In every single locality, Transformers is been seen connected across the power lines. From small compact size to bulky giant one, These machines are available everywhere from a small electronic device to large power stations.
Stable & static, These machines are the most important Electrical machines, Performing the crucial task without any noise.
This post- A Basic Guide for Electrical Transformers, is about the transformer. Their working, Rating & their need.
ELECTRICAL TRANSFORMER
Electrical transformers are static machines without any moving part; These machines transfers electrical power from one circuit to another. Frequency do not alter in working of transformer. Transformers are easy & efficient method to change the voltage level. Transformers are also used to isolate one circuit from another.
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WORKING MECHANISM OF ELECTRICAL TRNASFORMER
“ Transformer works on the principle of faraday law of Electromagnetic Induction ! “
Generally, In basic design, It contains two windings primary & secondary. Both the windings are placed on a common core. Both primary & secondary are not directly connected to each other, Rather; They are magnetically coupled to each other.
When input supply is connected to primary winding, EMF get generated on secondary winding due to induction.
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In a GIF above,
” A basic transformer is shown with primary & secondary windings; winded on a common silicon steel stamping.
When an input voltage is applied across the primary winding. Input current starts flowing in primary winding which results an electromagnetic flux get created which links with secondary winding through common silicon steel stamping.
In response to primary field, On secondary winding, an EMF get generated.
Generated emf on secondary further create an electromagnetic flux which is equal but opposite to the primary flux which links further back with the primary winding.
Both the fields primary & secondary interacts with each other which is also known as ‘mutual induction’.
Current starts flowing on secondary winding, When an output load get connected across it.”
RATING OF TRANSFORMER
The 3phse Power formula is; √3*V*I*cosΦ [units ‘Watt’ (in terms of kilo it becomes Kilo Watt(KW)]
Where : V is Voltage | I is Current | cosΦ is power factor
The term power factor varies from 0 to 1, leading or lagging. This term Entirely depend upon the load that is connected across the secondary side of transformer. Because it is the load across the transformer which is consuming the power. That’s why term power factor needed to be neglected in transformer rating.
” Transformer is not consuming power Rather it is delivering it ! ” ( neglecting the other minor losses).
Than by neglecting the power factor, Power formula becomes :
P= √3*V*I [ units ‘VA’ (in terms of kilo- KVA)]
That’s why transformers are rated in KVA which is also known as Apparent power.
POWER RATING CALCULATIONS
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A Schematic diagram of an Ideal transformer is shown above. This diagram represents the both primary & secondary winding.
Vp= Primary voltage
Ip= Primary current
Np= Number of turns at primary
Vs= Secondary voltage
Is= Secondary current
Ns= Number of turns at secondary
As per conservation of Energy
Power rating primary = Power rating Secondary
√3*Vp*Ip*= √3*Vs*Is
For Better Explanation, Name plate of 500KVA transformer is discussed next.
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As per according to the name plate,
Vp= 11000
Ip= 26.24
Vs= 433
Is= 666.69
√3*Vp*Ip = 1.732*11000*26.24 = 499.9
√3*Vs*Is = 1.732*433*666.69 = 499.9
In ideal transformer As per according to faraday law of Electromagnetic Induction
Vp= -Np(dΦ/dt) . . .(Primary)
Vs= -Ns(dΦ/dt) . . .(Secondary)
From both the equations;
Vp/Np=Vs/Ns
Vp/Vs= Np/Ns
Vs= Vp*(Ns/Np) (// By changing the number of turns we can easily varies the voltage level)
Vp*Ip= Vs*Is
Vp/Vs=Is/Ip
Vp/Vs= Np/Ns=Is/Ip
From equation, Vs= Vp*(Ns/Np)
it is clear that,
If Ns>Np than Vs>Vp known as Step up transformer.
If Ns<Np than Vs<Vp known as Step down transformer.
A name plate of 320VA step down transformer is shown below. Voltage ratio is 400/230 V.
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An image of Step UP Transformer(12/230V) is shown below. This transformer is fitted inside 600VA UPS by MICROTEK.
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NEED oF TRANSFORMER !
IN POWER DISTRIBUTION
Source of Electricity can be thermal power plant, Hydropower plant or Nuclear power plant. These power generation utilities are far away from the consumer.
To deliver that much amount of power from that much distance at consumer level voltage ; is Impossible.
This is only possible by boosting the voltage at a higher level. That’s why at Generation end, Voltage been boosted to such a high level voltage. Further at consumer level, Voltage is been step down to consumer level.
To increase or decrease the voltage, A single electrical machine that is Transformer is required. Transformer easily step up (increase) or step down (decrease) the voltage.
” A Line diagram been shown next, In which it is clearly seen the working of transformers at different stages for different voltage levels. At Generating station, Generated 11KV been stepped up to 220KV & transmitted. At a Substation, 220KV been stepped down to 66KV & then to 11KV.
At last 11KV been stepped down to 415Volts Which is the consumer END voltage.”
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INSTRUMENTAL TRANSFORMERS
Whether it is high voltage or heavy current, It is difficult very much difficult to measure these heavy quantities directly. At such places, Instrumental transformers been used to measure these quantity indirectly.
Instrumental transformer actually lowers these heavy range quantities to a measurable level.
An image of 100/5 Current transformer fitted with Energy meter is shown below. The voltage is 11KV.
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ISOLATED TRANSFORMERS
Since primary & Secondary windings are not directly connected to each-other rather they are magnetically coupled. Isolated transformers are the special transformers in which input & output voltage remains the same. They are connected so that power supply get isolated from the load which actually helps to save the load from transients & noises occurring in power supply or vice versa, Isolated transformer used to isolate the load which is creating the transients.
SUM UP
- Transformer is static electrical machines which transfers electrical power from one circuit to another.
- While transferring, Power frequency remains the same in transformer.
- Transformer works on the principle of faraday law of electromagnetic induction.
- Generally, transformers have two sides primary winding & secondary winding.
- Both the winding sides are not directly connected to each other, Rather they are magnetically coupled.
- Transformers are rated in KVA, Known as apparent power.
- Voltage can easily be changed in transformer with higher efficiency that’s why used widely in distribution system.
- Transformers are also used as an instrumental transformer to measure high voltage & heavy current.
- Transformers are also used to isolate one circuit from another circuit.
Hope you like the post. If you have any doubt, Suggestion or query please do comments !