What is CURRENT TRANSFORMER..

[sohail qureshi]

hi experts...
i wanna asks about current transformer...?? what is current transformer..?? what is CT ratio..? and where we use current transformer....?? tnx in advance

 

[mtwieg]

A current transformer in general is a device that senses current flowing through some part of a circuit. The CT gives an output current on its secondary that is proportional to the current flowing through its primary. The ratio between the two is the turns ratio.

CTs are nice because they are inherently isolated measurements, so you can measure currents at nodes that are not ground referenced. Very common in medium to high power SMPS and motor controllers.

 

[sohail qureshi]

tnx alot for coopreation.....as we know that voltage transformer step up or step down ac voltage, can current trasnformer step up or step down the current.........?? or CT only measures the current.....??

 

[jpanhalt]

A couple of additions to what has been said...

1) Current transformers are for measuring AC. For DC, you might want to look at Hall sensors.
2) The turns ratio of a current transformer (CT) is usually quite high. So, if you have 1000 to 2000 turns and the wire being measured passes through it once, there will be a great increase in voltage across the CT. In other words, a CT can represent a significant shock hazard and should always have some load across its terminals.

John

 

[atripathi]

Typically (I think always) CT is step up. In CT primary winding is typically (always) 1 turn and secondary could have many turns (typically 100+). What it does: It steps down the primary current and hence steps up the voltage. CT is nothing but a type of transformer, one of the special configuration of transformer is called CT. Read more at Current transformer - Wikipedia, the free encyclopedia

 

[debjit625]

tnx alot for coopreation.....as we know that voltage transformer step up or step down ac voltage, can current trasnformer step up or step down the current.........?? or CT only measures the current.....??

Any transformer does the both.For example a step down transformer will step down voltage and step up current like a 230VAC to 12VAC 1Amp step down transformer will have a primary current around 12/230 = 0.0521739A or 52.174mA.Transformers just mutually transfer power ,if they step up voltage they step down current and if they step down voltage they step up current.

CT is also a transformer nothing different,its like this a ratio of 100:5 CT means that in primary if we have 100 amperes of current then in secondary you will find 5 amperes of current,now we don't measure current what we do is we use a resistor (load) in secondary so that their would be a voltage drop accross the load as per V = I * R,and we measure this voltage drop.The secondary's load is known as burden.Many times meters internal resistance or more properly impedance is used as burden.

Now above you can see the 100:5 CT is stepping down current so it will step up voltage,and this voltage is very high as the ratio is already given with out a burden connected to secondary this voltage is a shock hazard so be carefull.

Their are different types of CTs like Wound Primary CTs can measure upto 1 to 100 Amps,Ring core CTs can measure upto 50 to 5000 Amps and Split core CTs can measure upto 100 to 5000 Amps.

If you are trying to measure small current use Wound Primary CTs they are avaliable in ratios from 2.5:5 to 100:5.

As John already said use Hall sensors for DC they can also be used in AC for measuring current.

Good Luck

 

[goldsmith]

Hey Guy!
If you want to get sample from a big currents , you will have many way to obtain this purpose.
One of these ways is CT or(current transformer). it is very simple Device , really. if current going into its primary , according to the ratio of change ( for example 1/5) gives you , a current with this Ratio. for example you have 500 Amperes current in its primary. you will have 100 amperes in its secondary as well as.
Best wishes
Goldsmith

 

[LvW]

1) Current transformers are for measuring AC. For DC, you might want to look at Hall sensors.

For DC you also can use "current conveyors" (CC), which are active devices with current-in and current-out.

 

[mtwieg]

In general people refer to DC current transducers as current transformers, so long as they have a current output. From a black box perspective they're the same thing, except they use active electronics.

 

[sohail qureshi]

i m impoving alot.....tnx alot to all