What is the transformer
A transformer is a stationary device which is used for stepping up/down of voltage of alternating current. Stepping up is done to evacuate the generated power while stepping down is done for the consumer requirements. It is based on the principle of mutual induction, a transformer is an AC device it cannot work on DC a transformer can only change the AC current/voltage
Step-up and step-down transformers
A transformer which increases the ac voltage is the step-up transformer and the one which decreases the ac voltage is called a step-down transformer
Types of energy losses in the transformer
- Copper loss
- Iron loss
- Leakage of magnetic flux
- Hysteresis loss
- Magnetostriction
Types of transformers
Auto-transformers
It is an electrical transformer in which there is only one winding, a portion which is common to both the primary and secondary winding. the primary and the secondary has the same or all windings are common.
Autotransformer is 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 from 125volts – 250 volts or 250-125 volts
It uses common winding and it doesn’t offer any interference or disturbance isolation or it is a tapped winding transformer which can change the voltage available locally to the voltage required for a particular load
Polyphase transformers
A bank of three individual single-phase transformers can be used for a three-phase supply or all three phases can be incorporated as a single three-phase transformer and for this, a magnetic circuit is connected together with the core thus creating a three-phase flow of flux. A particular polyphase transformer is a zigzag transformer which is used for the grounding and suppression of harmonic currents
Leakage transformers
it has higher leakage inductance than the other transformers, sometimes increased by magnetic bypass or shut-in its core between the primary and secondary and it provides the transformer with an inherent current limitation due to the loose coupling between the primary and secondary windings
Thermal overload can be prevented because its output and input current is low under all load condition, leakage transformers are used for arc welding and high voltage discharge lamps
Resonant transformers
It is a kind of leakage transformer the leakage inductance of the secondary winding is used in combination with external capacitors so that it can create one or more resonant circuits. Tesla coil is a resonant transformer which is capable to produce very high voltages and it is capable to produce high current than the electrostatic high voltage generation machines
- It can be used for the CCFL inverter
- It can couple between the stages of a heterodyne receiver
Audio transformers
It is used in audio circuits and it can block the radio frequency interference or the DC component of audio signals. It could provide impedance matching between high and low impedance circuit. It is a magnetic device so it is susceptible to external magnetic fields. It could split or combine audio signals, it can do impedance matching between a high impedance instrument output and a low impedance input of a mixing console.
Instrument transformer
It is used to measure the current and voltage in an electrical power system and for the protection and control of power system. Isolation of measurement protection and control circuitry from the high currents or voltages present on the circuits being measured or controlled
Instrument transformers have predictable characteristics on overloads, voltage or current is too large to be conveniently used by an instrument so it can be scaled down to a standardized low value
Oil cooled transformer
Large transformers are used in power distribution or electrical substations and its core and coils are immersed in oil which is done for the cooling. The oil will circulate through the duct in the coil and around the coil and core assembly. Oil is cooled outside of the tank in small ratings and for large ratings air-cooled radiator is used. If the transformer is used in underground or in a building. Oil pumps are used to circulate the oil
Pulse transformer
It can be used for transmitting rectangular electrical pulses it has a duty cycle which is less than 1. The pulse shape of a pulse transformer must have low values of leakage inductance and distributed capacitance and a high open-circuit inductance to reduce the distortion
- It is used in digital logic and telecommunications circuit
- It is used for matching logic drivers to transmission lines
- It is used in radar to generate high power pulses
Isolation transformer
Mostly electric transformers are used to transform voltage from a higher level to lower voltage. Transformers can also be used to change the impedance of an electrical circuit to reduce the short circuit current
The properties of the isolation transformer can be applied to any transformer where there is no direct connection between the primary and the secondary windings. It provides isolation rather than voltage transformation
Advantages
- It can be used to protect against the danger caused by electric signals
- It can block the Dc signal from one circuit other
- It can block interference caused by a ground loop
Current transformer
It is a measurement device which is designed to provide a current in its secondary coil proportional to the current flowing in its primary. These transformers are commonly used in metering and protective relaying. These transformers safely isolate measurement and control circuitry from high voltages
Wideband current transformers with an oscilloscope can be used to measure high-frequency waveforms or pulsed currents
Applications
- It is used for control circuits and for instrumentation in high current power applications
- It can be used to detect single phasing on a three phase power system
- It does the safety protection and current limiting
Voltage transformer
These transformers can be used for metering and protection in high voltage circuits, it is another type of instrument transformer. It is designed to have an accurate transformation ratio in both magnitude and phase over a range of measuring circuit impedance, it is designed to present a negligible load to the supply being measured. The low secondary voltage will allow protective relay equipment and measuring instruments to be operated at lower voltages
Potential transformer
These transformers step down the voltage of a circuit to a low value which can be effectively and safely used for the operation of instruments such as ammeters, voltmeters, watt meters and relays
It is designed to monitor the single-phase and three-phase power line voltages in power metering applications. It is a special type of transformer which allows a meter to take reading from electrical service connections with a higher voltage than the meter is normally capable to handle. They are used to provide accurate voltage step down ratio as possible
Applications
- They are used in electrical instrumentation system due to its ability to step up and step down the voltage and current and the electrical isolation they provide
- They are used in transmission lines for voltage measurements, power metering and the protection of lines
- They are used for the substation service
Difference between a potential transformer and current transformer
- Potential transformers are used in high voltage voltmeters while current transformers are used in place of the ordinary ammeter
- There are several different winding on the primary of the potential transformer but in current transformer, there is only a single winding
- One potential transformer can be used for the three-phase transmission line but while using current transformers in three-phase transmission line three current transformer is needed
- Power transformer will step down the voltage and step up the current while the current transformer will step down the current and step up the voltage
