JPS6154462A - Measuring method of ground insulating resistance of cable way - Google Patents

Abstract

PURPOSE:To measure the insulation state of a cable way without stopping electricity by applying a rectangular wave voltage which differs in frequency from the cable way to an earth line, detecting a current at the moment when the rectangular wave changes from the plus side to the minus side, and obtaining only ground insulation resistance. CONSTITUTION:A rectangular wave generator 4 generates the rectangular wave voltage which differs in frequency from the cable way, and the voltage is applied to the earth line 2 through a transformer 3. The current flowed through the earth line 2 by the rectangular wave is as shown in the 2nd figure when the cable wave has only the insulating resistance, and the leak current of commercial frequency is applied thereto. Further, when the cable way has electrostatic capacity, it is as shown in the 3rd figure. For the purpose, the point Q of the current value corresponding to a point P where the rectangular wave almost rises is obtained to calculate the current due to only the insulating resistance, thereby finding the earth insulating resistance of the cable way from the voltage of the rectangular wave.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for measuring the insulation resistance to ground of a track.

The present invention will be described in detail below based on the drawings (1
) is a three-phase transformer for the circuit under test, (2) is a transformer (
A transformer is connected to the second type grounding wire (1) with one terminal grounded and (3) to the grounding wire (2), which superimposes a square wave voltage on the grounding wire (2). (4) is a transformer (3
), the current transformer (5) is connected to the ground wire (2), and the primary current of the amplifier (6) and the current transformer (5) is connected between the output terminals of the current transformer (5). Feedback resistor (
7). (8) is a feedback resistor (filter connected to the sword, which extracts only the current of the square wave. (9) Calculates the output from the square wave generator (4) and filter (8). It is a computing unit that extracts only the current caused by the ground insulation resistance using the voltage and current of the rectangular wave.

A display connected to the arithmetic unit (9) at αl, the arithmetic unit (9)
◇Ra, which displays the resistance value determined by
Rb and Rc are the ground insulation resistance of each phase of the electrical circuit under test +
CaHCb r Cc measures the ground capacitance of each phase of the electrical circuit under test.

In the above circuit, a square wave generator (4) generates a square wave voltage different from the frequency of the electrical circuit, and the transformer (3) superimposes this voltage on the ground line (2). The current flowing through the ground wire (2) due to this square wave voltage is:

When the electrical path has only insulation resistance, it will look like the one shown in Figure 2, and a commercial frequency leakage current will be added to this. Also, when there is capacitance in the electric circuit, it becomes as shown in Fig. 3.

Therefore, the current value at point P near the falling edge of the square wave is 9
If you find the point, you can find the current caused only by the insulation resistance, and from the voltage of the square wave, you can find the insulation resistance to ground of the electrical circuit.

In the present invention, a single-phase transformer may be used instead of the three-phase transformer (1).

The present invention is constructed as described above.

(1) The insulation state of the electric circuit can be measured without stopping the electricity. (2) Since the phase difference between the superimposed voltage and current is not measured, even insulation deterioration of the electric circuit including inductance can be accurately measured.

(Since DC voltage is superimposed on line 31E, it can be used as an insulation resistance meter for live wires.

It has the following advantages.

[BRIEF DESCRIPTION OF THE DRAWINGS] Part 1 is a diagram showing a circuit used to carry out the present invention, and Figure 2 is a waveform diagram of a current flowing through a grounding wire due to a rectangular wave voltage when the electric path has only insulation resistance. FIG. 3 is a waveform diagram of a current flowing through a grounding wire due to a rectangular wave voltage when there is capacitance in the electrical path.

Claims (1)

[Claims] In a three-phase transformer or single-phase transformer in which one terminal of the transformer is grounded, a rectangular wave voltage different from the frequency of the electric circuit is superimposed on the ground wire, and a current flowing due to that voltage is installed in the ground wire. A method for measuring the insulation resistance to ground of an electric circuit, which is characterized by detecting the electric current at the moment when it drops from the positive side to the negative side of the rectangular wave, and determining only the insulation resistance to earth.