PR 5P20 Protection CT

What does 5p20 & 5p10 mean?

CT's are categorized as Protection CT, Special Protection
CT and Measuring CT. Based on this, the CT's are
classified. Here is the meaning of the CT classes:

Class 5P20:
The letter 'P' indicates it is a protection CT.
The number 5 indicates the accuracy of the CT. Most common
accuracy numbers are 5 and 10.

The number 20 (called accuracy limit factor) indicates that
the CT will sense the current with the specified accuracy
even with 20 times of its secondary current flows in the
secondary. This is required for protection CT, because the
fault current is high and the CT should be able to sense
the high fault current accurately to protect the system.
The common numbers are 10, 15, 20 and 30.

Class PS:
PS is for 'Protection Special'. This class of CT's are used
for special protection such as differential protection,
distance protection etc.

Class 1M:
The letter 'M' indicates it is a measuring CT.
The number 1 indicated the accuracy of the CT. The
measuring CT's should be more accurate than the protection
CT. The most common accuracy numbers are 0.5 and 1.

Protection class (P class) CT is connected to the protection relay that gives tripping command to circuit breaker at the time of fault condition. At the time of the fault, the primary current of CT increases abnormally high and the core can get magnetized above its rated capacity and whatever fault current flowing in the circuit can’t be reflected in the secondary side of the CT. This phenomenon is known as the saturation of CT. If CT gets saturated at the time of the fault, the protection relay will not operate.

5P10 class CT: P stands for protection class. If the primary current is 10 times to the rated primary current of the CT, the CT will function perfectly, within the rated composite accuracy class 5 %.

5P20 class CT: P stands for protection class. If the primary current is 20 times to the rated primary current of the CT, the CT will function perfectly, within the rated composite accuracy class 5 %.

Please contact the technician to design the specification of 5P10 5P20 10p10 10P20 10P30 5P30