Types of Power Transformers

Transformers are very versatile, with a complete range of voltages and as well as special features for many specific applications.

1. Transformers for electronics

Transformers for electronic circuits are used either to match the supply voltage to the operating voltage of a component or accessory or to match the impedance of a load to the supply in order to maximize power throughput. They can be used to match the impedance of primary and secondary circuits.

In low power transformers. The winding usually consists of round enameled wire and the components may be varnished or encapsulated in resin for mechanical reinforcement and to prevent the ingress of moisture.

2. Small transformers

These transformers are used in fixed, portable, or hand-held power supply units, as isolation transformers, and for special applications such as burner ignition, shavers, shower heaters, clocks, and toys. They can be used to supply up to 40kVA of three-phase power at frequencies of up to 1MHz.

Safety is a major concern with these transformers and they are identified as Class I, II, or III. Class, I devices are insulated and protected by an earth terminal. Class II transformers have double or reinforced insulation. Class III transformers have an output of less than 50V ac or 120V dc at Safety Extra Low Voltage (SELV).

Power Transformer          

3. Distribution transformers

These transformers are used in domestic or industrial premises. They may be single or three-phase, pole, or ground-mounted, and they are rated from 16 kVA to 2500 kVA.

The windings and core are immersed in mineral oil, naturally cooled, and have two windings per phase. The primary (high voltage) winding has a maximum voltage of 3.6 kVA to 36 kVA; the secondary (low voltage) winding has a voltage of no more than 1.1 kVA. The high voltage winding usually has a ±2.5% break tap, or +2 x 2.5%, -3 x 2.5%. The losses are allocated according to a list, e.g. BS 7281-1, or by using the loss capitalization formula.

4. Transmission transformers

These are among the largest and highest voltage transformers in use. They are used to transmit power between high voltage networks. Ratings range from 60 MVA to 1000 MVA, with windings rated for the networks they are connected to, such as 33, 66, 132, 275, and 400 kV in the UK, or up to 500 kV or 800 kV in other countries.

The impedance of transmission transformers is typically 18% in the UK and 8% in continental Europe but can be as high as 30% under certain system conditions.

Dry Type Transformer

Transmission transformers are oil-filled and are usually fitted with oil pumps and radiator fans to help cool the windings and core. They are usually fitted with OLTC, but some 400 kV and 275 kV networks are connected by transformers without regulated windings.

5. Supply transformers

These are used to supply larger industrial premises or distribution stations. Ratings range from 4MVA to 30MVA with primary winding ratings up to 66kV and secondary windings up to 36kV.

Transformers in this category are fluid-cooled. Most power supply transformers use mineral oil; however, in residential buildings, oil rigs, and some factory applications, the coolant may be synthetic esters, silicone oil, or some other fluid with a higher fire point than mineral oil.

If you want to get more information about the transformer classes, welcome to contact us today or request a quote.