This technical article deals with power transformer and their installation, so we limit ourselves here to the procedures associated with their commissioning. Transformers should be inspected for any internal or external damage, especially if they have been dropped or knocked over.
This should include things like:
- Drain valves, selectors,
- Preservative tanks,
- Relais Buchholz and
- Winding temperature indicators.
All transformers should be tested for winding insulation resistance and readings confirmed as acceptable.
However HV DC testing on a connected cable, the transformer cannot be performed because the transformer windings create a short circuit to the dc test kit
If cross-core testing is required on the transformer power cables after installation then a junction box must be provided to disconnect the cable from the transformer windings. If the transformer covers are removed to perform the internal disconnection, the tools used must be clean and secured externally with white tape so that they can be retrieved in the event of an accidental drop.
All nuts and washers </ strong> </ em> should be accounted for and all officers should be instructed to empty their pockets while working on the open tank.
Impervious covers must be provided during the period when the transformer tank is open. If it is not possible to disconnect the cables after sealing, they should be tested beforehand. This means that the assembly and testing program must be carefully planned to avoid leaving the cable ends unsealed for long periods of time.
Transformer diagrams should be inspected and the phasing diagram confirmed as correct. Also, before powering up, the voltage selector should be set to the appropriate thread for the voltage level of the system.
Transformers to operate in parallel must be set to the same tap and they must be verified as having the same impedance. The voltage selectors must be locked in the defined position and, if they are of the “off” type, they must not be adjusted without the power supply is cut off first. Tank and neutral grounding arrangements or any other system grounding arrangements must be confirmed and completed prior to testing and commissioning.
When special tests for losses, phase shift ratio, the phase angle of winding resistances are specified, assistance should be sought from the manufacturer.
The following points should be checked on the particular type of transformer, if applicable:
Immersed oil with natural cooling (ON)
Make sure the oil level is adequate and that the breather tubes are clear. Commission silica gel units by removing the airtight seals from the canisters and filling the sealing well to the correct level with transformer oil.
the color of silica gel should be checked and the filling changed if it shows moisture (red for wet, blue for dry)
Dry transformers are more susceptible to external damage, so they should be handled with care and stored on site.
They should also be kept in a dry and warm atmosphere until they are put into service, to prevent moisture infiltration.
Satisfactory insulation tests are imperative before commissioning. Since they are entirely dependent on surface radiation and air convection for cooling, they should be checked for any accumulation of dust or dirt that could block the air ducts and reduce the airflow. Cleanliness is essential, especially when the connection cables leave the windings and on the terminal supports. Damp dust causes costly traces and damage.
It is particularly important to check the presence of dust in the transformers of this type of transformer, which could escape the notice of the personnel in charge of the commissioning.