Current and Potential transformers both are actually Instrument transformers, which step down or lower down the values of current and voltages for measuring purposes.But I have heard of that both CT and PT specifically are used for stepping up current and voltages at some point of transmission system.if this is correct then can anyone tell where they are used?If not then there are step up transformers for similar uses but my question is why they are not called as CT's or PT's.
Transformers that are called current transformers and potential transformers are designed specifically for instrumentation purposes. They are designed to provide reduced current or voltage signals that very accurately represent the primary current or voltage. They are designed to have a minimal effect on the primary circuit. The are manufactured only in sizes needed for instrumentation purposes. Instrumentation purposes include not only providing signals to meters but providing signals to protective relays and control systems. CTs and PTs may occasionally be used for purposes other than the purposes for which they are designed. I have heard of a CT being used backwards to supply a high current at a very low voltage for some testing purpose. This sort of thing is sometimes done as a temporary measure when more appropriate devices are not available.
Assume the source is our normal house electric supply. Assume that the following loads will work safely for the two voltages. Case 1. The load is impedence type. Then Power is Voltage^2/impedence. Example is our heater load. Hence by manupulation of the impedence, we can manupulate the power output. Case 2. Assume it is a constant horse power motor load similar to our fridge. Adjustment of voltage will not alter the power output. The power output will be entirely decided by the load horse power. But an increase voltage will reduce the input current, there by reducing the heat loss in the load.
The usual application of CTs and VTs is to provide isolation between the power system and instrumentation and/or protection equipment. And in this instance, the transformation is usually to reduce the magnitude of the voltage or current that is being measured. There occasionally are instances in which it is necessary to increase the magnitude of voltage or current. In most instances these situations involve relatively minor adjustments in the magnitude of voltage or current and take place in the CT or VT secondary. The transformers that are used to make these adjustments are typically called 'auxiliary' CTs or VTs. There are a few very specialized situations in which CTs or VTs are used to couple a signal into the power system itself. One example of this is where a high-frequency signal is superimposed onto the power system to establish a control communications channel. So-called 'power line carrier' signals are usually in the kHz range, and are typically coupled into the system via VTs - most often, capacitive VTs rather than inductive VTs.
