Power Transformers

Power transformers are generally used for stepping up or down the voltage levelat the electrical power generating station and distribution station (or substation) respectively. Power transformer is used two times while delivering electric power to a consumer who is far away from the generating station-

First - At power generating station to step-up the voltage generated by the generator.

Second - at the Distribution station (or State electricity substation) to step-down the voltage received at the end of the transmission line.

One of the most important and simple reason for using the power transformer is to reduce power losses during electric power transmission.



Difference between Power Transformer and Distribution Transformer

1. The power transformer is usually operated in full load because it is designed to have high efficiency at 100% load. On the other hand, the Distribution transformer has high efficiency when the load stays between 50% and 70%. So, distribution transformers are not suitable to run at 100% load continuously.

2. Since power transformer leads to high voltages during step-up and step-down, the windings have high insulation when compared with distribution transformers and instrument transformers.

3. Because they use high-level insulation, they are very bulky in size and are also very heavy.

4. Since power transformers are usually not connected to homes directly, they experience less load fluctuations, while on the other have distribution transformers experience heavy load fluctuations.

5. These are loaded fully for 24 hrs a day, so copper and iron losses take place throughout the day and they stay very much the same the entire time.

6. The flux density in the Power Transformer is higher than the Distribution Transformer.

IS 2026: 2011is a reference standardFor Oil immersed Distribution Transformers up to 2500 kVA

Salient Features

• Rated Power: 3 MVA up to 200 MVA
• Primary Voltages typically: 11, 22, 33, 66, 90, 132, 220 kV
• Secondary Voltages typically: 3.3, 6.6, 11, 33, 66, 132 kV or custom specification
• Phases: Single or three-phase transformers
• Rated frequency: 50 or 60 Hz
• Tapping: On-load or off-load tap changers
• Temperature rise: 60/65C or custom specification
• Cooling type: ONAN (oil natural air natural) or other types of cooling such as KNAN (max 33kV) on request
• Radiators: Tank-mounted cooling radiator panels
• Vector groups: Dyn11 or any other vector group as per IEC 60076
• Voltage regulation: Via on-load tap changer (with AVR relay as standard)
• HV & LV terminals: Air cable box type (33kV max) or open bushings
• Installations: Indoor or Outdoor