In the name plate of Current Transformer (CT) it is usually written 5P10 or 5P20 as Shown in figure. What does 5P10 or 5P20 mean ?
A current transformer is a device that is used for the stepdown the current from a higher value into a proportionate current to a lower value. It transforms the high voltage current into the low voltage current due to which the heavy current flows through the transmission lines is safely monitored by the ammeter.
In Industries Three types of Current Transformers are used.
- Metering type current Transformer : This type of current transformer is used for metering purpose. It is used to measure the heavy current.
- Protection Type Current Transformer : This type of Current Transformer is used for protection purpose. Its main job is to help protect electrical equipment and systems from damage in case of overcurrent or short-circuit conditions. The secondary terminals of this type of current Transformer is connected to relay.
- Protection Special Type Current Transformer : A “Protection Special Type Current Transformer” is a specific type of current transformer designed to accurately measure electric current in high-voltage systems and provide crucial information for protecting electrical equipment from faults and overloads. These transformers are specially crafted to have precise performance characteristics and can sense even tiny changes in current, helping to detect and respond to electrical issues quickly to prevent damage or accidents in power systems. These type of CT are generally used for differential protection of Power Transformer.
Now What does 5P10 or 5P20 Mean
The “5” repersent the composite error associated with the current transformer.
The letter “P” designates that it is a current transformer designed for protection purposes.
The numbers “10” or “20” represent the accuracy limit factor. This factor means that when the primary current of the current transformer is 10 or 20 times of its rated value, the core of the current transformer does not become saturated. Consequently, the error in the output of the current transformer remains within the range of plus or minus 5%.
The current Ratio of figure in question is 400/5 and class is 5P10.
It means the current Transformer is designed for protection purpose.
when current of 400A flow in the primary of current Transformer and the current in the secondary of current Transformer will be 5A.
the current transformer will work without getting core saturated upto 400/times10=4000A and error in output will be plus or minus 5% that is the current in the secondary of current transformer will be 5.25A or 4.75A
