1. Key points for preparation before testing

Before starting the operation, strictly follow the procedures of power outage, electricity inspection, and grounding wire hanging. Confirm that both the high and low voltage sides of the transformer are completely powered off and there is no residual voltage. Ensure proper safety fencing and warning signs are set up on site.

Check the transformer nameplate parameters, record the rated transformation ratio, wiring group, capacity, and voltage level, and set the tester's corresponding wiring mode and rated parameters in advance.

Check whether the instrument power cord, test line, and grounding clip are intact and undamaged, and ensure that the wiring terminals are clean and free from oxidation, to avoid test errors caused by poor contact.

Ground the instrument reliably, place it in a stable and dry location, keep it away from strong electromagnetic interference sources, and ensure that the site is ventilated and free from rain, snow, and moisture.

2. Key points of on-site wiring operation

Strictly follow the instrument wiring diagram corresponding to the transformer wiring group, and connect the test lines to the high-voltage side and low-voltage side respectively, ensuring one-to-one correspondence between phase lines. Misconnection and short-circuiting are strictly prohibited.

Clamp the test wire clip tightly onto the transformer bushing terminal to ensure tight contact, remove the surface oxide layer and oil stains, and reduce measurement deviations caused by contact resistance.

The three-winding transformer needs to be wired and tested in the order of high-medium, high-low, and medium-low gear positions, and no winding combination should be omitted.

After wiring is completed, conduct a phase-by-phase review again to confirm that there are no inter-phase short circuits or incorrect grounding connections. Irrelevant personnel should be evacuated from the testing area.

3. Key points of instrument operation and testing process

After powering on, the instrument performs a self-check. Select the automatic transformation ratio test mode, and correctly set the wiring group, tap position, and rated voltage ratio parameters.

Adjust and test the transformer tap changer position step by step, and save records after waiting for the data to stabilize at each position. Skipping positions during testing is strictly prohibited.

During the testing process, it is prohibited to touch the wiring terminals or tap switches, and it is not allowed to arbitrarily move the instruments to avoid vibration and external interference that may affect the accuracy of the data.

If data drift, errors, or excessive transformation ratio deviation occur, immediately stop the test, check the wiring, grounding, and gear setting, and re-measure after troubleshooting.

4. Data determination and key points for closing

Compare the actual measured transformation ratio with the rated transformation ratio on the nameplate, strictly refer to the allowable error range specified in the regulations, and determine whether it is qualified. At the same time, record the data for each gear transformation ratio, phase position, and group.

Save the original test data and screenshots for archiving, and annotate the test time, weather, staff, and transformer number for future traceability and comparison.

After the test is completed, first turn off the instrument power supply, then remove the test wires and grounding wires, organize the cables in order, and restore the equipment to its original state on site.

Clean up the work site, remove safety barriers, fill out test record reports, and promptly analyze the reasons for exceeding standards and abnormal data, and report for handling.