What is the Difference Between a Current Transformers and a Voltage Transformers ?

The Difference Between a Current Transformers (CT) and a Voltage Transformers(VT) with circuit diagram, A transformer is a device that steps up, or steps down voltage. During this process current is also stepped up or down:however, voltage and current are inversely proportional ( meaning an increase in voltage results in a decrease in current and vice versa ).

current ( 1 amrere ) at the secondary...and a step down transformer with the As an example: A step up transformer of 10:1 ratio with 12 volts and 10 amper of current applied to the primary will have ten times the voltage ( 120 volts ) and ten times less same turns ratio with 120 volts and 1 ampere applied to the primary will have 12 volts and ten ampere available at the secondary. The electricity supplied into homes and bussiness uses wires carrying very high voltage and low current over long distances, then uses step down transformers to step down the voltage and step up the current. 

However, in power engineering and protective relaying applications, there are what are called "instrument transformers" which have the specific purpose of providing information to devices (such as relays or meters) about the voltages or currents in the power system. Therefore, there are some differences in construction and connectivity between a Current Transformer (CT) and a Voltage (or Potential) Transformer (PT).

 A CT will typically have a toroidal core and evenly distributed secondary windings so as to minimize leakage reactance. The primary is typically the main power line conductor, which passes directly through the toroidal core. This type of transformer is specifically for the purpose of measuring current values, and the secondary windings cannot be left open-circuited, or a large voltage will be produce, resulting in dielectric failure (and often an explosion). If a device is not connected to the CT, its secondary must be short-circuited. 

A PT is connected between the main conductor and ground and can be either wound in the normal way, or the voltage can be taken from a subsection of a string of capacitors (this is called a Capacitive Voltage Tansformer or CVT, and is usually cheaper than the wound type, but is typically not as accurate). This type of transformer measures voltage values, and the secondary winding cannot be short-circuited, as this will produce excessively high currents, resulting in the failure of the PT or the wires it is connected to. A PT can be left open-circuited. 

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Differences Between C.T and P.T 

CURRENT TRANSFORMER	POTENTIAL TRANSFORMER
The secondary of a C.T can not be open circuited on any circumstance when it is under service.	The secondary of  a P.T can be open circuited without any damage being caused either to the operator or the transformer.
A CT may be considered as a series transformer.	P.T may be considered as a parallel transformer.
The primary current in a C.T is independent of the secondary circuit conditions (burden).	The primary current of a P.T depends upon the secondary circuit conditions (burden).
The primary winding of the CT is connected in series with the line carring the current to be measured. Hence it carries of the full line current.	The primary winding P.T is connected across the line of voltage to be measured. Hence the full line voltage is impressed across its terminal.
With the help of CT, a 5A ammeter can be used measure a high current like 200A.	With the help of P.T, a 120V voltmeter can be used to measure very high voltages like 11KV.