JP2873697B2 - Monitoring method for insulation deterioration of ungrounded circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for monitoring the deterioration of the insulation state of an ungrounded electric circuit.

(Prior art) Non-grounding method for medical equipment, communication / broadcasting equipment, etc. in order to suppress the leakage current at the time of ground fault and to prevent the noise current generated at the time of ground fault from affecting the human body and load equipment. Are used.

In the non-grounding method, the leakage current at the time of one-line ground fault is small, but when two or more wires are grounded, a large current flows and it is dangerous, so it is necessary to monitor the insulation of the electric circuit. A method has been proposed.

For example, there is a method disclosed in Japanese Patent Publication No. 1-16088.
This method applies an auxiliary voltage that is slightly different from the commercial frequency between the neutral point of the ungrounded circuit and the ground, and the voltage is approximately the same as the ground voltage of the circuit.The maximum value of the current flowing between the neutral point and the ground However, as described in the specification of this publication, this method only detects the deterioration of the impedance between the ungrounded electric circuit and the ground, and detects the insulation deterioration of only the insulation resistance. Instead of detecting, even when the ground capacitance becomes large, there is a disadvantage that the impedance is determined to be abnormal because the impedance is lowered.

By the way, electronic devices in recent years are often provided with a line filter for removing power supply noise, and the capacitance to ground of an ungrounded electric circuit tends to increase more and more as electronic devices are added.

In addition, the capacitance to the ground changes even when the power of these electronic devices is turned on and off.

Therefore, even if insulation deterioration of the electric circuit is detected by the impedance between the electric circuit and the ground, there is a problem that deterioration of the insulation resistance between the original electric circuit and the ground cannot be accurately detected. Furthermore, with the conventional insulation monitoring device of the ungrounded circuit, the insulation resistance of each circuit of the ungrounded circuit cannot be monitored independently.
It is not possible to determine which of the circuit's insulation resistance has deteriorated and whether both have deteriorated insulation and is in a dangerous state, and it requires an auxiliary power supply for measurement, which is not economical. there were.

(Object of the Invention) The present invention has been made in view of the problems of the conventional method for monitoring the insulation deterioration of an ungrounded electric circuit as described above, and monitors the ground insulation resistance of each ungrounded electric circuit with an accurate and economical device. It is an object of the present invention to provide a method for monitoring the insulation deterioration of an ungrounded electric circuit, which can be performed.

(Summary of the Invention) In order to achieve this object, a method of monitoring insulation deterioration in an ungrounded electric circuit according to the present invention comprises inserting a resistor between the neutral point of the ungrounded electric circuit and the ground, and measuring the leakage current flowing through the resistor. By comparing and judging the magnitude of the first effective component of the first effective component and the second effective component of the leakage current flowing through the resistor when a predetermined capacitor is inserted between one of the ungrounded electric circuits and the ground. The deterioration of the ground insulation resistance of the one electric circuit is determined.

(Examples) Hereinafter, the present invention will be described in detail based on examples shown in the drawings.

 FIG. 1 is a block diagram showing one embodiment of the present invention.

In the figure, 1 is a transformer, 2 and 4 are ungrounded electric circuits, 3 is a neutral point, 5 is a step-down transformer, and R1 and R2 are electric circuits 2, 4
In addition, the ground insulation resistance of the load Z, C1, C2 are the electric paths 2, 4 and the capacitance of the load Z to the ground. Neutral point 3 is grounded via resistor r. The voltage across the resistor r is amplified by the high input impedance amplifier A and applied to one input terminal of the synchronous detector M. The voltage of the electric circuit 2 and 4 is
And applied to another input terminal of the synchronous detector. The output of the synchronous detector M is applied to one input of a subtractor DIF and stored in a capacitor C via a switch 3, and the output of the capacitor C is applied to the other input of the subtracter DIF. Further, the output of the subtracter DIF is a comparator C for polarity determination.
P is entered. The electric circuit 2 is grounded by a capacitor C0 via a switch SW1, and the electric circuit 4 is similarly grounded by a capacitor C0 via a switch SW2.

When the switches SW1, SW2, and SW3 are turned off, the current I0 flowing through the resistor r is V0, the line voltage of the ungrounded electric circuits 2, 4, and the commercial frequency is ω0 / 2π. Becomes Therefore, if the voltage rI0 is amplified at both ends of the resistor r by the amplifier A and the line voltage of the circuit is obtained through the step-down transformer 5 and the output of the amplifier A is synchronously detected by the synchronous detector M, the circuit voltage becomes In-phase component, that is, effective component A0 Can be obtained at the output of the synchronous detector M. At this time, when the switch SW3 is turned on, the capacitor C
A value of 0 can be stored.

 After the storage, the switch SW3 is turned off.

Next, when the switch SW1 is turned on, the ground capacitance of the electric circuit 2 changes from C1 to C1 + C0. At this time, the current flowing through the resistor r is equivalent to the equation obtained by replacing C1 with C1 + C0.
The effective component A1 obtained at the output of the synchronous detector M at this time is Becomes Taking the difference between the synchronous detector output A1 at this time and A0 in the above equation already stored in the capacitor C, Becomes Since the expression of the numerator ^{(C1 + C0) 2 -C1 2} > 0 Becomes Therefore, if the output of the subtractor DIF is applied to the comparator CPC, it is possible to determine whether A0-A1 is positive or negative (polarity).

That is, it is possible to determine whether or not the ground insulation resistance R1 of the electric circuit 2 is larger or smaller than the resistance r, and if the resistance is smaller than the resistance r, an alarm signal is generated (not shown) and the insulation deterioration is monitored. You can do it.

The same applies to the electric circuit 4. If the switch SW1 is first turned off and the switch SW2 is turned on, the leakage current flowing through the resistor r at this time corresponds to a value obtained by converting C2 in the equation into C2 + C0. The difference from A0 already stored in the capacitor C0 is taken by the subtracter DIF, and the sign of the output of the subtractor is determined as in the case of the circuit 2 so that the ground insulation resistance R2 of the circuit 4 becomes the resistance r2. Obviously, it can be determined whether it is larger or smaller.

That is, insulation insulation can be monitored by operating the switches SW1, 2, and 3 sequentially as described above.

As described above, if the value of the resistance r is used as a reference value for generating an insulation deterioration alarm, it can be easily determined whether or not the ungrounded electric circuits 2 and 4 have a predetermined insulation resistance value r or more as described above. I understand.

For example, when the insulation resistance of each of the electric circuits 2 and 4 is 100 KΩ or less, and when it is desired to issue a deterioration alarm, the value of the resistance r is changed.
It should be 100KΩ.

Although the neutral point 3 is taken from the intermediate tap on the secondary side of the transformer 1 in the embodiment of FIG. 1, the present invention is not limited to this. The selection of the neutral point can be variously modified, for example, by inserting and setting the neutral point as the neutral point.

In the above description, the synchronous detector is used to detect the effective component. However, it is clear that the detection can be performed using another method (for example, Japanese Patent Application No. 59-18994). Can be modified as follows.

That is, as is clear from the equation, for example, when r = R1 with respect to the electric circuit 2, A0 = A1, so that the switch SW1 is turned on,
The effective component A1 obtained at the output of the synchronous detector M when turned off is
A1A0 automatically adjusts the value of resistor r so that A0 becomes equal.
If the value of the resistance r at this time is r1, it becomes r1R1, and the insulation resistance R1 of the electric circuit 2 can be measured. Similarly, for the electric circuit 4, the resistance r is automatically adjusted so that the output of the synchronous detector M when the switch SW2 is turned on and off is equalized. If the resistance r at this time is r2, it becomes r2R2, and the insulation of the electric circuit 4 is obtained. The resistance R2 can be measured. As described above, the means for automatically adjusting the resistance r can be easily realized.

In the method of the present invention, for example, when the switch SW1 is turned off → on, the ground capacitance of the electric circuit 2 changes from C1 → C1 + C0, but the electric circuit and the load device are switched while the switch SW1 is switched from off to on. It is also expected that the above-mentioned insulation resistance to ground and electrostatic capacitance to ground slightly fluctuate. In order to solve this, reliable measurement of insulation can be performed by performing several measurements instead of one measurement, and then performing an insulation deterioration alarm or insulation resistance measurement based on the results.

In the description of the present invention, the detection of the leakage current flowing through the resistor r is performed by using the voltage between both ends of the resistor r. However, other methods, for example, a zero-phase voltage is applied to the ground line grounded from the neutral point to the ground via the resistor r Even when a current transformer is connected, a leakage current flowing through the resistor r can be extracted in the same manner as that shown in this embodiment.

Furthermore, although the values of the capacitors connected to the switches SW1 and SW2 are both described as C0, it is apparent that the values are not limited to C0 and may be different from each other.

(Effects of the Invention) According to the present invention, the insulation deterioration is not determined based on the impedance between the ungrounded electric circuit and the ground unlike the related art, but the true insulation resistance deterioration is accurately determined for each electric circuit. The device can be configured at low cost because it does not require an auxiliary power supply for measurement, and is extremely effective in detecting insulation deterioration of ungrounded electric circuits used in communication equipment, electronic equipment, broadcasting equipment, medical equipment, etc. It is a target.

[Brief description of the drawings]

 FIG. 1 is a block diagram showing one embodiment of the present invention. A: Amplifier, M: Synchronous detector, DIF: Subtractor, CP: Comparator

Claims (2)

(57) [Claims] A resistor is inserted between a neutral point of an ungrounded circuit and the ground, and a first effective component in a leakage current flowing through the resistor is provided.
When a predetermined capacitor is inserted between one of the ungrounded circuits and the ground, the magnitude of the leakage current flowing through the resistor is compared with the second effective component to determine the ground insulation resistance of the one circuit. A method of monitoring insulation deterioration of an ungrounded electric circuit, characterized by determining deterioration of a circuit. 2. The insulation of an ungrounded circuit, wherein the ground insulation resistance of the one circuit is measured by adjusting the value of the resistor so that the first and second effective components are equal to each other. Deterioration monitoring method.