Join 60,000+ competitive exam aspirants
or with email
Your Cart
SubtotalтВ╣0
TotalтВ╣0
Examoogle тАв User тАв info@examoogle.com тАв EE-2024-8821
Chapter 1 of 12 тАв Page 1 of 248ЁЯФТ Protected PDF тАв Watermarked
Join 60,000+ competitive exam aspirants
The statements which support the points that auto transformers are advantageous I. Weight of conductor reduces II. Ohmic losses reduces III. Leakage reactance reduces IV. Lower short-circuit current
I, II, III
II, III, IV
I, II, III, IV
IV
I, II, III
An autotransformer is more efficient than a two-winding transformer because it uses a single continuous winding to serve as both primary and secondary, leading to reduced material usage and lower losses. This design results in lower weight, reduced ohmic losses (due to less copper), and improved voltage regulation due to lower leakage reactance.
An autotransformer is more efficient than a two-winding transformer because it uses a single continuous winding to serve as both primary and secondary, leading to reduced material usage and lower losses. This design results in lower weight, reduced ohmic losses (due to less copper), and improved voltage regulation due to lower leakage reactance.
WautoтАЛ=WtwтАЛ├Ч(1тИТV1тАЛV2тАЛтАЛ) тАФ weight of copper relative to two-winding transformer
IcommonтАЛ=тИгI2тАЛтИТI1тАЛтИг тАФ current in the common winding portion
In an autotransformer, power is transferred through both magnetic induction and electrical conduction. Because the portion of the winding that is common to both primary and secondary carries only the difference between the currents, the total conductor cross-section required is smaller. This physical reduction directly decreases total resistance, leakage flux paths, and weight.
Autotransformers are more compact due to the common winding section.
The reduction in conductor material lowers the total resistance, thereby reducing ohmic (I2R) losses.
Leakage reactance is lower because the windings are physically close and share a single magnetic core circuit.
Autotransformers are NOT used when DC isolation is required between primary and secondary.
High efficiency
Smaller size and weight
Lower cost of manufacturing
Better voltage regulation
No electrical isolation between input and output
If the common winding breaks, the full input voltage may appear at the output
Low impedance results in higher short-circuit currents compared to two-winding transformers
Voltage regulators in power systems
Starting induction motors
Interconnecting systems operating at different voltage levels
Statement IV is incorrect because autotransformers actually have higher short-circuit currents due to their lower leakage reactance.
Because impedance is lower, the fault current under a short-circuit condition is significantly higher than that of an equivalent two-winding transformer.
A is correct тАФ Statements I, II, and III are valid advantages of an autotransformer, while IV is a disadvantage due to lower impedance causing higher fault currents.
Always remember that 'lower leakage reactance' results in 'higher short-circuit current', which is often a disadvantage, not an advantage in power systems.