1. What is CT Ratio?

CT Ratio (Current Transformer Ratio) is the ratio of primary current to secondary current in a current transformer. It indicates how much the primary current is reduced to a standardized secondary current, typically 1A or 5A for measurement and protection purposes.

2. How Does the Calculator Work?

The calculator uses the CT Ratio formula:

Where:

• Primary Current — The current flowing in the primary winding (A)
• Secondary Current — The current flowing in the secondary winding (A)

Explanation: The CT ratio represents the transformation ratio between the primary and secondary currents, allowing measurement of high currents using standard low-current instruments.

3. Importance of CT Ratio Calculation

Details: Accurate CT ratio calculation is essential for proper meter readings, protective relay settings, and overall electrical system monitoring and protection.

4. Using the Calculator

Tips: Enter both primary and secondary current values in amperes (A). Both values must be positive numbers greater than zero.

5. Frequently Asked Questions (FAQ)

Q1: What are typical CT ratios used in industry?
A: Common CT ratios include 100:5, 200:5, 400:5, 800:5, 1000:5, 2000:5, etc., where the secondary current is typically 5A or 1A.

Q2: Why is CT ratio important in electrical systems?
A: CT ratio ensures that high primary currents can be safely measured and monitored using standard instruments with lower current ratings.

Q3: How does CT ratio affect meter readings?
A: Meter readings must be multiplied by the CT ratio to obtain the actual current value in the primary circuit.

Q4: What happens if the wrong CT ratio is used?
A: Using the wrong CT ratio will result in inaccurate measurements, potentially leading to incorrect billing, improper protection, and system monitoring errors.

Q5: Can CT ratio be changed after installation?
A: CT ratio is typically fixed based on the transformer's physical construction, though some multi-ratio CTs allow for ratio changes through tap connections.