JP2997527B2 - Ground voltage detection circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a ground voltage detection circuit.

[Conventional technology]

Conventionally, there is a circuit shown in FIG. 11 as a ground voltage detecting circuit provided in a switch. This detection circuit divides the voltage of both distribution lines L into ceramic capacitors C1 to C3 and film capacitors C4 to C6 for each phase (capacity ratio of each other is about
1: 1000), and impedance-converted by the voltage transformer 1 before being input to the slave station 2. And
The slave station 2 determines the ground voltage and its phase based on the input voltage, and determines, for example, whether or not the switch is turned on, the voltage drop of the system, the presence or absence of a disconnection, and the like at the loop point.

Further, as shown in FIG. 12, the above-described ground voltage detecting circuit is also used for the ground fault relay 3, and the ground fault relay 3 is connected to the zero-phase voltage detected by the ground voltage detecting circuit and the current transformer. The switch 5 is tripped by determining the direction of the ground fault based on the zero-phase current detected at 4.

[Problems to be solved by the invention]

However, as is well known, ceramic capacitor C1
~ C3 has a large variation of about ± 10%,
As a result, the error between the voltages detected by the ceramic capacitors C1 to C3 and the film capacitors C4 to C6 becomes very large. Therefore, there is a problem that only a rough determination result can be obtained with the switch installed at the former loop point.

In the latter, two or three types of film capacitors C4 to C6 having different capacitances are prepared in order to correct variations in the ceramic capacitors C1 to C3. C4-C6
The film capacitors C4 to C6 are selected and used so that the capacitance of the film capacitors C4 and C4 has a desired ratio. Therefore, there is a problem that the work of assembling the detection circuit is very complicated.

Further, as shown in FIG.
Since the temperature characteristics of C1 to C3 and the film capacitors C4 to C6 generally show the opposite tendency, an error occurs in the partial pressure due to the temperature change.
Has become one. Therefore, this film capacitor C4 ~
Although it is conceivable to change C6 to ceramic capacitors C1 to C3 to make the temperature characteristics the same, it is conceivable that the capacitance required for the film capacitors C4 to C6 is extremely large as described above, so the current ceramic capacitors This cannot be achieved with C1 to C3.

An object of the present invention is to achieve high detection accuracy by correcting an error in the capacitance of a capacitor, and to easily assemble without requiring complicated work such as selection of a capacitor. An object of the present invention is to provide a ground voltage detection circuit that can realize high detection accuracy by correcting an error caused by a temperature change.

[Means for solving the problem]

Also, the present invention provides a ground voltage detection circuit in which a voltage of an alternating current flowing through an electric wire is divided by a pair of capacitors, wherein at least one of the capacitors is connected in parallel with a variable resistor or a variable capacitor and a thermistor, respectively. This is a summary of a voltage detection circuit.

[Action]

In the present invention, if an error occurs in the capacitance of any of the capacitors, an error also occurs in the output voltage. At this time, the output voltage can be adjusted to an appropriate value by adjusting the resistance value of the variable resistor and the capacitance of the capacitor.

When the temperature changes, an error occurs in the output voltage due to the difference in the temperature characteristics of the two capacitors. At this time, the resistance value of the thermistor changes with the temperature change, and the error of the output voltage is corrected.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS.

The ground voltage detection circuit according to the present embodiment has almost the same configuration as the detection circuit described in the related art, and is different in that a compensation circuit is added to each phase. Therefore, the configuration of the compensation circuit will be described for one phase.

As shown in FIG. 1, a ceramic capacitor C1 and a film capacitor C4 are connected in series to a distribution line L as an electric wire, and a pair of variable resistors R1 and R2 connected in series are connected to the film capacitor C4 in parallel. I have. One resistor R1
Is connected in parallel with a negative thermistor NTC, and the other resistor R
The voltage at both ends of the output terminal 2 is output to the slave station 2 (shown in FIG. 11) and the ground fault relay 3 (shown in FIG. 12) as the output voltage | v |. As shown in FIG. 3, the negative characteristic thermistor NTC has a property that its resistance value decreases with an increase in temperature.

Next, the operation of the above-described ground voltage detection circuit will be described.

The ground voltage detection circuit of this embodiment can be replaced with an equivalent circuit shown in FIG. First, the procedure for adjusting the phase difference θ of the output voltage | v | with respect to the input voltage | V | (ground voltage value applied to the distribution line L) in this equivalent circuit will be described. This phase difference θ is expressed by the following equation. You.

Here, f is the frequency of the alternating current flowing through the distribution line L, R1 'is the combined resistance value of the variable resistor R1 and the negative characteristic thermistor NTC, R
2 'is the resistance value of the variable resistor R2, C1 and C4 are capacitors
These are the capacitances of C1 and C4.

Now, assuming that C1 → large, θ becomes small. At this time, if R1 '+ R2' is reduced, the error of C1 is absorbed and θ
Can be adjusted to an appropriate value, that is, the phase difference θ of each phase can be adjusted to a value shifted from each other by 120 °. Conversely, when C1 → small, θ can be adjusted to an appropriate value by increasing R1 ′ + R2 ′. Therefore, R1 ′ + R2 ′ is increased or decreased by increasing or decreasing the sum of the resistance values of the variable resistors R1 and R2, and as a result, the phase difference θ can be adjusted to an appropriate value.

Or, a procedure for correcting the output power | v | caused by an error in the capacitance C1 of the ceramic capacitor C1 will be described. The output voltage | v | of this detection circuit is expressed by the following equation.

Here, when R1 ′ + R2 ′ = constant conditions, each value other than C1 is replaced by A, B, D as a constant, Becomes

In the above equation, A = C1, B = C4, D = 1 / ｛2πf (R
1 ′ + R2 ′)｝ ² .

Assuming now that the capacitance C1 is large, Becomes small and the output voltage | v | becomes large. At this time, if the ratio of R2 'to R1' is reduced, R2 '/ (R1' + R2 ') increases, and the error of C1 is corrected, so that the output voltage v can be adjusted to an appropriate value. Conversely, when the capacitance C1 is smaller, the ratio of R2 'to R1' is increased to increase R2 '.
/ (R1 '+ R2') becomes smaller, and the output voltage | v | can be adjusted to an appropriate value. Therefore, by increasing or decreasing the ratio between the resistance values of the variable resistors R1 and R2, the ratio between R1 'and R2' is increased or decreased, and as a result, the output voltage | v | can be adjusted to an appropriate value. During this adjustment, the phase difference θ
It is necessary to keep R1 '+ R2' at a constant value in order to keep the value at an appropriate value.

On the other hand, as shown in FIG.
As the temperature rises, the capacitance C1 decreases and its impedance increases, and conversely, the film capacitor C4 increases its capacitance C4 and decreases its impedance as the temperature rises. As a result, when the temperature rises, the output voltage | v | of the detection circuit decreases. At this time, the resistance of the negative characteristic thermistor NTC decreases, so that the decrease of the output voltage | v |
The fluctuation of the output voltage v due to the temperature change is prevented.

Note that the compensating circuits added to the other two phases have the same configuration. Therefore, similarly, the phase adjustment of the output voltage | v | and the output voltage | v |
And the output voltage | v | is corrected by the temperature change.

As described above, the ground voltage detection circuit according to the present embodiment includes the variable resistor
By changing the ratio of the resistance values of R1 and R2, the error of the capacitance C1 of the ceramic capacitor C1 can be corrected, and the output voltage | v | can be adjusted to an appropriate value. Therefore, when this detection circuit is used for a switch or a ground fault relay, an accurate determination result can be obtained. Also, when assembling the detection circuit, the variable resistors R1, R2
Simply adjust the resistance of the ceramic capacitor
The error of C1 can be corrected.

Also, ceramic capacitor C1 and film capacitor C4
The difference in temperature characteristics between the two is corrected by the negative-characteristic thermistor NTC, so that an accurate output voltage | v | can always be obtained regardless of temperature changes.

The present invention is not limited to the above embodiment,
For example, it may be configured as described below.

(1) As shown in FIG. 5, a positive characteristic thermistor PTC is connected in parallel to the variable resistor R2 instead of the negative characteristic thermistor NTC. As shown in FIG. 3, since the resistance of the positive temperature coefficient thermistor PTC increases as the temperature rises, the decrease in the output voltage | v | due to the temperature rise can be corrected in the same manner as in the above embodiment.

(2) As shown in FIG. 6, a negative thermistor NTC is connected in series to the variable resistor R1. Similarly to the above embodiment, the resistance value of the negative temperature coefficient thermistor NTC decreases as the temperature rises, and the decrease in the output voltage | v | can be corrected.

(3) As shown in FIG. 7, a positive temperature coefficient thermistor PTC is connected in series to the variable resistor R2. Like the circuit of the above one item,
As the temperature rises, the resistance value of the positive temperature coefficient thermistor PTC increases and the decrease in the output voltage | v | can be corrected.

(4) As shown in FIG. 8, the negative characteristic thermistor NTC is connected in parallel to the variable resistor R1, and the positive characteristic thermistor PTC is connected in parallel to the variable resistor R2. Also in this case, the decrease in the output voltage | v | can be corrected.

(5) As shown in FIG. 9, the negative characteristic thermistor NTC is connected in series to the variable resistor R1, and the positive characteristic thermistor PTC is connected in series to the variable resistor R2. Also in this case, the decrease in the output voltage | v | can be corrected.

(6) As shown in FIG. 10, a variable resistor R1 and a positive temperature coefficient thermistor PTC are connected in parallel to the film capacitor C4. Even with such a configuration, an error in the capacitance of the ceramic capacitor C1 can be corrected by the variable resistor R1, and an error due to a temperature change can be corrected by the positive temperature coefficient thermistor PTC.

Further, in the above embodiment, the error caused by the temperature change is corrected by the negative characteristic thermistor NTC. However, the correction is not necessarily performed, and the thermistor NTC may be omitted.

Further, in the above embodiment, the variable resistors R1 and R2 are connected in series, but instead, a pair of capacitors having variable capacitance may be connected in series. Even with such a configuration, an error in the capacitance of the ceramic capacitor C1 can be corrected.

〔The invention's effect〕

As described in detail above, according to the ground voltage detection circuit of the present invention, it is possible to correct the error of the capacitance of the capacitor to achieve high detection accuracy and to perform complicated operations such as selection of the capacitor. It can be easily assembled without
Further, an excellent effect that a high detection accuracy can be realized by correcting an error due to a temperature change is exhibited.

[Brief description of the drawings]

1 to 4 show a ground voltage detecting circuit of an embodiment, FIG. 1 is an electric circuit diagram showing one phase of the detecting circuit, FIG. 2 is an electric circuit diagram showing an equivalent circuit thereof, and FIG. 3 is a thermistor FIG. 4 is a diagram showing temperature characteristics of a capacitor;
5 to 10 are electric circuit diagrams showing one phase of another example of the earth voltage detecting circuit, FIG. 11 is an electric circuit diagram showing a switch provided with a conventional earth voltage detecting circuit, and FIG. FIG. 2 is an electric circuit diagram showing a ground fault relay provided with the ground voltage detection circuit of FIG. L is a distribution line as an electric wire, C1 is a ceramic capacitor,
C4 is a film capacitor, R1 and R2 are variable resistors, NTC is a negative thermistor, and PTC is a positive thermistor.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01R 15/06

Claims (1)

(57) [Claims] In a ground voltage detection circuit wherein a voltage of an alternating current flowing through an electric wire (L) is divided by a pair of capacitors (C1, C4), a variable resistor (R1, R1) is connected to at least one of the capacitors (C4). R
2) A ground voltage detection circuit characterized by connecting a variable capacitor and a thermistor (NTC, PTC) in parallel.