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CT Ratio Formula:
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CT Ratio (Current Transformer Ratio) is the ratio between the primary current and secondary current in a current transformer. It indicates how much the primary current is reduced to produce a measurable secondary current for protection and metering purposes.
The calculator uses the CT Ratio formula:
Where:
Explanation: The CT ratio represents the transformation ratio between the high primary current and the standardized lower secondary current (typically 5A or 1A).
Details: Accurate CT ratio calculation is essential for proper protection relay operation, energy metering accuracy, and overall electrical system safety and reliability.
Tips: Enter primary current and secondary current values in amps. Both values must be positive numbers greater than zero for accurate calculation.
Q1: What are typical CT ratios used in electrical systems?
A: Common CT ratios include 100:5, 200:5, 400:5, 800:5, 1000:5, 1200:5, and 2000:5 for 5A secondary systems, with corresponding ratios for 1A secondary systems.
Q2: Why is CT ratio important in protection systems?
A: CT ratio ensures that protection relays receive accurate current signals proportional to the actual system current, enabling proper fault detection and system protection.
Q3: How does CT ratio affect energy metering?
A: The CT ratio multiplier must be applied to secondary current readings to calculate actual primary current values for accurate energy consumption measurement and billing.
Q4: What happens if wrong CT ratio is used?
A: Incorrect CT ratio can lead to inaccurate measurements, improper relay operation, system maloperation, and potential equipment damage due to incorrect protection settings.
Q5: Can CT ratio be changed after installation?
A: CT ratio is typically fixed based on the transformer's physical construction. Ratio changes usually require replacing the current transformer or using multi-ratio CTs with tap selections.