Factors Contributing in losses in Transformer

Factors contributing towards losses in transformer are:

- Oversized transformers operating at low loading: Improper selection of transformer based on its expected load and all day efficiency results in high no-load losses. The no-load losses in the lightly loaded transformers increase even more while facilities close for the day or on the weekend when most electrical equipment are turned off.

- Undersized transformers: This causes higher loading on the transformer, giving output in higher operating losses.

- Unbalanced loads in secondary side: There can be a important unbalance in the system because of load imbalance in various phase, as more consumers may be linked to a particular phase. This results in neutral shifting, particularly depending on the solidity of grounding of the neutral. Neutral shifting could cause over fluxing (and burning of the transformer) because of higher voltage on certain limbs, and also higher technical loss. The overloading also leads to lower voltages at the consumer end and lesser energy consumption leading to loss in revenue.

- Connector at bushings: There can be loose connection at bushings because of inadequate surface area for connections, and loose connections among the cables and bus bars. A recommended technique is to have double bus bars to assure full utilization of the contact area. It is observed in which over heating of connector at transformer bushing causes oil leakages on HT/LT bushings and along with pollution deposits electrical leakages begin at the bushing.

- Low oil level/oil leakages: Transformer oil serves the dual reasons of insulation and cooling. Leakages of transformer oil and contamination of oil along with moisture can reduce the insulation resistance (IR value) of oil. Sludge creation in oils could adversely affect the cooling and lead to higher temperatures and losses.

- Hot spots in core: Hot spots can establish in the core because of the loosening of the core bolts. Hot spots in core could lead to eddy currents and higher core losses. Gas chromatography can be used to detect such potential hazards.

- Use of energy efficient transformers: This could also help in avoiding distribution losses. Recently distribution transformers along with amorphous core have entered the global market and few utilities have installed these. The core losses (magnetizing or no load losses) get substantially decreased.  Therefore, the high cost is coming in the way for their large-scale use.  Efforts are being made to make amorphous core material indigenously and the cost is expected to go down considerably.