JPS5836195Y2 - Electric circuit insulation resistance monitoring device - Google Patents

Description

[Detailed Description of the Invention] This invention relates to an insulation resistance monitoring device that detects when the insulation resistance of a power distribution line has fallen below a preset value.

An example of this type of device is shown in FIG. 1, for example.

That is, in Fig. 1, 1, 2.3 are distribution lines (hereinafter referred to as electric lines), 4 is a transformer, and between the low voltage side neutral point of this transformer 4 and the ground, there is a current limiting resistor 5 and a diode. 6 and a detection device 7 are connected in series.

7A is a detection resistor of the detection device 7, and 7B is a voltage amplification operating device.

8 is a voltage amplification operating device 7B and a power transformer serving as a power source;
11, 12, and 13 are stray capacitances to the ground (hereinafter referred to as stray capacitances) generated corresponding to the electric lines 1, 2, and 3.

Next, to explain the operation of the device with the above configuration, when the circuits 1, 2.3 of each phase are normal, no ground fault current flows between the circuits 1, 2.3 and the ground, but when the circuits 1, 2.3 and the ground Since stray capacitances 11, 12, and 13 usually exist between the ground and the ground, a charging current may flow.

If the stray capacitances 11, 12 and 13 of each phase are balanced, this charging current will cancel and the vector sum will be zero and will not flow, but if the stray capacitances 11, 12
When 13 is unbalanced, the charging current flows to the neutral point of the transformer 4 via the detection resistor 7A, the diode 6, and the current limiting resistor 5 via the point B.

The current flowing at this time is rectified by the diode 6 and charges the stray capacitances 11, 12.13, and when the charging is completed, the discharge circuit is blocked by the diode 6, so the stray capacitances 11, 12.13 are in a charged state. Therefore, charging current no longer flows.

Therefore, a voltage signal due to the charging current appears temporarily across the detection resistor 7A, but after that, the voltage signal disappears and is no longer affected by the stray capacitances 11° and 12.13 of the electrical circuits 1 and 2.3. ing.

Next, if the insulation of the electrical path 3 deteriorates and a ground fault occurs at point A, the ground fault current becomes the discharge current of the stray capacitances 11, 12.13, and points A and C (of the stray capacitances 11, 12.13 It flows through the stray capacitors 11, 12, and 13 through the ground point).

Therefore, a current that charges the stray capacitances 11, 12, and 13 flows through the points C and B, the detection resistor 7A, the diode 6, and the current limiting resistor 5 during a certain section of each cycle of the power supply frequency.

This steady charging current causes a voltage signal to appear across the detection resistor 7A, and this voltage signal is detected by the voltage amplification actuator 7B to warn of deterioration in the insulation of the electrical circuits 1, 2.3.

In order to make it easier to understand the device having the above configuration, an equivalent circuit is shown as shown in FIG.

That is, C is a composite stray capacitance and is expressed as below.

CzCo+Cu+Cu mmmeaemHaHa@@
@ (1) C11 - Capacitance C1 of stray capacitance O - Capacitance C13 of stray capacitance 0 - Capacitance method of stray capacitance (to), R is the insulation resistance of the composite circuit is expressed as below.

R1-・Insulation resistance of the electric path (1) R2・-・Insulation resistance of the electric path (2) R3・Insulation resistance of the electric path (3) The voltage EN of the power supply 15 is the ground wire cut off at point B in Figure 1. It is the voltage that appears between the earth and the neutral point of the electric circuit when

In the above equation (3), EU: Phase voltage of U phase YU: Admittance of U phase (phase of electric circuit (B)) to the ground, YvFujwcH+- 11 Yy: Phase voltage of phase V (phase of electric circuit (■)) to the ground. The admittance to the ground is Yy = jw C12+-12 Yw: The admittance of the W phase ([path (2) phase) to the ground] Yw = = jWcts ” = In this equivalent circuit, if the insulation resistance R of the electrical circuit is sufficient When it is large, the stray capacitance C does not discharge, so the charging current ■ is zero. However, when the insulation resistance R of the circuit decreases, the charge of the stray capacitance C is discharged through the resistor R, so the voltage across the stray capacitance C increases .

falls below the piece value of EN as shown in Figure 6, and the charging current ■ for each cycle of the power supply frequency.

flows. This charging current■.

and discharge current■. There is the following relationship between them.

That is, The integral value of Ic for one cycle (amount of charge) 2■.

Integral value of 1 cycle (discharged charge amount) This is also the following relationship.

Average value of Ic” Average value of ID Also, the discharge current ■.

is 11. ) Average value = Average value of 7° In addition, the voltage V.

The relationship between the voltage EN and the voltage EN is uniquely determined by the circuit specifyer CXR.

■・Effective value =, (.

R) From the relationship above the effective value of EN, the charging current Ic flowing through the detection device 7,
The insulation resistance R between the electric circuit and the ground has the following relationship, and if there is no temporal change in the voltage EN and stray capacitance C, the charging current I
By detecting the magnitude of C, it was possible to know the decrease in insulation resistance R.

That is, the average value of ■・=8・0 effective value ・/(CR) However, as mentioned in the above explanation, the voltage EN and the function 1 are both functions of the mutual stray capacitance C, and the stray Since it is affected by the capacitance C, the sensitivity of the detection device 7 may be set for each circuit, or
It cannot be used where there are fluctuations in the stray capacitance C, and for these reasons, it has been difficult to improve the detection accuracy.

This idea was made to eliminate the above-mentioned drawbacks, and by inserting a capacitor with a capacitance approximately 10 times the stray capacitance in parallel with the stray capacitance of the circuit, the circuit of each phase can be improved. It is an object of the present invention to provide a device that can accurately detect the insulation resistance of an electric circuit by reducing the influence of the stray capacitance even if the stray capacitance changes somewhat over time.

An embodiment of this invention will be described below with reference to FIGS. 3 and 4.

In Fig. 3, 1, 2, and 3 are distribution lines (hereinafter referred to as electric lines), 4 is a transformer, 5 is a current limiting resistor, 6 is a diode, 7 is a detection device, 7A is a detection resistor, and 7B is a average value detection type voltage amplification operating device; 8 is a power supply transformer; 11;
12.13 is floating capacitance to ground (hereinafter referred to as stray capacitance)
These are all the same as shown in FIG. 1, including connection relationships.

A capacitor 14 is the gist of this invention, and is located only between the electric line 3 and the ground, and is inserted in parallel with the stray capacitances 11, 12, and 13.

Note that FIG. 4 shows an equivalent circuit, which is the same as the equivalent circuit shown in FIG. 2 except that a capacitor 14 is inserted.

Next, to explain the operation of the device of this invention, the fourth
In the equivalent circuit shown in the figure, when the insulation of the electric path is good, that is, when the insulation resistance R is very large, the stray capacitance C is charged with direct current rectified by the diode 6.

Container 14 is also charged in the same way. At this time, since a charging current flows, a voltage signal appears for a short time at both ends of the detection resistor 7A.

However, since the value of the insulation resistance R is large, the discharge time constant becomes thick, so the stray capacitance C and the capacitor 14 are not discharged but remain charged, and no charging current flows thereafter.

Next, when the insulation condition of the electrical circuit deteriorates and the value of the insulation resistance R decreases to about several tens of ohms with respect to the ground, the discharge time constant R
The value of XC becomes small and charging and discharging are repeated.

This can be explained using the equivalent circuit shown in FIG. 4. Since the capacitor 14 is connected to only one phase, the electric path becomes unbalanced with respect to the ground, and the value of the voltage EN is determined by the above equation (1) and C
From the relationship of engineering + C12 + C13<C14, IE
, N":"EU, and the power supply voltage and the phase voltage are approximately equal.

Also, the voltage ■.

Since the capacitor 14 is fixed, the relationship between the voltage EN and the voltage EN is determined only by the value of the insulation resistance R, and the 7°0 average value -4=f(C・4・R) is the effective value of EN. The charging current Ic is calculated from: Average value of Ic = Effective value of power supply phase voltage EU , (.

,4. R), which is uniquely determined only by the insulation resistance R of the electric circuit.

This charging current■. flows through the detection resistor 7A and generates a voltage signal across it.

Therefore, by detecting this voltage signal with the average value detection type voltage amplification operating device 7B, it is possible to accurately grasp the state of insulation deterioration of the electric circuits 1, 2.3.

In the above embodiment, the capacitor 4 is inserted only between the electric line 3 and the ground, but it is clear that the same effect can be obtained even if the capacitor 4 is inserted only between the electric line 1 or 2 and the ground.

In addition, a current limiting resistor 5, a diode 6, and a detection device 7 were inserted between the low voltage side neutral point of the transformer 4 and the ground.
As shown in the figure, each phase has current limiting resistors 5a, 5b,
5C and inserting a diode 6 and a detection device 7 between the neutral point and the ground.

Furthermore, even if the detection device 7 is simply a highly sensitive DC ammeter,
Since it indicates the average value, the current flowing through the insulation resistance R can be checked.

Further, the voltage amplification operating device 7 in the embodiment shown in FIG.
Even if a DC voltmeter is used as a substitute for B, the current flowing through the insulation resistance R can be checked because it indicates the average value.

As described above, according to this invention, a current limiting resistor, a diode, and an average value detection type detector are connected in series between the neutral point of the electric circuit and the earth, and the electric current limiting resistor, a diode, and an average value detection type detector are connected in series, and the electric current limiting resistor, a diode, and an average value detection type detector are connected in series with each other. Since a capacitor is inserted only in one wire, even if the insulation resistance of the electrical circuit decreases and a ground fault occurs, there will be no effect due to stray capacitance, and therefore the device can accurately detect the state in which the insulation resistance of the electrical circuit has decreased. becomes.

[Brief explanation of drawings]

Figure 1 is a circuit configuration diagram of a conventional device, Figure 2 is its equivalent circuit diagram, Figure 3 is a circuit diagram of a device showing an embodiment of this invention, and Figure 4 is its equivalent circuit diagram. , FIG. 5 is a circuit configuration diagram of another embodiment, and FIG. 6 is a voltage and current waveform diagram for explaining the operation. In the figure, 1, 2, 3 are electric circuits, 5 is a current limiting resistor, 6 is a diode, 7 is an average value detection type detection device, 7A is a detection resistance voltage, 7B is an average value detection type voltage amplification operating device, 11,
12 and 13 are floating capacitances, and 14 is a capacitor. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (5)

[Scope of utility model registration request] (1) A current-limiting resistor and a rectifier connected in series between the neutral point of the electric path and the ground, and a detection device that detects the average value of the ground fault current corresponding to the insulation resistance between the electric path and the earth; A capacitor is connected between only one wire of the electric circuit and the ground, and the electric circuit is made unbalanced with respect to the earth by the capacitor, so that the stray capacitance generated between the electric circuit and the earth can be ignored by the capacitor. A circuit insulation resistance monitoring device characterized by: (2) A circuit insulation resistance monitoring device according to claim 1, wherein the neutral point of the circuit is formed by connecting a current limiting resistor to each phase of the circuit. (3) The circuit insulation resistance monitoring device according to claim 1 or 2, wherein the detection device is a DC ammeter. (4) Claims 1 or 2 for registration of a utility model, characterized in that the detection device is composed of a detection resistor and a DC voltmeter connected in parallel to the detection resistor.
The circuit insulation resistance monitoring device described in Section 1. (5) Utility model registration claim 1, characterized in that the detection device is constituted by a detection resistor and an average value detection type voltage amplification operating device connected in parallel to the detection resistor. Or the circuit insulation resistance monitoring device according to item 2.