Explanation: Similar to normal transformers power transformers are also designed to get maximum efficiency at load which is near to the full load of a transformer specified. Only in the case distribution transformer maximum efficiency is achieved at 60% of full load.

Explanation: Power output= VI cosθ= 200*100*0.8 = 16000 W (Independent of lag and lead). While total losses are equal to iron loss+ k2*copper losses =120+ 300= 420 W. Efficiency is equal to 1- 420/(16000+420)= 97.44%.

Explanation: Voltage regulation is defined as change in the voltage or rise in voltage when transformer is load is thrown off. Thus, it is the difference of the no load voltage with the full load voltage divide by full load voltage to get % increase.

Explanation: The no-load current in a transformer is non-sinusoidal. The basic cause for this phenomenon, which lies in hysteresis and saturation non-linearities of the core material, will now be investigated; this can only be accomplished graphically.

Explanation: Auto transformer is a special type of transformer which has primary and secondary winding both located on same winding. Thus, winding material required for a transformer is very less in the case of autotransformer.

Explanation: For an auto transformer power is transferred partially inductively and partially conductively. Thus, out of total power, power transferred inductively is given by (1-k)*total power= 0.6*20= 12kVA.

Explanation: An important requirement of these transformers is that the amplitude voltage gain (ratio of output/input voltage amplitude) should remain almost constant over the range of frequencies (bandwidth) of the signal.

Explanation: In core type of the transformer, winding is done by normal method, while in the shell type transformer, winding is sandwiched between corresponding shells of core material. Hence, it is sandwich type.

Explanation: The shell-type five-limb type three-phase transformer construction is heavier and more expensive to build than the core-type. Five-limb cores are generally used for very large power transformers as they can be made with reduced height.

Explanation: Impedance test is done on a transformer in order to check net impedance offered by a transformer circuit at rated supply. Polarity test is also done before SC and OC test on transformer. Core insulation is also checked before installations in such tests.

Explanation: If secondary of current transformer is made open-circuited the transformer temperature will rise to higher value because of heavy iron losses taking place in the circuit due to high flux density.

Explanation: The increase in primary or secondary current of welding transformer increases the reactance voltage drop across the respective windings, which is essential to limit the welding current as the weld is practically a short circuit.

Explanation: Because of the effect of moisture on the resistivity of insulation material, it is necessary to obtain and maintain a high level of dryness in the insulation of HVDC transformers. This is equally important in service as it is in the factory at the time of testing.

Explanation: The supply voltage provides the input current to the transformer primary, here primary current is only sinusoidal magnetizing current. Thus, this sinusoidal magnetic current will produce core flux, flat-topped.

Explanation: Voltage in the primary of the transformer will get modified in the transformer secondary, according to the number of turns. Thus, turns are modified with 4 times the primary, we’ll get 4 times higher voltage at secondary.

Explanation: For a given transformer here, test is performed on low voltage side, thus we need the value of current on the low voltage side, by dividing the reactive power by the rated voltage value, i.e. 200*1000/100 = 445A.