ₀ becomes larger than ₀ after the measurement is started, the premises-to-ground admittance Y is calculated by a relational expression of −Y = (ΔI ₀ / ΔI _0S ) · Y _0S. Thus, the reciprocal 1 / Yr of the real part Yr of the premises-to-ground admittance Y can be measured as the ground fault resistance Rg in the definite mode. As described above, by measuring the ground fault resistance in the provisional mode and the ground fault resistance in the definite mode, it is possible to accurately determine the insulation deterioration state of the campus high piezoelectric path.

Also, each phase ground fault current Iga, Igb, Igc is calculated using the ground voltage as a reference phase, and the cube root (ΣIg ³ ) ^1/3 of the cube sum ΣIg ³ of each phase ground fault current Iga, Igb, Igc is resistance. By measuring the ground fault resistance by calculating the ground fault current Igr, the ground fault can be accurately detected even if the ground fault occurring in the non-grounded circuit is a micro ground fault. .

It is a figure for demonstrating the local high piezoelectric path at the time of a one-line ground fault, and the high voltage | pressure insulation monitoring method in embodiment of this invention. It is a figure for demonstrating the local high voltage path at the time of a one-line ground fault, and the high voltage | pressure insulation monitoring method in other embodiment of this invention. FIG. 6 is a waveform diagram showing zero-phase currents I ₀ and I _0S from when power is turned on to when measurement starts and after measurement starts. It is a block diagram which shows the local high piezoelectric path and high voltage | pressure insulation monitoring apparatus at the time of a micro ground fault in embodiment of this invention. It is a block diagram which shows the local high voltage path and high voltage | pressure insulation monitoring apparatus at the time of a micro ground fault in other embodiment of this invention. It is an equivalent circuit diagram at the time of occurrence of a one-line ground fault. It is a vector diagram at the time of occurrence of a one-line ground fault. In the resistive ground fault Rg, (A) is a vector diagram showing the phase ground fault currents Iga, Igb, Igc obtained by phase detection of the ground fault current Ig, and (B) is the magnitude of each phase ground fault current Iga, Igb, Igc. It is a graph which shows thickness. In the inductive ground fault Lg, (A) is a vector diagram showing each phase ground fault current Iga, Igb, Igc obtained by phase detection of the ground fault current IgL, and (B) is a magnitude of each phase ground fault current Iga, Igb, Igc. It is a graph which shows thickness. In the capacitive ground fault Cg, (A) is a vector diagram showing each phase ground fault current Iga, Igb, Igc obtained by phase detection of the ground fault current IgC, and (B) is a magnitude of each phase ground fault current Iga, Igb, Igc. It is a graph which shows thickness. It is a phase characteristic diagram showing each phase ground fault current Iga, Igb, Igc and its cube sum ΣIg ³ . It is the characteristic view which displayed the waveform of FIG. 11 by the polar coordinate. It is a phase characteristic diagram showing the result of normalizing the cube sum ΣIg ³ of each phase ground fault current Iga, Igb, Igc and calculating the square root a plurality of times. It is the characteristic view which displayed the waveform of FIG. 13 by the polar coordinate. It is a phase characteristic figure showing the result of offsetting the cube sum ΣIg ³ of each phase ground fault current Iga, Igb, Igc. It is the characteristic view which displayed the waveform of FIG. 15 by the polar coordinate. It is the figure which compared the monitoring sensitivity of a ground fault relay and a high voltage | pressure insulation monitoring apparatus in the case of a ground fault of A phase.

  Embodiments of the present invention are described in detail below. In the following embodiments, when a ground fault occurs in a non-grounded electric circuit, a zero-phase current flowing in a high-voltage road on the premises connected to the non-grounded electric circuit and a power cable (for example, a high-voltage bridge specified in JISC3606) A high voltage insulation monitoring method for measuring the ground fault resistance based on the zero-phase current flowing in the shield wire of the polyethylene cable) will be described.

  FIG. 1 shows one embodiment of the present invention, and FIG. 2 shows another embodiment of the present invention. In the 6.6 kV ungrounded electric circuit (three-phase circuit) shown in FIGS. 1 and 2, various electric facilities (for example, a transformer, an advancement) are connected to the power cable 13 installed on the campus high-voltage circuit 12 extending from the substation 11. Phase capacitors, instrument transformers, current transformers, etc.).

Upon the occurrence of a ground fault, by detecting the zero-phase current I _0S flowing through the shielded wire 14 of the private branch high-pressure path 12 zero-phase current I ₀ flows in, and the power cable 13, the land for the insulation deterioration of the premises high pressure path 12 Monitoring is performed by measuring the resistance of the wire. In this insulation monitoring, the load side from the power receiving point, which is the connection point between the high piezoelectric path 12 and the power cable 13, is referred to as the premise, and the protection side is referred to as the premise, and the system side from the power receiving point is referred to as the premise, and is outside the protective range.

1 and 2 exemplify a case where a one-line ground fault has occurred in the A phase of the on-premises electrical equipment connected to the power cable 13, and the ground fault current at that time is Ig and the ground fault resistance is Rg. 1 and 2, reference characters C _A1 , C _B1 , and C _C1 are off-site ground capacitances existing between the high piezoelectric path 12 and the ground, and reference characters C _A2 , C _B2 , and C _C2 are the power cables 13 and This is the ground capacitance on the premises that exists between various electrical devices and the ground. Symbols I _A , I _B , and I _C are currents flowing through the respective phases [I _A = (Ea−V ₀ ) · jωC _A2 , I _B = (Eb−V ₀ ) · jωC _B2 , I _C = (Ec−V ₀ ) · jωC _C2 ].

In the embodiment shown in FIG. 1, a configuration is adopted in which a zero-phase current transformer ZCT 15 installed in the high-voltage path 12 detects a zero-phase current I ₀ flowing in the local high-voltage path 12 when a ground fault occurs. On the other hand, in the embodiment shown in FIG. 2, a clamp-type current transformer 17 is connected to the secondary side of the existing zero-phase current transformer ZCT 15 to which the ground fault protection relay 16 is connected. A configuration is adopted in which the zero-phase current I ₀ flowing through the high-voltage road 12 on the premises is detected when a ground fault occurs.

  In the case of the embodiment shown in FIG. 2, insulation monitoring can be performed simply by attaching the clamp type current transformer 17 to the secondary side of the existing zero-phase current transformer ZCT15. Moreover, even if an overvoltage such as a lightning surge is applied to the power cable 13, the overvoltage is not directly applied to the high voltage insulation monitoring device 19, so that the protection against the overvoltage is ensured and the reliability can be improved. The current transformer connected to the secondary side of the zero-phase current transformer ZCT15 may be, for example, a through-type current transformer other than the clamp type.

In this high-voltage insulation monitoring device 19, a zero-phase current transformer ZCT15 (see FIG. 1) installed in the high piezoelectric path 12 or a clamp-type current transformer 17 (connected to the secondary side of the zero-phase current transformer ZCT15) ( 2), the zero-phase current I ₀ flowing through the campus high piezoelectric path 12 when a ground fault occurs is detected. In addition, a clamp type current transformer 18 is attached to the shield wire 14 of the power cable 13 installed in the campus high piezoelectric path 12, and the clamp type current transformer 18 allows the shield cable 14 of the power cable 13 to be connected when a ground fault occurs. The flowing zero-phase current I _0S is detected.

  The clamp type current transformer 18 can also be easily monitored for insulation just by being attached to the shielded wire 14 of the power cable 13, as in the above-described clamp type current transformer 17. Even if the overvoltage is applied, the overvoltage is not directly applied to the high voltage insulation monitoring device 19, so that the overvoltage is reliably protected and the reliability can be improved. The current transformer connected to the shield wire 14 of the power cable 13 may be, for example, a through-type current transformer other than the clamp type.

  These clamp type current transformers 17 and 18 have a structure in which a ring-shaped portion that constitutes a magnetic circuit and detects a current is provided at the front end of the main body so as to be opened and closed. The clamp-type current transformers 17 and 18 are attached to the secondary side of the zero-phase current transformer ZCT15 and the shielded cable 14 of the power cable 13 by manually opening the ring-shaped portion and connecting the ground fault protection relay 16 to the inside thereof. The connection line and the shield line 14 of the power cable 13 are taken in and then closed so that the connection line and the shield line 14 of the power cable 13 pass through the ring-shaped portion constituting the magnetic circuit. Since the attachment work is easy by such a simple operation, the work in the field can be carried out efficiently and its practical value is great.

Here, due to the occurrence of a ground fault, the zero-phase current I ₀ flowing through the campus high-piezoelectric path 12 and the zero-phase current I _0S flowing through the shield wire 14 of the power cable 13 are turned on to the on-site electrical equipment connected to the power cable 13. And fluctuates due to interruption. FIG. 3 shows zero-phase currents I ₀ and I _0S that increase after the measurement is started after the high-voltage insulation monitoring device 19 is turned on and after the measurement is started.

The standby mode is set until the zero-phase currents I ₀ and I _0S both increase to the lowest level L (for example, 2 mA) that can be calculated in the high-voltage insulation monitoring device 19 from when the power is turned on (point A in the figure). Measurement of ground fault resistance Rg is started when ₀ and I _0S both reach the lowest level L that can be calculated. The zero-phase currents I ₀ and I _0S at the start of measurement (point B in the figure) are set as zero-phase currents I ₀₁ and I _0S1, and the zero-phase current I ₀ measured after the start of measurement (point C in the figure). , I _0S is a current value and zero-phase currents I ₀₂ and I _{0S2 are} assumed.

Note that the zero-phase currents I ₀₁ and I _0S1 at the start of measurement described above have the role of a reference value when calculating the ground fault resistance Rg, and are handled as follows. That is, the first measured zero phase currents I ₀₁ and I _0S1 are set as fixed values. When the ground fault resistance Rg of the calculation result is close to infinity and it can be determined that there is no ground fault in the high voltage path 12 on the premises, the measured zero phase currents I ₀₂ and I _0S2 are _converted to zero phase currents I ₀₁ , I ₀₁ , _Update as I _0S1 automatically or manually. This update is performed by an external communication command or an external direct input means.

In the high voltage insulation monitoring device 19, when the zero phase currents I ₀ and I _0S reach the lowest level L that can be calculated, that is, when the measurement is started, the standby mode is shifted to the temporary mode. In this provisional mode, the variation ΔI ₀ (= I ₀₂ −I ₀₁ ) of the zero-phase current I ₀ is an interval in which it approximates 0 (I ₀₂ ≈I ₀₁ ). Further, when the variation ΔI ₀ (= I ₀₂ −I ₀₁ ) becomes larger than 0, the transition is made from the provisional mode to the fixed mode. The transition from the standby mode to the provisional mode and the transition from the provisional mode to the confirmation mode are performed by the determination unit 20 of the high-voltage insulation monitoring device 19. Incidentally, in the case where variation [Delta] I ₀ of the zero-phase current I ₀ is approximate to 0, the boundary value between the case where variation [Delta] I ₀ of the zero-phase current I ₀ is greater than 0, the measurement of the high voltage insulator monitoring device 19 It depends on the calculation performance.

Here, the zero-phase current I _0S flowing through the shield wire 14 of the power cable 13 is grounded between the core wire of the power cable 13 and the ground with the zero-phase voltage V ₀ appearing on the high piezoelectric path 12 due to the occurrence of a ground fault. Capacitance C _0S = C _AS + C _BS + C _CS (not shown) is a current that flows (I _0S = ω · C _0S · V ₀ , where ω = 2π · power supply frequency (Hz)). The ground capacitances C _AS , C _BS , C _CS of each phase between the core of the power cable 13 and the ground vary depending on the thickness, length, and specifications of the manufacturer, etc. of the power cable 13. As the ground capacitances C _AS , C _BS , C _CS , use the values shown in JISC3606 or the above-mentioned specifications, and the high-voltage insulation of the specifications of the power cable 13 based on the information recorded in the premises electrical equipment The monitoring device 19 is set manually or automatically.

As a manual setting method, the ground capacitances C _AS , C _BS , C _CS or specifications of the power cable 13 are set for each phase (by means of communication between the setting device (or personal computer) provided outside and the high voltage insulation monitoring device 19 ( (A phase, B phase, C phase) or by setting a setting circuit inside the high voltage insulation monitoring device 19 and using a dial switch, the ground capacitances C _AS , C _BS , C _CS of the power cable 13 or There is a method to input specifications for each phase.

When employing this method, premises ground impedance between Z _0S power cable 13 is the sum of the reciprocals though each phase of the capacitance to ground C _AS, C _BS, the angular velocity ω of C _CS and the power supply frequency obtained by multiplying [ Z _0S = (1 / ωC _AS + 1 / ωC _BS + 1 / ωC _CS )]. The premises-to-ground admittance Y _0S (hereinafter simply referred to as premises-to-ground admittance Y _0S ) of the power cable 13, which is the reciprocal of this premises-to-ground impedance Z _0S , is Y _0S = 1 / (1 / ωC _AS + 1 / ωC _BS + 1 / ωC _CS ) is used for arithmetic processing for calculating the premises admittance Y (hereinafter simply referred to as premises-to-ground admittance Y) when the premises high piezoelectric road 12 is healthy and when there is a ground fault.

As an automatic setting method, the imaginary part jYi of the premises-to-ground admittance Y is obtained by calculating the premises-to-ground admittance Y in the determination mode shown in FIG. Accordingly, the scalar quantity of the imaginary part jYi of the premises ground between admittance Y | Yi | and scalar amounts of premises ground between admittance Y _0S | Y _0S | is variation [Delta] I ₀ of the zero-phase current I ₀ and zero-phase current I _0S It is proportional to the ratio of the variation ΔI _0S of. That is, the scalar quantity of the premises-to-ground admittance Y _0S is obtained by the equation | Y _0S | = (ΔI _0S / ΔI ₀ ) · | Yi |, and is used for the arithmetic processing for calculating the premises-to-ground admittance Y. The When the imaginary part (| Yi | = | ωC |) of the premises-to-ground admittance Y is divided by the angular velocity ω (= 2π × power supply frequency) of the power supply frequency, the ground capacitance C (per three phases) is obtained.

The zero-phase current I ₀ that flows through the campus high piezoelectric path 12 when a ground fault occurs includes the zero-phase current If that is affected by the imbalance of the premises admittance Y [If = jω (C _A2 · Ea + C _B2 Eb + C _C2 Ec)]. The zero-phase current If due to imbalance of the premises ground between admittance Y is not affected by variation in the zero-phase voltage V ₀ since there is no term of zero-phase voltage V _0. Further, since each phase voltage (= Ea, Eb, Ec) on the power transmission side is a balanced three-phase voltage, it is not affected. The zero-phase current If is affected by fluctuations due to the unbalance of the ground capacitances C _A2 , C _B2 and C _{C2 on} the premises. Therefore, the zero-phase current If due to the imbalance of the premises-to-ground admittance Y is usually measured at 10 mA or less.

Further, the zero-phase current I _0S flowing through the shield line 14 of the power cable 13 includes the zero-phase current If _0S affected by the imbalance of the premises admittance Y _0S . The zero-phase current If _0S is affected by fluctuations in the ground capacitance of the power cable 13, but the ground capacitance of the power cable 13 is equal in each phase (C _AS = C _BS = C _CS ), the zero-phase current If _0S is normally measured as 0 mA.

In the high voltage insulation monitoring device 19, the zero phase current I ₀ detected by the zero phase current transformer ZCT 15 installed in the campus high piezoelectric path 12 or the clamp type current transformer 17 connected to the secondary side thereof, and the power cable 13 The zero-phase current I _0S detected by the clamp-type current transformer 18 attached to the shield wire 14 and the ground capacitances C _AS , C _BS , C _CS between the core wire and the ground of the power cable 13 are converted into the power cable 13. Based on the ground-to-ground admittance Y _0S obtained by manual setting or automatic setting according to the thickness, length and specifications of the manufacturer, etc., and the zero-phase current If due to the imbalance of the premises-to-ground admittance Y, The ground fault resistance Rg is measured in the manner described above.

First, the codes I _A , I _B , I _C , and Ig shown in FIG. 1 are I _A = (Ea−V ₀ ) · jωC _A2 , I _B = (Eb−V ₀ ) · jωC _B2 , I _C = (Ec −V ₀ ) · jωC _C2 , Ig = (Ea−V ₀ ) / Rg Further, the zero-phase current I ₀ detected by the zero-phase current transformer ZCT 15 installed in the campus high piezoelectric path 12 or the clamp-type current transformer 17 connected to the secondary side thereof is I ₀ = I _A + I _B + I _C + Ig.

Therefore, the zero-phase current I ₀ is expressed as I ₀ = Ig−jω (C _A2 + C _B2 + C _C2 ) · V ₀ + jω (Ea · C _A2 + Eb · C _B2 + Ec · C _C2 ). Here, since Y = jω (C _A2 + C _B2 + C _C2 ) and If = jω (Ea · C _A2 + Eb · C _B2 + Ec · C _C2 ), the zero-phase current I ₀ is I ₀ = Ig−Y • V ₀ + If.

The ground fault current Ig is represented by Ig = I ₀ − (− Y · V ₀ + If). In addition, since the ground electrical current of the premises electrical equipment is good and no ground fault current flows (Ig = 0) at the beginning of monitoring, the zero-phase current I ₀ is I ₀ = −Y · V ₀ + If. Further, the zero-phase current If caused by the imbalance of the premises-to-ground admittance Y is If = I ₀ − (− Y · V ₀ ). Since the zero-phase voltage V ₀ is not measured, if V ₀ = I _0S / Y _0S is used, If = I ₀ − {− Y · (I _0S / Y _0S )} = I ₀ − {− (Y / Y _0S ) · I _0S }.

In the standby mode shown in FIG. 3, _since the values of the zero-phase currents I ₀₁ and I _0S1 have not reached the lowest level L that can be calculated, insulation monitoring cannot be performed. When shifting to the next provisional mode, the zero-phase currents I ₀₁ and I _0S1 are used as reference values when the values reach the lowest level L that can be calculated. Here, the value of the zero-phase current I _0S1 is used as a reference value for the power cable 13 because of the characteristics of the insulator (crosslinked polyethylene). This is because a ground fault current due to internal deterioration of the power cable 13 hardly flows until just before the bridge phenomenon between insulators due to a tree phenomenon or the like. Further, since the three-phase wires in the power cable 13 have the same size and the same length, the zero-phase current If does not flow due to the imbalance of the premises premises admittance Y.

In addition, when the power cable 13 reaches dielectric breakdown, a large current flows through the power cable 13, but the dielectric breakdown state of the power cable 13 is not subject to insulation monitoring. As for the zero-phase current I ₀₁ as the reference value, it is assumed that no ground fault has occurred in the electrical equipment at the beginning of monitoring (ground fault current Ig = 0). The measured values thereafter are used as the values of the zero-phase currents I ₀₂ and I _0S2 to calculate the ground fault current Ig and the ground fault resistance Rg in the provisional mode. Hereinafter, the definite mode based on the basic formula will be described before the provisional mode.

In the definite mode in the high voltage insulation monitoring device 19, since the variation ΔI ₀ (= I ₀₂ −I ₀₁ ) of the zero-phase current I ₀ is larger than 0 (I ₀₂ ≠ I ₀₁ ), the variation ΔI _{0 is set} to a high voltage. It is easy to calculate with the insulation monitoring device 19. Therefore, in this fixed mode, in the high voltage insulation monitoring device 19, first, the calculation unit 23 detects the zero phase current I ₀ detected by the zero phase current transformer ZCT15 or the clamp current transformer 17, and the clamp current transformer. The premises-to-ground admittance Y is calculated by the following relational expression based on the zero-phase current I _0S detected by 18.

In this fixed mode, using the above-described formula I ₀ = −Y · V ₀ + If, the zero-phase current I ₀₁ becomes I ₀₁ = −Y · V ₀₁ + If, and the zero-phase current I ₀₂ becomes I ₀₂ = −Y · V ₀₂ + If. Calculate the difference I ₀₂ −I ₀₁ = −Y (V ₀₂ −V ₀₁ ) between the current zero-phase current I ₀₂ and the zero-phase current I ₀₁ at the start of measurement to calculate the premises admittance Y between the premises and the ground [−Y = (I ₀₂ −I ₀₁ ) / (V ₀₂ −V ₀₁ )].

Here, since the zero-phase voltages V ₀₁ and V ₀₂ are not measured, the zero-phase currents I _0S1 and I _0S2 of the shield wire 14 of the power cable 13 detected by the clamp type current transformer 18 are calculated _instead . Provide for processing. That is, these zero-phase currents I _0S1 and I _0S2 are _obtained by _multiplying these zero-phase voltages V ₀₁ and V ₀₂ by the premises admittance Y _0S (V ₀₁ = I _0S1 / Y _0S , V ₀₂ = I _0S2 / Y since it is _{0S), -Y = (I 02} -I 01) / (V 02 -V 01) _{is, -Y = (I 02 -I 01} ) / {(I 0S2 / Y 0S) - (I 0S1 a _{/ Y 0S)} = (I} 02 -I 01) / {(I 0S2 -I 0S1) / Y 0S)} = {(I 02 -I 01) / (I 0S2 -I 0S1)} · Y 0S .

Here, if the variation of the zero phase current I ₀ (I ₀₂ −I ₀₁ ) is ΔI ₀ and the variation of the zero phase current I _0S (I _0S2 −I _0S1 ) is ΔI _0S , −Y = (ΔI ₀ / ΔI _0S ) · Y _0S , and premises-to-ground admittance Y is obtained from this relational expression. In this way, the premises admittance Y is obtained from the zero phase current I ₀ flowing in the campus high piezoelectric path 12 with the zero phase current I _0S flowing in the shield wire 14 of the power cable 13 as a reference value. In other words, by multiplying the premises ground between admittance Y _0S to the ratio of the variation [Delta] I _0S of variation [Delta] I ₀ of the zero-phase current I ₀ and zero-phase current _{I 0S (ΔI 0 / ΔI 0S} ), premises ground between admittance Y Is required.

When this premises-to-ground admittance Y is calculated as a complex number, a real part Yr and an imaginary part Yi are obtained from -Y = Yr + jYi. When a ground fault current Ig between ground is included in the numerator of −Y = (ΔI ₀ / ΔI _0S ) · Y _0S , the reciprocal 1 / Yr of the real part Yr of the premises-to-ground admittance Y is calculated by the arithmetic unit 24. By calculating, the ground fault resistance Rg can be definitely measured [Rg = 1 / Yr].

Further, the ground fault current Ig is obtained from the zero-phase current I ₀₂ by using the above-described formula I ₀ = Ig−Y · V ₀ + If. At this time, since the zero-phase current If due to the imbalance of the premises-to-ground admittance Y is unknown, the premises-to-ground admittance Y and the zero-phase voltage are calculated from the zero-phase current I ₀ when the ground fault resistance Rg is close to infinity. A _{value obtained} by multiplying V ₀ is obtained by vector subtraction and determined (If = I ₀ + Y · V ₀ ).

Since the ground fault current Ig does not flow at the beginning of monitoring (Ig = 0), the ground fault current Ig is expressed by Ig = I ₀₂ − (If−Y · V ₀₂ ) from the current zero-phase current I ₀₂ . Since the zero phase voltage V ₀₂ is not measured, using V ₀₂ = I _0S2 / Y _0S , Ig = I ₀₂ − {If−Y · (I _0S2 / Y _0S )} = I ₀₂ − {If− (Y / Y _0S ) · I _0S2 }, and the ground fault current Ig is obtained.

  When the ground fault resistance is large when this ground fault is detected (Rg> about 10 kΩ), the real part | Yr | << the imaginary part | Yi | Therefore, the phase voltages Ea, Eb, Ec and the ground voltages Va, Vb, Vc are substantially equal. Since phase voltage = line voltage / √3 = 6600 V / √3 = 3810 V, ground fault resistance Rg is expressed by the following equation using ground voltages Va, Vb, Vc substantially equal to phase voltages Ea, Eb, Ec. Is required. That is, the ground fault resistance Rg = ground voltage / ground fault current = 3810 V / Ig.

  The present applicant conducted a ground fault experiment (determined mode) under the following test conditions using a simulated electric room (single wire ground fault current = 7.89 A).

-Power cable: Nominal cross-sectional area 22mm ² , length 20m = 0.0162 [μF] (per phase) power supply frequency 60Hz
・ Ground fault resistance Rg: 1000 [kΩ]
・ Ground capacitance C on ground: 0.2 [μF]
・ Residual voltage: about 100 [V]

[Calculated value]
Y _0S = 1 / (1 / ωC) = ωC = 6.107 × 10 ⁻⁶ ∠90 [S]
Y = {(35.3 × 10 ⁻³ ∠293.2-24.3 × 10 ⁻³ ∠293.2)} / {(0.696 × 10 ⁻³ ∠291.7−0.465 × 10 ^{− 3} ∠291.1)} × 6.107 × 10 ⁻⁶ ∠90
−Y = −1.031 × 10 ⁻⁶ + j0.2155 × 10 ⁻³
Rg = 1 / Yr = 1 / 1.031 × 10 ⁻⁶ = 970.1 [kΩ]
C = Yi / 3ω = 0.2155 × 10 ⁻³ /1130.97=0.1905 [μF]

  As described above, since the ground fault resistance Rg (970.1 [kΩ]) obtained as the calculation result in the definite mode approximates the actual ground fault resistance Rg (1000 [kΩ]), the ground fault resistance Rg It was found that can be detected with high accuracy. As for the ground capacitance on the premises, the ground capacitance C (0.1905 [μF]) on the premises obtained as the calculation result is the actual ground capacitance (0.2 [μF]) on the premises. It turns out to approximate.

Incidentally, in the fixed mode as described above, the zero-phase current I ₀₁ at the start of measurement, when the zero-phase current I ₀₂ after the start of measurement is equal to the variation [Delta] I ₀ of the zero-phase current I ₀ (= I ₀₂ - Since I ₀₁ ) [− Y = (ΔI ₀ / ΔI _0S ) · Y _0S numerator] is zero, the premises admittance Y is zero. As a result, since the reciprocal 1 / Yr of the real part Yr of the premises-to-ground admittance Y becomes infinite, it is determined that there is no ground fault resistance (Rg = ∞) and is sound.

On the other hand, when the zero-phase current I _0S1 at the start of measurement becomes equal to the zero-phase current I _0S2 after the start of measurement, the variation ΔI _0S [−Y = (ΔI ₀ / ΔI _0S ) of the zero-phase current I _0S Since the denominator of Y _0S ] is 0, the on-site admittance Y is infinite. As a result, since the inverse 1 / Yr of the real part Yr of the premises-to-ground admittance Y is 0, a ground fault resistance (Rg = 0) is obtained. In this case, the ground fault resistance Rg is not calculated. Alternatively, the ground fault resistance Rg is calculated in the provisional mode.

Next, in the provisional mode in the high voltage insulation monitoring device 19, the measured values of the zero phase currents I ₀ and I _0S measured in the standby mode are valid, and these two measured values are used as the reference zero phase currents I ₀₁ and I _0S1. When the measured value of the zero-phase current I _{02 and} the measured value of the zero-phase current I _0S2 are obtained as the current value, the temporary mode is set. Immediately after entering the provisional mode, the zero phase current I ₀₁ and the zero phase current I ₀₂ , and the zero phase current I _0S1 and the zero phase current I _0S2 are approximated. Thus, -Y = so _{(ΔI 0 / ΔI 0S) ·} Y variation [Delta] I ₀ of _0S is in a state approximating to 0, premises ground between admittance Y can not be accurately calculated.

Therefore, in this temporary mode, in the high voltage insulation monitoring device 19, first, the calculation unit 21 detects the zero phase current I ₀ detected by the zero phase current transformer ZCT 15 or the clamp current transformer 17, and the clamp current transformer. Based on the zero-phase current I _0S detected by 18, the premises-to-ground admittance Y is calculated by the following relational expression.

In this provisional mode, when the zero-phase current I _0S is used as a reference, the zero-phase current I ₀ is normally + 90 ° ≦ I ₀ ≦ −90 ° (phase corresponding to the ground fault on the campus). When the zero-phase current I ₀ is small or the waveform is disturbed by a lightning surge, the zero-phase current I ₀ may be −90 ° ≦ I ₀ ≦ + 90 ° (phase corresponding to an off-ground ground fault). Therefore, in the provisional mode, the premises-to-ground admittance Y is calculated when the zero-phase current I ₀ is + 90 ° ≦ I ₀ ≦ −90 ° and the zero-phase current I ₀ is −90 ° ≦ I ₀ ≦ + 90 °. This will be described separately for each case.

[Phase equivalent to ground fault on campus]
The zero-phase current I _0S1 when the reference, if the zero-phase current I ₀₂ becomes _{+ 90 ° ≦ I 0 ≦ -90} °, ΔI 0 ≒ 0, in the state of _{ΔI 0S ≒ 0, -Y = (} I 02 - The premises-to-ground admittance Y cannot be obtained by the calculation of I ₀₁ ) / (V ₀₂ −V ₀₁ ). At this time, since the zero-phase current If due to the imbalance of the premises-to-ground admittance Y is unknown, the imaginary part (= I) of the zero-phase current I ₀ (complex number) measured with reference to the phase of the zero-phase current I _{0S 0} image) is substituted into the imaginary part (= Ifimage) of the zero-phase current If. The real part (= Ifreal) of the zero-phase current If is set to 0 [mA] and used for the arithmetic processing. Therefore, the zero-phase currents I ₀₂ and I _0S2 measured as current values are applied to I ₀ = −Y · V ₀ + If. In addition, since it is immediately after the measurement, the ground fault current Ig is not observed.

The zero-phase current I ₀₂ is I ₀₂ = −Y · V ₀₂ + If. From this equation, the premises admittance Y between the premises and the ground is expressed by −Y = (I ₀₂ −If) / V ₀₂ . Here, since the zero-phase voltage V ₀₂ is not measured, if V ₀₂ = I _0S2 / Y _0S is used, −Y = (I _{02 −If} ) / (I _0S2 / Y _0S ) = {(I ₀₂ − If) / I _0S2 } · Y _0S , and the premises-to-ground admittance Y is obtained from this relational expression.

When this premises-to-ground admittance Y is calculated as a complex number, a real part Yr and an imaginary part Yi are obtained from -Y = Yr + jYi. -Y = {(I _{02 -If} ) / I _0S2 } · Y _{0S When} the ground fault Ig between ground is included in the numerator term, the reciprocal 1 / Yr of the real part Yr of the campus-to-ground admittance Y is By calculating the calculation unit 24, the ground fault resistance Rg can be provisionally measured [Rg = 1 / Yr].

Further, the ground fault current Ig is obtained from the zero-phase current I ₀₂ by using the above-described formula I ₀ = Ig−Y · V ₀ + If. That is, the ground fault current Ig is expressed as Ig = I ₀₂ − (If−Y · V ₀₂ ), and the zero-phase voltage V ₀₂ is not measured. Therefore, when V ₀₂ = I _0S2 / Y _0S is used, Ig _{= I 02 - {If-Y} · (I 0S2 / Y 0S)} = I 02 - {If- (Y / Y 0S) · I 0S2} next, the ground fault current Ig is obtained.

  When the ground fault resistance is large when this ground fault is detected (Rg> about 10 kΩ), the real part | Yr | << the imaginary part | Yi | Therefore, the phase voltages Ea, Eb, Ec and the ground voltages Va, Vb, Vc are substantially equal. Since phase voltage = line voltage / √3 = 6600 V / √3 = 3810 V, ground fault resistance Rg is expressed by the following equation using ground voltages Va, Vb, Vc substantially equal to phase voltages Ea, Eb, Ec. Is required. That is, the ground fault resistance Rg = ground voltage / ground fault current = 3810 V / Ig.

[Phase equivalent to ground fault]
When the zero-phase current I _0S1 is used as a reference and the zero-phase current I ₀₂ is −90 ° ≦ I ₀ ≦ + 90 °, the zero-phase current I ₀ is small or it is disturbed by a lightning surge. At this time, since the zero-phase current If due to the imbalance of the premises-to-ground admittance Y is unknown, the zero-phase current I ₀₁ measured with reference to the phase of the zero-phase current I _0S corresponds to the zero-phase current If. [If = I ₀₁ ].

The zero-phase current I ₀₂ becomes I ₀₂ = −Y · V ₀₂ + I ₀₁ , and the premises-to-ground admittance Y is expressed by −Y = (I ₀₂ −I ₀₁ ) / V ₀₂ from this equation. Since the zero-phase voltage V ₀₂ is not measured, the use of _{V 02 = I 0S2 / Y 0S} , -Y = (I 02 -I 01) / (I 0S2 / Y 0S) = {(I 02 −I ₀₁ ) / I _0S2 } · Y _0S , and the premises-to-ground admittance Y is obtained from this relational expression.

When this premises-to-ground admittance Y is calculated as a complex number, a real part Yr and an imaginary part Yi are obtained from -Y = Yr + jYi. -Y = {(I ₀₂ -I ₀₁ ) / I _0S2 } · Y _{0S When} the ground fault Ig between ground is included in the numerator term, the reciprocal 1 / Yr of the real part Yr of the local ground-to-ground admittance Y Can be tentatively measured by calculating the calculation unit 24 [Rg = 1 / Yr].

Further, the ground fault current Ig is obtained from the zero-phase current I ₀₂ by using the above-described formula I ₀₂ = Ig−Y · V ₀₂ + I ₀₁ . That is, the ground fault current Ig is represented by Ig = I ₀₂ − (I ₀₁ −Y · V ₀₂ ), and the zero phase voltage V ₀₂ is not measured. Therefore, when V ₀₂ = I _0S2 / Y _0S is used, _{Ig = I 02 - {I 01} -Y · (I 0S2 / Y 0S)} = I 02 - {I 01 - (Y / Y 0S) · I 0S2} next, ground fault current Ig obtained.

  When the ground fault resistance is large when this ground fault is detected (Rg> about 10 kΩ), the real part | Yr | << the imaginary part | Yi | Therefore, the phase voltages Ea, Eb, Ec and the ground voltages Va, Vb, Vc are substantially equal. Since phase voltage = line voltage / √3 = 6600 V / √3 = 3810 V, ground fault resistance Rg is expressed by the following equation using ground voltages Va, Vb, Vc substantially equal to phase voltages Ea, Eb, Ec. Is required. That is, the ground fault resistance Rg = ground voltage / ground fault current = 3810 V / Ig.

  The present applicant conducted a ground fault experiment (provisional mode) under the following test conditions using a simulated electric room (single wire ground fault current = 7.89 A).

-Power cable: Nominal cross-sectional area 22mm ² , length 20m = 0.0162 [μF] (per phase) power supply frequency 60Hz
・ Ground fault resistance Rg: 1000 [kΩ]
・ Ground capacitance C on ground: 0.2 [μF]
・ Residual voltage: about 100 [V]

[Calculated value]
Y _0S = 1 / (1 / ωC) = ωC = 6.107 × 10 ⁻⁶ ∠90 [S]
Y = {(I _{02 −If} ) / I _0S2 } × Y _0S
= {(24.3 × 10 ⁻³ ∠293.2−0.460 × 10 ⁻³ ∠180.0)} / (0.696 × 10 ⁻³ ∠291.7) × 6.107 × 10 ⁻⁶ ∠90
−Y = −6.910 × 10 ⁻⁶ + j0.1589 × 10 ⁻³
Rg = 1 / Yr = 1 / 6.910 × 10 ⁻⁶ = 144.7 [kΩ]
C = Yi / 3ω = 0.589 × 10 ⁻³ /1130.97=0.140 [μF]

  As described above, the ground fault resistance Rg (144.7 [kΩ]) obtained as the calculation result in the provisional mode becomes a value smaller than the actual ground fault resistance Rg (1000 [kΩ]), and the ground fault resistance is obtained. Although the accuracy of Rg is low, it has been found that the presence or absence of a ground fault can be monitored even in the provisional mode. As for the ground capacitance on the premises, the ground capacitance C (0.140 [μF]) on the premises obtained as a calculation result is the actual ground capacitance (0.2 [μF]) on the premises. It turns out to approximate.

As described above, the zero-phase current I _0S flowing through the shield wire 14 of the power cable 13 in the event of a ground fault is detected by the clamp-type current transformer 18, so that the on-site high voltage can be maintained in a live state by simple means. An inexpensive device that monitors the grounding resistance Rg for the insulation deterioration state of the electric circuit 12 can be realized.

Further, when the variation ΔI ₀ of the zero-phase current I ₀ approximates to ₀ at the start of measurement, the premises-to-ground admittance Y is set to −Y = {(I _{02 −If} ) / I _0S2 } · Y _0S or −Y = { By calculating with the relational expression of (I ₀₂ −I ₀₁ ) / I _0S2 } · Y _0S , the reciprocal 1 / Yr of the real part Yr of the premises premises admittance Y is measured as the ground fault resistance Rg in the provisional mode. be able to. In this way, by measuring the ground fault resistance Rg in the provisional mode, it is possible to accurately determine the insulation deterioration state of the campus high piezoelectric path 12 at the start of measurement.

Further, when the variation ΔI ₀ of the zero-phase current I ₀ becomes larger than ₀ after the measurement is started, the premises-to-ground admittance Y is calculated by a relational expression of −Y = (ΔI ₀ / ΔI _0S ) · Y _0S. Thus, the reciprocal 1 / Yr of the real part Yr of the premises-to-ground admittance Y can be measured as the ground fault resistance Rg in the definite mode. In this way, by measuring the ground fault resistance Rg in the definite mode, it is possible to accurately determine the insulation deterioration state of the campus high piezoelectric path 12 after the start of measurement.

  The ground fault current Ig described above may increase due to the on-site electrical equipment connected to the power cable 13 or the like. When such an increase in the ground fault current Ig occurs, a ground fault accident is erroneously detected. On the other hand, the resistive ground fault current Igr does not increase due to the on-site electrical equipment connected to the power cable 13 or the like. Therefore, by measuring the ground fault resistance Rg based on this resistive ground fault current Igr, it is possible to accurately detect a ground fault. It has also been found that when the ground fault is a micro ground fault (for example, 20 mA or less), it is necessary to measure the ground fault resistance Rg based on the resistive ground fault current Igr.

This resistive ground fault current Igr is calculated by the high voltage insulation monitoring device 25 shown in FIGS. 4 and 5 in the following manner. 4 and 5, the same parts as those in FIGS. 1 and 2 are denoted by the same reference numerals, and redundant description is omitted. FIG. 4 illustrates a configuration in which a zero-phase current transformer ZCT 15 installed in the high-voltage path 12 detects a zero-phase current I ₀ flowing in the local high-voltage path 12 when a ground fault occurs (see FIG. 1). FIG. 5 shows that a clamp-type current transformer 17 is connected to the secondary side of an existing zero-phase current transformer ZCT15 to which a ground-fault protective relay 16 is connected. A configuration for detecting the zero-phase current I ₀ that sometimes flows through the local high-voltage path 12 is illustrated (see FIG. 2).

  In order to add a function of measuring the resistive ground fault current Igr from the ground fault current Ig generated in the local electrical equipment of the local high piezoelectric path 12, the reference phases of the ground voltages Va, Vb, and Vc of the local high piezoelectric path 12 are specified. There is a need to. In order to specify the reference phase of the ground voltages Va, Vb, and Vc of the campus high piezoelectric path 12, a grounded instrument transformer (EVT) is used at the substation on the power supply side. However, the high voltage power receiving equipment regulations (JEAC8011-2008) do not allow the use of grounded-type instrument transformers (EVT) in private electrical equipment for private use.

In order to identify the reference phase of the ground voltages Va, Vb, and Vc without using the grounding instrument transformer (EVT) in the private electric equipment for private use of the private high-voltage path 12 shown in FIGS. 4 and 5, A zero-phase current I _0S flowing in the shield wire 14 of the triplex type power cable (CVT cable) 13 is used. The power cable 13 has a structure in which three single-phase cables 13a, 13b, and 13c are twisted together. 4 and 5, the zero-phase currents I _0SA , I _0SB , I _0SC flowing through the shield wires 14a, 14b, 14c of the phase cables 13a, 13b, 13c of the power cable 13 are clamped. The structure detected with current transformer 18a, 18b, 18c is illustrated.

The zero-phase current I _0S flowing in the shield wire 14 is obtained by vector addition of the zero-phase currents I _0SA , I _0SB , I _0SC flowing in the shield wires 14a, 14b, 14c of the phase cables 13a, 13b, 13c. It is done. By executing such arithmetic processing, the clamp-type current transformer 18 that detects the zero-phase current I _0S flowing through the shield wire 14 as a measurement value can be omitted. In addition, when only a power cable (CV cable) having a three-phase shield structure is laid, a short triplex type power cable (CVT cable) may be attached separately from the CV cable.

In addition, when the lengths of the respective phase cables 13a, 13b, and 13c are short, the zero-phase currents I _0SA , I _0SB , and I _0SC flowing through the shield wires 14a, 14b, and 14c become small, so that the clamp-type current transformers 18a and 18b , 18c makes it difficult to detect zero-phase currents I _0SA , I _0SB , I _0SC . In such a case, the number of turns (number of turns) in the clamp-type current transformers 18a, 18b, and 18c is multiplied by n to increase the detection sensitivity of the clamp-type current transformers 18a, 18b, and 18c. The detection of the currents I _0SA , I _0SB , I _0SC can be facilitated. The high-voltage insulation monitoring device 25 multiplies the measured values of the zero-phase currents I _0SA , I _0SB , I _0SC detected by the clamp-type current transformers 18a, 18b, 18c by 1 / n, so Correction for n times is performed. This correction is the same when the zero-phase current I _0S flowing through the shield wire 14 is detected by the clamp type current transformer 18.

In high-pressure insulation monitoring device 25, based on the relational expression -Y described above _{= (I 02 -I 01) /} (V 02 -V 01), the zero-phase voltage V ₀₂ of the current value, V ₀₂ = I _0S2 / Since ωC _0S and the zero-phase voltage V ₀₁ at the start of measurement is V ₀₁ = I _0S1 / _{ωC 0S} , the campus-to-ground admittance Y ₀ (hereinafter simply referred to as campus-to-ground) when the campus high- _{piezoelectric} path 12 is healthy. ( _Referred to as admittance Y ₀ ) is calculated by the calculation unit 26 with a relational expression of −Y ₀ = (I ₀₂ −I ₀₁ ) _{ωC 0S} / (I _0S2 −I _0S1 ). Here, the current zero-phase current I ₀₂ and the zero-phase current I ₀₁ at the start of measurement do not include the ground fault current Ig.

On the other hand, the campus-to-ground admittance Y is represented by -Y = Yr + jYi. The premises-to-ground admittance Y ₀ does not include the ground fault current Ig, and therefore corresponds to the imaginary part Yi of the premises-to-ground admittance Y. When a ground fault occurs, the zero-phase current I ₀ detected by the zero-phase transformer ZCT15 or the clamp-type current transformer 17 is a current including the ground fault Ig (I ₀ = I ₀₁ + Ig or I ₀ = I ₀₂ + Ig).

Therefore, when the zero-phase currents I ₀₁ and I _0S1 are used as a reference, the premises-to-ground admittance Y is calculated by a relational expression of −Y = (I ₀ −I ₀₁ ) _{ωC 0S} / (I _0S −I _0S1 ). 27. Further, when the zero-phase currents I ₀₂ and I _0S2 are used as a reference, the premises-to-ground admittance Y is calculated by a relational expression of −Y = (I ₀ −I ₀₂ ) _{ωC 0S} / (I _0S −I _0S2 ). 27. The real part Yr of the premises-to-ground admittance Y is calculated by the calculation unit 28 using the relational expression of Yr = Y−Y ₀ . As a result, the real part Yr of the premises-to-ground admittance Y is Yr = (Ig · _{ωC 0S} ) / (I _0S2 −I _0S1 ), and the ground fault current Ig is Ig = Yr (I _0S2 −I _0S1 ) / ωC _0S . Since the imaginary part Yi of the premises admittance Y is Yi = 1 / ω (C _A2 + C _B2 + C _C2 ), the ground-to-ground capacitance of the entire premises electrical equipment can be monitored.

FIG. 6 shows an equivalent circuit when a one-line ground fault occurs. As shown in FIG. 7, this ground fault current Ig is a component of each phase with reference to ground voltages Va, Vb, Vc (Va = Ea−V ₀ , Vb = Eb−V ₀ , Vc = Ec−V ₀ ). Iga, Igb, Igc (hereinafter referred to as each phase ground fault current). Therefore, the zero-phase currents I _0SA , I _0SB , I _0SC flowing in the shield wires 14a, 14b, 14c of the phase cables 13a, 13b, 13c of the power cable 13 are _detected by the clamp type current transformers 18a, 18b, 18c. .

The zero-phase currents I _0SA , I _0SB , I _0SC of the phases flowing in the shielded wires 14a, 14b, 14c of the phase cables 13a, 13b, 13c of the power cable 13 are the premises-to-ground admittances Y _0A , Y of each phase. _{From 0B} and Y _0C , I _0SA = Va · Y _0A , I _0SB = Vb · Y _0B , and I _0SC = Vc · Y _0C . These zero-phase currents I _0SA , I _0SB , I _0SC are currents flowing through the ground capacitance, and therefore have a leading 90 ° phase difference with respect to the ground voltages Va, Vb, Vc.

In order to add a function of measuring the resistive ground fault current Igr from the ground fault current Ig generated in the local electrical equipment of the local high voltage path 12, the reference phases of the ground voltages Va, Vb, and Vc of the local high voltage path 12 are specified. That is, in this high voltage insulation monitoring device 25, the _leading phase currents I _0SA , I _0SB , I _0SC of the phase shield wires 14a, 14b, 14c detected by the clamp type current transformers 18a, 18b, 18c are about 90 °. The calculation unit 32 corrects the phase difference.

As this correction processing, a method of simply providing a delay circuit (1/4 cycle time delay of 50 Hz or 60 Hz), a method of generating a high frequency multiplied by the power supply frequency by a PLL circuit synchronized with the power supply, and delaying by a logic counter, There are a method of multiplying a complex number obtained by ADC conversion of a zero-phase current and a Fourier transform by a unit vector having a delay of 90 °, a method of dividing the zero-phase current of each phase flowing through a shield wire by the ground-to-ground admittance of each phase, and the like. In this way, the ground voltages Va, Vb, and Vc are obtained by correcting the phases of the zero-phase currents I _0SA , I _0SB , and I _0SC by the calculation unit 32.

  Based on the ground voltages Va, Vb, and Vc, the ground fault current Ig is subjected to phase detection (Fourier transform) by the calculation unit 29 to obtain the respective phase ground fault currents Iga, Igb, and Igc. As shown in FIG. 7, when the ground voltages Va, Vb, and Vc are used as a reference, the respective phase ground fault currents Iga, Igb, and Igc flowing through the ground fault resistance Rg are in phase with the ground voltages Va, Vb, and Vc.

  Here, in the case of the resistive ground fault Rg (see FIG. 11), as shown in FIGS. 8A and 8B, when the A-phase ground fault current Iga is +1.0 pu for the ground fault current Ig, Phase ground fault current Igb is -0.5 pu, and C phase ground fault current Igc is -0.5 pu. In the case of the inductive ground fault Lg (see FIG. 11), as shown in FIGS. 9A and 9B, for the ground fault current IgL, the A-phase ground fault current Iga becomes 0.0pu, and the B-phase ground The fault current Igb is +0.866 pu, and the C-phase ground fault current Igc is -0.866 pu. Further, in the case of the capacitive ground fault Cg (see FIG. 11), as shown in FIGS. 10A and 10B, the A-phase ground fault current Iga is 0.0 pu for the ground fault current IgC, and the B-phase ground The fault current Igb is −0.866 pu, and the C-phase ground fault current Igc is +0.866 pu.

  As described above, it is assumed that a single-line ground fault occurs in a specific one phase (A phase) and the other two phases (B phase and C phase) are healthy. The high voltage insulation monitoring device 25 obtains the respective phase ground fault currents Iga, Igb, and Igc by performing phase detection based on the three-phase ground voltages Va, Vb, and Vc. Therefore, when the A phase has a ground fault, the A phase ground fault current Iga is meaningful in monitoring the ground fault, but the other B phase ground fault current Igb and the C phase ground fault current Igc are monitored in the ground fault. It has no meaning above.

  However, as described above, in consideration of not only the resistive ground fault Rg but also the inductive ground fault Lg and the capacitive ground fault Cg, the ground fault phase (A phase) and other faults that are not ground faults. Two phases (B phase and C phase) are detected. The high voltage insulation monitoring device 25 cannot distinguish and determine the A phase ground fault, the B phase ground fault, or the C phase ground fault at the stage where the respective phase ground fault currents Iga, Igb, and Igc are obtained. Therefore, it is necessary to obtain the resistive ground fault current Igr generated by the insulation degradation between the ground high-voltage path 12 and the ground from each phase ground fault current Iga, Igb, Igc.

Therefore, the arithmetic unit 30 of the high voltage insulation monitoring device 25 calculates the sum of squares ΣIg ³ = Iga ³ + Igb ³ + Igc ³ of each phase ground fault currents Iga, Igb, Igc. That is, when the trigonometric function is squared, the frequency is doubled. Similarly, when the trigonometric function is cubed, the frequency is tripled. From this, it is possible to obtain the resistive ground fault current Igr by synchronizing the waveform of the cube sum ΣIg ³ of each phase ground fault current Iga, Igb, Igc with the three-phase ground voltages Va, Vb, Vc. It becomes possible.

Here, the maximum value n of the cube sum ΣIg ³ is smaller than 1.0 as shown in FIG. That is, the maximum value n of the cube sum ΣIg ³ is (1 / π∫i ³ dθ) ^1/3 = (Imax ³ / π∫sin ³ θdθ) ^1/3 = Imax (4 / π) ^1/3 = 0.75 (i = Imax · sin θ, i = Iga, Igb, Igc). The arithmetic unit 30 corrects the cube sum ΣIg ³ by a reciprocal multiple (1 / n) of the maximum value n in order to make the maximum value n of the cube sum ΣIg ³ 1.0. true value of ΣIg ³ (ΣIg ³⁾ / n is obtained. By calculating the cube root {(ΣIg ³ ) / n} ^1/3 of the true value (ΣIg ³ ) / n of the cube sum ΣIg ³ , the resistance ground fault caused by the insulation degradation between the high voltage path 12 on the premises and the ground A current Igr is obtained.

  In this embodiment, the sum of cubes has been described, but it is also possible to use an odd sum of powers. As the order of this odd sum of power increases, it approaches 0.9375 for the fifth sum, 0.9844 for the seventh sum, 0.9961 for the ninth sum, 0.9990 for the eleventh sum. become. Thus, when using the odd-numbered sum of power, it is necessary to calculate the odd-numbered root of the odd-numbered sum of power to obtain the resistive ground fault current Igr. However, in the case of using an odd power sum with a normalized value, it is possible to omit the operation of the odd power root.

It is to be noted that the ground fault current Ig {= I ₀ − (− YV ₀ + If)} calculated from the high voltage insulation monitoring device previously proposed by the present applicant (see Japanese Patent Application Laid-Open No. 11-271384) is used to obtain the same The resistance ground fault current Igr can be calculated by calculation. In this embodiment, the resistive ground fault current Igr is calculated based on the fundamental harmonic. For example, a harmonic component including an odd harmonic including the third harmonic or the ninth harmonic is used. The resistive ground fault current Igr may be calculated.

  When the ground fault resistance is large when this ground fault is detected (Rg> about 10 kΩ), the real part | Yr | << the imaginary part | Yi | Therefore, the phase voltages Ea, Eb, Ec and the ground voltages Va, Vb, Vc are substantially equal. Since phase voltage = line voltage / √3 = 6600 V / √3 = 3810 V, ground fault resistance Rg is expressed by the following equation using ground voltages Va, Vb, Vc substantially equal to phase voltages Ea, Eb, Ec. Is required. That is, the ground fault resistance Rg is calculated by the calculation unit 31 with the relational expression of Rg = ground voltage / Igr.

  The present applicant conducted an artificial ground fault test for a resistive ground fault under the following test conditions using a simulated electric room (single wire ground fault current = 7.89 A).

-Power cable: Nominal cross-sectional area 22mm ² , length 20m = 0.0162 [μF] (per phase) power supply frequency 60Hz
・ Ground fault resistance Rg: 200 [kΩ]
・ Ground capacitance C on ground: 0.5 [μF]
・ Residual voltage: about 100 [V]

[Resistant ground fault] (When grounding in phase A)
Each measurement for calculating the premises ground between admittance Y ₀ is as follows.
I ₀₁ : 5.57 [mA] ∠ 178.18 [deg]
I ₀₂ : 21.55 [mA] ∠ 217.96 [deg]
I _0S1 : 0.69 [mA] ∠ 36.12 [deg]
I _0S2 : 1.77 [mA] ∠ 45.00 [deg]
ωC _0S : 2 × π × 60 × 3 × 0.607 × 10 ⁻⁶
= 4.574 × 10 ⁻³ [S ⁻¹ ] ∠90.0 [deg] (power supply frequency: 60 Hz)

The calculation of the premises-to-ground admittance Y ₀ using the above-described measured values is as follows.
−Y ₀ = (I ₀₂ −I ₀₁ ) _{ωC 0S} / (I _0S2 −I _0S1 )
= (21.55 [mA] ∠217.96 [deg] −5.57 [mA] ∠178.18 [deg]) × 4.574 × 10 ⁻³ [S] ∠90.0 [deg] / ( 1.77 [mA] ∠45.00 [deg] −0.69 [mA] ∠36.12 [deg])
= 0.739 × 10 ⁻³ [S ⁻¹ ] ∠269.00 [deg]

Each measurement value for calculating the premises admittance Y between the premises is as follows.
I ₀ (= I ₀₂ + Ig): 9.64 [mA] ∠75.80 [deg] (I ₀ is measured by adding Ig to I ₀₂ )
I _0S : 1.06 [mA] ∠41.52 [deg]

The calculation of the premises-to-ground admittance Y using the above-described measured values is as follows.
-Y = (I ₀ -I ₀₁ ) _{ωC 0S} / (I _0S -I _0S1 )
= (9.64 [mA] ∠75.80 [deg] −5.57 [mA] ∠178.18 [deg]) × 4.574 × 10 ⁻³ [S ⁻¹ ] ∠90.0 [deg] /(1.06 [mA] ∠41.52 [deg] −0.69 [mA] ∠36.12 [deg])
= 1.897 × 10 ⁻³ [S ⁻¹ ] ∠269.00 [deg]

The calculation of the real part Yr of this premises-to-ground admittance Y is as follows.
Yr = Y−Y ₀
= 1.897 × 10 ⁻³ [S ⁻¹ ] ∠269.00 [deg] −0.739 × 10 ⁻³ [S ⁻¹ ] ∠269.00 [deg]
= 1.158 × 10 ⁻³ [S ⁻¹ ] ∠269.47 [deg]

The calculation of the ground fault current Ig is as follows.
Ig = Yr (I _0S2 −I _0S1 ) / _{ωC 0S}
= 1.158 × 10 ⁻³ [S ⁻¹ ] ∠269.47 [deg] × (1.77 [mA] ∠45.00 [deg] −0.69 [mA] ∠36.12 [deg]) /4.574×10 ⁻³ [S ⁻¹ ] ∠90.0 [deg]
= 18.16 [mA] ∠ 49.6 [deg]

Here, the ground of the high _{piezoelectric} path 12 obtained by correcting the phase obtained from the zero-phase currents I _0SA , I _0SB , I _0SC flowing through the shield wires 14a, 14b, 14c of the phase cables 13a, 13b, 13c by 90 ° The reference phases of the voltages Va, Vb, and Vc have the following phase difference from the voltage phase of the power supply voltage AC100V.
Phase A: 49.5 [deg]
Phase B: 289.5 [deg]
Phase C: 169.5 [deg]

As a result of phase detection based on each of the aforementioned phases, the respective phase ground fault currents Iga, Igb, Igc are as follows.
Iga = (18.17 + j0.03) × 10 ⁻³ [A]
Igb = (− 9.11 + j15.73) × 10 ⁻³ [A]
Igc = (− 9.05−j15.73) × 10 ⁻³ [A]

The calculation of the cube sum ΣIg ³ using the real part of each phase ground fault current Iga, Igb, Igc is as follows.
ΣIg ³ = Iga ³ + Igb ³ + Igc ³
= 18.17 ³ + (− 9.11) ³ + (− 9.05) ³
= 4497.5

By correcting the cube sum ΣIg ³ of each phase ground fault current Iga, Igb, Igc by a reciprocal multiple of the maximum value n = 0.75, the true value (ΣIg ³ ) / n of the cube sum ΣIg ³ = 5996.7 is obtained. By calculating the cube root {(ΣIg ³ ) / n} ^1/3 of the true value (ΣIg ³ ) / n of the cube sum ΣIg ³ , the resistive ground fault current Igr = 18.17 [mA] is obtained. . As a result, the ground fault resistance Rg = Eg / Igr = 3810 [V] /18.17 [mA] = 209.7 [kΩ].

  As shown in the above table, in the case of the ground fault in the resistive ground fault, the result that the ground fault current Igr was 18.17 mA and the ground fault resistance Rg at that time was 209.7 kΩ when the ground fault occurred in the A phase. Moreover, when the ground fault occurred in the B phase, the result that the resistive ground fault current Igr was 19.60 mA and the ground fault resistance Rg at that time was 194.2 kΩ was obtained. Further, when a ground fault occurred in the C phase, the result was that the resistive ground fault current Igr was 19.89 mA and the ground fault resistance Rg at that time was 191.2 kΩ. In this way, in the case of a resistive ground fault, it has been found that the resistive ground fault current Igr and the ground fault resistance Rg can be measured.

  In the above description, the artificial ground fault test for the resistive ground fault has been described. However, the applicant of the present invention uses the simulated electric room (one-line ground fault current = 7.89 A) and the artificial ground for the inductive ground fault under the following test conditions. A tangle test was also performed.

-Power cable: Nominal cross-sectional area 22mm ² , length 20m = 0.0162 [μF] (per phase) power supply frequency 60Hz
・ Ground fault resistance Lg: 68 [kΩ] {Air-core coil 200 mH, 210 V (Tr6300 / 210 V tap)}
・ Ground ground capacitance 1C: 0.5 [μF] / phase

[Inductive ground fault] (When grounding in phase A)
Each measurement for calculating the premises ground between admittance Y ₀ is as follows.
I ₀₁ : 5.57 [mA] ∠ 178.18 [deg]
I ₀₂ : 21.55 [mA] ∠ 217.96 [deg]
I _0S1 : 0.69 [mA] ∠ 36.12 [deg]
I _0S2 : 1.77 [mA] ∠ 45.00 [deg]
ωC _0S : 2 × π × 60 × 3 × 0.607 × 10 ⁻⁶
= 4.574 × 10 ⁻³ [S ⁻¹ ] ∠90.0 [deg] (power frequency: 60 Hz)

The calculation of the premises-to-ground admittance Y ₀ using the above-described measured values is as follows.
−Y ₀ = (I ₀₂ −I ₀₁ ) _{ωC 0S} / (I _0S2 −I _0S1 )
= (21.55 [mA] ∠217.96 [deg] −5.57 [mA] ∠178.18 [deg]) × 4.574 × 10 ⁻³ [S] ∠90.0 [deg] / ( 1.77 [mA] ∠45.00 [deg] −0.69 [mA] ∠36.12 [deg])
= 0.739 × 10 ⁻³ [S ⁻¹ ] ∠269.00 [deg]

Each measurement value for calculating the premises admittance Y between the premises is as follows.
I ₀ (= I ₀₂ + Ig): 32.01 [mA] ∠ 323.39 [deg] (I ₀ is measured by a value obtained by adding Ig to I ₀₂ )
I _0S : 1.45 [mA] ∠ 339.79 [deg]

The calculation of the premises-to-ground admittance Y using the above measured values is as follows.
-Y = (I ₀ -I ₀₁ ) _{ωC 0S} / (I _0S -I _0S1 )
= (32.01 [mA] ∠ 323.39 [deg]-5.57 [mA] ∠ 178.18 [deg]) x 4.574 x 10 ^-3 [S ^-1 ] ∠ 90.0 [deg] /(1.45 [mA] ∠339.79 [deg] -1.77 [mA] ∠45.00 [deg])
= 1.121 × 10 ⁻³ [S ⁻¹ ] ∠168.75 [deg]

The calculation of the real part Yr of this premises-to-ground admittance Y is as follows.
Yr = Y−Y ₀
= 1.121 × 10 ⁻³ [S ⁻¹ ] ∠168.75 [deg] −0.739 × 10 ⁻³ [S ⁻¹ ] ∠269.00 [deg]
= 1.448 × 10 ⁻³ [S ⁻¹ ] ∠138.62 [deg]

The calculation of the ground fault current Ig is as follows.
Ig = Yr (I _0S2 −I _0S1 ) / _{ωC 0S}
= 1.448 × 10 ⁻³ [S ⁻¹ ] ∠138.62 [deg] × (1.77 [mA] ∠45.00 [deg] −0.69 [mA] ∠36.12 [deg]) /4.574×10 ⁻³ [S ⁻¹ ] ∠90.0 [deg]
= 55.64 [mA] ∠322.09 [deg]

Here, the ground of the high _{piezoelectric} path 12 obtained by correcting the phase obtained from the zero-phase currents I _0SA , I _0SB , I _0SC flowing through the shield wires 14a, 14b, 14c of the phase cables 13a, 13b, 13c by 90 ° The reference phases of the voltages Va, Vb, and Vc have the following phase difference from the voltage phase of the power supply voltage AC100V.
Phase A: 49.5 [deg]
Phase B: 289.5 [deg]
Phase C: 169.5 [deg]

As a result of phase detection based on each of the aforementioned phases, the respective phase ground fault currents Iga, Igb, Igc are as follows.
Iga = (2.52-j55.6) × 10 ⁻³ [A]
Igb = (46.9 + j30.0) × 10 ⁻³ [A]
Igc = (− 49.6 + j25.6) × 10 ⁻³ [A]

The calculation of the cube sum ΣIg ³ using the real part of each phase ground fault current Iga, Igb, Igc is as follows.
ΣIg ³ = Iga ³ + Igb ³ + Igc ³
= 2.52 ³ +46.9 ³ + (− 49.4) ³
= -17483.8

By correcting the cube sum ΣIg ³ of each phase ground fault current Iga, Igb, Igc by a reciprocal multiple of the maximum value n = 0.75, the true value (ΣIg ³ ) / n of the cube sum ΣIg ³ = −23311.8 is obtained. By calculating the cube root {(ΣIg ³ ) / n} ^1/3 of the true value (ΣIg ³ ) / n of the cube sum ΣIg ³ , the resistive ground fault current Igr = −28.56 [mA] is obtained. It is done. Thus, since the resistive ground fault current Igr becomes a negative value, the ground fault resistance Rg cannot be calculated.

  As shown in the above table, with the inductive ground fault, when the ground fault occurred in the A phase, the result was that the resistive ground fault current Igr was -28.56 mA and the ground fault resistance Rg at that time could not be measured. Moreover, when a ground fault occurred in the B phase, the result was that the resistance ground fault current Igr was −43.89 mA and the ground fault resistance Rg at that time could not be measured. Furthermore, when a ground fault occurred in the C phase, it was found that both the resistive ground fault current Igr and the ground fault resistance Rg could not be measured. Thus, in the case of an inductive ground fault, since the resistive ground fault current Igr is a negative value or cannot be measured, the ground fault resistance Rg is not measured.

  In the above, the artificial ground fault test of the inductive ground has been described. However, the applicant of the present invention uses a simulated electric room (single wire ground fault current = 7.89 A) to create a capacitive ground fault artificial ground under the following test conditions. A tangle test was also performed.

・ Ground fault resistance Cg: 0.2 [μF] (Internal to ground impedance Z _0S = 132.6 [kΩ], rated voltage 6600 V, 0.2 [μF])
・ Ground ground capacitance 1C: 0.5 [μF] / phase

[Capacitive ground fault] (When a ground fault occurs in phase A)
Each measurement for calculating the premises ground between admittance Y ₀ is as follows.
I ₀₁ : 5.57 [mA] ∠ 178.18 [deg]
I ₀₂ : 21.55 [mA] ∠ 217.96 [deg]
I _0S1 : 0.69 [mA] ∠ 36.12 [deg]
I _0S2 : 1.77 [mA] ∠ 45.00 [deg]
ωC _0S : 2 × π × 60 × 3 × 0.607 × 10 ⁻⁶
= 4.574 × 10 ⁻³ [S ⁻¹ ] ∠90.0 [deg] (power frequency: 60 Hz)

The calculation of the premises-to-ground admittance Y ₀ using the above-described measured values is as follows.
−Y ₀ = (I ₀₂ −I ₀₁ ) _{ωC 0S} / (I _0S2 −I _0S1 )
= (21.55 [mA] ∠217.96 [deg] −5.57 [mA] ∠178.18 [deg]) × 4.574 × 10 ⁻³ [S] ∠90.0 [deg] / ( 1.77 [mA] ∠45.00 [deg] −0.69 [mA] ∠36.12 [deg])
= 0.739 × 10 ⁻³ [S ⁻¹ ] ∠269.00 [deg]

Each measurement value for calculating the premises admittance Y between the premises is as follows.
I ₀ (= I ₀₂ + Ig): 23.53 [mA] ∠146.80 [deg] (I ₀ is measured by adding Ig to I ₀₂ )
I _0S = 0.78 [mA] ∠87.78 [deg]

The calculation of the premises-to-ground admittance Y using the above measured values is as follows.
-Y = (I ₀ -I ₀₁ ) _{ωC 0S} / (I _0S -I _0S1 )
= (23.53 [mA] ∠146.80 [deg] −5.57 [mA] ∠178.18 [deg]) × 4.574 × 10 ⁻³ [S ⁻¹ ] ∠90.0 [deg] /(0.78 [mA] ∠ 87.78 [deg]-1.77 [mA] ∠ 45.00 [deg])
= 0.917 × 10 ⁻³ [S ⁻¹ ] ∠344.9 [deg]

The calculation of the real part Yr of this premises-to-ground admittance Y is as follows.
Yr = Y−Y ₀
= 0.917 × 10 ⁻³ [S ⁻¹ ] ∠344.9 [deg] −0.739 × 10 ⁻³ [S ⁻¹ ] ∠269.00 [deg]
= 1.021 × 10 ⁻³ [S ⁻¹ ] ∠29.05 [deg]

The calculation of the ground fault current Ig is as follows.
Ig = Yr (I _0S2 −I _0S1 ) / _{ωC 0S}
= 1.021 × 10 ⁻³ [S ⁻¹ ] ∠29.05 [deg] × (1.77 [mA] ∠45.00 [deg] −0.69 [mA] ∠36.12 [deg]) /4.574×10 ⁻³ [S ⁻¹ ] ∠90.0 [deg]
= 29.45 [mA] ∠ 140.1 [deg]

Here, the ground of the high _{piezoelectric} path 12 obtained by correcting the phase obtained from the zero-phase currents I _0SA , I _0SB , I _0SC flowing through the shield wires 14a, 14b, 14c of the phase cables 13a, 13b, 13c by 90 ° The reference phases of the voltages Va, Vb, and Vc have the following phase difference from the voltage phase of the power supply voltage AC100V.
Phase A: 49.5 [deg]
Phase B: 289.5 [deg]
Phase C: 169.5 [deg]

As a result of phase detection based on each of the aforementioned phases, the respective phase ground fault currents Iga, Igb, Igc are as follows.
Iga = (− 0.29 + j29.44) × 10 ⁻³ [A]
Igb = (− 25.35−j14.98) × 10 ⁻³ [A]
Igc = (25.65−j14.47) × 10 ⁻³ [A]

The calculation of the cube sum ΣIg ³ using the real part of each phase ground fault current Iga, Igb, Igc is as follows.
ΣIg ³ = Iga ³ + Igb ³ + Igc ³
= (−0.29) ³ + (− 25.35) ³ +25.65 ³
= -5580.46

By correcting the cube sum ΣIg ³ of each phase ground fault current Iga, Igb, Igc by a reciprocal multiple of the maximum value n = 0.75, the true value (ΣIg ³ ) / n of the cube sum ΣIg ³ = -773.95 is obtained. By calculating the cubic root {(ΣIg ³ ) / n} ^1/3 of the true value (ΣIg ³ ) / n of the cube sum ΣIg ³ , the resistive ground fault current Igr = −9.18 [mA] is obtained. It is done. Thus, since the resistive ground fault current Igr becomes a negative value, the ground fault resistance Rg cannot be calculated.

  As shown in the above table, in the case of the ground fault in the capacitive ground fault, the ground fault current Igr was −9.18 mA and the ground fault resistance Rg at that time could not be measured. Moreover, when the ground fault occurred in the B phase, the ground fault current Igr was −8.83 mA, and the ground fault resistance Rg at that time could not be measured. Furthermore, when a ground fault occurred in the C phase, the ground fault current Igr was −15.3 mA, and the ground fault resistance Rg at that time could not be measured. Thus, in the case of a capacitive ground fault, since the ground fault current Igr becomes a negative value, the ground fault resistance Rg is not measured.

Next, FIG. 12 is a polar coordinate display of the waveform of the cube sum ΣIg ³ of each phase ground fault current Iga, Igb, Igc (see FIG. 11). As shown in FIG. 12, the value of the cube sum ΣIg ³ of each phase ground fault current Iga, Igb, Igc tends to decrease sharply even if it slightly deviates from the phase of each relative ground voltage Va, Vb, Vc. is there. In other words, in the waveform of the cube sum ΣIg ³ of each phase ground fault current Iga, Igb, Igc, the curvature in the vicinity of the phase of each relative ground voltage Va, Vb, Vc forms a large curve.

Therefore, the phase sum angle ΣIg ³ of each phase ground fault current Iga, Igb, Igc is normalized with a monitoring level (for example, 20 mA is set to 1), and the square root is calculated a plurality of times to obtain the phase detection angle φ. Wide angle can be achieved. In this way, the phase deviation from each relative ground voltage Va, Vb, Vc is obtained by normalizing the cube sum ΣIg ³ of each phase ground fault current Iga, Igb, Igc with the monitoring level and calculating the square root a plurality of times. Even if there is, the decrease in the value of the cube sum ΣIg ³ can be reduced, so that the resistive ground fault current Igr can be accurately calculated. The phase detection angle φ means an angle formed by 80% of the maximum value in each phase.

In other words, in the waveform of the cube sum ΣIg ³ of each phase ground fault current Iga, Igb, Igc, the curvature in the vicinity of the phase of each relative ground voltage Va, Vb, Vc is reduced as shown in FIGS. be able to. When the square root of the normalized cube sum ΣIg ³ is calculated a plurality of times, the waveform near the phase of each of the relative ground voltages Va, Vb, Vc can be made closer to a flat shape in the waveform of the cube sum ΣIg ^3. The angle φ can be widened.

For example, when the cube sum ΣIg ³ of each phase ground fault current Iga, Igb, Igc is normalized, the phase detection angle φ (0.8 value) becomes ± 12 °, and when the square root is repeated three times, the phase detection The angle φ is ± 16 ° at the first square root (ΣIg ³ ) ^1/2 , ± 20 ° at the second square root (ΣIg ³ ) ^1/4 , ± 24 at the ^third square root (ΣIg ³ ) ^1/8 °. As described above, when the square root is repeated three times, the phase detection angle φ can be widened to twice the normalization.

In order to set the maximum value n of the cube sum ΣIg ³ to 1.0, the arithmetic unit 30 multiplies the cube sum ΣIg ³ by a reciprocal multiple (1 / n) of the maximum value n to thereby reduce the resistance. The ground fault current Igr is corrected. Further, the phase angle of the resistive ground fault current Igr is corrected by normalizing the cube sum ΣIg ³ of each phase ground fault current Iga, Igb, Igc. The boundary between the healthy phase and the ground fault phase is distinguished by a ± 90 ° phase difference based on the ground voltage phase of the ground fault phase. A phase margin of about 6 ° or less may be provided at this phase boundary.

In addition to such means, as shown in FIG. 15 and FIG. 16, correction of the resistive ground fault current Igr is performed by offsetting the sum of squares ΣIg ³ of each phase ground fault currents Iga, Igb, Igc by a DC bias. And it is possible to realize phase angle correction.

  FIG. 17 shows a ground fault relay (GR / DGR) that has been widely used, a high-voltage insulation monitoring device previously proposed by the present applicant (Japanese Patent Laid-Open No. 11-271384), and an embodiment of the present invention. For the high voltage insulation monitoring device 25, for example, the monitoring sensitivity of each device when the A phase is grounded is compared.

As shown in the figure, in the ground fault relay (GR / DGR), the zero-phase current can be monitored in a region S ₁ larger than about 100 mA. In the high voltage insulation monitoring apparatus disclosed in Japanese Patent Laid-Open No. 11-271384 The zero-phase current can be monitored in a region S ₂ where the current is larger than 20 mA. In contrast, in the high-pressure insulation monitoring apparatus 25 according to an embodiment of the present invention, since the zero-phase current can be monitored in the following areas S ₃ 20 mA, it is possible to detect a small ground fault.

In the embodiment described above, the cube root {(ΣIg ³ ) / n} ^1/3 of the true value (ΣIg ³ ) / n of the cube sum ΣIg ³ of each phase ground fault current Iga, Igb, Igc is calculated. The ground fault resistance Rg is calculated using the resistive ground fault current Igr obtained by the above. In addition to this, it is also possible to use the ground voltages Va, Vb, and Vc obtained by correcting the phase by the calculation unit 32. That is, by dividing each relative ground voltage Va, Vb, Vc by each phase ground fault current Iga, Igb, Igc, each phase ground fault resistance Rga (= Va / Iga), Rgb (= Vb / Igb), Rgc. By calculating (= Vc / Igc) and calculating the cube root of the cube sum of each phase ground fault resistance Rga, Rgb, Rgc, an accurate ground fault resistance Rg can also be obtained.

  In addition, the high-voltage insulation monitoring device 25 can monitor the ground voltages Va, Vb, and Vc in the same manner as the grounded instrument transformer (EVT) by obtaining the ground voltages Va, Vb, and Vc. When the on-site electrical equipment is operating normally, the ground voltages Va, Vb, and Vc are balanced (Va≈Vb≈Vc). The ground voltages Va, Vb, and Vc are unbalanced due to insulation deterioration of the high piezoelectric path 12 and other abnormal factors. Therefore, the abnormality of the high piezoelectric path 12 can be determined by monitoring the ground voltages Va, Vb, and Vc.

Here, the ground voltage Va (= Ea−V ₀ ), Vb (= Eb−V ₀ ), Vc (= Ec−V ₀ ) of each phase is vector-added by the calculation unit 33 to obtain the zero phase voltage V ₀ . (Va + Vb + Vc = Ea + Eb + Ec−3V ₀ , where Ea + Eb + Ec = 0, so Va + Vb + Vc = −3V ₀ ). By using this zero-phase voltage V ₀ , it is possible to realize ground fault monitoring of an ungrounded electric circuit in an extra-high voltage power receiving facility.

Further, the high voltage insulation monitoring device 25 calculates the zero-phase voltage V ₀ and the premises admittance Y _0S . On the other hand, the zero-phase current I _0S flowing through the shield wire 14 of the power cable 13 is detected by a clamp type current transformer 18. Therefore, if the zero-phase current I _0S that is the measured value, the zero-phase voltage V ₀ that is the calculated value, and the premises admittance Y _0S satisfy the condition of Y _0S · V ₀ = I _0S , the power cable 13 It can be determined that the shield wire 14 is healthy. When the condition of Y _0S · V ₀ = I _0S is not satisfied, it can be determined that the insulation deterioration of the shield wire 14 of the power cable 13 has occurred.

  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.

12 (on-site) high piezoelectric path 13 power cable 14 shield cable of power cable 15 zero-phase current transformer ZCT
18 Current transformer (clamp-type current transformer)
19 High Voltage Insulation Monitoring Device 21 to 24 Arithmetic Unit 25 High Voltage Insulation Monitoring Device 26 to 32 Arithmetic Unit C Ground Ground Capacitance I ₀ Zero Phase Current Flowing in High Voltage Piezoelectric Path I _0S Zero Phase Current Flowing in Shield Wire of Power Cable Zero-phase current due to imbalance of premises-to-ground admittance Ig Ground fault current Iga, Igb, Igc Each phase ground fault current Rg Ground fault resistance Y When the campus high-voltage road is healthy and when ground fault occurs, the ground-to-ground admittance Y ₀ Premises-to-ground admittance Y _0S power cable premises-to-ground admittance Yr real-time part of premises-to-ground admittance Yi imaginary part of premises-to-ground admittance ω Angular velocity of power frequency

Claims (8)

When a ground fault occurs in a non-grounded circuit, the zero-phase current I ₀ that flows through the high-voltage yard connected to the non-grounded circuit, and the zero-phase that flows through the shield line of the power cable installed in the high-voltage yard This is a high voltage insulation monitoring method in which the current I _0S is detected by a current transformer, and the ground fault resistance is measured based on the zero phase current I ₀ flowing in the high voltage path on the premises and the zero phase current I _0S flowing in the shield line of the power cable. And
When the variation ΔI ₀ of the zero-phase current I ₀ approximates ₀ at the start of measurement, the premises-to-ground admittance Y is set to −Y = {(I _{02 −If} ) / I _0S2 } · Y _0S or −Y = {(I ₀₂ −I ₀₁ ) / I _0S2 } · Y _0S , and the reciprocal 1 / Yr of the real part Yr of the premises-to-ground admittance Y is measured as the ground fault resistance Rg in the provisional mode. When the variation ΔI ₀ of the zero-phase current I ₀ becomes larger than ₀ after the measurement is started, the premises-to-ground admittance Y is calculated by the relational expression of −Y = (ΔI ₀ / ΔI _0S ) · Y _0S Thus, the high voltage insulation monitoring method is characterized in that the inverse 1 / Yr of the real part Yr of the premises-to-ground admittance Y is measured as the ground fault resistance Rg in the definite mode. The high-voltage insulation monitoring method according to claim 1, wherein a zero-phase current transformer ZCT installed in the campus high-voltage path detects a zero-phase current I ₀ flowing through the campus high-voltage path when a ground fault occurs. A current transformer is connected to the secondary side of the zero-phase current transformer ZCT installed in the campus high-voltage path, and the current transformer detects the zero-phase current I ₀ flowing in the campus high-voltage path when a ground fault occurs. The high voltage insulation monitoring method according to claim 1, wherein the high voltage insulation is monitored.   The high-voltage insulation according to any one of claims 1 to 3, wherein the ground capacitance C is measured by dividing the imaginary part Yi of the ground-to-ground admittance Y by an angular velocity ω of a power supply frequency. Monitoring method. When a ground fault occurs in a non-grounded circuit, the zero-phase current I ₀ that flows through the high-voltage yard connected to the non-grounded circuit, and the zero-phase that flows through the shield line of the power cable installed in the high-voltage yard A high-voltage insulation monitoring device that detects current I _0S with a current transformer and measures the ground fault resistance based on the zero-phase current I ₀ flowing through the high voltage path on the premises and the zero-phase current I _0S flowing through the shield wire of the power cable. And
The on-site high-voltage road is sound and ground-to-ground admittance Y ₀ is calculated by a relational expression of −Y ₀ = (I ₀₂ −I ₀₁ ) _{ωC 0S} / (I _0S2 −I _0S1 ) and on-site high pressure The yard-to-ground admittance Y when the electric circuit is healthy is set to -Y = (I ₀ -I ₀₁ ) _{ωC 0S} / (I _0S −I _0S1 ) or −Y = (I ₀ −I ₀₂ ) ωC _0S / (I _0S −I _0S2 ), and the ground voltage Ig is calculated from the real part Yr of the ground-to-ground admittance Y which is the difference between the ground-to-ground admittance Y and the ground-to-ground admittance Y _0. The ground fault currents Iga, Igb, Igc are calculated as follows, and the cube root (ΣIg ³ ) ^1/3 of the cube sum ΣIg ³ of each phase ground fault current Iga, Igb, Igc is calculated as the resistive ground fault current Igr. To provide a calculation unit that measures the ground fault resistance. A high voltage insulation monitoring device characterized by The phase ground fault current Iga, Igb, by correcting the cube sum ShigumaIg ³ of Igc in reciprocal of the maximum value n, the true value (ΣIg ³⁾ of said cube sum ΣIg ³ / n to calculate the The high-voltage insulation according to claim 5, wherein a cube root {(ΣIg ³ ) / n} ^1/3 of a true value (ΣIg ³ ) / n of the cube sum ΣIg ³ is calculated as a resistive ground fault current Igr. Monitoring device. The cube sum ΣIg ³ of each phase ground fault current Iga, Igb, Igc is normalized at the monitoring level, and the square root of the normalized cube sum is calculated a plurality of times. High voltage insulation monitoring device. The phase ground fault current Iga, Igb, high insulation monitoring device according to any one of claims 5-7 for the cube sum ShigumaIg ³ of Igc was to offset the DC bias.

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