Measurement Transformers

The Measurement transformers are used for measuring high voltage and high currents. These are mostly helpful in isolating the circuits from them. Usually, the Primary of a transformer is connected with high inputs of voltages and currents whereas Secondary of the transformer is connected to some relay or circuit which has to be provided some isolation.

These are mainly of two types, Current transformers and Voltage transformers. Let us have a look at each of them.

Current Transformer

The Current transformers provide current in the secondary circuit proportional to the current in the primary circuit. These are used in protective relays and for measurement purposes.

A single turn primary winding is passed through a well-insulated toroidal core transformer which is wounded with many turns, which makes a Current Transformer. This is always connected in series.

The secondary winding can be designed to provide single output or it may have several tapping for different values. Care must be taken that the secondary winding is connected to its load having low impedance, while current flows in primary. This is to avoid sudden high voltages in open circuited secondary which might permanently damage the accuracy of the transformer.

Voltage Transformers

The Voltage Transformers provide voltage in the secondary circuit proportional to the voltage in the primary circuit. These transformers are also called as Potential Transformers. These are connected in parallel to the circuit.

The primary of this transformer may have phase to phase connections but the secondary will have one terminal to ground. The figure below shows an image of a voltage transformer.

There are three main types of a voltage transformers. They are

· Electromagnetic − uses a wire wound transformer having good flux linkages.

· Capacitor − uses a capacitor with potential divider network.

· Optical − makes use of electrical properties of optical materials.

The voltage transformers are used in protective relays and for measurement purposes and also for phasor phase shift isolation.

Protection Transformers

These transformers are very accurate than measuring transformers, as these are used only to protect the circuits from high voltages and currents. The primary of these transformers are connected with high inputs whereas the secondary of the transformer keeps the circuit or relay, isolated from the sudden spikes or surges which might damage the circuit.