Transformers Short Interview Questions
Transformers Short Interview Questions
Transformers Short Interview Questions
Ans. Since the induced primary ampere-turns and secondary ampere-turns always neutralize one
another, the flux in the core on load is the same as the flux on no load. Hence, the iron losses are
constant and are independent of load.
What is the difference between power transformers and distribution transformers ?
Ans. Those transformers installed at the sending or receiving end of long high-voltage
transmission lines are the power transformers. The distribution transformer (generally pole
mounted) are those installed in the localities of the city to provide utilization voltage at the
consumer terminals.
(i) Power transformers generally operate at nearly full-load. However, distribution transformers
operate at light loads during major part of the day.
(ii) The performance of a power transformer is generally judged from commercial efficiency
whereas the performance of a distribution transformer is judged from all-day efficiency
(iii) The rating of a power transformer is many times greater than that of a distribution transformer.
What would happen if a power transformer designed for operation on 50 Hz is
connected to a 500 Hz source of the same voltage ?
Ans. Power transformers are made to operate on one particular frequency, usually 50 Hz. If the
frequency is too high, the inductive reactance of the primary will prevent the primary from
drawing sufficient power. The hysteresis and eddy current losses will be excessive.
What would happen if a power transformer designed for operation on 50 Hz were
connected to a 5 Hz source of the same voltage ?
Ans. Power transformers are made to operate on one particular frequency, usually 50 Hz. If the
frequency is too low, the primary will have insufficient reactance and too much primary current
will flow, producing considerable copper losses. The transformer may start to smoke.
If part of a primary winding of a transformer were accidentally short-circuited, what
would be the immediate effect ?
Ans. If a few turns of the primary of a transformer short out for some reason, a high current will
be induced in the turns, producing excessive heat in the transformer. This is not only because of
the 'shorted turns' heating but also because of the cancellation of the inductance of the primary
by the magnetic field set up by the shorted turns. Cancellation of the inductance decreases the
inductive reactance of the primary and excessive primary current flows. This causes excessive
heat in the transformer.
Why are autotransformers not safe for supplying a low-voltage from a high-voltage
source ?
Ans. Autotransformers are not safe for supplying a low voltage form a high voltage source. It is
because if the winding that is common to both primary and secondary accidentally becomes
open-circuited, the full primary voltage will appear across the secondary. This may cause severe
shock to the operating personnel.
What functions are performed by instrument transformers ?