1)Generally current transformers are distinguished for measuring purpose and protection purposes. Instrument transformers are assigned for connection direct reading, writing and counting measuring equipment and protecting these additional from overcurrent. Protection transformers are assigned for connecting plants protection equipment.
2)Fundamentally current transformation is very important in transformers. it can be distinguished between single conductor current transformers and wound primary current transformers. the most important type of single ct’s are the window type ct which are designed to be pushed onto the primary conductor.
3)Current transformers can perform circuit control, measure current for power measurement and control, and perform roles for safety protection and current limiting. they can also cause circuit events to occur when the monitored current reaches a specified level. Current monitoring is necessary at frequencies from the 50 Hz/60 Hz power line to the higher frequencies of switch mode transformers that range into the hundreds of kilohertz.
4) The object with current transformers is to think in terms of current transformation rather than voltage ratios. Current ratios are the inverse of voltage ratios. The thing to remember about transformers is that Pout=(Pin – transformer power losses). with this in mind, lets assume we had an ideal loss-less transformer in which Pout=Pin.
since power is voltage times current, this product must be the same on the output as it is on the input.
5) If a transformer had one-turn primary and a ten-turn secondary, each amp in the primary results in 0.1A in the secondary, or a 10:1 current ratio.
some expected questions :
ques 1) how we can use this transformer and knowledge to produce something useful?
ans- Normally, an engineer wants to produce an output on the secondary proportional to the primary current. quite often , this output is in volts output per amp of primary current. The device that monitors this output voltage can be caliberated to produce the desired results when the voltage reaches a specified level.
ques 2) What does a transformer transform?
A transformer transforms one level of voltage and current into another. A step up transformer raises voltage and lowers current, usually to make long power lines more efficient, and a step down transformer raises current and lowers voltage, usually to make it safe for homes and appliances. There are other more specialized transformers as well. isolation transformers provide galvanic(DC) isolation between primary and secondary.
ques 3) What is the transformation ratio of an electrical transformer?
This is the ratio of input voltage (VP) to output voltage (VS). It can also be expressed as the number of turns on the input or primary winding (NP) side of the transformer to the number of turns on output or secondary winding (NS) side of transformer. Also another way of expressing the transformation ratio is output current (IS) to input current (IP).