JPS5847034B2 - Insulation resistance measurement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for measuring insulation resistance, and particularly to a method for measuring a partial insulation resistance value of a DC circuit having an ungrounded rectified power source.

Conventionally, in order to manage the insulation of low-voltage electrical machines, such as large DC circuit machines, maintenance personnel had to check each time with a megger meter after the machine stopped operating, which limited opportunities for measurement.
The drawback was that it required a lot of man-hours.

The present inventor has developed a device (patent application) that makes it possible to constantly and continuously measure the insulation resistance value of a DC circuit and a rotor in the circuit under operating conditions, which was impossible with the conventional megameter. No. 51-144905, Special Publication No. 55-503
(see Publication No. 06).

However, since this measuring device targets the entire DC system, it is possible to measure the overall variation in insulation value, but it is not possible to determine in which part of the system the variation occurred (for example, on the power supply side or on the load side). However, there was a drawback that it was not possible to make sufficient decisions based on location.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a method by which partial insulation values of a DC power system can be continuously measured under operating conditions.

A more detailed explanation will be given below with reference to the drawings.

FIG. 1 is a diagram illustrating the measurement principle of an insulation resistance measuring device suitable for application to the present invention.

In the figure, a portion 1 surrounded by a broken line is the other circuit of the measuring device, and the other portions equivalently represent the insulation state of the circuit to be measured, that is, the equivalent circuit.

This device alternately switches the switch SW to 1.2 in the figure, reads the voltage value PVN at that time, performs various calculations, and determines the RP, RN, tγR, etc. of the paper edge circuit. .

Here, in order to increase accuracy, the measurement resistance γ is determined according to RPRN.
, and read vp jVN after setting the discharge time (τ8e0) in view of the capacitance of the system.

Each symbol in the figure and the formula for determining its value % Formula % However, γR is the insulation value of the rotor or single Sirisk, etc., △Vp and △vN are the average fluctuating voltage values, and the subscript 1
, 2 indicate positions 1 and 2 of switch S■.

The principles and specific configuration of the above-mentioned insulation resistance measuring device are not directly related to the present invention and will not be described in further detail. Reference).

2 to 5 are circuit diagrams for explaining the principle of measuring partial insulation values according to the present invention.

FIG. 2 is a diagram showing the circuit connection for the measurement method according to the present invention, in which 2 is a partial insulation resistance measuring device applying the above-mentioned one, and 3 is an isolated type differential current detector for direct current, which may be an ordinary one. (hereinafter abbreviated as ZCT).

The ZCT is inserted into the required positions of the power lines P and H and inputs the value i of the difference current passing through that part to the insulation resistance measuring device 2.

Then, we will divide the insulation value into two with ZCT as the boundary.

That is, in FIG. 2, RPI 2 RNt 2
is limited as follows.

RPl: P side shear resistance facing the load side from ZCT
**RNl:Z
N-side leak resistance RP2 facing the load side from CT: P-side leak resistance RN2 facing the power supply side from ZCT: N-side leak resistance facing the power supply side from ZCT In the above insulation resistance measurement, the entire system RPtRN is displayed, and there is a relationship between this and the above-mentioned bisected insulation value as shown below.

However, for the sake of simplicity, it is assumed that there is no loop in which one end of the load side is connected to the power supply side in FIG.

On the other hand, to explain the current i, referring to FIG. 3, since the difference current i detected by ZCT3 is a current that does not pass through the P and N conductive parts, the circuit is as shown in FIG. 3.

If the arrow direction as shown in Fig. 3 is taken in the correct direction, Fig. 3 can be further replaced with a bridge circuit as shown in Fig. 4.

Since FIG. 4 is a typical bridge circuit, analysis is relatively easy.

Now, determine the operating voltage of the DC system.

It becomes a binding.

By the way, in Fig. 2, the insulation resistance measuring device 2 is ZCT3.
connected to the power supply side.

The operating principle of the insulation resistance measuring device is that the measuring resistor γ is alternately grounded between P and E and between N and E, and the P
Since each voltage between -E and N-E is measured and various insulation values are calculated and displayed from the changes, the bridge circuit of FIG. 4 can be further represented as shown in FIG. 5.

In FIG. 5, a shows the case where the P side measuring resistor is grounded and the insulation resistance measuring device measures the voltage (VP) between P and E, and b shows the case where the N side measuring resistor is grounded and the insulation resistance measuring device measures the voltage (VP) between P and E. This is a case where the voltage (VN) between E and E is measured.

Equation 8 holds true even if RP2 and RN2 are replaced with each other in Equation 8 from FIGS. 5a and 5b.

Therefore, if we rewrite the 8th equation using the 9th equation, the 10th and 11th equations are hyperbolic pure functions for RP 2' and RN2', respectively, and the 10th equation is RP2'→(1 ), and equation 11 monotonically increases with respect to RN2'→(1).

N* Now, for the known quantity, the unknown quantity RP1. To obtain RN1°RP2 t RN2, it is sufficient to simultaneously solve the 5th, 9th, 10th, and 11th equations.

Solving the above equation, we get the following result.

RP2 t RN2 is determined from the 12th equation, the 13th equation, and the 5th equation, but since the equation is obvious, it will be omitted here.

Equations 12, 13, and 16 are represented by the function f, but in actual equipment, the current i is detected by ZCT, so the operating voltage is ■.

Assuming that is constant, return to equation 7 and let the difference current when the P-side measuring resistor is grounded be 1 (RP2, and the difference current when the N-side measuring resistor is grounded i (RN2'). 17 below
The ceremony will be collected.

Therefore, the 12th, 13th, and 16th equations end up being like the 18th equation.

In the 18th equation, the voltage is volts M1 resistance is megohms (
M, 2), $f current is measured in microamperes (μA).

Therefore, the partial insulation resistance measuring method according to the present invention is as follows.

1. Set the value of γ as a constant.

2. Corresponding to the operation of the insulation resistance measuring device, measure the difference current t (RP2') when the measuring resistance γ is set to the RP2 side.

3.Similarly, when the measuring resistance γ is set to the RN and 2 sides, the difference current t
(RN2') is measured.

4. As mentioned above, RP and RN are measured using the insulation resistance measuring device.
Calculate.

5. Do the same ■.

Calculate. 6. Calculate RPl and RNl from Equation 18.

7. Calculate R1 in the same way.

FIG. 6 is a block diagram illustrating one embodiment of an apparatus suitable for carrying out the method according to the invention.

FIG. 6 is a block diagram illustrating one embodiment of an apparatus suitable for carrying out the method according to the invention.

In the figure, reference numeral 2 denotes a partial insulation resistance measuring device according to the present invention, which includes the above-mentioned insulation resistance measuring device 4 and 2 from the device.

A storage device 5 that receives and temporarily stores the values of tRP, RN, and γ, and the value of i from a DC isolated current detector (ZCT) 3, which will be described later, and a storage device 5 that receives and temporarily stores the values of tRP, RN, and γ, and the storage device 5 that receives and temporarily stores the values of It consists of an arithmetic device 6 that calculates and outputs required values such as RPI t RNt t R1, and a control device 7 that controls the various devices mentioned above.

The ZCT 3 is separated from the current transformer 8 and buffer amplifier 9 for differential current detection.

Note that among the above-mentioned components, the insulation resistance measuring device does not necessarily have to be the one according to the invention of the present inventor described above.
■Any device that can continuously measure the values of o, RN, RP, etc. under operating conditions can be used, and other components may be conventional and commonly used devices. .

In the example, one ZCT is used, but the number of ZCTs can be increased as required, and installed in each circuit section whose insulation resistance value is to be measured. It is also possible to monitor insulation resistance values.

In addition, in the explanation, the insulation resistance measuring device 2 is connected to the power supply side from the ZCT 3 as shown in FIG. It is clear that the partial insulation resistance value can be measured in the same way with only a slight modification of the equation.

By carrying out the partial insulation resistance measuring method according to the present invention using the above-described apparatus, it is possible to continuously measure the necessary partial values of the insulation resistance of an ungrounded DC circuit in the operating state, which has been impossible in the past. It is now possible to monitor, display, record, and issue an alarm if necessary, making it possible to centrally and constantly automatically manage the insulation of ungrounded DC power systems in factories, etc. As a result, safety can be ensured and operation rates can be improved.

[Brief explanation of the drawing]

FIG. 1 is an equivalent circuit diagram showing the principle of an insulation resistance measuring device according to an earlier invention by the present inventor. 2 to 5 are circuit diagrams for explaining the principle of the partial insulation resistance measuring method according to the present invention. FIG. 6 is a block diagram showing an embodiment of a partial insulation resistance measuring device according to the present invention. 1.4... Insulation resistance measuring device, 2...
Partial insulation resistance measuring device, 3...Insulated differential current detector for direct current, 5...Storage device, 6...
Arithmetic device, 7...Control device, 8...Current transformer, 9...Buffer amplifier.

Claims (1)

[Claims] 1. A method for measuring partial insulation resistance of an ungrounded DC circuit and a load device connected to the circuit, comprising the following steps: (a) connecting to positive and negative lines of the ungrounded DC circuit; Selectively and alternately ground the measurement resistors, measure the difference current 1 (RP2') between the currents flowing through the positive and negative lines when the positive side resistance is grounded, and measure the current flowing through the positive and negative lines when the negative side resistance is grounded. (0) Measuring the difference current i (RN2') between the positive and negative wires using an insulation resistance measuring device; (c) measuring the measured difference current value 1 (R
P2'), 1 (RN2') Earth insulation resistance value R of positive and negative wires
P yRNs Average voltage value between positive and negative lines■. and calculating a partial insulation resistance value on the power supply side or load side from the measurement point of the difference current using the value γ of the measurement resistor.