Instrument Transformers Instrument transformers are used for metering and protection in a power system. Electrical measurements and relaying decisions in a power system are made based on the current and voltage obtained from the system. Relays work with smaller magnitudes of these signals. Real life currents and voltages thus have to be scaled to lower […]
The current transformers are always used with the secondary windings circuit closed through ammeters, current coils of watt-meters or relay coils. Its secondary winding circuit should not be opened while its primary winding is energized. A violation of this precaution may lead to serious consequences. Here, I am discussing the reasons behind it. As we
Instrument transformers are essential parts of many electrical metering and relaying systems. The quality of instrument transformers will affect directly the overall accuracy and performance of these systems. Instrument transformer performance is critical in protective relaying since the relays can only be as good as the instrument transformers. They serve two basic functions: To change
The main tests that are conducted on instrument transformers are as follows: Polarity Test of Instrument Transformers Instrument transformers are marked to indicate the instantaneous direction of primary and secondary currents. Usually, one primary and one secondary terminal are marked with a cross (×) or a dot (•) or a square (■) to indicate the
For the measurement of large currents and high voltages in AC circuits, specially constructed accurate ratio transformers are used in conjunction with low range AC instruments. These specially constructed transformers are known as instrument transformers. Types of Instrument Transformer There are two types of instrument transformer. These are: Potential Transformers (PTs) Current Transformers (CTs) These instrument