PowerPoint Presentation

St. Thomas College of Engineering and Technology

Subject: Technical report writingTopic: Role of Transformers in Power System

Group members: Debojyoti Mukherjee-37Sayantan mondal-38Sourav mondal-42Yogesh Kumar verma-62

Definition of Transformer

A transformer is a static machine used for transforming power from one circuit to another without changing frequency. It also transfers electrical energy between two or more circuits throughprinciple of electromagnetic induction. Commonly, transformers are used to increase or decrease the voltages of alternating current in electric power applications.

Types of transformer

Step up transformer If the no. of turns on the secondary is more than the no. of turns on the primary windings, then the secondary voltage is more than the primary winding. This type of transformer is called step up transformer.Step down transformer If the no. of turns on the secondary is less than the no. of turns on the primary windings, then the secondary voltage is more than the primary winding. This type of transformer is called step down transformer. Applications of power transformer

It can rise or lower the level of level of Voltage or Current ( when voltage increases, current decreases and vice versa because P =V x I, and Power is same ) in an AC Circuit.It can increase or decrease the value of capacitor, an inductor or resistance in an AC circuit. It can thus act as an impedance transferring device. It can be used to prevent DC from passing from one circuit to the other. It can isolate two circuits electrically.Signal and audio transformers are used to couple stages of amplifiers and to match devices such as microphones and record players to the input of amplifiers.Transformers are also used extensively in electronic products to decrease (or step-down) the supply voltage to a level suitable for the low voltage circuits they contain.

Power Transmission

1.Generate the electricity: different generators produce different voltages, but a very rough typical value might be 1,000 volts.2.Increase voltage via a step-up transformer at an electrical station near the power plant, up to maybe 500,000 volts.3.Send electricity long distance over high-voltage transmission lines.4.Decrease voltage at a local substation via a step-down transformer to perhaps 3,000 volts .5.Send electricity a few miles via "telephone poles" (or underground cables.6.Divert some electricity to an individual building, decreasing the voltage to 240 volts with another step-down transformer.7.When it first enters the building, run electricity through a fuse-box or set of circuit breakers. Most of the wiring inside the house is arranged so that it makes use of only 120 volts.

Basic formulas of transformerWhy High Voltage is Used in Transmission System?Small Conductor Size: Let us consider we have to transmit a power of W watts over a distance L. Now consider two situations a) Power is being transmitted in line at V voltsa) Power is being transmitted in line at 2V voltsWe know that P=VI,WhereP=Power in the systemV=Voltage of the lineI=Current in the linein first case I=P/V=k(say) but for second case I=P/2v=k/2.Hence double the voltage level half will be the current in the line.We know that for a small current small area of cross section of the conductor is required as transmission lines are designed at a constant current density (Current/Area). This shows that increase in transmission voltage will result in reduction of conductor area and hence conductor weight. Thus an increase in voltage level will result in saving of conductor cost.

Reduction In Copper Losses : We know that Copper Losses, Pc = I2RWhere, Pc = Copper loss in transmission LineI=Current in Lineand R= Resistance of Line.Now resistance of line is constant (once installed) so if we increase voltage level then this will reduce the copper losses in the transmission line which further result in saving of power and ultimately saving of money.Better Voltage Regulation : Voltage Regulation is given by the formula, VReg=(Vnl-Vfl)/VflWhere Vnl= Voltage at no loadVfl= Voltage at full loadFor a transmission line Vfl=Vnl-VDropVDrop being drop at the transmission line and this is given by VDrop=I*R, now if I is reduced in line then Voltage regulation will be reduced and operation of machines and line will be good.If we can generate power at high voltage and why we cant use it at high voltage level?

It is not possible due to insulation problems in generators and also due to safety reasons this is not practical. Also our systems are designed for a low voltage so it can not be generated or consumed at very high level.

Limitations to Voltage Level in Transmission System

As insulation is a big issue. We use transformers which has to withstand the voltage in the line but there is only a limited voltage for which insulation can be provided. Further if we increase voltage then for very high voltage we'll require high steel tower and at a point cost of installing line will be more then cost saved due to high voltage. Hence ,these things limit the voltage level in transmission line.

Circuit diagram of a TransformerRole of transformers in power system

Energy is lost in the process of transmitting electricity long distances, such as during the journey from a power plant to us. Less energy is lost if the voltage is very high, so electrical utilities use high voltage in long-distance transmission wires. However, this high voltage is too dangerous for home use. Electrical utilities use transformers to change the voltage of electricity as it travels from the power plant to us.The voltage of electricity coming from the power plant is "stepped up" using transformers to the right level for long-distance transmission. Later, the voltage is stepped down before it enters your home - once again using transformers.

for power distribution ,voltages must be stepped up before power is transmitted great distances over power lines. One major problem is that power is lost between the power plant and the consumers because currents use some of the power to heat the transmission lines. The power transmitted along the line is equal to the voltage times the current. The higher the voltage the lower the current that must flow within the transmission lines to deliver the same power.Lower currents produce much less heating and much less power loss. Of course, the high voltages (needed to drive the low currents) must be stepped back down before power is supplied to our homes.

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