I have always known that a current tranformer's secondary winding is NOT to left open circuited under no circumstances under load as it will burn out,I am hearing rumours that there is a current transformer that will not ? can someone clear the air?
current transformer
- Thread starter a.bisnath
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ohmhead
Senior Member
- Location
- ORLANDO FLA
Well i dont know about burning out i dont see how it would but a ct left open under load is a dangerous condition of high voltage potential we usally short them out when around these . take care best to ya
gar
Senior Member
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- Ann Arbor, Michigan
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- EE
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a.bisnath:
A current sensor based on a Hall device will not have an open circuit problem. The Hall device produces a small voltage output proportional to the magnetic field intensity applied to the Hall device and the current thru the Hall element.
This device uses a constant current in the MA range thru the semiconductor as a bias and the magnetic field from the current in the wire of interest is what is measured, and that magnetic field from the wire of interest is proportional to the wire current up to a saturation point.
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a.bisnath:
A current sensor based on a Hall device will not have an open circuit problem. The Hall device produces a small voltage output proportional to the magnetic field intensity applied to the Hall device and the current thru the Hall element.
This device uses a constant current in the MA range thru the semiconductor as a bias and the magnetic field from the current in the wire of interest is what is measured, and that magnetic field from the wire of interest is proportional to the wire current up to a saturation point.
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brian john
Senior Member
- Location
- Kilmarnock, Va
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- Retired after 52 years in the trade.
I have replaced dozens of CTs that were left open some were not longer operating, some were inaccurate others were a burn pile of junk. I have posted pics here before of damaged (burnt) CTs.
- Location
- Massachusetts
Left open the high voltage can exceed the insulations ratings and cause failures.
ohmhead
Senior Member
- Location
- ORLANDO FLA
Well Iwire , we dont do service work ya learn each day something new.
So they burn up if left open never have i seen one ever after were done left open on any job. take care
So they burn up if left open never have i seen one ever after were done left open on any job. take care
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
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- Electrical Contractor
An unterminated CT acts like a PT and reverses the CT's current ratio. A 400:5 CT, with an 80:1 turns ratio, can act as a 1:80 PT. The result can be thousands of volts in what is now the secondary.
Cold Fusion
Senior Member
- Location
- way north
Rogowski Coil current sensors don't burn up if open circuited. They are available, but I haven't seen very many - don't know why not. As I understand, the concept is 70+years old, but they weren't practical until the electronics bcame available.
One would have expected them to become popular after the electronic relays started coming out.
cf
One would have expected them to become popular after the electronic relays started coming out.
cf
broadgage
Senior Member
- Location
- London, England
If a traditional current transformer is open circuited whilst current flows in the primary, then a very high voltage will be induced in the transformer. This voltage is likely to be far in excess of the insulation rating, and the current transformer is liable to burn out.
Current transformers are available that will withstand an open circuit, they have a built in circuit that protects against high voltage by Zener diodes or similar means.
Alternativly current sensors are available that are not in fact transformers at all (though they are sometimes so called), these units sense the magnetic field, and produce an output to a meter or overload relay etc.
These may be open circuited without harm.
Current transformers are available that will withstand an open circuit, they have a built in circuit that protects against high voltage by Zener diodes or similar means.
Alternativly current sensors are available that are not in fact transformers at all (though they are sometimes so called), these units sense the magnetic field, and produce an output to a meter or overload relay etc.
These may be open circuited without harm.
ohmhead
Senior Member
- Location
- ORLANDO FLA
Well yes that kinda makes sense in the fact that a simple Metal Oxide Varistor that little MOV at rated voltage of the ct used can protect this open circuit self induction problem in the ct circuit and prevent it from burning up when left open and they been around since the am radio was invented .
And so old stuff can be used today . Take care be safe gezz ya learn something eveyday
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