Let us take an example to understand protection CT as per IEC 60044-1

- rated primary current: 200 A,

- rated secondary current: 5 A.

CT specs: 15 VA 5P10

that means:-
accuracy limit factor = 10

accuracy class = 5P

accuracy power = 15 VA

To simplify, for the protection CT given in example, the ratio error is less than 5% at 10 times of rated current (In) if the real load consumes 15 VA at In .

Scorpio31

Hi

Let us take an example to understand protection CT as per IEC 60044-1

- rated primary current: 200 A,

- rated secondary current: 5 A.

CT specs: 15 VA 5P10

that means:-
accuracy limit factor = 10

accuracy class = 5P

accuracy power = 15 VA

To simplify, for the protection CT given in example, the ratio error is less than 5% at 10 times of rated current (In) if the real load consumes 15 VA at In .

DILIP_1111

Scorpio31

Hi

...To simplify, for the protection CT given in example, the ratio error is less than 5% at 10 times of rated current (In) if the real load consumes 15 VA at In .

Thanks for this post,

but will you differentiate between 5P10 & 5P20. also let me explain which one better for protection.

PISCEAN 2010

Hello Experts,
In protection equipments, I have come across CT terminology as 5P10 or 5P20. What is it significance?

DILIP_1111

Scorpio31

Hi

To simplify, for the protection CT given in example, the ratio error is less than 5% at 10 times of rated current (In) if the real load consumes 15 VA at In .

Thanks for this post,

but will you differentiate between 5P10 & 5P20. also let me explain which one better for protection.

PISCEAN 2010

Hello Experts,
In protection equipments, I have come across CT terminology as 5P10 or 5P20. What is it significance?

jeet2907

PISCEAN 2010

Hello Experts,
In protection equipments, I have come across CT terminology as 5P10 or 5P20. What is it significance?

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.

Hell Everyone,

I have seen one of the electrical equipment where 1000/1 CT's are installed. Nominal voltage is 11000 KV and FLA of the equipment is 50 Amps. 

When i see then name plate of the CT's i can see, 0.5 VA 5P10, 1000/1.

Thanks,

Anil