Below is a standard method statement which can be used as learning purpose and to prepare further professional method statement for testing and commissioning of transformers.
Required tools for transformer testing & commissioning.
- Portable Hand Tools / Tool Box.
- Digital Multimeter
- Earth Resistance Tester
- Megger Tester.
- Safety requirements tools such as safety shoes, safety helmet, safety glasses, fluorescent vest, and safety gloves to ensure maximum ability of safe work and dust mask when require.
Procedure Of Transformer Testing & Commissioning
- Ensure only trained persons shall operate the power tools.
- Ensure all concerned personals shall use PPE and all other items as required.
- Ensure adequate lighting is provided in the working area at night time.
- Ensure service area/work area openings are provided with barricade, tape, and safety nets.
Preparation for testing
- Prior to the commencement of any permanent works, areas and access will be inspected to confirm that they are in a condition for permanent works to commence ensuring the environment is clean and dry. Testing will commence only after the equipment is completely installed as per approved method statement for the installation of the Transformer and released for testing commissioning.
- All materials and relevant documentation to this testing works shall be checked by the responsible personnel prior to the commencement of testing activities.
- Before any Item of equipment is accepted for testing a visual inspection will be carried out on that equipment. Where defective equipment is found it will be reported to Consultant for further action.
- The testing Electrical Engineer/Supervisor should confirm the availability of necessary Three Phase AC power supply and Single phase for testing activities.
- The testing Electrical Engineer/Supervisor should confirm the availability of proper access to the site area in which the equipment have to be tested.
- When a satisfactory pre-testing inspection has been carried out, the testing work will commence.
- The testing Engineer will instruct the supervisor regarding the testing works and will arrange for all necessary schematic drawings, data sheets and test formats to be available at the testing area.
- The supervisor will check that all the necessary tools and equipment’s to be used for testing are available in the testing area.
- After the testing work is completed the supervisor checks all the testing equipment and returns to the storage cabin.
- While carrying out the testing work the Testing Engineer will fill all the necessary test formats. After completion of testing work the Testing Engineer will obtain the signature of relevant officials: Consultant.
Method of testing of Transformers:
Visual inspection:
– Correctness of installation, assembly.
– Damage, paint, cracks checks.
– Tightness Checks.
– Earthing Connection Checks.
– Labels/Markings Rating Plate Correctness Checks.
– Ferrules/ terminal Numbering Checks.
Insulation Resistance measurement for primary winding
– Earth the Secondary winding
– Apply Voltage on the Primary winding
– Observe readings and record in the test format
Insulation Resistance measurement for Secondary windings
– Earth the Primary windings
– Apply Voltage on the Secondary windings
– Observe readings and record in the test format
Windings Resistance measurement
– Ensure the contacts at bushings are cleans
– Hold the sensing probes across the conduct between which the contact resistance is to be measured (Test Current 10A DC).
– Observe the reading and record in the test format.
Ratio Measurement
– Ensure that both the Primary and Secondary windings are not connected to any cables/Bus bar.
– Ensure the tap Changer in lowest tap Position.
– Apply three phase supply voltage (415 V AC) across the Primary Termination of the Transformer.
– Measure the secondary (LV) voltage at the LV termination. Observe the reading and record in the test format.
– If the tap changer is Off load type, switch of the power supply and rise one step and apply the Three phase 415 V AC across the Secondary termination and measure the voltage at both Secondary and Primary side.
– The above step to be carried-out until the highest tap.
Alternatively, test is performed with a digital ratio meter which measures the ratio value of the transformer and simultaneously checks the vector group and the polarity.
Vector group Checks
– Ensure that both the Primary and Secondary windings are not connected to any cables /Bus bars.
– Connect the “R” phase of the Primary winding and “R” phase of the Secondary winding (Short R phase of Primary and Secondary termination).
– Apply 3 phase supply voltage (415 V AC) across the Primary Termination of the Transformer. Measure the voltage at the both Primary and Secondary termination at all the phases. Observe the reading and record in the test format.
– Apply the formula or plot the values in the graph to get the vector group.
Magnetic Balance Test
– Ensure that both the Primary and Secondary windings are not connected to any cables/Bus bars.
– Apply 3 phase supply voltage (415 V AC) across the 1U & 1V and measure the Corresponding Voltage for 1U-1V, 1V1W & 1U1W.
– Switch off the Supply and repeat the test again by applying the voltage in 1V & 1W and Measure the corresponding voltage for 1U-1V, 1V1W & 1U1W.
– Again, Switch off the Supply and repeat the test again by applying the voltage in 1U & 1W and Measure the corresponding voltage for 1U-1V, 1V1W & 1U1W.
– Observe the reading and record in the test format.
On site Protection
Until the Equipment is permanently energized, client should ensure that a protective cover will Remain over all the equipment that is being tested.