JPS5819224B2 - Insulation resistance measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an insulation resistance measuring device, and more particularly to a device for continuously measuring the insulation resistance of an entire DC circuit having an ungrounded rectified power source and its parts.

Conventionally, in order to manage the insulation of low-voltage electrical machines, such as large DC rotating machines, maintenance personnel had to check each time with a megameter after stopping the machine, 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 [Refer to Special Publication No. 55-50306]
) was proposed.

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 Accordingly, it is an object of the present invention to provide a device capable of continuously measuring insulation values in whole and in parts of an ungrounded DC power system.

The device according to the present invention alternately and selectively grounds the measuring resistors connected to the positive and negative lines of an ungrounded DC circuit, and in each grounding state, the voltage between the positive and negative lines and the ground line, and the power supply. Measure the difference current flowing in the positive and negative wires between the power supply and the connection point of the measurement resistor, and the difference current flowing in the positive and negative wires between the power supply and the part where you want to measure the partial insulation resistance, and compare these measured values with , the required insulation resistance value is calculated using predetermined constants.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The measurement principle of the insulation resistance measuring device according to the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a basic block diagram of a measuring device according to the invention.

In the figure, 1 and 2 are both differential current detectors, and 1
2 is for measuring the difference current value that is mainly used to calculate the partial insulation value of load 3 of the circuit under test, and 2 is the difference current value that is mainly used to calculate the insulation value of the entire system. ZCT
Abbreviated as I and ZCTl.

Reference numeral 4 denotes a power supply for the circuit under test, which supplies a voltage Vo between the 2nd line and the N line.

The resistors r connected to the lines P and N, respectively, are measuring wipes and are alternately and selectively grounded by a switching device SW having contacts 1 and 2.

Vp is vN for measuring the voltage between line 2 and ground 8.
is a voltage measuring device for measuring the voltage between the N line and the ground 8.

These ZCTI, ZCTl. The measured values from Vp and (2) are supplied to the arithmetic unit 5, and the arithmetic unit uses these values to calculate and output the required insulation value.

In the figure, the difference current detector for the partial insulation value is zCT
Although only 1 is provided, it may be installed at multiple locations if necessary, and in that case, the insulation value on the load side can be calculated using each ZCT as a boundary.

Further, it is assumed that ZCTl is always connected to the power supply side from ZCTl in the following.

Even if ZCTl is connected to the load side than zCTl, the essence of this mechanism will not be lost at all, and it can be handled in the same way by making some modifications in the calculation as explained later, but it is easy to explain. For the sake of compatibility, we will make the above assumptions.

Next, from the viewpoint of insulation value, the entire equivalent circuit is as shown in FIG.

Here, the meaning of each symbol is as follows.

r: Measurement resistance ρ: Electrometer internal resistance RP□: P-side insulation value RN2 in the section between ZCTl and zCTl
; N side + Rpt: P side insulation value RNl on the load side from ZCT1; N side i2: Difference current value detected from ZCTl (direction of arrow in Figure 2 is positive) i :Difference current value detected by ZCTl (direction of arrow in Figure 2 is positive) Since the difference current 11 detected by ZCTI is a current that does not pass through the P and N conductor parts, the equivalent circuit is shown in Figure 3. It is given as the current value passing through the earth common (E) as shown in .

If SW is now connected to 1 and this is expressed as 11(1), then FIG. 3 can be replaced as shown in FIG. 4.

As you can see by comparing it with the overall equivalent circuit in Figure 2, holds true.

Then, considering R as the overall insulation value, the following equation is obtained.

Figure 4 shows a well-known bridge circuit, and now we will analyze it as follows: 11 (1) = f, (1) vo...
......(3) holds true.

Hereinafter, the analysis will be performed using the function f, assuming that vo is constant.

If we consider and organize the circuit using the same method as described above, we will eventually obtain four independent equations.

Solving the above four equations simultaneously, the unknowns R1, R22, RNl,
Just give RN2.

First, by focusing only on ZCT2 and solving it, we obtain Equation 03 from Equations 7 and 8.

From the above, it can be seen that the total insulation value R, the P side and N side insulation values, RP, and RN can be given only by ZCT2.

Next, by focusing on both ZCT 1 and ZCT2 and calculating using Equations 5 to 8, the following is obtained.

Here, if we set the SWl and 2 o'clock values of VP and V in Figure 2 as VP1.2 and VN, respectively, then Vo=Vpt +VN
1 = "P2 +VN2 ...... From the third equation of QI, f is the detection current i and this ■.

Since which quotient is given, by substituting f=- into Equations 9 to 017, all insulation values can be calculated.

In this device, Vo detection is not so important.

If the operating voltage V.

If we decide to give it from the outside by some method, the second
The VP and VN measuring mechanisms in the figure may be removed.

In this case, by setting ρ→■ in Equations 9 to 17, the desired insulation value can be obtained.

It is also possible to move the vPvN mechanism of FIG. 2 to the section between ZCTl and ZCTl.

At this time, calculate each insulation value as ρ→■ in Equations 9 to 17, and then calculate again since RP2 and RN2 that are displayed are actually parallel resistance values of true RP2 and RN2 and each ρ. All you have to do is

Although it is very inconvenient, ■When connecting the PNN measurement mechanism to the load side from ZCTi, you can place it in a similar circuit and recalculate.

As explained above, by measuring and calculating with the apparatus of the present invention, the total and partial insulation resistance values of an ungrounded DC circuit can be continuously obtained.

Although ZCTl and ZCTl are preferably insulated DC differential current detectors, they are not necessarily limited to this, and it is clear that various electronic computers can be used as the calculation device.

[Brief explanation of the drawing]

FIG. 1 is a basic block diagram of an insulation resistance device according to the present invention. FIG. 2 is an overall equivalent circuit diagram for explaining the measurement principle. 3 and 4 are equivalent circuit diagrams further showing a part of the circuit of FIG. 2. FIG. 1.2: difference current detector, 3: load, 4: power supply, 5: arithmetic unit.

Claims (1)

[Scope of Claims] 1. An insulation resistance measuring device for measuring insulation resistance of an ungrounded DC circuit, comprising the following: (a) a measuring resistor connected to the positive and negative wires of the ungrounded DC circuit; (b) a switching device that selectively grounds the measuring resistor; ←→ formed between the positive and negative wires and the grounding wire. A device that measures the voltage between two lines. (ii) a device that is inserted between the power source of the ungrounded DC circuit and a point to which the measurement resistor is connected, and that measures a first difference current between the currents flowing through the positive and negative wires at the insertion point; (7f9 A device that is inserted between the power supply of the ungrounded DC circuit and the load device and measures a second difference current between the currents flowing through the positive and negative wires at the insertion point, 2. Insulation resistance measurement according to claim 1. A device in which the device that measures the difference current is a direct current insulated difference current detector.