1, high pressure test requirements

When an electrical connection is serviced and tested at the same time, a working ticket can be used, but the approval of the maintenance supervisor should be obtained before the test. In the same electrical connection part, when the high-voltage test '> high-voltage test ticket is issued, the maintenance ticket that has been issued shall be recalled first, and the second ticket shall not be issued. If in the process of the test, maintenance cooperation is needed, maintenance personnel should be filled in the high pressure test '> high pressure test work ticket.

Shielding bars or fences shall be installed on the test site. There shall be sufficient safety distance between the shielding bars or fences and the high voltage part of the test equipment. The "Stop, high voltage danger" sign shall be hung outwards and guarded by personnel.

Use portable instruments to work on high voltage circuits, by two people. Substation work ticket should be filled in for those who need power outage or safety measures for high-voltage equipment.

Do not measure the grounding resistance of the grounding grid when a system grounding fault is found in a substation. Do not measure the insulation of the line during lightning.

2, high voltage insulation test pressure method and related requirements

In no-load test, there will be excitation inrush current when the low-voltage winding is excited by rated frequency and rated voltage, so it is generally closed with no more than one third of the rated voltage, and then gradually boost the voltage. In this way, some defects can also be found in advance, such as inter-turn short circuit. The step-down voltage is also gradually reduced, and the power supply is cut off when the voltage is below one third of the rated voltage. In this way, there is no overvoltage in the residual magnetic core. When the power supply is cut off at full voltage, the energy in the transformer inductance changes to the overvoltage in the capacitor. Before conducting no-load test, the remanence caused by measuring resistance and operating wave test should be eliminated. But the transformer in the actual operation of the general can not do zero boost, so the transformer should withstand the three-phase three-phase switching generated over voltage. Overvoltage at the midpoint of an ungrounded transformer, especially in effectively grounded systems. The transformer should also withstand the action of inrush current generated when the full voltage is switched on.

Load test and temperature rise test In load test and short circuit method for temperature rise test, the voltage applied is only impedance voltage, so the voltage can be impedance voltage when closing. But the current has to be high enough. When measuring the load loss and impedance voltage, the current value should be greater than 50% of the transformer rated current or large tap current. Temperature rise test should be greater than 90% transformer tap current. When the generator capacity is insufficient, capacitor banks can be used to compensate.

Power frequency voltage resistance for full insulation transformer power frequency voltage resistance or insulation transformer midpoint power frequency voltage resistance of the way and no load test pressure the same, gradually increase and gradually reduce. In the power frequency voltage value of less than one third can be closed and open. Because the tested transformer is equivalent to a capacitor, it is necessary to prevent excitation phenomenon, especially when the generator at the same time to pay attention to. In addition, when the power frequency voltage withstand value exceeds 95kV, the voltage must be measured at the high voltage side, and the low voltage side voltage cannot be converted to the high voltage by voltage ratio. High voltage can be adjusted by capacitive voltage divider or ball gap.

Induction voltage including short and long time induction voltage and measurement of partial discharge induction voltage also want to step up and step down. The high frequency generator should be selected in the test, especially the generator frequency of the transformer with three-phase five-column core. In order to prevent the self-excitation of the generator and the resonant overvoltage on the transformer, it is necessary to connect the shunt reactor at the outlet end of the generator, or choose the generator of 200Hz and above.

Short circuit test generally in advance short circuit method for short circuit test. The winding near the core column is short-circuited first, and the winding far away from the core column is suddenly applied full voltage. A phase selector switch is used to close the full voltage when the voltage sinusoidal waveform is just over zero.

The impact test includes full wave lightning shock test, intercept wave lightning shock test and operation wave shock test. After adjusting the voltage waveform and amplitude, apply the full impact test voltage to the transformer. The main capacitor of impulse voltage generator must be large enough, otherwise the specified waveform cannot be called up. In the mid-point impact test, the multistage impulse voltage generator can be changed to connect several stages in parallel, so as to increase the main capacitance, easy to meet the specified waveform. We should pay attention to the influence of remanence magnetism on the waveform of operating wave impact. And try to make the operating wave-to-phase test voltage equal to 1.5 times of the ground test voltage. After finishing the operation wave impact test, attention should be paid to eliminating the residual magnetism in the core. From the above various test pressure way, most of the processing frequency voltage test items are zero boost, step-down. However, the transformer should be able to withstand the requirement of full voltage impact closing, which must be taken into account in the insulation design of uHV transformers.

Some problems should also be noted: in the high pressure test, such as power frequency pressure test, impact test, must pay attention to the requirements of the provisions before the test. The product should have a parking time assessment, all the vent plug vent steps, necessary accessories to be installed. Low voltage assessment of the project must be qualified. Such as insulation resistance, absorption ratio or polarization index, media loss Angle, etc. Tap switch is located in the specified position.