Description
SCE offers three phases, oil immersed, and naturally cooled (ONAN) distribution transformers. SCE manufacture these transformers under a licensing agreement with IEC 60076. The standard manufacturing range is from 10 kVA to 20000 kVA with a maximum voltage of 35kV.
Core
The core is manufactured from cold-rolled grain oriented (CRGO) silicon steel. The silicon steel is either conventional or laser treated and the choice depends on the desired loss level. The steel sheets are cut into required dimensions on automated machines thereby ensuring reduced air gap, low exciting current and low noise. Each lamination is insulated from each other to ensure a long trouble-free lifetime of the core. Suitably designed core clamping system ensures vibration free operation.
Windings
The windings are made of high-grade electrolytic cooper and are concentrically positioned. Usually copper foil is used for the low voltage windings. Round shaped, enamel insulated wire is used for the high voltage windings. It is exclusively of layered construction and is wound directly onto the low voltage winding, giving a maximum mechanical strength, rigidity and compactness.
Tap changer
The tap changer is fixed on the high voltage winding for voltage regulation.
Off-load tap changer.
It is basically a 3, 5 positions switch, which helps to adjust the voltage at a desired level. The tap changer handle is either on the top cover or sidewall and acts directly on the switching mechanism. As the name indicates, the off-load tap changer must only be operated when the transformer is de-energized.
On-load tap changer.
For higher ratings power transformer, it is basically 7, 9, 11, 17 positions switch which can be operated with energized. Brand of MR, Huaming are our options for on-load tap changer.
Tank
The tank is of hermetically sealed design and is made from corrugated steel sheets. This type of construction allows a degree of flexibility that is needed to accommodate the expansion and contraction of oil due to varying service conditions. The tank cover is bolted to the body of the tank. The surface is shot blasted first to eliminate all signs of rust, welding spatters, greese, oil and mill scale to achieve a good abrasive surface for the paint to hold for a long period of time. The two coats of primer paint are applied followed by one coat of standard "Cement Gray" (RAL 7033). (Colour Code can be customized)
Bushings
Several types can be provided depending on the requirement and applications. Porcelain bushings are used on the HV side as a norm while on the LV side porcelain or polyamide bushings are provided.
Other designs are also available on request.
Regular Accessories
The regular accessories would include:
Oil conservator(available on request, usually used for ratings above 2000kVA)
Temperature indicator
Pressure release valve
Oil level indicator
Oil drain valve
Oil sample valve
Earthing device
Lifting lug
Cable box (available on request)
Tests
All the manufactured units undergo the following tests in the factory as described in IEC-60076.
Transformer ratio and connection
Measurement of load losses and short circuit impedance.
Measurement of no-load losses.
Separate source withstand voltage test
Induced over-voltage test
On-load tap changer test (only for on-load power transformer)
Transformer oil test
Sealing test of tank
Temperature rise test
Lighting impulse withstand voltage test
Measurement of partial discharge
Complaint
