CT & PT

That's covered on page 238 of your text book.

This will get you half of the way there:

Link

CT's are pretty basic and much more common...you probably already know that.

a CT is spelt with a "C" and a PT is spelt with a "P", hope this helps!

This is a very basic question and you did misuse the word "there" - should have been "their" but I suppose you deserve an answer. I have to assume you know what a transformer is or else this is a real waste of time. Current transformers change the current - usually they step it down. Potential transformers change the voltage - usually down. Lots of power equipment operates at too high of a voltage and with too much current (amps) for the control equipment or the metering equipment. CT's reduce the current and PT's reduce the voltage to levels that are acceptable for the controls or metering. This is a basic answer to a basic question and there are lots of potential answers to the current question.

Dear Mr. Jim,

thanks a lot for the answer.

Current and voltage transformers are used to reduce high current and voltage to levels where they can be connected to instrumentation without damaging the instrumentation.

Current transformers ratio's are normally selected to reduce the current to 5 amps on the secondary when you have full load current on the primary side of the transformer. Example a 100:5 current transformer will provided 5 amps at the secondary when 100 amps is applied to the primary of the transformer. The ratio in this example is 20:1.

Voltage transformers ratio's are normally selected to provide 120 volts on the secondary when full voltage is applied to the primary. Example a 100:1 voltage transformer will have 120 volts on the secondary when 12kV is applied to the primary of a PT. The ratio in this example is 100:1.

The multiplier for the CT and VT selected above would be CTR X PTR= 20 X 100 = 2000. If the above CT and PT were connected to some type of intrument the reading of the instrument would be multiplied by 2000 to get the correct results.