JPH0652280B2 - Method of measuring insulation resistance of cable or electric equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention is a method of measuring the insulation resistance of a crosslinked polyethylene power cable or high-voltage electrical equipment (motor, transformer, etc.) under a hot line to know the degree of insulation deterioration. It is about.

This method can be used for both high voltage and low voltage. The application fields for cables are all high voltage cables, low voltage cables, underground and aerial cables, submarine and submarine cables.

[Prior Art] A technique is known in which the insulation resistance of a cable is measured under a live line by an AC / DC superposition method.

An example thereof is shown in FIG. 5 (see Japanese Patent Application No. 61-143485).

40 is the insulation resistance (resistance value R _X ) to be measured.

As shown in FIG. 7, this is the insulation resistance of the cable insulator 12 for the cable 10 and also the resistance between the cable conductor 14 and the cable shielding layer 16.

In addition to the cable 10, devices such as a motor and a transformer are connected to the high voltage bus bar 44. All of them are put together and shown as an electric device 30 in FIG. 8.
Resistance between 4 and.

42 is a ground resistance (resistance value R _S ).

In the cable 10 (FIG. 7), this is mainly the resistance of the cable sheath 18 and also the resistance between the cable shielding layer 16 and the ground when the cable shielding layer 16 is floated from the ground.

Further, in the electric device 30 (FIG. 8), it is mainly the resistance of the insulating frame 36 and also the resistance between the case 34 and the ground when the case 34 is floated from the ground.

44 is a high voltage busbar, 46 is a grounding transformer, and 48 is its neutral point.

A detection resistor 52 is connected between the cable shielding layer 16 or the case 34 and the ground through a known filter circuit 50.

A reference resistor 54 (resistance value R) is also connected between the neutral point 48 of the grounding transformer 46 and the ground through a known filter circuit 51.

Further, a proportional resistance 56 (resistance value r _X ) and an adjusting resistance 58 (resistance value r _S ) are provided, and these proportional resistance 56 and adjusting resistance 58 are provided.
The measurement circuit is configured so that a bridge circuit is formed by the insulation resistance 40 and the reference resistance 54.

Then, the measuring DC power supply 60 is applied to adjust the proportional resistance 56 and the adjusting resistance 58 to balance the bridge circuit.

Then, Can be asked as

[Problems to be Solved by the Invention] The above method requires processing the neutral point 48 of the grounding transformer 46.

However, in the case of a customer who is receiving power at 6.6 kV from the power company, the grounding transformer 46 is located in the substation of the power company, so the above measurement method cannot be applied to the cable of the customer.

That is, the application is limited to only the electric power company or the customer who receives the extra high power.

[Means for Solving the Problems] As shown in FIG. 1, it should be in parallel with the ground resistance 68 of the cable shielding layer 16 or the intermediate metal layer 20 (the term will be described later) of the case of the power equipment. Is connected to a reference resistor 86 (resistance value R), a measurement proportional resistance 72 (resistance value r _X ) and a measurement adjustment resistor 74 (resistance value r _S ) are provided, and the reference resistance R and the measurement are provided. By processing the measurement circuit so that a bridge circuit is formed by the resistances r _X , r _S and the insulation resistance R _{X of the} cable insulating layer or the electric device winding, the neutral point 48 of the grounding transformer 46 is processed. The insulation resistance can be measured without adding.

[Embodiment] In FIGS. 1 and 2, 40 is an insulation resistance, 44 is a high voltage bus bar, 46 is a grounding transformer, and 48 is a neutral point thereof, which are the same as in the case of FIG. 5 above. .

64 is an intermediate resistance, which is the resistance between the cable shielding layer 16 or case 34 and the intermediate metal layer 20 (see below).

68 is the earth resistance, which is the resistance between the intermediate metal layer 20 and the earth.

-About the intermediate metal layer 20: By using this intermediate metal layer 20, the processing of the grounding transformer 46 becomes unnecessary, which is important in the present invention.

Here, the intermediate metal layer 20 will be described.

(1) In case of high voltage CV cable with insulation (Fig. 3a): Steel strip insulation, iron wire insulation, corrugated steel pipe insulation is in contact with the intermediate metal layer 20. Therefore, the intermediate resistance 64 is mainly the resistance of the cable sheath 18, and the ground resistance 68 is the resistance of the anticorrosion layer 22.

(2) In the case of high voltage CV cable (Fig. 3b): Use a special cable in which the insulating layer 24 (consisting of tape or sheath) is provided on the cable shielding layer 16 and the intermediate metal layer 20 is provided thereon. To do. The intermediate metal layer 20 is made of annealed copper tape or the like.

In this case, the intermediate resistance 64 is the resistance of the insulating layer 24, and the ground resistance 68 is the resistance of the cable sheath 18.

(3) In the case of a submarine cable (Fig. 3c): Between the cable shielding layer 16 and the iron wire insulator 26, a layer composed of the insulating layer 24, the intermediate metal layer 20 and the insulating layer 28 is provided. The intermediate metal layer 20 is made of copper or brass tape or steel strip. The insulating layer 28 may be the same as the insulating layer 24.

In this case, the intermediate resistance 64 is the resistance of the insulating layer 24, and the ground resistance 68 is the resistance of the insulating layer 28.

The anticorrosion layer 22 here is a wound layer of jute or polypropylene yarn, and is not useful as an insulating layer because it infiltrates seawater.

(4) In the case of the electric device 30 (FIG. 4): An insulating layer 38 and an intermediate metal layer 20 are provided between the case 34 and the insulating frame 36.

In this case, the intermediate resistance 64 is the resistance of the insulating layer 38, and the ground resistance 68 is the resistance of the insulating frame 36.

Referring again to FIGS. 1 and 2, 70 is a filter circuit on the cable side, which is a known one.

Reference numeral 72 is a proportional resistance (resistance value r _X ) made up of resistances having several different resistance values, and 74 is an adjustable resistance (resistance value r _S ).

These resistance values make it possible to measure the resistance range of R _X = 0.1 to 10 ⁶ MΩ of the actual laying line. ・ The proportional resistance 72 is 100 kΩ, 1 MΩ, 10 MΩ, 100 MΩ is switched. ・ The adjustable resistance 74 is 0.1 to 10 Ω 1 to 100 Ω 0.1 to 10 kΩ dial type adjustment.

Reference numeral 76 is a DC power supply for measurement, and its voltage E is superimposed on the AC voltage during hot line. Therefore, considering the influence on other equipment, 10
It is suitable to be set to 100V. Further, in the bridge circuit, sufficient measurement sensitivity can be obtained with such a voltage.

Reference numeral 78 is a switch, and 80 is a voltmeter.

Reference numeral 82 is a detection resistor, which is a detection resistor connected between the output side of the filter circuit 70, that is, between the cable shield layer 16 and the ground in terms of direct current, and has an appropriate time constant (in relation to the capacitance forming the filter). It is selected between 5 and 100 kΩ to be about 2 seconds).

Reference numeral 84 is an adjustable voltage source for canceling noise voltage appearing in the cable shielding layer during measurement.

A voltmeter 88 is used not only for bridge balance but also for canceling noise voltage.

Reference numeral 86 is a reference resistance (resistance value R), which is connected between the intermediate metal layer 20 and the ground in terms of direct current.

An equivalent circuit of the insulation resistance measuring method of the present invention thus constructed is shown in FIG.

As is clear from this, each side of the bridge has an insulation resistance of 4
0 (R _X ), reference resistance 86 (R), proportional resistance 72
(R _X ) and the adjustable resistor 74 (r _S ).

Measurement method: In order to cancel the noise voltage appearing across the detection resistor 82, the variable voltage source 84 is adjusted so that the indication of the bridge balance pressure gauge 88 becomes zero.

In this case, the variable voltage source 84
It is desirable to configure so that the polarity of can be changed.

Next, the switch 78 is closed to apply a voltage to the bridge circuit, and the proportional resistance 72 and the adjustable resistance 74 are adjusted so that the indication of the bridge balance pressure gauge 88 becomes zero.

At the balance point, the following equation holds.

Therefore, R _X is Can be asked as

When the bridge balance is established, the proportional resistance 7
2 and the terminal voltage of the adjustable resistor 74 are equal, so a voltmeter 80
From the indicated value V _X and the voltage E of the measuring DC power supply 76 You can also ask.

[Advantages of the Invention] (1) It is not necessary to process the ground wire for the neutral point 48 of the grounding transformer 46.

(2) Since it can be measured at the terminal part such as the cable to be measured, there is no restriction on the measurement location.

(3) Since the cable sheath insulation resistance R _S is not included in the measurement side of the bridge, it can be measured without being affected by R _S.

(4) Since the measuring circuit is a bridge circuit,
Higher accuracy and wider measuring range than current method (10 ⁶ M
Ω can be measured).

(5) Since it is a bridge circuit, it is not affected by stray current in the ground.

(6) Since the time constant of bridge balance can be set to about 2 seconds, the measurement is quick and easy.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a circuit for carrying out the method of the present invention, FIG. 2 is an equivalent circuit diagram thereof, and FIGS. 3a, 3b and 3c are explanations of an intermediate metal layer 20 for different measurement targets. 4 and 5 are explanatory views of the intermediate metal layer 20 of the electric device 30, FIG. 5 is an explanatory view of a conventional technique, FIG. 6 is an equivalent circuit diagram thereof, and FIG. 7 is a case where a measurement target is a cable. Explanatory drawing, FIG. 8 is explanatory drawing in case a measuring object is the electric equipment 30. FIG. DESCRIPTION OF SYMBOLS 10: Cable, 12: Cable insulator 14: Cable conductor, 16: Cable shielding layer 18: Cable sheath 20: Intermediate metal layer, 22: Anticorrosion layer 24: Insulating layer, 28: Insulating layer 26: Iron wire garment, 30: Electric equipment 32: Winding, 34: Case 36: Insulation frame, 38: Insulation layer 40: Insulation resistance, 42: Earth resistance 44: High voltage bus bar, 46: Grounding transformer 48: Neutral point 50, 51: Filter circuit 52 : Detection resistance, 54: Reference resistance 56: Proportional resistance, 58: Adjustable resistance 60: DC power supply for measurement 62: Bridge balance voltmeter 64: Intermediate resistance, 68: Earth resistance 69: Switch, 70: Filter circuit 72: Proportional Resistance, 74: Adjustable resistance 76: DC power supply for measurement 78: Switch, 80: Voltmeter 82: Resistance for detection, 84: Adjustable voltage source 86: Reference resistance 88: B Jjibaransu test pressure gauge

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Isao Mizunuma 1-5-1, Kiba, Koto-ku, Tokyo Fujikura Electric Wire Co., Ltd. (72) Inventor Takashi Shingen 1-1-5, Kiba, Koto-ku, Tokyo Fujikura Electric Wire Co., Ltd.

Claims (1)

[Claims] 1. A resistance for bridge balance detection is connected between a cable shielding layer or a case of a power device and an intermediate metal layer through a filter circuit so that the resistance is parallel to the ground resistance of the intermediate metal layer. While connecting the resistance R, a proportional resistance r _X for measurement and an adjustable resistance r _S for measurement are provided, and the reference resistance R and the measurement resistances r _X , r _S and the cable insulating layer or the electric equipment winding A measurement circuit is configured so that a bridge circuit is formed with the insulation resistance R _X, and the proportional resistance r _X and the adjustable resistance r _S are adjusted to balance the bridge circuit. A method for measuring insulation resistance of a cable or an electric device, characterized by measuring insulation resistance of a winding.