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In electrical engineering, an autotransformer is an electrical transformer with only one winding. The "auto" (Greek for "self") prefix refers to the single coil acting alone. In an autotransformer, portions of the same winding act as both the primary winding and secondary winding sides of the transformer. In contrast, an ordinary transformer ...
This basic principle explains the source of the destructive transient voltage in the Korndörfer motor starter apparatus. A further transient problem is that with a single coil construction and a star switch, the autotransformer acts as a step-up transformer during the <5 microsecond period at contact separation of the Star point switch.
A transformer or autotransformer can be used; (auto)transformers are inherently reversible, so the same transformer can be used to step the voltage up, or step it down by the same ratio. Lighter and smaller devices can be made using electronic circuitry; reducing the voltage electronically is simpler and cheaper than increasing it.
A leakage transformer, also called a stray-field transformer, has a significantly higher leakage inductance than other transformers, sometimes increased by a magnetic bypass or shunt in its core between primary and secondary, which is sometimes adjustable with a set screw. This provides a transformer with an inherent current limitation due to ...
A conventional six-winding, grounding transformer or zigzag bank, [1] with the same winding and core quantity as a conventional three-phase transformer, can also be used in zigzag winding connection. In all cases the first coil on each zigzag winding core is connected contrariwise to the second coil on the next core.
For example, a 24 VCT transformer will measure 24 VAC across the outer two taps (winding as a whole), and 12 VAC from each outer tap to the center-tap (half winding). These two 12 VAC supplies are 180 degrees out of phase with each other, measured with respect to the tap, thus making it easy to derive positive and negative 12 volt DC power ...
However, a transformer may include a tap changer on each winding if there are advantages to do so. For example, in power distribution networks, a large step-down transformer may have an off-load tap changer on the primary winding and an on load automatic tap changer on the secondary winding or windings. The high voltage tap is set to match long ...
Generally, static VAR compensation is not done at line voltage; a bank of transformers steps the transmission voltage (for example, 230 kV) down to a much lower level (for example, 9.0 kV). [5] This reduces the size and number of components needed in the SVC, although the conductors must be very large to handle the high currents associated with ...