JP2010187446A - Power cable ground fault detecting apparatus and power cable ground fault protection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power cable ground fault detecting apparatus for ground fault protection in a power cable line without installing an expensive grounded measurement device transformer and a neutral point resistor. <P>SOLUTION: The power cable ground fault detecting apparatus 10 is provided with a ground fault accident determination circuit 12, a sheath current comparison circuit 13, and an AND circuit 14. The ground fault determination circuit functions as ground fault accident occurrence detection means for detecting occurrence of a ground fault accident in a power cable line based on a zero phase current I<SB>0</SB>input from zero phase converters 5 installed in R-phase/S-phase/T-phase power cables 2<SB>R</SB>, 2<SB>S</SB>and 2<SB>T</SB>, which constitute a power cable line, and a sheath current I<SB>S</SB>input from a sheath current detecting transformer 6 arranged in each sheath ground fault line 4 for grounding a metal sheath of the R-phase/S-phase/T-phase power cables 2<SB>R</SB>, 2<SB>S</SB>and 2<SB>T</SB>. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a power cable ground fault detection device and a power cable ground fault protection device, and in particular, a power cable ground fault detection device and a power cable ground fault protection suitable for ground fault protection of a power cable line in a non-grounded power system. Relates to the device.

  Conventionally, as a method of ground fault protection for power cable lines in a non-grounded power system, a method of interrupting an accident using only a ground fault overvoltage relay that inputs zero phase voltage, and a zero phase voltage and zero phase current are used. There is a method of interrupting accidents using a ground fault direction relay as input.

  In addition, as a technique for reliably interrupting an accident line without using a zero-phase voltage, the ground fault line selective protection relay device disclosed in Patent Document 1 below is a line zero-phase current detected by a current detector. And determine whether the ratio of the neutral-point zero-phase current is greater than 1 / number of lines, and if the ratio is greater than 1 / number of lines, determine that a ground fault has occurred and supply a circuit breaker to the circuit breaker. By separating the accident line from the bus line, the accident line can be reliably interrupted regardless of the magnitude of the accident point resistance in the event of a ground fault.

In the fine ground fault detection device disclosed in Patent Document 2 below, when the load equipment is insulated and the fine ground fault current flows through the main circuit cable, the secondary side of the grounded current transformer is In contrast to the unbalanced portion of the circuit cable ground charging current, a current in which a fine ground fault current is superimposed flows. On the other hand, in the grounded current transformer installed on the sheath ground wire, the ground charging current unbalance of the main circuit cable By adopting a configuration in which the detection output of two grounded current transformers is subtracted by the comparison / determination device and only the micro ground fault current due to the insulation deterioration of the load equipment is detected as a result of detecting only the shunt current. In addition, it is possible to detect with high sensitivity an insulation deterioration state of a load device connected to a distribution line of a non-grounded power supply system.
JP-A-5-328588 JP-A-5-076131

However, in the case of ground fault protection using a ground fault overvoltage relay or a ground fault direction relay, it is necessary to install an expensive grounded instrument transformer (GPT) for taking in a zero-phase voltage (voltage element). there were.
Further, in the ground fault line selective protection relay device disclosed in the above-mentioned Patent Document 1, it is possible to determine the presence or absence of a ground fault without using a zero-phase voltage (voltage element), but the neutral point resistance Because it is necessary to compare the neutral point zero-phase current flowing in the voltage generator (NGR) and the line zero-phase current, it is necessary to install an expensive neutral point resistor in the non-grounded power system There's a problem.
In the fine ground fault detection device disclosed in Patent Document 2 above, the grounding type current transformer provided on the sheath ground wire detects only the unbalanced current of the ground charging current of the main circuit cable, Due to the insulation deterioration of the load equipment by subtracting the current obtained by superimposing the fine ground fault current on the unbalanced current of the main circuit cable ground detection current detected by the grounded current transformer installed in the main circuit cable. This is for detecting only a minute ground fault current.

  An object of the present invention is to provide a power cable ground fault detection device and a power cable ground fault protection device capable of performing ground fault protection of a power cable line without the need to install an expensive grounding-type instrument transformer and neutral point resistor. Is to provide.

A power cable ground fault detection device according to the present invention is a power cable ground fault detection device (10) for detecting the occurrence of a ground fault in a power cable line, wherein the power cables (2 _R , 2 _S, 2 _T) zero-phase current transformer installed in (5) zero-phase current inputted from the (I _0), placed in the sheath ground wire for grounding the metallic sheath of the power cable (4) Ground fault occurrence detection means (12-14) for detecting the occurrence of a ground fault in the power cable line based on the sheath current (I _S ) input from the sheath current detection current transformer (6). It is characterized by comprising.
Here, the ground fault occurrence detection means has a current value of the zero-phase current equal to or greater than a zero-phase current set value, and a phase difference between the zero-phase current and the sheath current falls within the phase set value. A ground fault determination means (12) for outputting an output signal, a sheath current comparison means (13) for outputting an output signal when the current value of the sheath current is equal to or greater than a sheath current settling value, A ground fault detection signal output means (14) may be provided for outputting a ground fault detection signal when an output signal is input from both of the ground fault judgment circuit and the sheath current comparison circuit.
The power cable line has a section of the power cable and a section other than the power cable, and the phase set value includes a phase set value in the power cable section and a phase set value outside the power cable section, and the ground fault The accident determination means determines that a ground fault has occurred in the power cable section when the phase difference between the zero-phase current and the sheath current is within the phase set value in the power cable section, On the other hand, if the phase difference between the zero-phase current and the sheath current is within the phase set value outside the power cable section, it may be determined that a ground fault has occurred in a section other than the power cable.
The sheath current setting value is “f” for the commercial power supply frequency, “Ca” for the capacitance between the core of the power cable and the metal sheath, and “0” for the zero-phase voltage at a predetermined ground fault resistance. If V ₀ ″, it may be set to a value smaller than 2πfCaV ₀ .
The power cable ground fault protection device of the present invention is a power cable ground fault protection device (50) for protecting a power cable line from a ground fault, and includes a power cable (2 ₁ to 2) constituting the power cable line. zero-phase current transformer installed in ₄₎ (5 ₁ to 5 zero-phase current inputted from ₄₎ and (I ₀₁ ~I _04), sheath ground wire for grounding the metallic sheath of the power cable (4 ₁ to 4 ₄ ) based on the sheath currents (I _{S1 to} I _S4 ) input from the sheath current detection current transformers (6 _{1 to} 6 ₄ ) installed in ₁ to 4 ₄ ). Judgment means (52, 53) for judging the presence or absence is provided.
Here, the power cable ground fault protection device may be used as a substitute for a ground fault protection relay that performs ground fault protection of the power cable line by both a current element and a voltage element.
Moreover, the power cable ground fault protection device of the present invention is a power cable ground fault protection device (50) for protecting a plurality of power cable lines branched from the bus (1) from a ground fault. a plurality of power cables ₍₂₁ to ₂₄₎ a plurality of zero-phase current transformer installed respectively (5 ₁ to 5 ₄₎ a plurality of zero-phase current inputted from each of the respective constituting the power cable line of the (I _{01 to} I ₀₄ ) and a plurality of sheath current detection current transformers (6 ₁ to ₄ ) installed on a plurality of sheath ground wires (4 ₁ to 4 ₄ ) for grounding the metal sheaths of the plurality of power cables, respectively. 6 ₄ ) Based on the plurality of sheath currents (I _{S1 to} I _S4 ) respectively input from the ground fault, the occurrence of a ground fault in the power cable line is detected, and the ground fault for identifying the fault line in which the ground fault has occurred Accident detection means (52, 53).
Here, when the ground fault detection means is one of the plurality of power cable lines, the phase difference between the zero-phase current and the sheath current is within a phase settling value. It is determined that a ground fault has occurred in the one power cable line, and the ground fault determination means (52) for specifying the one power cable line as the fault line, and the fault line is specified by the ground fault determination means. If the current value of the sheath current is greater than or equal to the sheath current set value for the single power cable line, sheath current comparing means (53) for outputting an output signal may be provided.
The power cable line has a section of the power cable and a section other than the power cable, and the phase set value includes a phase set value in the power cable section and a phase set value outside the power cable section, and the ground fault The accident determination means determines that a ground fault has occurred in the power cable section when the phase difference between the zero-phase current and the sheath current is within the phase set value in the power cable section, If the phase difference between the zero-phase current and the sheath current is within the phase set value outside the power cable section, it may be determined that a ground fault has occurred in a section other than the power cable.
On the condition that the current value of the sheath current is greater than or equal to the sheath current set value by the sheath current comparison unit, the ground fault determination unit has identified the fault line among the plurality of power cable lines power cable line breaker which is installed in (7 ₁ to 7 ₄₎ may further include a relay output means for generating (54) a trip signal (TR) for collectively blocking.
The sheath current set value is “f” as a commercial power supply frequency, “C _i ” as a capacitance between the core of the power cable and the metal sheath, and a zero-phase voltage at a predetermined ground fault resistance. If “V ₀ ” is set, the value may be set to a value smaller than 2πfC _i V ₀ .

The power cable ground fault detection device and the power cable ground fault protection device of the present invention have the following effects.
(1) Since it is not necessary to use a zero-phase voltage (voltage element), it is not necessary to install an expensive grounding-type instrument transformer for taking in the zero-phase voltage.
(2) Since it is not necessary to use the NGR current, it is not necessary to newly install an expensive neutral point resistor even in a non-grounded power system.
(3) Since there is no need to install a grounded-type instrument transformer, the high-voltage contact portion can be eliminated, and the safety of work can be improved.
(4) Even when a power cable is laid in the middle of the distribution system, a ground fault in the section of the power cable can be prevented by installing a clamp type zero-phase current transformer and a ground fault current detection current transformer. Can be detected.
(5) The ground fault overvoltage relay used with the ground fault direction relay can be eliminated.

  For the above purpose, a sheath current detection current transformer is installed on the sheath ground wire for grounding the metal sheath of the power cable constituting the power cable line, and the sheath current input from the sheath current detection current transformer is It was realized by detecting the occurrence of ground fault in power cable line by using instead of voltage element.

Hereinafter, embodiments of a power cable ground fault detection device and a power cable ground fault protection device of the present invention will be described with reference to the drawings.
As shown in FIGS. 1A and 1B, a power cable ground fault detection apparatus 10 according to an embodiment of the present invention includes a zero-phase current I input from a clamp-type zero-phase current transformer (ZCT) 5. _The occurrence of a ground fault in the power cable line is detected based on ₀ and the sheath current I _S input from the clamp-type sheath current detection current transformer 6.

Here, the zero-phase current transformer 5 includes R-phase, S-phase, and T-phase power cables 2 _R , 2 _S , 2 _T and R-phase, S-phase, and T-phase power cables 2 _R , 2 that constitute the power cable line. _The zero-phase current I ₀ is detected by penetrating through the sheath ground wire 4 for grounding the _S and 2 _T metal sheaths. The opposite ends of the R-phase, S-phase, and T-phase power cables 2 _R , 2 _S , 2 _T are connected to the R-phase, S-phase, and T-phase overhead distribution lines 3 _R , 3 _S , 3 _T Each is connected.
The sheath current detection current transformer 6 is used to detect the sheath current I _S through the sheath ground wire 4.

  As shown in FIG. 2, the power cable ground fault detection apparatus 10 includes an input circuit 11, a ground fault determination circuit 12, a sheath current comparison circuit 13, and a logical product circuit 14.

The input circuit 11 includes an input converter, a bandpass filter, a sampling hold circuit, a multiplexer circuit, and an analog / digital converter, and a zero-phase current I ₀ input from the zero-phase current transformer 5 and a sheath current detection current transformer. The sheath current I _S input from the vessel 6 is converted into digital data for processing in the ground fault determination circuit 12 and the sheath current comparison circuit 13.

The ground fault determination circuit 12 uses a zero phase current I ₀ converted to digital data input from the input circuit 11 as a zero phase current set value (for example, a ground fault direction relay used in a conventional ground fault direction relay). If the phase difference between the zero-phase current I ₀ and the sheath current I _S is within the phase settling value, the high-level output signal is ANDed. 14 for output.

Sheath current comparison circuit 13, the current value of the sheath current I _S that is converted to digital data input from the input circuit 11 is the is the sheath current setting value or more, outputs an output signal of high level to the AND circuit 14 .

Here, the phase set value and the sheath current set value are determined as follows.
For example, when a ground fault occurs in the T-phase power cable 2 _T (interval power cable) as shown in FIG. 1 (a), the fault current of the T-phase power cable 2 _T power supply terminal → T-phase power cable 2 _T Since the current flows through the ground fault point → T-phase power cable 2 _T metal sheath → sheath ground wire 4 → sheath ground wire 4 ground point, the phase relationship between the zero-phase current I ₀ and the sheath current I _S and the sheath current I The current value of _S is expressed by the following equation.
θ (I ₀ ) −180 ° = θ (I _S )
I _S = I _g -I _Ca -I _Cb
here,
I _g = the capacitance Ca (here, between the core wire and the metal sheath of the ground fault current I _Ca = T-phase power cable 2 _T flowing to earth絡点T-phase power cable 2 _T, R-phase and S-phase (The capacitance between the cores of the power cables 2 _R and 2 _S and the metal sheath is also Ca.) The current I _Cb = the capacitance Cb between the T-phase overhead distribution line 3 _T and the ground (here in the electrostatic capacitance between the R-phase and S-phase overhead distribution lines 3 _R, 3 _S and ground is also a Cb.) Meanwhile the current flowing through, for example, a T-phase power cable 2 _T as shown in FIG. 1 (b) When a ground fault occurs in the connected T-phase overhead distribution line 3 _T (section other than the power cable), the fault current is the power supply end of the T-phase power cable 2 _T → T-phase overhead distribution line 3 _T → T-phase overhead distribution to flow a path of land絡点of the wire 3 _T, the phase relationship between the zero-phase current I ₀ and the sheath current I _S is expressed by the following equation.
θ (I ₀ ) = θ (I _S )
The current value of the sheath current I _S does not exceed 2πfCaV ₀ (“f” is the commercial power supply frequency, “V ₀ ” is the zero-phase voltage when the ground fault resistance is 6000Ω, for example).
Accordingly, the phase set value is set in the range of 180 ° ± α (for example, α = 10 °) as the phase set value in the power cable section, and the range of 0 ° ± α (for example, α = 10 °) is set in the power cable. Set as out-of-interval phase settling value. Further, the sheath current set value is set to a value smaller than 2πfC _a V ₀ .

The logical product circuit 14 takes the logical product of the output signal of the ground fault determination circuit 12 and the output signal of the sheath current comparison circuit 13, and when both are high, the R-phase, S-phase, and T-phase power cables. 2 _R, 2 _S, 2 outputs a ground fault detection signal of a high level indicating a ground fault occurs in the _T.

Thus, on condition that the current value of the sheath current I _S is equal to or greater than the sheath current set value, the current value of the zero phase current I ₀ is equal to or greater than the zero phase current set value, and the zero phase current I ₀ and the sheath When the phase difference between the current I _S is in the power cable in a section in the phase setting value or power cable section outside phase matching in value, earth fault detection signal of high level is outputted from the power cable ground fault detector 10 .
Further, when the phase difference between the zero-phase current I ₀ and the sheath current I _S is in the power cable section in phase matching in value, the power cable section (R-phase of the power cable line, S-phase and T-phase power It can be seen that a ground fault has occurred in the cables 2 _R , 2 _S , 2 _T ), while the phase difference between the zero-phase current I ₀ and the sheath current I _S is within the phase setpoint outside the power cable section. In this case, it can be seen that a ground fault has occurred in the section of the power cable line other than the power cable (R-phase, S-phase, and T-phase overhead distribution lines 3 _R , 3 _S , 3 _T ).

As described above, in the power cable ground fault detection device 10 according to the present embodiment, the occurrence of the ground fault in the power cable line is detected based on the zero phase current I ₀ and the sheath current I _S. There is no need to install a grounded instrument transformer (GPT) for taking in the voltage element or a neutral point resistor for taking in the NGR current.

Next, a power cable ground fault protection device 50 according to an embodiment of the present invention will be described with reference to FIGS.
As shown in FIG. 3, the power cable ground fault protection device 50 according to the present embodiment includes _{first to fourth} inputs from _{first to fourth} zero-phase current transformers (ZCT) 5 _{1 to} 5 ₄ , respectively. a zero-phase current I ₀₁ ~I ₀₄ based on the first to the first to fourth sheath current I _S1 ~I _S4 are input from the fourth sheath current detecting current transformer _{61 through} 65 _4, While detecting the ground fault which occurred in the 1st thru | or 4th electric power cable track | line, the fault line where the ground fault occurred has been identified, and the circuit breakers (first, second, second) installed in the identified fault line the third or fourth breaker 7 _{1-7 4),} characterized in that blocking.

Here, the first to fourth zero-phase current transformers 5 _{1 to} 5 ₄ are the first to fourth power cables 2 ₁ to 4 constituting the first to fourth power cable lines branched from the bus 1. 2 ₄ and _first to _fourth sheath ground wires 4 ₁ to ₄ 4 for grounding the metal sheaths of the _first to _fourth power cables 21 to 24, respectively, are passed through, respectively. The zero-phase currents I _{01 to} I ₀₄ are detected. The ends of the _first to _fourth power cables 2 ₁ to 2 ₄ opposite to the power supply ends are connected to the _first to _fourth overhead distribution lines 3 _{1 to} 3 ₄ , respectively.
First to fourth sheath current detecting current transformer _{61 through} 65 _4, first to fourth sheath ground wire 41 _{to 4} by penetrating respectively, first to fourth sheath current I _S1 ˜I _S4 is detected.

In this example, the first to fourth power cable line constituted by the first to fourth power cables 21 _{to 24} and first to fourth overhead distribution lines 3 ₁ to 3 ₄ However, any one of the first to _fourth overhead distribution lines 3 _{1 to} 3 ₄ may be provided.

  As shown in FIG. 4, the power cable ground fault protection device 50 includes a relay input circuit 51, a ground fault determination circuit 52, a sheath current comparison circuit 53, a relay output circuit 54, a settling circuit 55, and a settling command. An input / output circuit 56 and a transmission control circuit 57 are provided.

The relay input circuit 51 includes an input converter, a band-pass filter, a sampling hold circuit, a multiplexer circuit, and an analog / digital converter, and is input from the _{first to fourth} zero-phase current transformers 5 _{1 to} 5 ₄ , respectively. First to fourth sheath currents I _{S1 to} I 4 input from _{first to} fourth zero-phase currents I _{01 to} I ₀₄ and first to fourth sheath current detection current transformers 6 _{1 to} 6 ₄ , respectively. _S4 is converted into digital data for processing in the ground fault determination circuit 52 and the sheath current comparison circuit 53.

The ground fault determination circuit 52 includes first to fourth zero-phase currents I _{01 to} I ₀₄ and first to fourth sheath currents I _{S1 to} I _S4 converted into digital data input from the relay input circuit 51. Based on the above, it is determined whether or not a ground fault has occurred in the first to fourth power cable lines, the fault line is specified, and an fault line specifying signal indicating the specified fault line is output to the relay output circuit 54 To do.
At this time, as will be described later, the ground fault accident determination circuit 52 detects that a ground fault has occurred in the sections of the power cables of the _first to _fourth power cable lines ( _first to _fourth power cables 2 ₁ to 2 ₄ ). It is also determined whether or not a ground fault has occurred in a section other than the power cable of the first to fourth power cable lines ( _first to _fourth overhead distribution lines 3 _{1 to} 3 ₄ ).

When the fault line identification signal is input from the ground fault determination circuit 52, the sheath current comparison circuit 53 converts the first to fourth sheath currents I _{S1 to} I converted to digital data input from the relay input circuit 51. Determine whether the current value of the sheath current of the fault line in _S4 is equal to or greater than the sheath current set value in the power cable section or the sheath current set value outside the power cable section. When it is equal to or greater than the sheath current set value in the cable section or the sheath current set value outside the power cable section, a high level output signal is output to the relay output circuit 54.

When a fault line identification signal is input from the ground fault determination circuit 52 and a high level output signal is input from the sheath current comparison circuit 53, the relay output circuit 54 receives a circuit breaker (first circuit) installed in the fault line. , A trip signal TR for interrupting the second, third or fourth circuit breakers 7 _{1 to} 7 ₄ ) is generated.

That is, relay output circuit 54, on condition that the output signal of high level is input from the sheath current comparison circuit 53, a first power cable line (first power cable 2 ₁ or the first overhead distribution lines 3 ₁ ) When an accident line identification signal specifying the accident line is input from the ground fault determination circuit 52, a trip signal TR for breaking the _first circuit breaker 71 is generated, and the second power cable line blocking accident line specifying signal for specifying the (second power cable 2 ₂ or the second overhead distribution lines 3 ₂₎ as the accident line to ground fault determining circuit 52 from the input second breaker 7 ₂ trip signal generates a TR, a third power cable line (third power cable 2 ₃ or third overhead distribution lines 3 ₃₎ accident line specific signal ground fault determining circuit for identifying the accident line for 52 The trip signal TR for breaking the third circuit breaker 7 ₃ is generated when it is inputted from the fourth power cable line (fourth power cable 2 ₄ or fourth overhead distribution line 3 ₄ ). accidents line specifying signal for specifying a fault line to generate a trip signal TR for blocking the fourth breaker 7 ₄ is input from the ground fault determining circuit 52.

  The settling circuit 55 is based on a settling command signal received from the outside via the transmission control circuit 57 and the settling command input / output circuit 56, and a zero-phase current settling value and a phase settling value (a phase settling value in a power cable section described later and A settling process is performed to determine a phase setting value outside the power cable section) and a sheath current setting value.

Next, the operation of the power cable ground fault protection device 50 will be described with reference to FIGS. 5 and 6.
First, the first to _fourth zero-phase currents I when a ground fault occurs in the section of the power cables of the first to fourth power cable lines ( _first to _fourth power cables 2 ₁ to 2 ₄ ). ₀₁ ~I current value of _04, the phase relationship between the first to fourth zero-phase current I ₀₁ ~I ₀₄ and the first to fourth sheath current I _S1 ~I _S4, and ground fault occurs 1 to about the current value of the first to fourth sheath current I _S1 ~I _S4 flowing through the fourth metal sheath of the power cable 21 _{to 24,} ground fault in the first power cable 2 ₁ as shown in FIG. 5 A case where an accident occurs will be described as an example.

When a ground fault occurs in the first power cable 2 _1, as shown by the arrows in FIG. 5, the first power cable 2 ₁ first the first zero-phase current I ₀₁ from the interior direction (bus 1 1 The _second to _fourth power cables 2 ₂ to 2 ₄ receive _second to _fourth zero-phase currents I _{02 to} I ₀₄ in the external direction ( _second to second power cables 2 ₂ to 2 ₄₎ . 4 in the direction from the end of the power cable line 4 to the bus 1). At this time, the current value of the first zero-phase current I ₀₁ is the sum of the current values of the second to fourth zero-phase currents I _{02 to} I ₀₄ as shown by the equation (1).
I ₀₁ = I ₀₂ + I ₀₃ + I ₀₄ (1)
The first sheath current I _S1 flowing in the first power cable 2 ₁ metal sheath ground fault occurs, contact from a first power cable 2 ₁ metal sheath of the first sheath ground wire 4 ₁ The _second to _fourth sheath currents 2 _S2 to 2 _S4 flowing in the metal sheaths of the _second to _fourth power cables 2 ₂ to 2 ₄ that flow in the direction toward the point, but no ground fault, respectively, It flows in a direction from the ground point of the _second to _fourth sheath ground wires 4 ₂ to 4 ₄ toward the metal sheath of the _second to _fourth power cables 2 ₂ to 2 ₄ .
Therefore, the phase relationship between the first to fourth zero-phase currents I _{01 to} I ₀₄ and the first to fourth sheath currents I _{S1 to} I _S4 is expressed by equation (2).
_{θ (I 01) -180 ° ≒} θ (I S1)
θ (I ₀₂ ) ≒ θ (I _S2 ) (2)
θ (I ₀₃ ) ≒ θ (I _S3 )
θ (I ₀₄ ) ≒ θ (I _S4 )
The current value of the first sheath current I _S1 flowing in the first power cable 2 ₁ metal sheath ground fault occurs is represented by the equation (3).
I _S1 = I _g −I _C1 −I _C11 (3)
here,
I _g = the current flowing through the capacitance C ₁ between the first power cable 2 ₁ flows to the ground絡点ground fault current I _C1 = first power cable 2 ₁ of core wire and the metal sheath I _C11 = Current flowing through the capacitance C ₁₁ between the _first overhead distribution line 3 ₁ and the ground

Next, the first to _fourth zeros when a ground fault occurs in a section other than the power cables of the first to fourth power cable lines ( _first to _fourth overhead distribution lines 3 _{1 to} 3 ₄ ). Phase currents I _{01 to} I ₀₄ , phase relationship between the first to fourth zero-phase currents I _{01 to} I ₀₄ and the first to fourth sheath currents I _{S1 to} I _S4 , and a ground fault occurs As shown in FIG. 6, the first overhead distribution line 3 for the current values of the first to fourth sheath currents I _{S1 to} I _S4 flowing through the metal sheaths of the _first to _fourth power cables 21 to ₂₄ . _The case where a ground fault occurs in ₁ will be described as an example.

When a ground fault occurs in the first overhead distribution line 3 _1, as shown by the arrows in FIG. 6, the first power cable 2 ₁ first the first zero-phase current I ₀₁ from the interior direction (bus 1 The first to _fourth power cables 2 ₂ to 2 ₄ receive _second to _fourth zero-phase currents I _{02 to} I ₀₄ in the external direction ( _second to second power cables 2 to _{2 4).} It flows in the direction from the end of the fourth power cable line to the bus 1. At this time, the current value of the first zero-phase current I ₀₁ is the sum of the current values of the second to fourth zero-phase currents I _{02 to} I ₀₄ as shown in the equation (1).
The _first to _fourth sheath currents I _{S1 to} I _S4 flowing through the metal sheaths of the _first to _fourth power cables 21 to ₂₄ are all _first to fourth sheath ground wires 4 ₁ to 4. It flows in the direction from the _four grounding points toward the metal sheaths of the _first to _fourth power cables 2 ₁ to 2 ₄ .
Therefore, the phase relationship between the first to fourth zero-phase currents I _{01 to} I ₀₄ and the first to fourth sheath currents I _{S1 to} I _S4 is expressed by equation (4).
θ (I ₀₁ ) ≒ θ (I _S1 )
θ (I _S1 ) ≒ θ (I _S2 ) ≒ θ (I _S3 ) ≒ θ (I _S4 ) (4)
θ (I ₀₁ ) −180 ° = θ (I ₀₂ ) = θ (I ₀₃ ) = θ (I ₀₄ )
In addition, the current values of the first to fourth sheath currents I _{S1 to} I _S4 are expressed by Equation (5).
I _S1 / C ₁ = I _S2 / C ₂ = I _S3 / C ₃ = I _S4 / C ₄ (5)
here,
C ₁ = the first power cable 2 ₁ of the electrostatic capacitance between the core wire and the metal sheath C ₂ = the second power cable 2 capacitance between the _second core and the metal sheath C ₃ = a 3 of the capacitance between the power cables 2 ₃ core wire and the metal sheath C ₄ = capacitance between the fourth power cables 2 ₄ core wire and the metal sheath

Therefore, the ground fault determination circuit 52 has the current values of the first to fourth zero-phase currents I _{01 to} I ₀₄ converted into the digital data input from the relay input circuit 51 equal to or greater than the zero-phase current settling value. Then, it is determined whether or not the current value of one zero-phase current among the first to fourth zero-phase currents I _{01 to} I ₀₄ is substantially equal to the sum of the current values of the other three zero-phase currents ( (See equation (1) above).

As a result, for example, when the current value of the first zero-phase current I ₀₁ is substantially equal to the sum of the current values of the second to fourth zero-phase currents I _{02 to} I ₀₄ , the ground fault determination circuit 52 The phase difference between the first zero-phase current I ₀₁ and the first sheath current I _S1 is obtained.
If the obtained phase difference falls within the phase settling value in the power cable section (for example, a range of 180 ° ± 10 °), the ground fault determination circuit 52 determines that “the ground fault has occurred in the _first power cable 21”. (Refer to the above formula (2)), an accident line specifying signal for specifying the _first power cable 21 as an accident line is output to the sheath current comparison circuit 53 and the relay output circuit 54.
On the other hand, if the obtained phase difference is within the phase set value outside the power cable section (for example, in the range of 0 ° ± 10 °), the ground fault determination circuit 52 determines that “in the first overhead distribution line 3 ₁ . it is determined that the ground fault has occurred "(see above equation (4)), the first accident line specifying signal for specifying the overhead distribution lines 3 ₁ as fault line sheath current comparator circuit 53 and the relay output circuit 54 Output to.

Sheath current comparison circuit 53, for example, an accident line specifying signal for specifying the first power cable 2 ₁ or first the overhead distribution lines 3 ₁ as accident line is input from the ground fault determining circuit 52, a first the current value of the sheath current I _S1 it is determined whether a sheath current setting value or more, a relay output signal of high level when the current value of the first sheath current I _S1 is the sheath current setting value or more Output to the output circuit 54.

Here, the sheath current settling value is determined as follows.
The current values of the first to fourth sheath currents I _{S1 to} I _S4 are 2πfC _i V ₀ (“f” is the commercial power supply frequency, “V ₀ ” is the zero-phase voltage when the ground fault resistance is 6000Ω, for example, C _i = C ₁ , C ₂ , C ₃ , C ₄ ) or more, the sheath current settling value is set to be smaller than “2πfC _i V ₀ ”.

When a fault line identification signal is input from the ground fault determination circuit 52 and a high level output signal is input from the sheath current comparison circuit 53, the relay output circuit 54 receives a circuit breaker (first circuit) installed in the fault line. , A trip signal TR for interrupting the second, third or fourth circuit breakers 7 _{1 to} 7 ₄ ) is generated.

That is, relay output circuit 54, on condition that the high-level output signal from the sheath current comparison circuit 53 is input, identifying a first power cable 2 ₁ or the first overhead distribution lines 3 ₁ as accident line When the fault line identification signal is input from the ground fault determination circuit 52, a trip signal TR for breaking the _first circuit breaker 71 installed in the first power cable line is generated, and the second power is generated. an accident line specifying signal for specifying the cable 2 ₂ or the second overhead distribution lines 3 ₂ as the accident line is input from the ground fault determining circuit 52, a second circuit breaker installed in the second power cable line 7 generates a trip signal TR for interrupting _2, accident line specifying signal for specifying a third power cable 2 ₃ or third overhead distribution lines 3 ₃ as the accident line is input from the ground fault determining circuit 52 Then Third generating a trip signal TR for blocking the third breaker 7 ₃ installed in the power cable line, specifying the fourth power cables 2 ₄ or fourth overhead distribution lines 3 ₄ as the accident line When the fault line identification signal to be inputted is inputted from the ground fault judgment circuit 52, a trip signal TR for breaking the _fourth circuit breaker 74 installed in the fourth power cable line is generated.
Thereby, the circuit breaker of the accident line is cut off and the accident line is disconnected from the bus 1.

  In the above description, the power system in which the first to fourth power cable lines are branched from the bus 1 has been described as an example, but the number of distribution lines branched from the bus 1 may be two or more. .

  Moreover, although the electric power cable ground fault protection apparatus 50 for protecting the electric power system from which the 1st thru | or 4th electric power cable line was branched from the bus 1 from a ground fault accident was demonstrated, for example, one electric power cable line is connected. In a ground fault direction relay that protects against a ground fault, the power cable line can be similarly protected from the ground fault by using the sheath current instead of the voltage of the bus 1 (bus voltage). In this case, instead of the ground fault determination circuit 52 and the sheath current comparison circuit 53 shown in FIG. 2, the zero-phase current input from the zero-phase current transformer installed in the power cable line and the power Whether or not a ground fault has occurred is determined based on the sheath current input from the current transformer for sheath current detection installed on the sheath ground wire for grounding the metal sheath of the power cable constituting the cable line. A determination circuit for determination may be used.

It is a figure for demonstrating the power cable ground fault detection apparatus 10 by one Example of this invention. It is a block diagram which shows the structure of the power cable ground fault detection apparatus 10 shown in FIG. It is a figure for demonstrating the power cable ground fault protection apparatus 50 by one Example of this invention. It is a block diagram which shows the structure of the power cable ground fault protection apparatus 50 shown in FIG. Is a diagram for explaining operation of the power cable ground fault protection device 50 shown in FIG. 3 when a ground fault accident occurs in the first power cable 2 ₁ shown in FIG. Is a diagram for explaining operation of the power cable ground fault protection device 50 shown in FIG. 3 when a ground fault accident occurs in the first overhead distribution lines 3 ₁ shown in FIG.

1 bus 2 _R , 2 _S , 2 _T R phase, S phase and T phase power cables 2 ₁ to 2 _{4 1st} to _4th power cables 3 _R , 3 _S , 3 _T R phase, S phase and T phase aerial Distribution lines 3 _{1 to} 3 ₄ First to _fourth overhead distribution lines 4 Sheath ground wires 4 ₁ to ₄ 4 _First to _fourth sheath ground wires 5 Zero-phase current transformers 5 _{1 to} 5 ₄ First to fourth Zero-phase current transformers 6 6 _{1 to} 6 ₄ Current transformers 6 _{1 to} 6 ₄ 1st to 4th current transformers 7 _{1 to} 7 ₄ 1st, 2nd, 3rd or 4th breaking 10 Power cable ground fault detection device 11 Input circuit 12, 52 Ground fault detection circuit 13, 53 Sheath current comparison circuit 14 AND circuit 50 Power cable ground fault protection device 51 Relay input circuit 54 Relay output circuit 55 Setting circuit 56 Setting Command input / output circuit 57 Transmission control circuit I ₀ Zero-phase current I _{01 to} I ₀₄ First to fourth zero-phase current I _S Sheath current I _S1 ~I _S4 first to fourth sheath current I _g ground fault current _{I Ca, I Cb, I C1} , I C11 current _{Ca, Cb, C 1 ~C 4} , C 11 ~C 14 capacitance TR trip signal

Claims (11)

A power cable ground fault detection device (10) for detecting occurrence of a ground fault in a power cable line,
A zero-phase current (I ₀ ) input from a zero-phase current transformer (5) installed in a power cable (2 _R , 2 _S , 2 _T ) constituting the power cable line, and a metal sheath of the power cable Occurrence of a ground fault in the power cable line based on the sheath current (I _S ) input from the sheath current detection current transformer (6) installed in the sheath ground wire (4) for grounding A power cable ground fault detection apparatus comprising ground fault occurrence detection means (12-14) for detection. The ground fault occurrence detection means is
A ground fault that outputs an output signal when the current value of the zero phase current is equal to or greater than the zero phase current set value and the phase difference between the zero phase current and the sheath current is within the phase set value. Determination means (12);
When the current value of the sheath current is equal to or greater than the sheath current set value, sheath current comparison means (13) for outputting an output signal;
When an output signal is input from both the ground fault accident determination circuit and the sheath current comparison circuit, a ground fault detection signal output means (14) for outputting a ground fault detection signal;
The power cable ground fault detection device according to claim 1, comprising: The power cable line has a section of the power cable and a section other than the power cable;
The phase settling value includes a phase settling value within the power cable section and a phase settling value outside the power cable section,
If the phase difference between the zero-phase current and the sheath current is within the phase set value in the power cable section, the ground fault accident has occurred in the section of the power cable. On the other hand, when the phase difference between the zero-phase current and the sheath current is within the phase setting value outside the power cable section, it is determined that a ground fault has occurred in a section other than the power cable.
The power cable ground fault detection device according to claim 2, wherein: The sheath current setting value is “f” for the commercial power supply frequency, “Ca” for the capacitance between the core of the power cable and the metal sheath, and “0” for the zero-phase voltage at a predetermined ground fault resistance. 4. The power cable ground fault detection device according to claim 2, wherein V ₀ ″ is set to a value smaller than 2πfCaV _{0. 5} . A power cable ground fault protection device (50) for protecting a power cable line from a ground fault,
Zero phase currents (I _{01 to} I ₀₄ ) input from zero phase current transformers (5 _{1 to} 5 ₄ ) installed in the power cables (2 ₁ to 2 ₄ ) constituting the power cable line, and the power Sheath currents (I _{S1 to} I _S4 ) input from the sheath current detection current transformers (6 _{1 to} 6 ₄ ) installed on the sheath earth wires (4 ₁ to 4 ₄ ) for grounding the metal sheath of the cable A power cable ground fault protection device comprising: determination means (52, 53) for determining the presence or absence of a ground fault in the power cable line based on the above.   6. The power cable according to claim 5, wherein the power cable ground fault protection device is used in place of a ground fault protection relay that performs ground fault protection of the power cable line by both a current element and a voltage element. Ground fault protection device. A power cable ground fault protection device (50) for protecting a plurality of power cable lines branched from a bus (1) from a ground fault,
A plurality of power cables ₍₂₁ to ₂₄₎ respectively installed in a plurality of zero-phase current transformer (5 ₁ to 5 ₄₎ a plurality of zero-phase current inputted from each constituting each of the plurality of power cable line and (I ₀₁ ~I _04), a plurality of sheaths ground wire for grounding each metal sheaths of the plurality of power cables ₍₄₁ to ₄₎ a plurality of sheath current detecting current transformer installed in (6 _{1 to} 6 ₄ ), based on a plurality of sheath currents (I _{S1 to} I _S4 ) respectively input, the occurrence of a ground fault in the power cable line is detected and the fault line in which the ground fault has occurred is specified. A power cable ground fault protection device comprising ground fault detection means (52, 53). The ground fault detection means is
When a phase difference between the zero-phase current and the sheath current is within a phase settling value for one of the plurality of power cable lines, a ground fault occurs in the one power cable line. A ground fault determination means (52) for determining that the power cable line has occurred and identifying the one power cable line as an accident line;
A sheath current comparing means (53) for outputting an output signal when the current value of the sheath current is greater than or equal to a sheath current set value for the one power cable line specified as an accident line by the ground fault determination means;
The power cable ground fault protection device according to claim 7, comprising: The power cable line has a section of the power cable and a section other than the power cable;
The phase settling value includes a phase settling value within the power cable section and a phase settling value outside the power cable section,
When the phase difference between the zero-phase current and the sheath current is within the phase set value in the power cable section, the ground fault accident determination means determines that a ground fault has occurred in the section of the power cable. On the other hand, if the phase difference between the zero-phase current and the sheath current is within the phase setting value outside the power cable section, it is determined that a ground fault has occurred in a section other than the power cable.
The power cable ground fault protection device according to claim 8, wherein: On the condition that the current value of the sheath current is greater than or equal to the sheath current set value by the sheath current comparison unit, the ground fault determination unit has identified the fault line among the plurality of power cable lines and further comprising a relay output means (54) for generating a trip signal (TR) for collectively blocking circuit breaker which is installed in a power cable line (7 ₁ to 7 _4), according to claim 8 Or the electric power cable ground fault protective device in any one of 9. Wherein the sheath current setting value is set to "f" of the utility frequency, the capacitance between the power cable core and the metal sheath and "C _i", the zero-phase voltage during a predetermined ground fault resistance 11. The power cable ground fault protection device according to claim 8, wherein “V ₀ ” is set to a value smaller than 2πfC _i V ₀ .