There are many different types of testing that may be conducted on transformers, each designed to discern specific details about the equipment's ability to perform as required. Typically, these tests are divided into two main categories, routine tests and type tests. Routine tests are performed during or immediately after the manufacturing process while type tests are carried out on each type of transformers to ensure they meet the required specs.
The test items as following;
1 - Insulation Resistance Test
Used to measure the insulation resistance of the transformer components.
Apply HV DC then measure resistance.
Indicate the condition of the insulation.
2 - Insulation Resistance Test
Used to measure the turns ratio of the transformer (Primary and Secondary Windings.
Apply voltage on winding then measure the voltage induced in the other winding.
Percentage between voltages is the turns ratio of the primary and secondary windings.
Accurate test.
East to perform.
3 - Winding Resistance Test
Used to measure the resistance of the transformer windings (primary and secondary).
Done using LV DC source + Multimeter
4 - Polarity Test
Conducted to verify the polarity of the transformer windings.
Apply DC source to the primary then measure secondary voltage.
Polarity of the windings determined based on the direction of the induced voltage in the secondary winding.
Simple and quick.
5 - Open Circuit Test
Performed to determine: No load losses, Magnetizing current
Keep the secondary open circuited then apply voltage on the primary winding, then measure the primary(current and voltage)
Calculate (No-Load Losses & Magnetizing Current).
Determine the equivalent circuit then calc Efficiency and Regulation
6 - Short Circuit Test
Performed to determine:
Full Load Current.
Transformer Impedance.
Keep the secondary short circuited then apply voltage to the primary winding, then
measure the primary (current and voltage).
Calculate (Full-Load Current & Impedance).
Determine Winding Resistance.
Determine Leakage Inductance.
7 - Sweep Frequency Response Analysis (SFRA)
Non-destructive test used to detect any changes in the transformer mechanical
structure.
It can detect Winding Deformation or Shorted-Turns.
It makes comprehensive assessment of the transformer condition
8 - Dissolved Gas Analysis Test (DGA)
Used to detect the presence of combustible gases in the transformer oil.
Analyze a sample of the transformer oil to detect any changes in the gas concentration.
It can detect incipient faults before they become major problems which allows
predictive maintenance.
9 - Partial Discharge Test
Used to detect any partial discharges occurring within the transformer insulation.
Apply HV to the transformer, then measure any partial discharge in the insulation.
Can detect insulation faults before they cause significant issues to the transformer
10 - Dielectric Withstand Test
Apply HV to the transformer to test the ability of the insulation to withstand any voltage
stress.
Detect insulation weakness and that enables us to ensure the safety and reliability of
the transformer.
11 - Thermal Imaging Test
Uses infrared imaging to detect hot spots or temp gradients.
It can detect problems such as:
Loose Connections.
Overload components
It provides a non-invasive assessment of the transformer condition