Preparatory work procedures and tests before maintenance

Preparatory work procedures
(1) Collect data, understand the operating conditions, and formulate construction plans.
(2) Large tools and instruments enter the substation in advance.
(3) Apply for a job.
(4) Handle the work ticket and deliver the work ticket to the power plant operation branch in advance.
(5) After the work is permitted, read out the work ticket, explain the safety measures, and assign the work.
(6) Work begins.

Test before overhaul
(1) Pre-control of dangerous points and preparation of personnel organization and tools during the test

(2) Personnel organization.

(3) The main tools are as follows.
1) Instrumentation. Megger, voltmeter, clamp ammeter, DC microammeter, multimeter.
2) Instruments. Dielectric loss tester, DC high voltage tester, DC resistance tester, tap switch tester, group transformation ratio tester, contact resistance tester, test transformer, voltage regulator, single-arm bridge.
3) Tools and equipment. Power cord, voice alarm box, wire box, thermometer, ladder, fence, insulating pole, insulating pad, insulating table, tool box, recording paper.

(4) The technical measures and safety measures are as follows.
①Technical measures mainly include: 0 According to the requirements of the main transformer pre-test, overhaul, and handover test items, select the corresponding instruments and meters, and must have items and omissions; ②The test data must be carefully analyzed, compared, and judged. If there is a problem, it should be Immediately report to the higher-level technical management department; ③Each individual test must be strictly implemented in accordance with the working procedures.

Safety measures mainly include: ①Strictly implement on-site safety work regulations; ②Strictly implement on-site work dangerous point control.

Main test items
According to preventive test items, other test items (such as characteristic test, high-voltage partial discharge test, etc.) can be added when necessary for comparison after overhaul. The main test items are as follows.
(1) Measure the insulation resistance and absorption ratio or polarization index of the winding.
(2) Measure the leakage current of the winding together with the bushing.
(3) Measure the dielectric loss angle tgỡ of the winding together with the bushing.
(4) Test of insulating oil in body and casing.
(5) Measure the DC resistance of the winding together with the bushing (all tap positions)
(6) Casing test.
(7) Measure the insulation resistance of the iron core to the ground.