current transformer

http://en.wikipedia.org/wiki/Current_transformer

Also see previous CR4 threads on this subject.

If by "blasts", you mean 'voltage spikes' or 'sparks':

A CT behaves similar to a car's ignition coil which discharges via the secondary, (to the spark plug), when the primary is open circuited. This is the simplist explaination I could find http://en.wikipedia.org/wiki/Induction_coil

A Tesla coil is the same working principal. http://en.wikipedia.org/wiki/Tesla_coil

If this hasn't answered - or put you on the path - come back to me.

note; the terminology of primary and secondary is always 'true' to: 'primary' is the supply/input and 'secondary' is the output.

Or it's about the direction of the process, not the coil wire thickness or number of turns. These are to do with VA ratio - not 'process direction'.

http://www.control.com/thread/1026220105

If you mean does the current transformer explode when the secondary is opened (circuit energized), it depends on the voltage of the measured circuit. If the CT is in a low voltage (120 - 600 volts) circuit, probably no "blast" will occur. However, if the circuit is much higher in voltage (say 13.8 kv to 500 kv) then if the secondary is opened the primary potential will develop across the secondary terminals and the insulation will fail causing a blast or worse. For this reason CT secondaries are always short circuited if the secondary wiring must be moved, opened, reconnected, etc. Hope this helps.

Regarding current transformers (CT), they differ from your normal potential transfomer (voltage ) in that the primary current depends entirely on the load on the system and not on the secondary load.Therefore if the secondary is opened while the primary windings are carrying a heavy load, the demagnetising effect of the secondary current will no longer exist and there will be an increase in the flux in the secondary circuit, this could very well puncture the insulation or produce a dangerous shock to anyone coming into contact with it. therefore the seondary of CT should never be opened while the primary is energised. I hope this helps.

give correct explanation

Defines it as close as anything to be a home work. At my times at least the questions (in home work or in exams used to end like this.)

The subject came many times. Students, trying the easy way to answer the questions to their homework. Well, what if is the instructor the one having difficulties answering his own (or compiled from books) questions?

There was a related thread started yesterday on short-circuiting CT's prior to removing the load. Answers to it explain your question. However, this sounds like a homework assignment. Please explain why you are asking this question and also look at the other thread. If you can give a good reason for not understanding, then we'll continue.

Regards--John M.

Mate, when you say Blasts, i presume you mean burn out!

A current transformer is like any other transformer, the only difference is that the primary winding only has one winding, the one going through the CT. The secondary which is your current transformer, has hundreds if not thousands of windings, so when the CT is open circuit, the voltage generated in the secondary winding (your CT) can get very high, causing a total breakdown in the insulation of the CT. If you have to service a CT, i recomend that you either disconnect the power or short out the terminals of the CT to avoid failure, any other action is asking for failure. Simple croc clips across the terminals of the CT will allow you to do any repairs further down the line without damage to to CT. Just remember to remove the croc clips when you have finished you service work. Cheers Joe Sparky

Dear Mr.Rukmagoud,

The answer for your question, WHY CURRENT TRANSFORMER BLASTS WHEN SECONDARYIS OPEN CIRCUITED in simple terms, is,

THE VOLTAGE IS MULTIPLIED BY THE RATIO OF THE CURRENT TRANSFORMER.

For example, if you use 5000/5 RATIO CURRENT TRANSFORMER, THE RATIO IS

1000, AND IF THE VOLTAGE IS 420, THE TERMINAL VOLTAGE AT THE LOW CURRENT

SIDE WILL BE 420 x 1000 = 4,20,000 Volts, and this high voltage results in blasting of

the transformer.

DHAYANANDHAN.S,

CR 4 MEMBER,

INDIA.