JPH07104377B2 - 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 (Japanese Patent Application No. 61-012780).

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

As for the cable 10, as shown in FIG.
The insulation resistance of the cable insulator 12.

In addition, the high voltage bus bar 44 has a motor,
Devices such as transformers are connected. All of them are shown together as an electric device 30 in FIG. 7,
For that matter, it is the resistance between the conductor of the winding 32 and the case 34.

42 is the earth resistance (resistance value R _S ).

In the cable 10 (FIG. 6), 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. 7), 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 bus, 46 is a grounding transformer, and 48 is its neutral point.

DC power supply between cable shield layer 16 or case 34 and ground
The voltage V 52 is applied to measure the voltage V between the cable shielding layer 16 or the case 34 and the ground.

Further, a measuring resistor 58 (resistance value R) is connected between the neutral point 48 of the grounding transformer 46 and the ground, and the voltage v across the resistor 58 is measured.

Then the insulation resistance R _X is Can be asked as

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

However, in the case of a customer receiving 6.6 kV from the electric power company, the grounding transformer 46 is located in the substation of the electric 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 Problems] A cable or a power device having a measurement metal layer 20 described later is used. As will be described later in detail, if the measurement metal layer 20 is originally provided, it is used. If not, the measurement metal layer 20 is specially added.

Then, as illustrated in FIG. 1a, (1) a DC ammeter 76 is connected via a filter circuit 70 between the measuring metal layer 20 and the cable shielding layer 16 or the power equipment 34, Apply the voltage of DC power supply 72,
The DC current i is measured, or (2) or instead of the DC ammeter 76, a voltage detecting resistor 80 is connected and the terminal voltage V of the detecting resistor is measured as shown in FIG.

By taking such a method, the insulation resistance can be measured without processing the neutral point of the grounding transformer.

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

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

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

-Measurement metal layer 20: By using this measurement metal layer 20, the grounding transformer 46 does not need to be processed, which is important in the present invention.

Here, the measurement metal layer 20 will be described.

(1) In case of high voltage CV cable with insulator (Fig. 3a): Steel strip insulator, iron wire insulator, corrugated steel pipe insulator is on the metal layer 20 for measurement. 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 case of high voltage CV cable (Fig. 3b): Special cable with insulation layer 24 (consisting of tape or sheath) on cable shielding layer 16 and metal layer 20 for measurement on it use. The measurement 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) Submarine cable (Fig. 3c): Between the cable shielding layer 16 and the iron wire insulator 26, the insulating layer 24 ~
A layer composed of the measurement metal layer 20 to the insulating layer 28 is provided. The measurement 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, and is not useful as an insulating layer because it infiltrates seawater.

(4) In the case of electric device 30 (Fig. 4): An insulating layer 38 and a measuring 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.

72 is a DC power supply for measurement, which is 10 to 100V.

74 is a switch.

Reference numeral 76 is a DC ammeter, and the lower limit of the measurement sensitivity is 0.01 nA in order to enable the measurement range of R _X = 0.1 to 10 ⁵ .

78 is a variable voltage source for canceling the nozzle voltage appearing on the cable shielding layer 16 during measurement.

・ Measurement method: The DC equivalent circuit of Fig. 1a is shown in Fig. 1b. During measurement, switch 69 (Fig. 1a) is opened. At first, open the switch 74 and set the voltage of the power supply 72 to zero V, and
To cancel the noise voltage appearing at 76,
The variable voltage source 78 is adjusted so that the ammeter 76 indicates zero. .

In this case, it is desirable that the polarity of the variable voltage source 78 can be switched in consideration of the polarity of the noise voltage.

Next, a predetermined power supply voltage E is applied, and the current value i at that time is measured.

Intermediate resistance 64 is a variable voltage source 78 with very low internal resistance.
And because it is shafted by the series circuit of ammeter 76, current i flowing through cable insulation resistance (measurement insulation resistance) 40 does not flow through intermediate resistance 64 (large resistance value), and variable voltage source 78 and ammeter are all used. It flows into the DC circuit of 76, and there is no voltage effect due to this (because of the small internal resistance).

Therefore, the insulation resistance R _X is Can be asked as

[Another Embodiment] FIG. 2 shows a case where a DC voltmeter is used instead of the DC ammeter 76.

However, FIG. 2 shows the terminal A of the filter circuit 70 of FIG.
Only the parts from B and C are shown (all other parts are the same).

80 is a detection resistor and is selected from the range of 10 kΩ to 10 MΩ.

Reference numeral 82 is a DC voltmeter, and the measurement sensitivity has a lower limit of 0.01 mV.

-Measurement method: In this case, the basics are the same as when the above ammeter is used.

From the resistance value r of the detection resistor 80 and its terminal voltage V, the insulation resistance R _X is given by the following equation.

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

(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) It is possible to measure 10 ⁵ MΩ.

[Brief description of drawings]

FIG. 1a is an explanatory diagram of a circuit for carrying out the method of the present invention,
1b is a DC equivalent circuit diagram thereof, FIG. 2 is an explanatory diagram of another embodiment thereof, FIGS. 3a, 3b, and 3c are explanatory diagrams of the measurement metal layer 20 for different measurement targets, FIG. 4 is an explanatory view of the measuring metal layer 20 of the electric device 30, FIG. 5 is an explanatory view of a conventional technique, FIG. 6 is an explanatory view when a measurement target is a cable, and FIG. Explanatory drawing in the case of the apparatus 30. 10: Cable, 12: Cable insulator 14: Cable conductor, 16: Cable shield layer 18: Cable sheath 20: Metal layer for measurement, 22: Anticorrosion layer 24: Insulation layer, 28: Insulation layer 26: Iron wire siding, 30 : Electric equipment 32: Winding, 34: Case 36: Insulation frame, 38: Insulation layer 40: Insulation resistance to be measured, 42: Earth resistance 44: High voltage busbar, 46: Grounding transformer 48: Neutral point 50, 56: Filter circuit 52: DC power supply, 58: Measurement resistance 64: Intermediate resistance, 68: Earth resistance 69: Switch, 70: Filter circuit 72: Measurement DC power supply 74: Switch 74, 76: DC ammeter 78: Variable voltage source , 80: Detection resistor 82: DC voltmeter

 ─────────────────────────────────────────────────── ─── 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 power cable having a shielding layer outside a cable insulator or a power device having a metal case, wherein the insulating layer, the metal layer and the ground are electrically contacted to the outside of the cable shielding layer or the case. The metal layer is used as a metal layer for measurement in a state where an insulating layer is present in that order, or the insulating layer, the metal layer, and the insulating layer in electrical contact with the ground are provided outside the shielding layer or the case. When present in order, the metal layer is used as a measurement metal layer, and a DC ammeter is connected through a filter circuit between the cable shielding layer or the case of the power device and the measurement metal layer. , By applying a DC voltage and measuring the DC current, or by connecting a voltage detection resistor instead of a DC ammeter and measuring the terminal voltage of the detection resistor. A method for measuring insulation resistance of a cable or an electric device, which comprises measuring an insulation resistance of an insulating layer or a winding of an electric device.