What is autotransformers, Electrical Engineering

Q. What is Autotransformers?

In contrast to a two-winding transformer, the autotransformer is a single-winding transformer having a tap brought out at an intermediate point. Thus, as shown in Figure a-c is the single N1-turn winding wound on a laminated core, and b is the intermediate point where the tap is brought out such that b-c has N2 turns. The autotransformer may generally be used as either a step-up or a step-down operation. Considering the step-down arrangement, as shown in Figure, let the primary applied voltage be V1, resulting in amagnetizing current and a core flux φm. Voltage drops in the windings, exciting current, and small phase-angular differences are usually neglected for the analysis. Then it follows that


in which a> 1 for step-down, a< 1 for step-up transformers.

The input apparent power is S1 = V1I1, while the output apparent power is given by S2 = V2I2. The apparent power transformed by electromagnetic induction (or transformer action) is Sind = V2I3 = (V1-V2)I2. The output transferred by electrical conduction (because of the direct electrical connection between primary and secondarywindings) is given by Scond = V2I2-V2I3 = V2I1.


For the same output the autotransformer is smaller in size, weighing much less than a two- winding transformer, and has higher efficiency. An important disadvantage of the autotransformer is the direct copper connection (i.e., no electrical isolation) between the high- and low-voltage sides. A type of autotransformer commonly found in laboratories is the variable-ratio autotransformer, in which the tapped point b is movable. It is known as the variac (variable ac). Although here, for the sake of simplicity, we have considered only the single-phase autotransformer, three-phase autotransformers, which are available in practice, can be modeled on a per-phase basis and also analyzed just as the single-phase case.

Posted Date: 6/27/2013 12:31:05 AM | Location : United States

Related Discussions:- What is autotransformers, Assignment Help, Ask Question on What is autotransformers, Get Answer, Expert's Help, What is autotransformers Discussions

Write discussion on What is autotransformers
Your posts are moderated
Related Questions
define propagation characteristic in transformer

Determine the equivalent inductance: Two coils of inductances 4H and 6H are connected in parallel. If their mutual inductance is 3 H, determine the equivalent inductance of th

Q. Working of Electrically erasable programmable rom EEPROM is used for remote-area applications. The device is provided with special pins which, when activated electrically, a

) Design a suitable double –layer lap winding for a 6-pole dc armature with 18 slots

What are the predefined interrupts in 8086? The predefined interrupts are, DIVISION BY ZERO (type 0) Interrupt. SINGLE STEP (type 1) Interrupt. NONMASKABLE (ty

Q. Suppose a ROM holds a total of 8192 bits. (a) How many bits long would the individual addresses have to be? (b) If the bits are organized into 8-bit memory words or bytes,

Q. With a neat circuit diagram explain the working of a Hartley oscillator using an npn transistor and obtain the expression for oscillation frequency and for minimum gain for sust

an example and code for bargaining problem

Define voltage divider rule Voltage drop at every resistor that connected by serial can be search by using voltage divider rules (VDR).