The following tests and checks should be performed at a minimum to ensure that the transformer is ready to be energized. Do not energize the transformer without performing these tests and checks. If any of below explained tests fail and transformer is energized anyway, it may lead to the serious hazard, and that’s not good ;) That’s not what we want.
Let’s see these 15 tests.
1. Insulating Fluid Test
Draw a fluid sample and test its dielectric strength. Dielectric strength of new fluid should be 26 kv or greater.
2. Pressure Test
Check the transformer tank for leaks by pressurizing the tank with dry air or dry nitrogen through the pressure test fitting to a pressure of 3 to 4 PSIG. let the tank stand under pressure for one to two hours, then examine the tank and fittings for leaks. leaks above the fluid level can be detected by applying soap solution to all welds, joints, pipe fittings, and cable connections.
Upon completion of this test, reduce the internal pressure to 1 or 2 PSIG.
3. Insulation Megger Test
Perform a 1000-volt Megger test and a power factor test to ensure that none of the windings is grounded. See the complete procedure here.
4. Ratio Test
Perform a ratio test at each tap position to ensure that transformer coil ratios and tap changer connections are correct. Read the complete procedure of transformer turns ratio test step by step.
5. Continuity Test and Resistance Test
Perform a continuity check on each winding. Measure the winding resistance of each winding and compare results to factory test values.
6. Line Connections
In preparation for making line connections, check to make sure that all mating connector surfaces are clean and smooth. Connections must be tightened appropriately to prevent overheating and possible subsequent failure of the connection.
Connections to should be made with care to avoid placing undue stress on the bushings.
7. Tap Changer Setting
Check the tap changer setting to ensure it is set to the proper position for the required voltage. See an example of transformer tap-changer correct adjustment.
8. Delta/Wye and Series/Multiple Switch Settings
Check delta/wye and series/multiple switch settings to make sure they are set correctly.
If these connections are made using an internal terminal board, check to ensure that these connections are made properly according to the chart on the transformer nameplate.
Check to ensure that the transformer tank is permanently and effectively grounded. The transformer tank ground pad is located near the bottom of the tank.
Check wiring of control and alarm circuits (if provided) to make sure there are no loose connections and no damage to insulation.
11. Fluid level
Check to make sure the fluid level as indicated by the fluid level gauge is as follows:
12. Tank Finish
Check all painted surfaces to make sure that there is no damage or corrosion.
13. Bolted Connections
Check all bolted connections for tightness.
Check to make sure that all tools and equipment are accounted for and have been removed from the transformer.
15. Fluid Temperature
Read the fluid temperature gauge and make sure the temperature is no lower than minus 20°C before the unit is energized.
Reference: Installation, Operation, and Maintenance of Medium Power Substation Transformers – Howard Industries
Thanks for the good article but the 1st item Insulating Fluid Test requires further clarity on what is required for this important component. It vital to draw an oil sample(IEC 60475) but the testing requirement in accordance with IEC 60422 is more than just doing the Dielectric Strength and reference should be made to the requirements to IEC 60422 Table 3. Unfortunately your reference that the insulating oil should have Dielectric Strength > 28 kV needs to be questioned as the IEC Standard for the Voltage classification for the Transformer you have in this article should be >60 kV.
Please I want us to be communicating constantly through email and wasap .I really feel delighted for this useful information.
How do I pressurizing the tank with dry air or dry nitrogen through the pressure test fitting?
Thanks a great deal for this.
Was the CT ratio coil being connected properly to the meter gauge. Chk the passing through cable to the CT coil
Was 2012 I worked with al GAhaz trading company one year WITH SWEET progact THIS IS MY STORY
Just I want to know about ELR. We have connected ELR With Incoming panel(800A). That ELR is getting Trip within Seconds. Equipments are not getting any Earth Leakages. No shock effect from equipments… I am not able to Understand what is exact problem..Pls Let me know Reason.
Very thanks for this article
I’m very glad about this, but if i want know more, how to discussaed with you as electrical engineer?
I am a protection engineer and I carry out all such tests . I just want to know that why magnetic balance test of 160MVA tfr is diferrent from < = 100 MVA tfr.
Good information for an executive.
Very very important. Articles for sub station maintenance. Great thank u
Thanks for such a informative article