Transformers and Their Types
A transformer is an electrical device designed to transfer alternating current or voltage from one circuit to another through electromagnetic induction. Electrical transformers convert AC voltage from one value to another, and can be designed to “step” a voltage up or down. There are many different types of transformers used to carry out different functions. In this blog, we will discuss the twelve most commonly used types of transformers.
Auto Transformers
Auto transformers are electrical transformers in which there is only one winding. Portions of the same winding act as both the primary and secondary windings of the transformer. Transformers of this type are mostly used for the voltage conversion of a local power line to the desired voltage value needed for particular electrical equipment. The conversion is in the range of 125 - 250 volts, either up or down.
Polyphase Transformers
In polyphase transformers, a bank of three individual single-phase transformers is used for a three-phase supply. All three phases can also be incorporated as a single three-phase transformer via a magnetic circuit connected with the core. A specific example of a polyphase transformer is the zigzag transformer, which is used for the grounding and suppression of harmonic currents.
Leakage Transformers
Leakage transformers have higher leakage inductance than other transformers, increased by a magnetic bypass or shunt in its core between primary and secondary, sometimes adjustable with a set crew. It provides the transformer with an inherent current limitation due to the loose coupling between its primary and secondary windings.
Resonant Transformers
These are a type of leakage transformer in which one or both windings has a capacitor across it and functions as a tuned circuit. They are used at radio frequencies, and resonant transformers can also function as high Q factor bandpass filters.
Audio Transformers
Audio transformers are used in audio circuits to block the radio frequency interference or the DC component of audio signals. They can also provide impedance matching between high and low impedance circuits. They are magnetic devices, and therefore are susceptible to external magnetic fields.
Instrument Transformers
Instrument transformers are commonly used to operate instruments from high voltage lines or high current circuits, safely isolating measurement and control circuitry from the high voltages or currents. The primary winding of the transformer is connected to the high voltage or high current circuit, and the meter or relay is connected to the secondary circuit. Instrument transformers may also be used as an isolation transformer so that secondary quantities may be used without affecting the primary circuitry.
Oil Cooled Transformers
These are large transformers used in power distribution or electrical substations. For cooling, the core of these transformers is immersed in oil. The oil circuits through the duct in the coil and around the coil and core assembly. If a higher rating is required, or if the transformer is in a building or underground, oil pumps are used to circulate the oil.
Pulse Transformers
A pulse transformer is a transformer optimized for transmitting rectangular electrical pulses (pulses with fast rise and fall times and a constant amplitude). These can only transmit pulses with a duty cycle of less than 1. The transformer must have low values of leakage inductance and distributed capacitance in order to reduce the distortion.
Isolation Transformers
An isolation transformer is a transformer used to transfer electrical power from a source of alternating current power to a device while isolating the powered device from the power source, typically for safety. Isolation transformers provide galvanic isolation, meaning no conductive path is present between the source and the load. This isolation protects against electric shock, suppresses electrical noise, and transfers power between two unconnected circuits.
Current Transformer
A current transformer is formed by connecting a series of measurement devices. They are designed to provide a current in its secondary coil proportional to the current flowing in its primary winding. Transformers of this type are commonly used in metering and protective relays.
Voltage/Potential Transformers
Voltage transformers, also known as potential transformers, are instrument transformers parallelly connected and used for metering and protection in high-voltage circuits or phasor phase shift isolation. They are designed to present negligible load to the supply being measured and have an accurate voltage ratio to provide accurate metering. There are three types of voltage transformers: electromagnetic, capacitor, and optical.
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