JP2000187045A - Voltage transformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a voltage transformer which can correctly measure the voltage and is safe. SOLUTION: Electrode plates 3 are placed opposite to the main circuits 2 in a container 1 of an electric apparatus. Capacitance C1 is generated between the main circuit 2 and the electrode plate 3. A charging current flowing to the capacitance C1 is measured by a current transformer 14, and a voltage impressed to the main circuit 2 is calculated from the charging current. Since the electrode plate 3 is fixed to a ground potential, even if a capacitance or resistance is present between a measurement circuit and the ground, measurement values are prevented from being influenced and a high voltage is prevented from being generated to the electrode plate 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage transformer for measuring a voltage of a main circuit in electric equipment.

[0002]

2. Description of the Related Art A conventional voltage transformer will be described with reference to FIG. FIG. 1 shows a three-phase gas insulated switchgear (hereinafter, referred to as a “gaseous switchgear”)
"GIS". 2) shows the configuration of the voltage transformer. In a cylindrical metal container 1, three-phase buses 2, 2, 2 are arranged. In the container 1, an electrode plate 3 is provided so as to be insulated from the container 1 so as to face the bus 2 of each phase. The distance between the electrode plate 3 and the busbar 2 is a ₁ , and the electrode plate 3 and the container 1
The distance between the a _2. The electrode plate 3 of each phase is drawn out to the outside through the drawer 4, and is connected to the determination display 6 by a cable 5.

Here, the first plate is provided between the electrode plate 3 and the busbar 2.
Is generated, and a second capacitor C2 is formed between the electrode plate 3 and the container 1. Further, a third capacitor C3 is formed between the cable 5 and the ground. Therefore, the voltage V _{2 of the} signal input to the determination display unit 6 (the voltage of the X part) is
If the voltage applied to the bus 2 is assumed to be V _1, the following equation.

V ₂ = V ₁ × C ₁ / (C ₁ + C ₂ + C ₃ ) where C ₃ = 1000 pF, C ₁ = 10 pF, C ₂ =
When _{100pF, V 2 = V 1/} 1000 becomes, V
_In the case of ₁ = 44.5 kV, it becomes about 45V. In the judgment display section 6, the input signal of each phase is supplied to the amplifier 7 and the A-D
The data is input to the CPU 9 via the converter 8. CPU 9
Calculate the applied voltage V ₁ of the bus 2 of each phase from the input signal,
A voltage is displayed on the display unit 11 via the interface 10. Also, the relay 12 is driven to output a contact output.

[0005]

In the above conventional voltage transformer [0005], the break in the cable 5 occurs, C ₃ = 0 becomes, since the _{V 1 = V 2 · 10/100,} 44 · 5k
In the case of V, a high voltage of 4.5 kV is induced in the electrode plate 3. Also, when the cable 5 is not connected, a high voltage is induced similarly to the above.

In order to prevent the generation of such a high voltage, it is necessary to shorten the distance a ₂ between the electrode plate 3 and the container 1 and to ensure insulation between the two. Therefore, the structure of the electrode plate becomes complicated and the shape becomes large. Further, the voltage of the X portion fluctuates by the influence of the capacitance C ₃ between the ground and the cable 5. For example, a cable of 100 pF / m
m, it becomes 2000pF, and 5m, 50
Since it is 0 pF, the voltage of the X section fluctuates. For this reason,
The present invention, which requires adjustment in the CPU 9 every time a cable to be used is changed, enables accurate voltage measurement, and
It is an object to provide a safe voltage transformer.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to achieve the above object. The voltage transformer according to the present invention is a voltage transformer for measuring a voltage of a main circuit arranged in a grounded container of an electric device, wherein the container is provided on an inner surface side of the container facing the main circuit. And a current transformer connected between the electrode and the ground for measuring a charging current flowing through a capacitive coupling between the main circuit and the electrode. .

According to the present invention, a capacitor is formed between the electrode plate and the main circuit. The current for charging the capacity is detected by the current transformer, and the voltage of the main circuit is calculated from the charging current. Here, since the electrode plate is grounded via a current transformer which is a low impedance load, no high voltage is generated on the electrode plate. Further, since there is no need to control the distance between the electrode plate and the container, the structure of the electrode plate can be simplified. Furthermore, between the electrode plate and the container of the electric equipment, and
Even if a large capacitance occurs between the cable and the ground,
Since the electrodes are grounded via a low-impedance load, fluctuations in charging current due to changes in cable capacity are small, and accurate voltage measurement can be performed.

In the present invention, the electric device has a multi-phase main circuit arranged in the grounding container, and the main circuit of each phase has a shield for suppressing induction from another phase. In this case, the electrode plate can be arranged on an inner surface of the cylindrical shield via an insulating layer. In this case, it is only necessary to dispose a thin electrode plate on the inner surface of the cylindrical shield with an insulating layer interposed therebetween, so that there is no increase in the size for securing the insulating dimensions, and the structure of the electrode plate is simplified. be able to.

[0010] The present invention further relates to a case where the electric device has a multi-phase main circuit arranged in the grounded container without a shield between the phases, and the current transformer is provided for each main circuit of each phase. In addition, the influence of the charging current induced from another phase can be eliminated. When a multi-phase main circuit exists in the same container without shielding between the phases, an electrode plate provided so as to be capacitively coupled to one phase may be capacitively coupled to the main circuit of another phase. Is configured. Therefore, even if an attempt is made to measure the voltage of the main circuit of the phase by measuring the charging current, an error occurs due to the influence of the charging current from another phase. On the other hand, by providing a winding through which the charging current of the other phase flows in the current transformer and winding it in the opposite direction, it is possible to cancel the influence of the capacitive coupling.

[0011]

Embodiments of the present invention will be described with reference to the drawings. (Embodiment 1) FIG. 2 is a diagram showing a configuration of a voltage transformer according to a first embodiment of the present invention. In a cylindrical metal container 1, three-phase buses 2, 2, and 2 of A phase, B phase, and C phase are arranged. The figure shows a cross section of the container 1 cut in the axial direction. An electrode plate 3 is provided in the container 1 so as to be insulated from the container 1 so as to face the bus 2 of each phase. The electrode plate 3 of each phase is drawn out to the outside through the drawer 4, and is grounded by the ground wire 13 for each phase. In the outer lead portion 4, the grounding line 13 is connected to the container 1 via a resistor R and a capacitor C _4. This resistance R and capacitance C ₄ are connected to ground line 1
3 prevents a high voltage from being generated in the electrode plate 3 when the wire is disconnected or not connected.

A current transformer 14 having a low impedance is provided for the ground line 13 of each phase. Also, a three-phase ground wire 1
3 is grounded by a common ground line 15. The current transformer 14 is also provided on the common ground line 15. In addition, B phase and C
Although the illustration of the secondary side circuit is omitted for the phase current transformer 14, it is configured in the same manner as the current transformer 14 shown in the figure. Here, a first capacitance C ₁ is generated between the electrode plate 3 and the bus bar 2, and a second capacitance C ₂ is formed between the electrode plate 3 and the container 1, as in the above-described conventional example. Is done. In addition, cable 5
Between the ground, the third capacitor C ₃ is formed. As described above, the capacitance C ₁ is formed between the electrode plate 3 of each phase and the main circuit 2, and the electrode plate 3 of each phase is grounded by the ground line 13, and the impedance of the low impedance CT can be ignored. , the ground line 13, equal charging current flows into the only capacitance C ₁ is present. Also, a common ground line 15
, A combined current of the three-phase charging current flows.

Each of the ground wires 13 and 15 constitutes a primary winding of each current transformer 14. Secondary winding 1 of each current transformer 14
The 6, the light emitting diode 17 is connected via a capacitor C _5. Further, the light emitting diode 17 has a resistor r
₅ , a DC power supply 18 is connected, and the light emitting diode 1
7, a bias current i ₀ is supplied. The light emitting diode 17
Although a high impedance is shown for a small current, by flowing the bias current i ₀ in this way, a low impedance is shown for a small current flowing through the secondary winding 16 of the current transformer 14. On the other hand, a CT for measuring a normal charging current on the order of μA generally requires a load of several kΩ.

In addition, by setting the light emitting diode 17 to have a low impedance, the impedance seen from the primary side of the current transformer 14 can be reduced. The charging current detected by the current transformer 14 is converted into light by the light emitting diode 17 and supplied to the determination display unit 6 by the optical fiber 19. In the judgment display section 6, each input signal is converted into an electric signal by the optical / electrical converter 20 and input to the CPU 9 via the amplifier 7 and the A / D converter 8.
The CPU 9 calculates the applied voltage of the bus 2 of each phase from the input signal. Here, since the charging current I is I = jωC ₁ × V ₁ , the voltage V ₁ applied to the bus 2 is I / ωC ₁
Can be obtained by In addition, according to the charging current obtained from the current transformers 14 of the A phase, the B phase, and the C phase, the applied voltage of each phase can be measured, and according to the charging current obtained from the common current transformer 14,
Zero phase voltage can be measured. The voltage waveform can be reproduced by connecting a current source that outputs the voltage in proportion to the output voltage of the optical / electrical converter, and flowing this current to an appropriate capacity load. According to this, distortion of the charging current due to harmonics other than the fundamental wave can be reproduced in the original voltage waveform.

The CPU 9 displays the calculated voltage value on the display unit 11 via the interface 10. If the calculated voltage value exceeds a predetermined value, the relay 12 is driven to output a contact output. According to this example, because a voltage measurement by detecting the charging current flowing into the capacitor C _1, the voltage measurement irrespective of the presence of the capacitor C _2, C ₃ is performed.

In this embodiment, since each electrode plate 3 is grounded via a current transformer 14 having a low impedance, the potential is fixed at a low voltage. Therefore, even when the ground line 13 is broken or when the ground line 13 is not connected, no high voltage is generated on the electrode plate 13. For example, the capacitance C ₁ is 10 pF, the resistance R is 1 kΩ, the applied voltage of the bus 2 is 44.5 kV, and the frequency is 5
At 0 Hz, when the ground line 13 is not connected, the voltage generated on the electrode plate 3 is a low voltage of about 0.14V.

Furthermore, even if connected by the resistor R and the capacitor C ₄ of the large value and the ground line 13 and the container 1 in order to lower the voltage induced to the electrode plate 3, it does not affect the voltage measurement. (Embodiment 2) FIG. 3 is a diagram showing a configuration of a voltage transformer according to a second embodiment of the present invention. (A) shows the container 1 of the GIS in cross section, and (B) shows the shield and the bus bar in an enlarged manner.

In the illustrated GIS, a three-phase bus 2,
Each of 2 and 2 is housed in a cylindrical shield 21 to prevent induction from other phases. The shield 21 is made of a conductive material such as aluminum.
Grounded. In FIG. 3, only the configuration of the electrode plate is different from that of the above-described first embodiment, and the configurations of the ground wire, the current transformer, and the determination display unit are the same as those of the first embodiment. I have.

On the inner surface of the shield 21, a thin insulating film 22 is stuck. Further, on the inner surface of the insulating filter 22,
An electrode plate 23 made of a thin metal plate is attached. A capacitance C ₁ is generated between the electrode plate 23 and the bus 2. The electrode plate 23 is connected to the ground line 13 in the same manner as in the first embodiment.
It is pulled out of the container 1 from the drawer unit 4 and connected to the determination display unit 6.

In this embodiment, when the three-phase bus 2 has the shield 21, the electrode plate 23 can be easily provided by using the shield 21. The electrode plate 2
3 can have a large area, and the voltage can be measured more accurately. (Embodiment 3) FIG. 4 is a diagram showing a configuration of a voltage transformer according to a third embodiment of the present invention. In this example, only the configuration of the winding of the current transformer is different from that of the first embodiment, and the GI
Since the configurations of S, the ground line, and the determination display unit are the same as those in the first embodiment, the display of the determination display unit 6 is omitted.

In FIG. 4, the phase A of the three-phase bus 2 is
Only the current transformer 14 is shown. However, with phase B
The current transformer 14 is similarly provided for the C phase.
is there. Therefore, the ground line 13 from the A-phase bus 2 changes.
A predetermined number of turns na is wound around the iron core 24 of the flow
25_AIs configured. Furthermore, contact from other phases B and C
The ground wire 13 is also wound around the iron core 24._B, 25_CRolled as
It is. B-phase winding 25 _BIs n_bTimes, the C-phase winding 25C
n_cIt is wound. Furthermore, the windings 25 of the B phase and the C phase _B, 25
_CIs A-phase winding 25_AIt is wound in the opposite direction. Current transformer
Fourteen secondary windings 16 are connected to the judgment display unit 6.

Although not shown, the B-phase and C-phase current transformers are inserted into the ground wires 13 of each phase. The operation principle of this example will be described. Between the bus 2 and the electrode plate 3 of the A-phase, normal capacity C _A is generated, the charging current i _A flows to the capacitor C _A. This charging current i _A is A
It corresponds to the voltage applied to the phase bus 2. However, the A-phase electrode plate 3 has another phase B-phase,
Capacitances C _BA and C _CA are also generated between the buses 2 of the C phase and induced by these capacitances C _BA and C _CA , and induced currents i _BA and i _CA flow. Accordingly, the windings 25A of turns n _a is the charge current i _A and the induced current i _BA, combined current of i _CA flows. The current flowing through the winding 25A is shown by a solid line in FIG.

On the other hand, the windings 25B and 25 having the winding numbers n _b and n _c
C has a normal current i _B (= i _A ) of B phase and C
A normal current i _C (= i _A ) of the phase flows. In addition, winding 2
The winding directions of 5B and 25C are reversed from those of winding 25A. Now, the constant k is set as k = C _BA / C _A = C _CA / C _A, and the number of turns n _b and n _c of the windings 25B and 25C is set as the winding 2
Respect 5A of turns n _a, is set to _{n b = n c = k ×} n a. Then, the currents i _BA ′, i _CA ′ flowing through the windings 25 _B , 25 _C are as shown by the broken lines in FIG. 5, and the induced currents i _BA , i _CA flowing through the winding 25 A are cancelled.

According to this embodiment, the capacitive coupling with another phase can be canceled by providing an additional primary winding in the current transformer, so that an error due to the capacitive coupling with another phase is generated. Can be prevented.

[0025]

According to the present invention, the voltage is measured by the charging current flowing through the capacitance formed between the main circuit and the electrode plate. Therefore, the influence of the capacitance or resistance generated in the measuring circuit is reduced, and the voltage is accurately measured. A measurement is taken. Further, since a high voltage is not generated on the electrode plate, a safe voltage transformer can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a conventional voltage transformer.

FIG. 2 is a diagram showing a configuration of a first embodiment of a voltage transformer according to the present invention.

FIG. 3 is a diagram showing a configuration of a voltage transformer according to a second embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of a third embodiment of the voltage transformer according to the present invention.

FIG. 5 is a diagram showing the principle of cancellation of other-phase induction in the voltage transformer of FIG. 4;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Container 2 ... Busbar 3 ... Electrode plate 4 ... Lead-out part 5 ... Cable 6 ... Judgment display part 7 ... Amplifier 8 ... A / D converter 9 ... CPU 10 ... Interface 11 ... Display part 12 ... Contact output 13 ... Grounding wire DESCRIPTION OF SYMBOLS 14 ... Current transformer 15 ... Common ground wire 16 ... Secondary winding 17 ... Light emitting diode 18 ... DC power supply 19 ... Optical fiber 20 ... Optical / electrical converter 21 ... Shield 22 ... Insulating film 23 ... Electrode plate 24 ... Iron core 25 ... primary winding _{C 1, C 2, C 3} , C 4, C 5 ... capacity r _4, r ₅ ... resistance i ₀ ... bias current

Claims (3)

[Claims] 1. A voltage transformer for measuring a voltage of a main circuit arranged in a grounded container of an electric device, wherein the voltage transformer is insulated from the container on an inner surface side of the container opposite to the main circuit. And a current transformer connected between the electrode and the ground for measuring a charging current flowing through a capacitive coupling between the main circuit and the electrode; and And a light output unit provided on the output side and having an analog light conversion circuit whose impedance is reduced by the application of a DC bias current. 2. A voltage transformer for measuring a voltage of a multi-phase main circuit arranged in a grounded container of an electric device, wherein for each phase of the main circuit, induction from other phases is suppressed. And an electrode disposed on the inner surface of the shield via an insulating layer. The electrode is connected between the electrode and the ground, via a capacitive coupling between the main circuit and the electrode. And a current transformer for measuring a charging current flowing through the voltage transformer. 3. A voltage transformer for measuring a voltage of a multi-phase main circuit disposed in a grounded container of an electric device, wherein the voltage transformer is provided for each phase of the main circuit so as to face the main circuit. An electrode disposed insulated from the container on the inner surface side of the container; and a charging current connected between the electrode of each phase and ground and flowing through the capacitive coupling between the main circuit and the electrode. A current transformer for each phase, wherein the current transformer for each phase is wound in the reverse direction in which the charging current of the other phase flows, in addition to the primary winding through which the charging current of the phase flows. A voltage transformer having a secondary winding.