All current transformers operate on the same principles, and all provide a similar role in protecting instruments and equipment. They are designed to provide a protective relay that allows for the measurement and metering of the power through equipment that operates on lower voltage and current requirements.
The current transformer has the role of stepping down the voltage and current and also providing isolation to further protect the equipment and measuring instruments from exposure to high voltage circuits. Each CT or current transformer is designed to provide one current ratio, which is determined by the configuration of the transformer.
A multi ratio current transformer has the same basic design as a standard current transformer, but it has some crucial differences. It has a single primary winding, but instead of the secondary winding with one terminal, there are additional secondary terminals. This allows for the taps to be accessed on the secondary winding to allow customers to utilize multiple current ratios from the same current transformer.
The choice of the multi ratio current transformer has obvious cost-saving potential. With most standard models it is possible to obtain up to ten different ratios on one current transformer. With custom models and design options, this can be further refined to meet the specific requirements for the customer and the application.
While the option to use a customized multi ratio current transformer includes an additional cost over a standard off the shelf option, there are important considerations to keep in mind. The customized design in the current transformer allows for the exact requirements needed for metering, measuring and monitoring, which can extend the life of the current transformer and also increase efficiency and accuracy, all which are essential considerations to keep in mind.