What is a Transformer?
A Transformer is a static electrical machine which transfers AC electrical power from one circuit to the other circuit at the constant frequency, but the voltage level can be altered that means voltage can be increased or decreased according to the requirement.
It works on the principle of Faraday’s Law of Electromagnetic Induction which states that “ the magnitude of voltage is directly proportional to the rate of change of flux.”
Here are some key reasons why electrical transformers are necessary:
Voltage Transformation: Transformers are primarily used for voltage transformation. They can step up or step down the voltage levels as required. High voltage is used for efficient transmission of electricity over long distances, while low voltage is suitable for safe distribution and utilization of power in homes, offices, and industries.
Power Distribution: Transformers facilitate the distribution of electrical power across various locations. They are used in substations to step down the high-voltage electricity transmitted through power lines to lower voltage levels suitable for local distribution networks.
Loss Reduction: Transformers help reduce power losses during transmission and distribution. High-voltage transmission lines are used to minimize the current and hence the I2R losses, as power loss is proportional to the square of the current. By stepping up the voltage at the generation end, the current is reduced, resulting in lower transmission losses.
Isolation and Safety: Transformers provide electrical isolation between input and output circuits. This isolation ensures the safety of individuals and equipment by preventing direct contact with high-voltage components. It also helps protect sensitive equipment from voltage fluctuations and electrical disturbances.
Impedance Matching: Transformers are used to match the impedance between different electrical systems. Impedance matching ensures efficient transfer of power between the source and load, maximizing power transfer and minimizing reflection losses.
Power Conversion: Transformers are integral to various power conversion processes. They are used in AC to DC conversion (rectifiers) and DC to AC conversion (inverters) to adapt electrical power to different types of equipment and applications.
Overall, electrical transformers are essential components in modern power systems, enabling efficient transmission, distribution, and utilization of electrical energy while ensuring safety, minimizing losses, and enabling power conversion.
Construction of Transformer:
Basically a transformer consists of two inductive windings and a laminated steel core. The coils are insulated from each other as well as from the steel core. A transformer may also consist of a container for winding and core assembly (called as tank), suitable bushings to take our the terminals, oil conservator to provide oil in the transformer tank for cooling purposes etc. The figure at left illustrates the basic construction of a transformer.
In all types of transformers, core is constructed by assembling (stacking) laminated sheets of steel, with minimum air-gap between them (to achieve continuous magnetic path). The steel used is having high silicon content and sometimes heat treated, to provide high permeability and low hysteresis loss. Laminated sheets of steel are used to reduce eddy current loss. The sheets are cut in the shape as E,I and L. To avoid high reluctance at joints, laminations are stacked by alternating the sides of the joint. That is, if joints of first sheet assembly are at front face, the joints of the following assembly are kept at the back face.
Working:
The basic principle behind working of a transformer is the phenomenon of mutual induction between two windings linked by common magnetic flux. The figure at right shows the simplest form of a transformer.
Basically a transformer consists of two inductive coils; primary winding and secondary winding. The coils are electrically separated but magnetically linked to each other. When, primary winding is connected to a source of alternating voltage, alternating magnetic flux is produced around the winding. The core provides magnetic path for the flux, to get linked with the secondary winding. Most of the flux gets linked with the secondary winding which is called as 'useful flux' or main 'flux', and the flux which does not get linked with secondary winding is called as 'leakage flux'. As the flux produced is alternating (the direction of it is continuously changing), EMF gets induced in the secondary winding according to Faraday's law of electromagnetic induction. This emf is called 'mutually induced emf', and the frequency of mutually induced emf is same as that of supplied emf. If the secondary winding is closed circuit, then mutually induced current flows through it, and hence the electrical energy is transferred from one circuit (primary) to another circuit (secondary).
Parts of Transformer:
Laminated Core:
The main function of a laminated core is to separate primary and secondary windings. The core is laminated in order to reduce the core losses in a transformer. The core is generally made up of Cold Rolled Grain Oriented (CRGO) steel material windings.
Insulating materials:
The main function of insulating material is to provide insulation to windings so that it does not come in contact with the transformer core or other conducting material. The windings are wrapped in insulating paper or cloth.
Transformer oil:
The main function of the transformer oil is to provide insulation as well as act as a cooling agent due to its chemical properties and dielectric strength. It dissipates heat generated from the core and windings to the environment. Hence cooling the transformer.
Conservator tank:
The main function of a conservator tank is to provide extra space to accommodate the transformer oil during oil expansion inside the transformer when the ambient temperature rises. It is a cylindrical tank mounted on the top of the supporting structure of a transformer. It is generally half-filled with transformer oil.
Buchholz Relay:
The main function of the Buchholz relay is to protect the transformer from different internal faults such as inter-turn fault, short circuit fault, etc. It detects the occurrence of a fault and generates the alarm circuit. It is present between the main tank and the conservator tank.
Breather:
The main function of a breather is to prevent moisture to enter the transformer during the breathing cycle of a transformer. It contains the silica gel that absorbs the moisture from the air and hence prevents transformer oil to contaminate and thereby saves the internal parts.
Cooling tubes:
The main function of the cooling tubes is to transfer heat from the transformer core and coils to the environment. The heated transformer oil circulates through the cooling tubes where the heat radiates out by natural airflow and hence cooling the transformer oil.
Tap Changer:
The main function of the tap changer is to regulate the transformer output voltage by altering the number of turns in one winding and thereby changing the turn ratio of the transformer.
Protective Devices for Transformer:
1. Transformer-Electrical Protection Types:
- Over Current/Earth Fault:
- Under Impedance/Distance relay protection.
- Differential Current Protection.
- Restricted Earth fault Protection.
- Three Phase Overload Protection.
- Over Fluxing Protection.
- Over Voltage /Under Voltage protection.
2. Transformer-Mechanical Protection Types:
- Oil Temperature Indicator.
- Winding Temperature Indicator.
- Oil Pressure.
- Gas Accumulation using Gas. Accumulation Relay (Buchholz Relay).
Interview Questions.
1. What is the transformer?
Ans: Transformer is static device which transfer the power from one AC circuit to another AC circuit without change in frequency.
2. What is the working principle of a transformer.?
Ans: Transformer works on the principle of Faraday's law of mutual induction. When primary winding energized by supply voltage then due to mutual induction secondary winding is also energized.
3. Can we use a transformer in DC system?
Ans: No, we can't use DC supply for transformer because when DC supply apply on primary winding then it does not create mutual induction (emf) that's why secondary winding will not energized. AC supply have sine waves that's why it create mutual induction.
4. How neutral is create in transformer?
Ans: when windings second end is meet at one point then neutral is create. At that point voltage & current is zero. When secondary winding energized then it will reduced due to winding resistance & it becomes zero.
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