JPH03214074A - Investigation of fault point for cable - Google Patents

Abstract

PURPOSE:To specify a distance to a fault point without being affected by a resistance value at the fault point by a method wherein a fault phase is connected to a sound phase with a receiving end and a current the same in value as both the phases flows in an opposite direction to determine the ground potential at a transmitting end of the fault phase attributed to a current source. CONSTITUTION:A receiving end A' of a fault phase 10 of a three-phase cable is con nected 16 to a receiving end B' of a first sound phase 12. Transmitting ends A and B of the fault phase 10 and the sound phase 12 are earthed through current sensors 18 and 20 and current sources 22 and 24 (opposite in polarity to each other) respective ly. Moreover, voltage sensors 26 and 28 are connected in parallel to the current sources 22 and 24 respectively. A transmitting end C and a receiving end C' of the sound phase 14 are made open. Current I1 flows to the transmitting end A from the current source 22 and a current as current I2 opposite in direction to the I1 flows to the trans mitting end B. Here, the setting of current of the current sources 22 and 24 is adjusted to meet the current I1=I2. When a distance to a fault point F is represented by L, a proportional constant between a resistance of the cable and the distance, (k) and a measuring voltage value of the sensor 26, V1, the distance L=V1/kI1 is given. That is, the distance L can be specified at a high accuracy irrelevant to a resistance Rg at the fault point.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention solves the problem of single-line ground fault points in three-phase cables.
The present invention relates to a method for detecting a cable fault point that can be identified with high accuracy without being affected by the magnitude of the fault point resistance value.

[Conventional technology]

Conventionally, as a fault point detection method for this type of cable, there has been known a fault point detection method that applies the Wheatstone bridge principle, which is called the Murray-Rose method. Figure 3 shows
FIG. 3 is a diagram showing an accident point detection method using the Murray loop method. In Figure 3, AA' is the fault line, BB' is the sound line, F is the fault point, G is the galvanometer, and R is the sliding resistor.
The fault point detection method using the Murray loop method is to connect the receiving ends A'B' in Fig. 3, and then measure the tX dynamic resistance so that the galvanometer G connected between the sending ends A and B shows zero. The position of the sliding resistor R is adjusted, and the fault point is determined based on the position of the sliding resistor R at this time. That is, the position a (a<1) of the sliding resistor R when the bridge is balanced can be determined, and the distance 1 to the accident point F can be determined from the relationship of the following equation.

1-a:a=L+(L-Jl):J-(1),",
J=2La...(2) Furthermore,
This Murray loop method is a fault point detection method that can be applied as long as the cable conductor is not broken at the fault point F.

[Problem to be solved by the invention]

However, the fault point detection method using the Murray loop method described above is a method of determining the distance 'Mj to the fault point by determining the mechanical position of the sliding piece in the sliding resistor. There were limits to accuracy due to factors.

■ Error factors in operating the sliding resistor to reduce the galvanometer swing to zero.

■ Error factors due to the pitch of the sliding resistor.

■ Error factors due to contact stability of sliding pieces in sliding resistors.

■ Error factors due to the accuracy of the correspondence between the sliding piece and the scale in the TG dynamic low resistance resistor.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a fault point detection method for identifying single-line ground fault fault points in three-phase cables, which can obtain high ranging accuracy without being affected by the magnitude of fault point resistance that is widely distributed. It is an object of the present invention to provide a cable failure point detection method that reduces error factors such as human operations and mechanical elements during measurement and can be easily automated.

[Means to solve the problem]

A fault point detection method for a cable according to the present invention is a fault point detection method for identifying a single line ground fault fault point in a three-phase cable. After the current is passed in opposite directions between each sending end of the phase and the first healthy phase and the ground using a current source, the current value flowing to the faulty phase and the current value flowing to the healthy phase are made to be the same. , the fault point of the cable is identified by determining the ground potential at the sending end of the fault phase caused by the current source.

Further, the fault phase and the first healthy phase of the cable are connected at the receiving end, and a voltage is applied between the fault phase and the ground to flow a current,
By determining this current value and the potential difference between the fault phase and the first healthy phase at the sending end, the fault point of the cable can be identified.

[For production]

According to the fault point detection method of a cable according to the present invention, in the case of a one-line ground fault accident in a three-phase cable, after connecting the receiving ends of the faulty phase and healthy phase of the cable, current flows from the sending end of the faulty phase and the healthy phase. By sending currents of the same value with opposite polarities through the sources, the voltage due to the effect of the resistance at the fault point is canceled out, and each voltage on the sending end measured at this time is simply a voltage drop proportional to the distance to the fault point. Obtainable. Therefore, by knowing the proportionality coefficient between cable resistance and distance, the distance to the accident point can be specified.

In addition, after connecting the fault phase and the first healthy phase of the cable at the receiving end, the fault phase and the first healthy phase at the sending end obtained when a voltage is applied between the fault phase and the ground and current flows. The potential difference between the phases does not include the voltage due to the effect of the fault point resistance, and represents only the potential drop in the cable from the sending end of the fault phase to the fault point. Therefore, by knowing the current and the potential difference at the sending end of the fault phase, and the proportionality coefficient between the resistance of the cable and the distance, it is possible to specify the distance to the fault point.

〔Example〕

Next, an embodiment of the cable fault detection method according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a wiring diagram for fault point exploration showing an embodiment of the present invention. In FIG. 1, reference numeral 10 indicates the fault phase of the three-phase cable in which a ground fault has occurred, and the receiving end A' of the fault phase 10 is connected! ! 16 to the receiving end B of the first healthy phase 12
′. On the other hand, the sending end A of the faulty phase 10 is grounded via the current sensor 18 and the current source 22, and the sending end A of the faulty phase 10 is grounded via the current sensor 18 and the current source 22.
The sending end B of No. 2 is grounded via a current source 24 having a polarity opposite to that of the current sensor 20 and current source 22. A voltage sensor 26 is connected in parallel with the current source 22, and a voltage sensor 28 is further connected in parallel with the current source 24. The sending end C and the receiving end C' of the remaining healthy phase 14 are left open.

By connecting the lines in this way, the distance to the accident point can be determined as follows. In Figure 1,
The current source 22 causes a current I to flow through the sending end A of the faulty phase 10, and a current I2 in the opposite direction to 11 flows through the sending end B of the first healthy phase 12. At this time, each current ■1■ The current settings of the current sources 22 and 24 are adjusted so that the magnitudes of 2 and 2 are equal. As shown in Figure 1, if the distance to the fault point F is 1, the resistance at the fault point is R1, the distance between the sending end and the receiving end is k, and the proportional constant between the cable resistance and distance is k, The following formula holds true.

'V+ = kJ II +R, (II I2)・
(3) Note that Vl is the voltage value measured by the voltage sensor 26. Here, since the current setting of each current source 22.24 is adjusted so that I+=12, equation (3) is as follows: j = V + / k I +
(4) Therefore, as is clear from equation (4), it is possible to determine the distance O to the accident point F with high accuracy without being influenced by the value of the accident point resistance R.

Similarly, the distance AiJ to the accident point F can be specified with high accuracy using the measured voltage value v2 of the voltage sensor 28.

However, it is assumed that the resistance of the connection line 16 is negligible.

V2 = k (L+L-1) ■2 +R, (r+ I2) ... (5) Here, since l1 = I2, in this case, J = 2 L
(V 2 / k I 2 ) ... (6
), therefore, the fault point resistance R in equation (6) as well.

The distance 1 to the accident point F can be specified with high accuracy without being influenced by the value of .

FIG. 2 is a connection diagram for accident point exploration showing another embodiment of the present invention, and the same components as in FIG. 1 are given the same reference numerals and will be described.

In FIG. 2, the receiving ends A' and B' of the failed phase 10 and the first healthy phase 12 are connected by a connecting wire 16. On the other hand, accident phase 10
The sending end A of
Connect to sending end B of The sending end C and the receiving end C' of the remaining healthy phase 14 are placed in an oven state.

By connecting the lines in this way, the distance to the accident point can be specified as follows. In FIG. 2, a current 11 is caused to flow through the sending end A of the failed phase 10 by the power supply 22, and the potential difference V between the sending ends A and B at this time is measured. Second
As shown in the figure, Ii'f' 41 to accident point F is 1,
The fault point resistance is R, the distance between the sending end and the receiving end is L,
If k is a proportionality constant between cable resistance and distance, the following equation holds true.

Vl=1. jk (7) Therefore, O=V+/X+ k (8) is obtained. As is clear from equation (8), even with this fault point detection method, the fault point resistance R.

It can be seen that the distance Wlj to the accident point F can be found regardless of the distance Wlj.

〔Effect of the invention〕

As is clear from the above embodiments, according to the cable fault point detection method of the present invention, when identifying a single line ground fault fault point in a three-phase cable, the fault point resistance ranges from 0Ω to several tens of ohms depending on the nature of the fault. However, by measuring the voltage and current at the sending end using the faulted and healthy phases, it is possible to determine the distance to the fault point without being affected by the resistance value at the fault point.

In addition, it is a fault point detection method that conveniently uses a current source, power supply, voltage sensor, and current sensor, and does not use a sliding resistor that has a large error factor due to human operation as in the conventional method, so it is easy to use. It can also be automated.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and it goes without saying that various design changes can be made without departing from the spirit of the present invention.

[Brief explanation of drawings]

FIG. 1 is a wiring diagram showing one embodiment of the cable fault point detection method according to the present invention, FIG. 2 is a connection diagram showing another embodiment of the cable fault point detection method according to the present invention, and FIG. is a wiring diagram showing a conventional fault point detection method. 10...Fault phase 12, 14...Key metal phase 16...Connection line 18.20...Current sensor 2224...Current source 26.28.32...Voltage sensor 30...Power supply 8. B, C... Sending end ^', B', C''... Receiving end E... - line ground fault accident point [... Distance between sending end and receiving end O... Accident Distance to point Patent applicant Fuji Electric Co., Ltd.

Claims (2)

[Claims] (1) In a fault point detection method for identifying single-line ground fault fault points in three-phase cables, the fault phase and the first sound phase of the cable are connected at the receiving end, and each of the fault phase and the first sound phase is Current is passed in opposite directions between the sending end and the ground by current sources, and after adjusting the current value flowing in the faulty phase and the current value flowing in the healthy phase to be the same, the sending end of the faulty phase is set by the current source. A cable failure point detection method characterized by identifying a cable failure point by determining the ground potential of the cable. (2) In a fault point detection method for identifying single-line ground fault fault points in three-phase cables, the fault phase and the first healthy phase of the cable are connected at the receiving end, and a voltage is applied between the fault phase and the ground. A method for detecting a fault point in a cable, characterized in that the fault point in the cable is specified by passing a current through the cable and determining the current value and the potential difference between the fault phase and the first healthy phase at the sending end.