Instrument Transformers are transformers which convert high currents or voltages into measurable and standardized currents or voltages. These are then proportional and in-phased to the primary signal. They are intended to supply electrical measuring instruments, meters, relays or other electrical devices. Furthermore the connected measuring and protective devices are electrically insulated against live parts.
A) Voltage Transformer
Voltage Transformers have only one iron core with an attached secondary winding. If an open delta circuit is necessary, an additional winding can be provided for the Single Pole Insulated Transformers.
For Single Pole Insulated Transformers the end of the primary winding is grounded as "N" inside of the secondary terminal box and must not be removed during operation
B) Current Transformer
Current Transformer is designed to convert the primary rated current which flows though the primary winding. The secondary winding must generally be short circuited at all times, otherwise dangerous high voltages can occur at the secondary terminals.
The secondary connected devices are connected in series. Current Transformers can be equipped with one or more independent magnetic cores with equal or different characteristics for measuring, metering and/or protective purposes.