Search results
Results from the WOW.Com Content Network
In electrical engineering, a transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits.A varying current in any coil of the transformer produces a varying magnetic flux in the transformer's core, which induces a varying electromotive force (EMF) across any other coils wound around the same core.
Power ratings for electrical apparatus and transmission lines are a function of the duration of the proposed load and the ambient temperature; a transmission line or transformer, for example, can carry significantly more load in cold weather than in hot weather.
VA ratings are also often used for transformers; maximum output current is then VA rating divided by nominal output voltage. [5] Transformers with the same sized core usually have the same VA rating. The convention of using the volt-ampere to distinguish apparent power from real power is allowed by the SI standard. [6] [page needed]
Transformers step down transmission voltages, 35 kV or more, down to primary distribution voltages. These are medium voltage circuits, usually 600–35 000 V. [1] From the transformer, power goes to the busbar that can split the distribution power off in multiple directions. The bus distributes power to distribution lines, which fan out to ...
A high-voltage current transformer may contain several cores, each with a secondary winding, for different purposes (such as metering circuits, control, or protection). [7] A neutral current transformer is used as earth fault protection to measure any fault current flowing through the neutral line from the wye neutral point of a transformer.
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 ...
Distribution transformers typically have ratings less than 200 kVA, [3] although some national standards allow units up to 5000 kVA to be described as distribution transformers. Since distribution transformers are energized 24 hours a day (even when they don't carry any load), reducing iron losses is vital in their design.
Another way to avoid the transformer inrush current is a "transformer switching relay". This does not need time for cool down. It can also deal with power-line half-wave voltage dips and is short-circuit-proof. This technique is important for IEC 61000-4-11 tests. Another option, particularly for high-voltage circuits, is to use a pre-charge ...