Ques-11: What is exciting current?
Ans: Exciting current, when used in connection with transformers, is the current or amperes required for excitation. The exciting current on most lighting and power transformers varies from approximately 10% on small sizes of about 1 KVA and smaller to approximately. 5% to 4% on larger sizes of 750 KVA. The exciting current is made up of two components, one of which is a real component and is in the form of losses or referred to as no load watts; the other is in the form of reactive power and is referred to as KVAR.
Ques-12: What is the use of iron core in a transformer?
Ques-14. What wil happen if 50 Hz Transformer is operated at 100 Hz Frequency?
Ans: According to EMF equation of the transformer frequency is directly proportional to winding voltage.
If we double the frequency the sinusoidal root mean winding voltage also doubled. So if the frequency is increased induced emf also increased and the induced emf will damage the insulation of the winding.
Ans: Exciting current, when used in connection with transformers, is the current or amperes required for excitation. The exciting current on most lighting and power transformers varies from approximately 10% on small sizes of about 1 KVA and smaller to approximately. 5% to 4% on larger sizes of 750 KVA. The exciting current is made up of two components, one of which is a real component and is in the form of losses or referred to as no load watts; the other is in the form of reactive power and is referred to as KVAR.
Ques-12: What is the use of iron core in a transformer?
Ans: The iron core is used in a transformer to provide continuous easy magnetic path of low reluctance.
Ques-13: What is the emf equation of transformer?
Ans: EMF equation of transformer, E = 4.44*f*N*φmax volts
f = Applied frequency of voltage wave
N = Number of turns on primary or secondary winding.
φmax = Maximum flux ( φmax = Bmax x A)
Bmax = Maximum flux density
A = Area of cross section of the core.
N = Number of turns on primary or secondary winding.
φmax = Maximum flux ( φmax = Bmax x A)
Bmax = Maximum flux density
A = Area of cross section of the core.
Ques-14. What wil happen if 50 Hz Transformer is operated at 100 Hz Frequency?
Ans: According to EMF equation of the transformer frequency is directly proportional to winding voltage.
If we double the frequency the sinusoidal root mean winding voltage also doubled. So if the frequency is increased induced emf also increased and the induced emf will damage the insulation of the winding.
Ques-15: Why should Dry-Type Transformers never be over-loaded?
Ans: Overloading of a transformer results in excessive temperature. This excessive temperature causes overheating which will result in rapid deterioration of the insulation and cause complete failure of the transformer coils.
Ques-16: Are temperature rise and actual surface temperature related?
Ans: No. This can be compared with an ordinary light bulb. The filament temperature of a light bulb
can exceed 2000 degrees, yet the surface temperature of the bulb is low enough to permit touching with bare hands.
can exceed 2000 degrees, yet the surface temperature of the bulb is low enough to permit touching with bare hands.
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