1. What Is CT Ratio Error?

The CT (Current Transformer) ratio error measures the accuracy of a current transformer by comparing its actual ratio to the nominal ratio. It's expressed as a percentage of deviation from the expected value.

2. How Does the Calculator Work?

The calculator uses the CT ratio error formula:

Where:

• \( K_n \) — Nominal ratio (expected value)
• \( K_a \) — Actual ratio (measured value)

Explanation: The formula calculates the percentage difference between the nominal and actual transformation ratios of a current transformer.

3. Importance of CT Ratio Accuracy

Details: Accurate CT ratios are critical for proper metering, protection, and control in power systems. Excessive ratio errors can lead to incorrect current measurements affecting system operation and safety.

4. Using the Calculator

Tips: Enter both nominal and actual ratios as positive numbers. The calculator will determine the percentage error between them.

5. Frequently Asked Questions (FAQ)

Q1: What is an acceptable CT ratio error?
A: For metering CTs, typically ±0.3% to ±0.6%. For protection CTs, ±5% to ±10% may be acceptable depending on application.

Q2: What causes CT ratio errors?
A: Manufacturing tolerances, burden impedance, saturation effects, and temperature variations can all contribute to ratio errors.

Q3: How is actual ratio (K_a) determined?
A: Through ratio testing where primary current is applied and secondary current is measured under specified conditions.

Q4: Does this calculator work for voltage transformers?
A: The same formula applies for VT ratio error calculation, though the acceptable error limits differ.

Q5: What does a negative error percentage indicate?
A: A negative error means the actual ratio is higher than the nominal ratio (under-transformation).