1. What is CT Ratio Error?

CT Ratio Error is a percentage value that represents the difference between the nominal (expected) ratio and the actual measured ratio of a current transformer. It helps assess the accuracy of the transformer.

2. How Does the Calculator Work?

The calculator uses the CT Ratio Error formula:

Where:

• \( nominal \) — Expected or rated ratio value
• \( actual \) — Measured or actual ratio value

Explanation: The formula calculates the percentage difference between what the transformer should theoretically provide (nominal) and what it actually provides (actual).

3. Importance of CT Ratio Error Calculation

Details: Calculating CT ratio error is essential for maintaining accurate current measurements in power systems, ensuring proper protection relay operation, and maintaining billing accuracy in metering applications.

4. Using the Calculator

Tips: Enter both nominal and actual ratio values. Both values must be positive numbers. The result shows the percentage error (positive or negative).

5. Frequently Asked Questions (FAQ)

Q1: What is an acceptable CT ratio error?
A: Typically, metering CTs should have ≤ 0.3% error, while protection CTs may allow up to 10% error depending on the class.

Q2: What causes CT ratio errors?
A: Errors can come from manufacturing tolerances, saturation effects, burden impedance, or incorrect turns ratio.

Q3: How is actual CT ratio measured?
A: Actual ratio is typically measured using a ratio test set that applies current to the primary and measures secondary output.

Q4: What does negative error indicate?
A: Negative error means the actual ratio is higher than nominal (secondary current is lower than expected).

Q5: How often should CT ratio be verified?
A: Verification frequency depends on application - metering CTs may need annual testing, while protection CTs might be tested every 2-5 years.