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    Current Transformer (CT) Ratio Calculator | CT Ratio Calculation

    Created by Md jony islam

    CT Ratio Conversion Calculator

    Use the CT Ratio Calculator to determine the Current Transformer (CT) ratio. Enter primary and secondary current values to calculate the CT ratio for electrical systems. The Current Transformer Ratio Calculator serves as a measurement device to establish CT ratios within electrical systems to make primary current measurement possible at secondary levels for precise probing and safety reasons. The CT ratio calculation process requires division of primary current by secondary current using the CT Ratio = Primary Current / Secondary Current formula. The CT ratio obtains values of 200:1 from dividing 1000A primary current by 5 A secondary current. The power system relies on this ratio to understand how current transformers perform their operations for metering and protection as well as system monitoring applications. The CT Ratio Calculator aids in the execution of transformer sizing calculations as well as the efficient operation of electrical systems and their relays and measurement equipment.

    Current Transformer Ratio Calculator

    CT Ratio Calculator
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    What do you need to know to calculate Current Transformer Ratio?

    The current transformer ratio calculator serves to establish the necessary CT ratio for electrical systems when measuring currents in order to perform protection and metering tasks. The CT ratio establishes the relationship between primary current transformation to obtain a measurable secondary current used in protection relay setup. The basic formula to find the CT ratio requires division of primary current by secondary current.

    The CT ratio becomes 200:1 when the primary current runs at 1000A while the secondary current measures at 5A. The fundamental calculation for electrical engineering helps to maintain the correct operation of current transformers used in power systems. Users can streamline essential electrical system operation through the CT Ratio Calculator, which performs this essential calculation regardless of working on system design, protection relays, or maintenance responsibilities.

    🙋 Try our Rms Voltage Calculator . If you want to learn more about conversions using Electrical Engineering Project Calculators.

    Conversion using the Current Transformer Ratio Calculation Formula

    The CT Ratio (Current Transformer Ratio) formula is:

    CT Ratio = Primary CurrentSecondary Current

      Where:

    • Primary Current (I₁) = is the current flowing on the high-current side (primary side) of the transformer.
    • Secondary Current (I₂) = is the current on the low-current side (secondary side) of the transformer.

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    To use the CT Ratio Calculator, follow these simple steps:

    Current Transformer Ratio conversion chart

    Primary Current (I₁) in AmperesSecondary Current (I₂) in AmperesCT Ratio
    1000A5A200:1
    1500A5A300:1
    500A1A500:1
    800A4A200:1
    100A1A100:1

    Frequently Asked Questions - CT Ratio Calculate Conversion FAQs:

    How do you calculate CT ratio for electrical systems?

    Calculate the CT ratio by dividing the primary current by the required secondary current (typically 5 A or 11 A). For example, for a 400A load with 5A secondary, the CT ratio is 400:5 (or 80:1). This ensures accurate current measurement.

    What is the relationship between CT burden and ratio accuracy?

    CT burden affects ratio accuracy. Calculate maximum burden using Burden (VA) = I²secondary × Z, where Z is impedance. For example, a 5A secondary CT with a 0.5Ω burden has a 12.5VA burden rating.

    How do you determine CT sizing for motor protection?

    Size CT based on motor FLA (full load amperes): CT primary rating ≥ 1.25 × FLA. For example, a 100A motor requires a minimum 125A primary CT rating for proper protection.

    Why is proper CT ratio selection important for metering?

    CT ratio affects measurement accuracy and protection system operation. Improper ratio can cause metering errors and protection misoperation. Select a ratio to use 40-100% of the CT primary rating.

    How do you calculate CT secondary current?

    Calculate using Isecondary = (Iprimary × CTsecondary) / CTprimary. For example, with 800:5 CT and 400A primary current, secondary current is 2.5A.

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    About the Author

    Md Jony Islam

    Md Jony Islam: Multidisciplinary Engineer & Financial Expert:

    Md. Jony Islam is a highly skilled professional with expertise in electronics, electrical, mechanical, and civil engineering, as well as finance. Specializing in transformer service and maintenance for 33/11kV substations, he ensures reliable and efficient electrical systems. His mechanical engineering skills drive innovative designs, while his financial acumen supports effective project budgeting. With a strong foundation in civil engineering, he contributes to robust infrastructure development. Md. Jony Islam's multidisciplinary approach ensures efficiency, quality, and reliability across all projects.