CT Ratio Calculator

Primary Current (PC) in Amps:


Secondary Current (SC) in Amps:


Calculate

CT Ratio:

The CT Ratio Calculator is a handy tool for electrical engineers, technicians, and students who work with current transformers in power systems. It allows quick and accurate computation of the CT ratio based on primary and secondary current inputs. Understanding the CT ratio is essential for accurate metering, protection, and monitoring in electrical networks.

Formula
The formula to calculate CT ratio is: CT = Primary Current (PC) divided by Secondary Current (SC).

How to use

1. Enter the primary current (PC) value in amps.
2. Enter the secondary current (SC) value in amps.
3. Click the “Calculate” button.
4. The calculator will display the CT ratio as a value followed by “: 1”.

Example
If a current transformer has a primary current of 1000A and a secondary current of 5A, the CT ratio is:
CT = 1000 / 5 = 200 : 1
This means the transformer reduces 1000A down to 5A for safe measurement.

FAQs

1. What is a CT ratio?
   It’s the ratio of primary current to secondary current in a current transformer.
2. Why is the CT ratio important?
   It ensures accurate measurement and protection in electrical systems.
3. What is the standard secondary current in CTs?
   Most commonly, it is 5A or 1A.
4. Can I use this calculator for any CT size?
   Yes, as long as you know the primary and secondary currents.
5. What unit is used for input?
   Both currents are input in amperes (A).
6. What does a CT ratio of 200:1 mean?
   It means 200A of primary current is transformed to 1A in the secondary.
7. Is CT ratio always expressed as X:1?
   Yes, it’s typically normalized against 1A or 5A secondary output.
8. What if I get a decimal result?
   The calculator rounds the ratio to two decimal places.
9. Is a higher CT ratio better?
   Not necessarily—it depends on system design and measurement needs.
10. Can I reverse-engineer primary current from the CT ratio?
    Yes, by multiplying the ratio by the secondary current.
11. What is the typical use of CTs?
    They’re used for metering, monitoring, and protection in power systems.
12. Can CT ratio affect accuracy?
    Yes, incorrect ratios can cause errors in current measurement.
13. Do all transformers have CTs?
    Not all, but they’re common in power distribution systems.
14. Is the CT ratio affected by load?
    No, the ratio remains constant regardless of load.
15. What happens if I input zero in the secondary current?
    The calculator will return an error as division by zero is undefined.
16. Is this tool suitable for educational purposes?
    Yes, it’s a simple and effective tool for learning transformer basics.
17. Can CTs be used for high voltage?
    Yes, they’re essential for safely measuring high current in HV systems.
18. Is there a difference between metering and protection CTs?
    Yes, metering CTs are designed for accuracy, protection CTs for durability under fault conditions.
19. Can this calculator be used offline?
    Yes, if saved as an HTML file with embedded JavaScript.
20. Is the CT ratio the same as the turns ratio?
    Not exactly, but they are related concepts in transformer design.

Conclusion
The CT Ratio Calculator simplifies an essential calculation in the field of electrical engineering. Whether for field use, academic practice, or system design, this tool offers quick and reliable results. By understanding and applying the CT ratio, professionals can ensure safe, accurate, and efficient system operations.