JPH0631435Y2 - Cable diagnostic equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a cable diagnostic device suitable for measuring the insulation characteristics of a power cable, particularly its dielectric loss.

(Technical background of the invention and its problems) Dielectric loss has a great influence on the power loss of the power cable, and is one of the important factors that determine the performance of the cable. Generally, the dielectric loss of a power cable is evaluated using tanδ. The tan δ of a cable that has not been laid yet before shipment is measured using a Schering bridge or the like. On the other hand, the measurement of tan δ of the existing live power cable is performed as follows.

FIG. 2 shows an explanatory diagram of the measuring method.

In the power cable 1 shown in the figure, one end 2a of the conductor 2 is connected to the power source 3 and the other end 2b is connected to the load 4. The one end 2a is grounded via two voltage dividing resistors 5 and 6 connected in series. On the other hand, one end of the cable sheath 7 of the cable 1 is directly grounded via the ground wire 8. Usually, if both ends of the cable sheath 7 are directly grounded, a large induced current flows through the cable sheath 7, and thus such a one-end grounding method is often adopted. A current transformer 9 is attached to this ground wire for current measurement.

A terminal voltage measuring terminal 10 is provided at the connection point 11 of the two voltage dividing resistors 5 and 6, and a charging current measuring terminal 12 is provided at the terminal of the coil 9a of the current transformer 9.

When connected in this way, the cable sheath 7 is grounded at one end, so that only the charging current based on the capacitance of the cable 1 flows through the ground wire 8. Therefore, the terminal voltage measuring terminal 10
Is proportional to the alternating voltage E applied to the conductor 2 of the cable 1, and the output voltage of the charging current measuring terminal 12 is
It is proportional to the charging current I. tan δ can be obtained from the phase angle between the alternating voltage E and the charging current I.

By the way, in the method shown in FIG. 2, the charging current of the cable must be measured from the ground wire 8 of the cable without leakage. Therefore, this method can be applied only to a so-called single-core cable in which one cable is independently coated with a metal sheath. That is, the method shown in FIG. 2 could not be carried out for a power cable in which three cores were collectively inserted in one metal sheath. In addition, even if it is a single-core cable, if the part other than the ground line for which current is to be measured is also grounded, it is necessary to temporarily remove all of the ground line except for one. was there. Such work is complicated, and the measurement time is long, which hinders improvement of work efficiency.

(Purpose of the Invention) The present invention has been made in view of the above points, and even if the sheath of the cable to be diagnosed is grounded at multiple points or is integrated with another cable sheath, It is an object of the present invention to provide a cable diagnostic device capable of measuring the charging current regardless of the situation.

(Summary of the Invention) The cable diagnostic device of the present invention comprises a voltage measuring unit for measuring an applied voltage applied to one of a plurality of cables to be diagnosed and a circuit breaker for disconnecting the load of the cable to be diagnosed. A charging current measuring unit for measuring a charging current charged in the cable to be diagnosed through the cable conductor; and a dielectric loss calculating unit for obtaining a dielectric loss of the cable to be diagnosed based on the applied voltage and the charging current. It is characterized by having and.

(Embodiment of Device) FIG. 1 is a block diagram showing an embodiment of a cable diagnostic device of the present invention.

In the figure, the cable to be diagnosed 2 to be diagnosed here
It is assumed that 0 is collectively covered with the metal sheath 23 together with the other two cables 21.

Here, a predetermined high voltage is applied from the power supply 25 to one end 24 of the cable to be diagnosed 20. or,
A circuit breaker 27 is provided at the other end 26 of the cable 20 to be diagnosed.
A load 28 is connected via. Then, in the vicinity of one end 24 of the cable to be diagnosed 20, the voltage measuring unit 30 including a voltage divider as described above with reference to FIG. 2 is connected.

On the other hand, a current transformer 32 is attached so as to measure the current flowing through the cable conductor of the cable to be measured 20. The output terminal of the current transformer 32 is connected so as to be input to the charging current measuring unit 31. Then, the outputs of the charging current measuring unit 31 and the voltage measuring unit 30 are connected to the dielectric loss calculating unit 33 so as to be input to them.

The current transformer 32 has a configuration in which a measurement wire is wound as a secondary coil around a known toroidal coil or the like, but is divided into two parts so that the cable can be attached to and detached from the already attached diagnostic cable 20. It is preferable to use the one having the constitution.

The charging current measuring unit 31 converts this current into a voltage signal,
This is a known circuit that outputs to the dielectric loss calculation unit 33. The dielectric loss calculation unit 33 is a circuit including a microprocessor or the like that calculates the dielectric loss based on the charging current of the cable and the voltage applied to the cable, as described above with reference to FIG.

The cable diagnostic device of the present invention having the above configuration operates as follows.

First, at the start of diagnosis, the circuit breaker 27 is opened to disconnect the load 28 connected to the cable to be diagnosed 20. In this state, when the current flowing through the cable conductor of the cable to be diagnosed 20 is measured by the current transformer 32, only the charging current with which the cable to be diagnosed 20 is charged from the power supply 25 can be measured. That is, since the cable to be diagnosed 20 is separated from the load 28, no current other than the charging current flows through the cable conductor. Further, the metal sheath 23 collectively covers the other cable 21 provided side by side with the metal sheath 23, but has no influence on the charging current.

As a result, the charging current charged in the cable to be diagnosed 20 is input through the charging current measuring unit 31 to the dielectric loss calculating unit 33 together with the applied voltage measured by the voltage measuring unit 30, and the dielectric loss is measured. It

After the above measurement work is completed, if the circuit breaker 27 is closed again, power transmission via the cable 20 to be diagnosed is restarted.

The present invention is not limited to the above embodiments.

As long as the circuit breaker 27 is opened and the charging current charged in the cable to be diagnosed 20 can be measured through the cable conductor, the combination of the current transformer and the charging current measuring unit as described above is not always required. Need not be used. For example, even if an ammeter or the like inserted in series with the conductor of the cable to be diagnosed is used, the same effect can be obtained. (Effect of the Invention) According to the cable diagnostic device of the present invention described above, the charging current is obtained from the current flowing through the cable conductor, so that the charging current of the cable is measured from the current flowing through the ground wire of the cable sheath, which has been conventionally performed. Compared to the case where the cable is used, the charging current can be measured accurately even for a cable with a sheath grounded at multiple points or a 3-core batch sheath cable, and the workability and safety of cable diagnostic work can be improved. You can

[Brief description of drawings]

FIG. 1 is a connection diagram showing an embodiment of the cable diagnostic device of the present invention, and FIG. 2 is a connection diagram showing a conventional method for measuring dielectric loss. 20 ... Cable to be diagnosed, 21 ... Other cable, 23 ... Metal sheath, 24, 26 ... Termination, 25 ... Power supply, 27 ... Circuit breaker, 28 ... Load, 30 ... Voltage measuring unit, 31 ... Charging current measurement unit, 32 ... Current transformer, 33 ... Dielectric loss calculation unit.

Claims (1)

[Scope of utility model registration request] 1. A voltage measuring unit for measuring an applied voltage applied to one of a plurality of cables to be diagnosed, a circuit breaker for disconnecting a load of the cable to be diagnosed, and a circuit for the cable to be diagnosed. A charging current measuring unit that measures a charging current charged through a cable conductor; and a dielectric loss calculating unit that determines a dielectric loss of the cable to be diagnosed based on the applied voltage and the charging current. Cable diagnostic device.