RETROFITTING
RETROFITTING:-
Retro-fitting is usually done when there is need to upgrade the Transformer under use to meet additional technical requirements that may arise from time to time to cope up with increasing demands. Retrofitting is also carried out when the costly resource like transformer remain unutilized & remain as dead asset. Products like transformer remain unutilized when substituted by new transformer either due to field problems or increased technical requirements. It is important that costly resource like transformer is re-used & not allowed to go waste. With this objective, AUM Transformers are now offering specialized Retro-fitting services.
The state of art facility at AUM Transformers supported by qualified technical specialist & mentored by experienced professional in the field give the advantage to AUM Transformers to offer retrofitting services.
AUM Transformers have done retro-fitting for number of customer and are now offering as a specialized service on a regular basis.
The key aspects to look at is Retro fitting is offering brand New Transformer combined with a competitive price.
process:-
Data Collection:-
⇨ Dismantling of core-coil assembly. We scrape all the LV/HV coils and assembly insulation.
⇨ We collect the data of core in details for proper assembly of winding.
⇨ Details of LV/HV windings with measurement of dimensions and size of winding conductors.
⇨ Clearances from winding to core, HV-LV, Hilo, Winding to tank.
⇨ Details of cooling radiators.
⇨ Condition of tap switch, bushings, fittings and Accessories.
DESIGN:-
We have computerized system of making designs for all types of transformers. The system is made under guideline of our design team who have experience of 50 years in design, manufacturing and quality assurance. We used same system for redesign of the transformers
⇨ The details of core are entered in design system.
⇨ LV Windings:
Suitable size of foil is selected to maintain area of conductor. The foil is electrolyte grade. The epoxy dotted paper is used as interlayer insulation and corrugate press board end strip is used at both the end. The solid bus bars are used as lead take out. The bus bar is tig welded with foil using automatic tig welding machine.
Cooling ducts are provided in the windings for oil circulation and for cooling.
⇨ HV Windings:
HV Windings is made using PIC/SE wire or PIC rectangle strip as required to match the area of conductor. The winding is made in the same electrical winding length. Epoxy dotted paper is used as inter layer. The thickness of paper is to withstand high voltage and impulse. The corrugated press board end strip at both ends is used. The cooling duct is provided.
Tapings are taken out from the layer providing sufficiently thick paper tube.
⇨ The performance parameters are maintained in design for better performance of transformers.
⇨ Production data for windings, insulation assembly are issued for production.
Production:-
⇨ The preparation of LV/HV windings, assembly, and insulation is done as per data received from design department.
⇨ The core is washed by transformer oil to remove all dust and carbon deposited.
⇨ Assembly – connection – drying is done in same line of new transformer manufacturing.
⇨ Oil filling is done under vacuum. Filtration of oil is done.
Testing:-
All the Routine tests are conducted as per IS 2026/IS 1180/IEC.
Type and Procedure for Pre-Commissioning Test:-
Magnetic Balance Test:-
To Carry out the test, you will require following:
⇨ A single phase supply source preferably having voltage of 230-250 Volts.
⇨ A multi-meter or a similar voltmeter will also work.
⇨ A pair of PVC insulated cable to be used to apply voltage to the transformer from your supply source.
Now the procedure to carry-out the test:-
⇨ On the transformer, you have primary high-voltage terminal (11/22/33 kV etc. ) & Secondary low-voltage terminal (400/415/575/750 V etc.).
⇨ Disconnect cables from both sides of the transformer.
⇨ Connect single phase 230 Volts supply between first and second phase of primary side of transformer (between 1U & 1V).
⇨ Measure voltages between 1U-1V , 1V-1W and between 1W-1U.
⇨ Then connect single-phase supply between second and third phase on primary side (between 1V-1W), and again record readings as mentioned in point no.4 above.
⇨ Then single-phase supply between third and first phase on primary side (between 1W-1U), and again record readings as mentioned in point no.4 above.
Insulation Resistance Test :-
The Megger Insulation Tester:-
Insulation resistance tests are made to determine insulation resistance from individual windings to ground or between individual windings. Insulation resistance tests are commonly measured directly in mega ohms or may be calculated from measurements of applied voltage and leakage current.
The recommended practice in measuring insulation resistance is to always ground the tank (and the core). Short circuit each winding of the transformer at the bushing terminals. Resistance measurements are then made between each winding and all other windings grounded.
Voltage and Turns Ratio Test:-
To Carry out the test, you will require following:-
⇨ A Three phase supply source preferably having voltage of 415-440 Volts.
⇨ A multi-meter or a similar voltmeter will also work.
⇨ A 3 Phase PVC insulated cable to be used to apply voltage to the transformer from your supply source.
Now the procedure to carry-out the test:-
⇨ First, the tap changer of transformer is kept in the lowest position and LV terminals are kept open.
⇨ Then apply 3-phase 415 V supply on HV terminals. Measure the voltages applied on each phase (Phase-phase) on HV and induced voltages at LV terminals simultaneously.
⇨ After measuring the voltages at HV and LV terminals, the tap changer of transformer should be raised by one position and repeat test.
⇨ Repeat the same for each of the tap position separately.
Vector Group:-
To Carry out the test, you will require following:-
⇨ The Three phase supply source preferably having voltage of 415-440 Volts.
⇨ A multi-meter or a similar voltmeter will also work,
⇨ A 3 Phase PVC insulated cable to be used to apply voltage to the transformer from your supply source.
Now the procedure to carry-out the test:-
⇨ Apply 3-phase 415 V supply on HV terminals. Measure the voltages applied on each phase (Phase-phase) on HV and induced voltages at LV terminals simultaneously. And check the following condition as per the group.
1. Connect neutral point of star connected winding with earth.
2. Apply 415 V, three phase supply to HV terminals.