JPS59630Y2 - Transformer testing equipment - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a device that performs a so-called lightning impulse voltage test in which an impulse voltage is applied to a transformer or an instrument transformer to test its insulation.

In transformers with a large number of turns and potential transformers, the inductance is significantly greater than the capacitance within the windings, so lightning impulse currents can more easily pass through the capacitance circuit.

Therefore, even if inter-turn bridging occurs in some turns within the winding during a lightning impulse voltage test, the inductance value of the entire winding will hardly change, and the lightning impulse current It is difficult to detect changes in lightning impulse current with a detector (eg, a resistor).

That is, during the test, as shown in FIG.
When connected to the terminal 8 of the primary winding 2 and grounded via the current detector 9, the lightning impulse voltage which is the output of the impulse voltage generator 6 is applied to the other terminal 4 of the primary winding 2 via the lead wire 5. , lightning impulse current flows from primary winding 2 to terminal 7
- Flows through the current detector 9 to the ground point.

At this time, the lightning impulse current signal detected by the detector 9 is guided to the oscillograph 10, and its waveform is drawn on the oscillograph and observed.

If an insulation failure occurs in part of the primary winding 2 during the test due to the lightning impulse voltage, the value of the winding inductance changes, which causes a disturbance A in the lightning impulse current as shown in FIG.

However, in transformers with a large number of turns, as mentioned above, the change in winding inductance due to insulation failure is small, and the disturbance in the lightning impulse current is also small, so it is difficult to detect insulation failure in the winding from the current waveform. It is.

This idea was devised to solve the above-mentioned problems by inducing alternating current voltage in the winding under test using other windings. This is intended to improve accuracy in lightning impulse current detection by creating a potential difference, prolonging the failure state and increasing the scale of the failure when an insulation failure occurs due to lightning impulse voltage.

An embodiment of this invention will be described in detail below with reference to FIG.

A primary winding 2 and a secondary winding 3 wound around an iron core (not shown) are housed in an outer box 1, and both terminals 8 and 18 of the secondary winding 3 are provided with a wire of, for example, 60 H2. Alternatively, an AC power source 13 of 180 H2 is connected to induce an AC voltage between the conductor base turns of the primary winding 2.

The ground terminal 7 of the primary winding 2 is connected to a low frequency cutoff filter 14.
and is grounded via the current detector 9.

Note that there is a contact prevention plate 11 between the primary winding 2 and the secondary winding 3.
If there is, the contact prevention plate 11 is connected to the ground terminal 7 in order to improve the accuracy of failure detection.

In this state, when the output of the impulse voltage generator 6 is applied to the other terminal 4 of the primary winding 2 via the lead wire 5 and the discharge gap 12, a lightning impulse current flows from the primary winding 2 to the terminal 7 to the filter. 14 through detector 9 to the ground point.

In this case, an alternating current voltage is induced in the primary winding 2,
An impulse wave is superimposed on this, resulting in the result shown in FIG.

At this time, if an insulation failure occurs between some turns of the primary winding 2, the inductance of the winding changes and the lightning impulse current is disturbed.

Although this disturbance is difficult to see when it is superimposed on the alternating current wave as shown in Fig. 4, a filter 14 is inserted in series with the detector 9, and this cuts off the alternating current, as shown in Fig. 5. The lightning impulse current waveform is shown on the oscilloscope 10.
, and disturbance B can be clearly observed.

In other words, when a lightning impulse voltage is applied with a potential difference created between each turn of the winding conductor, if an insulation failure occurs between the turns of the conductor, the failure condition will continue for a relatively long time, and the failure will occur. Since the scale of the lightning tends to increase, the change in the winding inductance also increases, and the disturbance in the lightning impulse current becomes more significant, resulting in easily visible disturbances such as disturbance B in FIG. 5, for example.

As described above, according to this invention, a lightning impulse voltage is applied to the winding under test while an alternating current voltage is induced using another winding, and the alternating current is cut off by a filter so that only the lightning impulse current is generated. Detects insulation failures in windings of transformers with a large number of turns, instrument transformers, etc.
Moreover, it can be easily detected, which improves the reliability in use of electrical equipment, and also has the advantage of being able to prevent insulation troubles during factory tests and reducing economic damage.

[Brief explanation of the drawing]

Figure 1 is a wiring diagram to explain the conventional lightning impulse voltage testing method for transformers, Figure 2 is a wiring diagram showing an embodiment of this invention, and Figures 3 to 5 are waveforms of lightning impulse current. It is a diagram. 1...Outer box, 2...Primary winding, 3...Secondary winding,
4゜7, 8.18... Winding terminal, 6... Impulse voltage generator, 9... Current detector, 10... Oscillograph, 11... Contact prevention plate, 12... Discharge gap, 13...AC power supply, 14...filter. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Scope of utility model registration request] When performing an impulse lightning voltage test on a transformer having multiple windings with multiple turns, a low frequency cutoff filter and a current detector are installed between one end of the winding under test and the ground, and the A transformer testing device characterized in that an impulse-like test voltage is applied to the other end of the winding, and an alternating current voltage is applied to the above-mentioned winding.