How to test a Current Transformer (CT) ? thanks in advance
Yes, Current transformers can produce dangerous voltages, but I don't think they are properly loaded with an ac milliamp meter. If the primary has 1/2 turn and the secondary 5000 turns, the turns ratio is 10,000:1. One millivolt drop in the primary produces 10 volt ac in the secondary, but the volt meter loads the primary somewhat, so the voltage is somewhat less. A calibration curve can be made of ac current verses ac voltage for the particular volt meter, possibly up to 1000 volts ac, which may represent several thousand amps. Neil
BE CAREFUL! A Current transformer can generate very high voltages - hundreds or even thousands of volts - if it doesn't have a load! So the first rule of safety when working with CT's is to ALWAYS have a load on it!!! Start off with a load resistor, say a 10 Ohm, 5 Watt resistor. Connect the resistor directly across the CT's winding. Then read the voltage across the resistor. Run a single wire through the CT, and put a small current - say 1 Amp or so - this can be one of the 2 wires feeding a 100 Watt light bulb. This will give you a little less than 1 Amp. (Actually, by Ohms law: 0.8333 Amperes) P 100 E 120 I 0.8333 Amps R Then the voltage developed across the resistor with a known current will tell you the sensitivity of the CT. It is likely that the CT is made to connect to an ammeter - which has a resistance of only an ohm or two - which has been calibrated for that CT, in which case the voltage you get across a 10 Ohm resistor could be quite high. NOTE that a CT, like any transformer, only works with AC.
