Question 1 of 10
In the CT accuracy class notation '5P20', what does the letter 'P' signify?
The letter 'P' stands for 'Protection class', indicating the CT is designed for use in protective relaying applications.
Question 2 of 10
What is the primary purpose of the 'Accuracy Limit Factor' (ALF) in a CT?
The ALF is the multiple of rated primary current up to which the CT will maintain its specified composite error.
Question 3 of 10
For a 5P10 current transformer, what is the maximum composite error allowed at the accuracy limit factor?
In the notation 5P10, the '5' represents the percentage composite error (5%) permitted at the specified accuracy limit factor.
Question 4 of 10
If a CT is rated 400/5A with an ALF of 20, what is the maximum primary current it can handle while maintaining specified accuracy?
The maximum primary current = Rated primary current * ALF = 400A * 20 = 8,000A.
Question 5 of 10
Why is it important for a protection class CT to avoid saturation?
Saturation causes the secondary current to become non-linear, which would cause protective relays to malfunction during fault conditions.
Question 6 of 10
Which of these CT classes is generally considered more accurate in terms of error percentage?
A lower number indicates a lower composite error percentage. Therefore, class 5 is more accurate than class 10.
Question 7 of 10
In a 5P20 CT, if the rated secondary current is 5A, what is the secondary current at the accuracy limit?
Secondary current at limit = Rated secondary current * ALF = 5A * 20 = 100A.
Question 8 of 10
What happens when a CT reaches its 'knee point' voltage?
The knee point is the transition point where the magnetizing current increases significantly, causing the core to saturate.
Question 9 of 10
Where is the accuracy class usually displayed for a current transformer?
The accuracy class, along with power rating and ratio, is specified on the CT's nameplate.
Question 10 of 10
Which application is most suitable for a 'Protection Class' (P) CT?
Protection class CTs are designed to function reliably during high-current fault conditions, making them ideal for overcurrent relay schemes.
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