Applications of Transformers

Electrical Technology

Uses and Applications of Transformers

The operation principle of all kinds of transformers designed for different applications are the same e.g. electromagnetic induction whereas the applications of transformers are different based on the system requirements. The main application of a transformer is to step-up or step-down the level of voltage or current in power plant generation stations, receiving end substations and distributing the electrical power to the consumer units for demotic and industrial applications.

The main purpose of an electrical transformer is to step-up (increase) or step-down (decrease) the level of AC voltage while the power and frequency is constant. The customized level of voltages are used to transmit and distribute electric power to the end users e.g. residential and commercial.

Keep in mind that the DC power transmission has some advantages over AC power transmission but the initial cost of DC transmission is too much high, for this reason, AC transmission is preferred over DC (which is costly and not suitable economically) in most cases as changing the values of voltage is easily done by transformer, (keep in mind that a transformer can’t be operated on DC) where buck and boost converters are used to change the level of DC voltage according to the needs of the systems.

High frequency reactors and chocks based on low noise and small size transformers are also used in UPS, CVCF (Constant Voltage Constant Frequency), VVVF (Variable Voltage Variable Frequency), railway car auxiliary power supply and dispersed power sources. The shunt reactors (single winding per phase) is also used to absorb and compensate the reactive power in cables and high voltage long transmission lines which leads to increase the efficiency of the transformer, overall power and energy systems.

High frequency transformers are used in medical X-ray power supply, welding machines and high frequency power supply equipment.

Rotary transformers are used for high speed motor & generator, axial gap motor/generator and high pole number motors and generators.

Instrument transformers are also widely used in the electrical systems and networks. For example, CT (current transformer) is used to measure the current of another circuit and monitor the high voltage lines across power grids. On the other hand, PT (voltage or potential transformer) are used to step-down the high level of primary current and voltage to the lower level of voltage and current as output in the power system. In addition, autotransformer are used for compensation of the voltage drop in the distribution transformers, starting induction and synchronous motors, to achieve continuous variable output voltage and mostly, to interconnect many systems operating at different voltage levels. At last but not least, yoke shunt / tank shield or magnetic shunt transformers are used to reduce stray losses in the tank of large size transformers.

General Applications of Transformers

The most important applications of transformer are:

It can rise or lower (step-up or step-down) the level of AC voltage or current (when voltage increases, current decreases and vice versa because P = V x I, where power is constant at both input and output sides). This setup is used in both power transformers and distribution transformers for transmission and distribution of the electric power in a power system for further utilization and applications.
It can increase or decrease the value of capacitor, an inductor or resistance in AC circuits i.e. a transformer thus acts as an impedance transferring device.
It can be used to prevent DC from passing from one circuit to the other. In other words, they are used as ripple filters which compensate for the pulsating DC.
It can be used to electrically isolate two electric circuits

Application of Transformer in a Power System:

A power transformer steps-up the level of voltage at the generation side before transmission and distribution. For example, it increases the generated voltage in power plants from 7200kV-12kV to 33kV, 66kV, 220kV or even more up to 400+ kV for power transmission to the distribution centers.

In the distribution centers, the distribution transformer steps-down the level of voltage for commercial and domestic use of electricity. For example, it decreases the level of voltage from 11kV to 230V single phase and 400V three phase (UK and IEC). In the US and Canada, the utility transformer steps-down the level of voltage from 2700V to 120V, 240V (most common residential via center-tapped transformer), 208V, 277V and 480V in the US and Canada.

Finally, autotransformers, shunt-reactors, current transformers and potential transformers, are also used in a typical power system. Additionally, transformers are also used for impedance matching.

Click image to enlarge

In the given fig above (from left to right)

A 100MVA, 165kV power transformer installed in a substation – Columbia, Mississippi. It’s known to be the the world first flexible large power transformer manufactured by GE research.
A 100kVA, 11kV & 230V400V Pole-mounted 3-Phase distribution transformer to provide single-phase & three-phase supply to the consumer units – UK.
USA – A 25kVA, 7.2kV & 120/240V Pole-mounted distribution transformer with center-tapped secondary winding used to provide “split-phase” power for residential & light commercial service – USA.