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Understanding how transformers change values of voltage and current is important to the information presented in later units. Many AC motors operate on these principles. We will…
Transformers are among the most common devices found in the electrical field. They range in size from less than one cubic inch to the size of rail cars. Their ratings can range from milli-volt-amperes (mVA) to giga-volt amperes (GVA). It’s imperative that anyone working in the electrical field have an understanding of transformer types and connections. This unit presents transformers intended for use in single-phase installations. The two main types of voltage transformers, isolation transformers and autotransformers, are discussed.
+++++1 All values of a transformer are proportional to its turns ratio. Primary 1000 turns; Secondary 250 turns
+++++2 An isolation transformer has its primary and secondary windings electrically separated from each other. Load Secondary Primary
A transformer is a magnetically operated machine that can change values of voltage, current, and impedance without a change of frequency. Transformers are the most efficient machines known. Their efficiencies commonly range from 90% to 99% at full load. Transformers can be divided into three classifications:
1. Isolation transformer
3. Current transformer
All values of a transformer are proportional to its turns ratio. This does not mean that the exact number of turns of wire on each winding must be known to determine different values of voltage and current for a transformer.
What must be known is the ratio of turns. For example, assume a transformer has two windings. One winding, the primary, has 1000 turns of wire; and the other, the secondary, has 250 turns of wire (). The turns ratio of this transformer is 4 to 1, or 4:1 (1000 turns/250 turns=4). This indicates there are four turns of wire on the primary for every one turn of wire on the secondary.
Different formulas can be used to find the values of voltage and current for a transformer. The following is a list of standard formulas, where ...
NP=number of turns in the primary
NS = number of turns in the secondary
EP=voltage of the primary
ES=voltage of the secondary
IP = current in the primary
IS = current in the secondary
The primary winding of a transformer is the power input winding. It’s the winding that is connected to the incoming power supply. The secondary winding is the load winding, or output winding. It’s the side of the trans former that is connected to the driven load).
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