JP2578766B2 - Live tan δ measuring device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cable insulation deterioration diagnosis apparatus, and particularly to performing insulation deterioration diagnosis of a cable under test in a live state, where a ground fault occurs in a measurement system. The present invention also relates to a live-line tan δ measuring device capable of preventing a cable to be measured from being stopped due to a power failure and from stopping power supply.

[Technical Background and Problems of the Invention] Conventionally, as a method for diagnosing insulation deterioration of a cable, after stopping power transmission to a cable, a DC voltage, an extremely low frequency or an AC voltage is applied, and 1) a DC leakage current is reduced. Measurement, 2) measurement of partial discharge, 3) measurement of tan δ, and the like.

However, in reality, it is often difficult to perform a power outage, and a method of diagnosing in a live state is desired. Until now, methods for measuring leakage current and partial discharge in a live state have been developed.
The measurement of δ is performed using a Schering bridge circuit (FIG. 5) in the case of a dead line, but it has not been developed yet because it is difficult to take in a voltage signal and a current signal from a cable in a live state. Is the actual situation.

JP-A-59-211867 discloses a live wire insulation diagnosis for determining insulation deterioration by inputting a voltage value of a core wire of a cable in a live state and a current value of a sheath grounding portion and calculating tan δ. A law has been proposed. However, in this hot wire insulation diagnosis method, the
When the cable diagnosis of δ is performed, there is a problem in that when a ground fault occurs in the measurement system, the cable to be measured is in a power outage state, and power supply is stopped.

[Object of the Invention] The present invention has been made in order to solve the above-mentioned conventional problems. In performing insulation deterioration diagnosis of a cable under test in a live state, even if a ground fault occurs in a measurement system, the measurement is performed. It is an object of the present invention to provide a live-line tan δ measuring device capable of preventing a power failure of a cable from stopping power supply.

[Summary of the Invention] In order to achieve such an object, a live wire tan of the present invention is used.
The δ measuring device balances the current signal and the voltage signal from the cable under test in the live state with an electronic balance circuit.
Using a tan δ meter, the current signal is taken out from the ground wire that grounds the shield layer of the cable to be measured by a current transformer and input to the tan δ meter, and the voltage signal is connected to the high voltage section of the cable to be measured It is taken out from the high voltage lead cable and input to the tan δ meter via the voltage divider.

This hot-line tanδ measuring device is connected to a ground wire for grounding the shield layer of the cable under test in a live state, a current transformer for detecting a current flowing through the ground line, and a high-voltage part at the end of the cable under test in a live state. A high-voltage lead cable, a voltage divider that divides the voltage of the high-voltage lead cable, a tanδ meter that inputs a current signal from the current transformer and a voltage signal from the voltage divider and displays a tanδ value, and A circuit breaker operated by a ground fault detection current of the device is provided between the circuit breaker and the pressure transformer.

A tan δ meter having an electronic balance circuit is known, and has a basic circuit as shown in FIG. 2 and its principle is as follows.

That is, the current signal Ix obtained from connected to the shielding 1a of the measured cable first ground line 2 enters the amplifier A _2. Here, the current signal Ix is a combination of a capacitor component of the cable 1 and a tan δ component (a component having the same phase as the applied voltage). On the other hand, the voltage Vs and the phase component voltage es taken out from the high pressure section of the measured cable 1, the current Is flowing in the parallel circuit of a capacitor Cs and the variable resistor D / A also enters the amplifier A _1. Out of Is, the current flowing through the capacitor Cs and the capacitor component of the current signal Ix have opposite phases (180
゜).

In the amplifier A ₃ Is and Ix is synthesized (in phase consideration of the difference is taken) into the detecting circuit M _2. The detection circuit M detects only a component (capacitor component) advanced by 90 ° with respect to the applied voltage, and adjusts the variable resistor D / A ₄ so that this output becomes zero. However, if tan δ = 0, the variable resistance D / A
₄ the output of the amplifier A ₃ servants adjusted does not become zero. So then it detects only the applied voltage and the common-mode detection circuit M ₁ (tan [delta min), when the output is not zero, by adjusting the variable resistor D / A _1, is zero.

When the above adjustment is performed, the value of the resistance D / A ₁ corresponds to tan δ, and the value of the resistance D / A ₄ corresponds to the capacitor of the cable under test 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the hot-line tan δ measuring apparatus according to the present invention will be described below with reference to the drawings.

The device shown in FIG.
The ground wire 2 is connected to the shielding layer 1a of the cable under test 1 in a live state. At one end of the ground wire 2, a current flowing through the ground wire 2 to which a current measuring AC (CT) 4 is attached is detected and input to a tan δ meter 5.

In addition, one end 6a of the high-voltage lead cable 6 is connected to the high-voltage section 1b at the end of the cable under test 1 in a live state by a hot stick. The other end 6b of the high-voltage lead cable 6 is a circuit breaker 7
Connected to.

The circuit breaker is a device for connecting the high-voltage lead cable 6 and the voltage divider 8 and comprises a contactor 9 and a relay 10, which are mounted on the circuit breaker 7 together with the high-voltage lead cable 6 and the voltage divider 8. And the circuit breaker 7 are grounded by the ground line 3.

An AC current detector (ZCT) 12 for fault current detection is attached to the ground wire 3. If a ground fault occurs in the measurement system, a ground fault current flowing through the ground wire 3 is supplied to the fault current detection current transformer 12. It is detected, and the detection signal is input to the relay 10. The relay 10 operates the contactor 9 in response to the input of the detection signal, disconnects the connection between the high-voltage lead cable 6 and the voltage divider 8, and protects the measured cable from power failure.

The voltage divider 8 divides the voltage from the high voltage lead cable 6 and inputs it to the tan δ meter 5 as a voltage signal. The tan δ meter 5 balances the current signal Ix from the current measuring current transformer 4 attached to the ground line 2 and the voltage signal Vs from the voltage divider 8 with the electronic balance circuit as described above, and measures tan δ. indicate. In the figure, reference numeral 13 denotes a generator as a power supply for the circuit breaker 7 and the tan δ meter 5, but power supply means other than the generator can be used.

FIG. 3 shows a tan δ meter 5 used in this embodiment,
Voltage signal display 51, balance sensitivity switch 52, Cx R
ange53, Power switch 54, tanδ display unit 55, capacitance meter 56, measurement frequency switch 57,
The specifications are as shown in Table 1.

Table 1 Specifications tanδ measurement range 0 to 12% Measurement accuracy ± 0.1% in tanδ value Capacitance range 4nF to 12nF 12nF to 40nF 4 ranges 0.04μF to 0.12μF 0.12μF to 0.4μF Measurement voltage 3.8kV ± 15 (50HZ or Input power supply AC100V ± 15% 50 / 60HZ 10VA (Power supply can also be applied to battery inverter type) Weight 5kg Size 200 (H) × 180 (W) × 310 (D) Next, live line of the present invention The operation of the tan δ measuring device will be described. First, a current signal from the cable under test 1 in a live state is input to the tan δ meter 5 detected by the current measuring current transformer 4 attached to the ground line 2. The voltage signal from the cable under test 1 in the live state is divided from the high voltage lead cable 6 via the voltage divider 8 and input to the tan δ meter 5. The tan δ meter 5 measures and displays tan δ by balancing the current signal and the voltage signal with an electronic balance circuit.

FIG. 4 shows a comparison between a value actually measured by the hot-line tan δ measuring apparatus of the present invention and a tan δ measured value by a shaping ridge, and an error between both measured values is ± 0.1%.
Within the range.

[Effects of the Invention] As is clear from the above embodiments, the live line tan of the present invention is
According to the δ measurement device, when performing insulation deterioration diagnosis of the cable under test in the live state, a circuit breaker that operates by detecting a ground fault current is provided between the high-voltage lead cable and the voltage divider. Even if a ground fault occurs in the measurement system, the circuit breaker will be opened by detecting the ground fault current, so prevent the power supply from being stopped due to the power failure of the cable under test beforehand. Can be.

[Brief description of the drawings]

FIG. 1 is a diagram showing an outline of a live line tan δ measuring apparatus of the present invention,
2 is a circuit diagram of the tan δ meter, FIG. 3 is a diagram showing a front panel of the tan δ meter, and FIG. 4 is a live line ta according to the present invention.
FIG. 5 is a graph showing a comparison between the measured value of nδ and the measured value by a sharing bridge, and FIG. 5 is a sharing bridge circuit. DESCRIPTION OF SYMBOLS 1 ... Cable under test in a live state 1a ... Shielding layer 2 ... Grounding wire 4 ... Current transformer for current measurement 5 ... tan delta meter 6 ... High voltage lead cable 7 ... Circuit breaker 8 ... Voltage divider 13 ... Power supply

Claims (1)

(57) [Claims] 1. A ground wire for grounding a shield layer of a cable under test in a live state, a current transformer for detecting a current flowing through the ground wire, and a high voltage lead connected to a high voltage section at the end of the cable under test. Cable, a voltage divider for dividing the voltage of the high-voltage lead cable, and a current signal from the AC device and a voltage signal from the voltage divider that are input to display a tan δ value.
δ meter, a power supply for the shield and the tan δ meter, and a circuit breaker for disconnecting the high voltage lead cable and the voltage divider by detecting a ground fault current when a ground fault occurs in a measurement system. Characteristic live line tanδ
measuring device.