Voltage and Potential Transformers

Voltage transformers and potential transformers are used to measure voltage in electric circuits. Their main role is to condition (step down) the voltage to be measured to levels suitable for the measuring instrument. Voltage and potential transformers have a secondary voltage that is substantially proportional to the primary voltage, but differs in phase by an angle that is approximately zero for an appropriate direction of the connections. A low voltage transformer converts normal line voltage (120 VAC) to low voltage (typically 12 VAC). This lower voltage can then be used to power an incandescent low-voltage lamp. A dimmer is specifically designed for an electronic low-voltage transformer. A low voltage lighting transformer converts 120-volt currents to a relatively safe and energy efficient 12-volt (low-voltage) current for many outdoor lighting applications.

There are many different types of voltage transformers and potential transformers. A high voltage transformer operates with high voltages. Typically, these voltage transformers are used in power transmission applications, where voltages are high enough to present a safety hazard. A medium voltage transformer can be connected directly to a primary distribution circuit and generally has the most load diversity. These voltage and potential transformers have installation practices that are generally in accordance with application recommendations from the Institute of Electrical and Electronic Engineers (IEEE). Voltage transformers such as a constant voltage transformer maintain a relatively constant output voltage for variations of up to 20% in the input voltage. A transformer and voltage regulator is a transformer whose voltage ratio of transformation can be adjusted. A variable voltage transformer is a transformer that changes voltage, such as changing the ratio between primary and secondary coils. These voltage and potential transformers usually provide automatic adjustment controls to maintain "constant" (regulated) voltage output.

Selecting voltage transformers and potential transformers requires and analysis of performance specifications such as single-phase or three-phase primary configuration, primary frequency, maximum primary voltage rating, maximum secondary voltage rating, maximum power rating, and output type. The size and cost of a single-phase voltage transformer increases with the number of leads. A five-lead primary requires more copy than a quad or 2+2 primary. A ladder is the least economical primary configuration. Three phase voltage and potential transformers are connected in delta or wye configurations. A wye (Y) - delta transformer has its primary winding connected in a wye and its secondary winding connected in a delta. A delta - wye (Y) transformer has its primary winding connected in a delta and its secondary winding connected in a wye.

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