In this article, we will discuss the crucial differences between a current transformer (CT) and a potential transformer (PT).
A transformer is
an electrical machine that can increase or decrease the level of alternating
voltage or alternating current. A transformer typically consists of three main
parts: a magnetic core, a primary winding, and a secondary winding. Transformer
works on the principle of electromagnetic
induction (mutual inductance). It is a static electrical machine which does
not have any moving or rotating parts.
Transformers are primarily classified into the following three types depending on their application:
- Distribution Transformer – Used in the distribution segment of the electric power system to reduce the voltage.
- Power Transformer – Used in the transmission segment of the electric power system to increase or decrease the voltage.
- Instrument Transformer – Used in power systems for protection and measurement purposes. Instrument transformers are further classified into two types namely, Current Transformer (CT) and Potential Transformer (PT).
Introduction to Current Transformer (CT)
A Current Transformer (CT) is a type of instrument transformer
that is used to decrease the value of electric current in a transmission line
for measurement and protection. A current transformer is basically a current
step-down and voltage step-up transformer.
The current transformer consists of two windings namely, a
primary winding and a secondary winding. The primary winding of a current
transformer has a lesser number of turns as compared to the secondary winding. Practically,
the primary winding of a current transformer has only one turn and the secondary
winding has a number of turns depending on the CT ratio.
The primary winding of the current transformer is connected
in series with the line conductor whose current is to be measured and the
secondary is connected to an ammeter to measure the current.
Introduction to Potential Transformer (PT)
A Potential Transformer (PT) is also a type of instrument
transformer used in electrical power systems for measurement and protection
purposes.
The potential transformer is a voltage step-down transformer.
Hence, it consists of a primary winding with a larger number of turns as compared
to the secondary winding. This transformer reduces a high voltage to a lower
value which can be measured with a normal voltmeter. The number of turns in
primary and secondary windings depends upon the PT ratio.
The primary winding of the potential transformer is
connected in parallel with the electric line whose voltage is to be measured and
the secondary winding is connected to a voltmeter to measure the line voltage.
Difference between Current Transformer (CT) and Potential Transformer (PT)
The important differences between CT and PT are listed in
the following table:
|
Current Transformer |
Potential Transformer |
|
A current transformer is abbreviated as CT. |
The potential transformer is abbreviated as PT. |
|
The current transformer decreases the high current to a lower value. |
Potential transformer decreases the high voltage to a lower value. |
|
A current transformer is a step-up transformer. |
The potential transformer is a step-down transformer. |
|
Types of current transformers include – bar-type CT, wound-type CT, toroidal CT, and summation CT. |
Types of potential transformers include – electromagnetic PT and capacitive PT. |
|
In a current transformer, the primary winding has less number of turns as compared to the secondary winding. |
In a potential transformer, the primary winding has more turns as compared to the secondary winding. |
|
The transformation ratio of the current transformer is known as the CT ratio. |
The transformation ratio of the current transformer is known as the PT ratio. |
|
The secondary winding of a current transformer can never be opened while the CT is in operation because it can cause an accident. |
There is no problem opening the secondary winding of a PT while it is operating. |
|
The primary winding of a current transformer is made of thick wire, while the secondary winding is made of thin wire. |
The primary winding of a potential transformer is made of thin wire, while the secondary winding is made of thick wire. |
|
For CT, the standard secondary current rating is 1 A and 5 A. |
For PT, the standard secondary voltage rating is 110 volts. |
|
The accuracy of a current transformer is independent of the burden on it. |
The accuracy of a potential transformer is a function of the burden on it. |
Hence, this is all about the differences between the current
transformer (CT) and the potential transformer (PT).
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