JPH075421Y2 - High voltage measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a device for measuring a high voltage such as a voltage of a transmission line.

(Prior Art) In order to measure the voltage of a transmission line or the like, a voltage divider using a capacitor is usually used in the past. As shown in FIG. 4, capacitors C ₁₁ and C ₁₂ are connected between the transmission line L and the ground to divide the ground voltage V ₀ of the transmission line L into the voltages V ₁ and V _2. The voltage V ₂ is measured by the meter M.

According to such a configuration, for example, when the transmission line L is a 77KV circuit, the ground voltage V ₀ is about 45KV, and the voltage V ₂ is preferably 100V or less for the convenience of measurement.
Generally, the ratio of V ₁ and V ₂ is 1/1000.

To satisfy this relationship, capacitors C ₁₁ and C ₁₂
As a result, it is necessary to use a capacitor having a capacitance of 2000 pF and 2 μF. That is, a low voltage, large capacity capacitor is required as the capacitor C ₁₂ .

On the other hand, it is considered to use a ceramic capacitor as the capacitor C ₁₁ for such measurement.
However, the electrostatic capacity of a ceramic capacitor may change depending on the voltage, so even for capacitor C ₁₂ ,
It is necessary to use a dielectric whose capacitance changes similarly.

However, capacitor C that requires low voltage and large capacity
Constructing ₁₂ with a sintered ceramic capacitor is extremely difficult. That is, in order to increase the capacity, a thin ceramic may be used, but at present, it is extremely difficult to fire a ceramic single plate having a thickness of 1 mm or less and a large area.

It is conceivable to use a ceramic having a small area in order to increase the capacity, but in that case, a large number of capacitors are connected in parallel, which increases the number of working steps and is not preferable. It is also difficult to obtain a dielectric capacitor C ₁₂ that exhibits the same characteristics as the capacitor C ₁₁ .

(Problems to be solved by the device) This device enables measurement even if a capacitor whose capacitance changes with voltage is used, without using other capacitors with similar characteristics. The purpose is to

(Means for Solving the Problems) In this invention, a first capacitor whose electrostatic capacity changes with voltage and a second capacitor whose electrostatic capacity does not change with voltage are provided on different sides, and another A bridge circuit is formed by connecting impedance elements such as resistors and capacitors for measurement to each side, and between the connection point of the side to which the first and second capacitors are connected and the connection point opposite thereto. In addition, the voltage to be measured is measured from the change rate of the capacitance of the first capacitor when the voltage to be measured is applied and the bridge circuit is balanced.

(Embodiment) This invention will be described with reference to FIG. The capacitor C ₁ is
It has a characteristic that its capacitance changes with voltage, and is specifically composed of a ceramic capacitor. It is desirable that this capacitor has a capacitance that reproducibly changes with respect to voltage. For example, as shown in FIG. 3, a capacitor having a characteristic that the rate of change of capacitance with respect to voltage is always the same is used.

As the capacitor C _{2, a} capacitor whose characteristic does not change depending on the voltage is used. When measuring the voltage of a normal transmission line, a capacitor having a capacitance of 50 to 100 pF is sufficient, so that a capacitor using SF ₆ gas as a dielectric material may be used.

One end of each of the capacitors C ₁ and C ₂ is connected to the power transmission line L. The other ends A and B are the resistances (variable resistances) R ₃ for measurement.
And to the ground via resistor R ₄ . A measuring capacitor C ₄ is connected in parallel with the resistor R ₄ . A galvanometer G is connected between the other ends A and B of the capacitors C ₁ and C ₂ .

The equivalent circuit of the circuit of FIG. 1 is a general bridge circuit BC as shown in FIG. In the figure, R ₁ is the capacitor C ₁
Is the loss (tan δ) of the dielectric of The impedance of each side is expressed as follows.

Assuming that the bridge circuit BC is balanced by adjusting the resistance R ₃ , from the balanced condition, Z ₁ · Z ₄ = Z ₂ · Z ₃ If this is rearranged, jωC ₂ R ₁ R ₄ = R ₃ (1 + jωC ₁ R ₁ ) (1 + jωC ₄ R ₄ ) = R ₃ (1-ω ² C ₁ R ₁ C ₄ R ₄ ) + jω (C ₁ R ₁ + C ₄ R ₄ ) R ₃ Therefore, by comparing the real and imaginary parts, ω ² C ₁ R ₁ C ₄ R ₄ −1 = 0 C ₂ R ₁ R ₄ = (C ₁ R ₁ + C ₄ R ₄ ) R ₃ Here so , More, ωC ₄ R ₄ = tanδ, more, Substituting ′ and ′ into Eliminating ω R ₁ using From this, C ₁ is calculated as in the following equation.

Here as above However, the target here is the commercial frequency, and at 50-60Hz, tanδ is about 0.02 as can be understood from the tanδ-frequency characteristics of the ceramic capacitor shown in Fig. 5. And the error is at most about 0.04%, so the above equation is approximately However, for C ₂ , it is desirable to use a capacitor with sufficiently small tan δ, and in that sense, SF ₆
A gas condenser is suitable.

Assuming that the equilibrium condition is satisfied when a certain voltage is applied to the bridge circuit BC, C ₁ can be measured from the above equation. When the capacitor C ₁ is a ceramic capacitor, its capacitance has a voltage characteristic, and the voltage characteristic has reproducibility. Since the capacitor C ₂ and the resistor R ₄ are constants, the capacitor at each voltage is 1V.
The change ratio of the capacitance of C ₁ can be obtained in advance as shown in FIG.

In this way, if the change ratio of the electrostatic capacity of each voltage to the electrostatic capacity of the capacitor C ₁ when the voltage of 1 V is applied to the bridge circuit BC is obtained in advance as shown in FIG. By obtaining the change ratio of the electrostatic capacitance of the capacitor when the voltage is applied and comparing it with the characteristic curve of FIG. 3, the voltage of the measurement object applied to the bridge circuit BC at that time can be known. .

For example, if the bridge circuit BC has C ₂ = 50 pF and R ₄ = 200 Ω, and the resistance R ₃ is 10 Ω when a voltage of 1 V is applied to the bridge circuit, the capacitor C ₁
According to the previous formula, the capacitance of is C ₁ = C ₂ · R ₄ / R ₃ = 50 · 200/10 = 1000 (pF).

Then, when a voltage Va of a certain object to be measured is applied to the bridge circuit BC and the resistance R ₃ is adjusted in order to balance the bridge circuit BC, if it is balanced at 9.52Ω, the capacitor C ₁ ′ at this time is The capacitance is C ₁ ′ = C ₂ · R ₄ / R ₃ = 50 · 200 / 9.52 ≈ 1050.4 (pF).

Therefore, the capacitance change ratio when the voltage Va to be measured is applied to the capacitance of the capacitor C ₁ when the applied voltage is 1 V is C ₁ ′ / C ₁ = 1.05, and the characteristic curve of FIG. Voltage Va = 1000
You can ask for V.

Note that the above explanation was about the direct measurement of the voltage, but if the bridge circuit BC is balanced in a steady state, the balance breaks when the measured voltage changes, and the galvanometer G swings. . From now on, it becomes possible to detect the fluctuation of the voltage.

(Effects of the Invention) As described in detail above, according to the present invention, it becomes possible to measure the voltage by using a capacitor whose electrostatic capacity changes according to the voltage, and moreover, the low voltage side as in the conventional case. Therefore, the difficulty such as when a large-capacity capacitor is realized by a ceramic capacitor does not occur here.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is an equivalent circuit diagram of FIG. 1, FIG. 3 is a characteristic diagram of a capacitor, and FIG.
Figure is the circuit diagram of the conventional example, and Figure 5 is the ceramic capacitor.
It is a tan (delta) -frequency characteristic figure. C ₁ , C ₂ , ... Capacitor, R ₃ , R ₄ ... Resistor, BC ... Bridge circuit, G ... Galvanometer,

Claims (1)

[Scope of utility model registration request] 1. An impedance element for measurement, wherein a first capacitor whose capacitance changes with voltage and a second capacitor whose capacitance does not change with voltage are provided on different sides, and on each of the other sides. A bridge circuit in which a voltage to be measured is applied between a connection point on the side to which the first and second capacitors are connected and a connection point opposite thereto, and the bridge circuit is connected. A high-voltage measuring device obtained by measuring the voltage of the measurement target from the change rate of the capacitance of the first capacitor when the two are balanced.