JPS6373164A - Transformer for testing - Google Patents

Abstract

PURPOSE:To divide and reduce a surge voltage and to make a protecting device compact, by inserting the protecting device comprising a parallel circuit of a resistor and electrostatic capacitors between the secondary output terminal of a testing transformer and a load. CONSTITUTION:A secondary output terminal 3 of a main body 2 of a testing transformer, which is enclosed in a container 1, is connected to an electric unit 9 in a container 8 through a protecting device 5 in a container 4 and an insulating spacer 7 in a container 6. The device 5 is constituted by a parallel circuit of a resistor element 5a and capacitor elements 5b. When a high voltage is applied from the main body 2 and a surge voltage is generated on a load side, the surge voltage is applied to the terminal through the device 5. The peak value of the voltage is divided by the impedance ratio between the circuit 5 and the main body 2. The divided surge voltage is applied to the main body 2. In this constitution, the resistance value of the element 5a can be made small in comparison with the case where only the resistor is used. The resistance drop due to a load current can be reduced, and the protecting device can be made compact.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to test transformers.

[Conventional technology]

When performing a withstand voltage test on a target electrical device, such as a gas-insulated switchgear, a high voltage is applied to the electrical device using a test transformer.

[Problem that the invention seeks to solve]

In this case, if the secondary output terminal of the test transformer is directly connected to the target electrical equipment and high voltage is applied, if a flash short occurs on the electrical equipment side, a sudden surge voltage will be generated and the test transformer will There is a risk of entering the secondary side of the device and causing insulation breakdown.

To prevent this, if an inductance such as a choke coil is inserted between the two to suppress the surge voltage,
When a flash fault occurs, series resonance occurs between the inductance and the stray capacitance of the test transformer, and a high surge voltage is also generated, which may lead to dielectric breakdown of the test transformer.

Furthermore, if a resistor is inserted instead of an inductance to prevent surge voltage from entering, the high resistance value causes large power loss due to load current, making the resistor large and expensive, and the stray static electricity of the resistor itself increases. This is because the capacity is smaller than that of the test transformer.

The problem is that the capacity is shared against high-frequency surges, and the entire surge voltage is applied, making insulation difficult.

[Means for solving problems]

In order to solve the above-mentioned drawbacks, the present invention divides the surge voltage by inserting a protection device consisting of a parallel circuit of resistance and capacitance between the secondary output terminal of the test transformer and the load. This is intended to reduce the surge voltage applied to the secondary side of the test transformer.

〔Example〕

FIG. 1 shows the configuration of an embodiment according to the present invention, in which the secondary output terminal 3 of the test transformer main body 2 housed in a container 1 is connected to a container 6 via a protective device 5 provided in a container 4. It passes through an insulating spacer 7 and is connected to an electrical device 9 housed in a container 8.

The containers 1.4 and 6 are connected to each other so that the insulating gas filled therein at a predetermined pressure can freely flow therein, and the container 8 is blocked from gas flow by the insulating spacer 7 and is separately filled with insulating gas. It is filled to a predetermined pressure. Also, in the same figure, containers 1°4.6 and 8 are shown stacked one after the other, but this shows that the containers are connected in series, and such a stacked configuration is not necessarily required. Alternatively, a configuration in which gases 1 and 4.6 are separated by insulating spacers is also conceivable.

Figure 2 shows the above protective equipment! 5 shows a cross-sectional view of the embodiment No. 5, which includes a resistive element 5a formed by forming a non-inductively wound metal oxide film or carbon film on the surface of a cylindrical insulator made of ceramic or the like, and a resistor element 5a provided inside the resistor element 5a, which is made of a cylindrical insulator made of ceramic or the like. It is constructed of a parallel circuit with a capacitive element 5b made of a capacitor or a plastic film capacitor, and has shields 5C and 5d for mitigating electric fields at both ends.

Note that FIG. 3 shows an equivalent circuit of the protection device 5.

FIG. 4 shows a state in which the secondary output terminal 3 of the test transformer body 2 is connected to an electrical device, that is, a load 9, through the protection device 5. In a steady state, the current from the test transformer body 2 flows through the resistive element. Flows to load 9 via 5a. in this case,
As will be described later, the resistance element 5a has a small resistance value, and the power loss caused by the load current is small, so it is configured in a small size.
As shown in FIG. 1, it can be housed in a container 4 filled with insulating gas.

If a flash fault occurs on the load side and a surge voltage is generated while a high voltage is being applied from the test transformer main body 2, this surge voltage flows backwards and is sent to the secondary output terminal 3 of the test transformer main body 2 through the protection device 5. join. FIG. 5 shows an equivalent circuit of the protection device 5 and the test transformer main body 2 viewed from the load IO side.

Here, on the load side, for example, the falling and rising edges are 0 and 1.
When a steep surge voltage such as psec occurs and is applied to the secondary side of the test transformer body 2 through the protective device 5, and the peak value of the surge voltage is Vs as shown in Fig. 5, Vs is The voltage is divided by the impedance ratio between the protection circuit 5 and the test transformer body 2, and the divided surge voltage Vt is applied to the test transformer body 2.

However, since the frequency of the surge voltage is extremely high, both the reactance due to the capacitance Cp of the capacitive element 5b of the protection device 5 and the reactance due to the secondary side stray capacitance Ct of the test transformer main body 2 decrease. The peak value Vs of the surge voltage is almost divided by the reactance ratio of both capacitances.

Therefore, by setting the capacitance Cp of the protection device 5 to an appropriate value with respect to the equivalent capacitance Ct of the test transformer main body 2, the surge voltage Vs applied to the test transformer 2 can be divided by dividing the surge voltage Vs. can be reduced.

In this case, the resistance value of the resistor element 5a is made smaller than that in the case where only a conventional resistor is inserted, and the resistance loss due to the load current is reduced, thereby making it possible to downsize the protection device. As a matter of course, the capacitance value of the capacitive element 5b of the protection device 5 is selected to be an appropriate value including its stray capacitance.

Capacitance value Cp of capacitive element 5b of protection device 5 = 200P
F, resistance value Rp of resistance element 5a = 5 KΩ, equivalent capacitance value Ct of test transformer body 2 = 200PF, reactance value Lt = 1,800H.

As a result of actual measurements when the equivalent resistance value Rt = 20 KΩ, by using the protection device 5, the surge voltage applied to the test transformer main body 2 is approximately halved as the frequency increases, and the waveform steepness is sufficiently suppressed. As shown in FIG. 6, the surge voltage waveform A without the protection device was changed to Vt as shown in B when the protection device was used.

In other words, if a resistor is inserted between the test transformer and the load in order to suppress surge voltages caused by flashovers on the load side, a resistor with a high resistance value is required; Power loss due to current was large, the resistor was large and expensive, and it was impossible to store it in a container filled with insulating gas.

In contrast, in the present invention, a protection device consisting of a parallel circuit of a resistive element and a capacitive element is used, and the surge voltage generated on the load side is divided and applied to the parallel circuit and the test transformer. By making the resistance value of the element smaller than when only the resistor is used, resistance loss due to load current can be reduced, and the protection device can be downsized and housed in an insulating gas-filled container.

〔Effect of the invention〕

As described above, according to the present invention, the surge voltage applied to the test transformer can be divided and reduced by a protection device consisting of a parallel circuit of a resistance element and a capacitance element, and the protection device can be downsized.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the configuration of an embodiment of the present invention, Fig. 2 is a sectional view showing an embodiment of the protection device, Fig. 3 is its equivalent circuit diagram, and Fig. 4 is a test transformer and protection device. Figure 5 is an equivalent circuit diagram of the surge voltage protection device and the test transformer, and Figure 6 is a waveform diagram showing the effect of the protection device on suppressing waveform steepness of surge voltage. be. 2...Test transformer body, 3 Secondary output terminal, 5...
Protective device, 5a...resistive element, 5b...capacitive element,
9...Load.

Claims (1)

[Claims] A protective device consisting of a parallel circuit of resistance and capacitance is inserted between the secondary output terminal of the main body of the test transformer and the load, and a protection device consisting of a parallel circuit of resistance and capacitance is installed to prevent the load from reaching the secondary output terminal due to a flash short circuit on the load side. A test transformer, wherein the protection device has an equivalent impedance of a predetermined ratio to an equivalent impedance of the main body of the test transformer with respect to applied surge voltage.