CT Ratio To Current Calculator
Easily calculate secondary current from the CT ratio and primary current. Ideal for electrical protection, metering, and transformer testing applications.
current transformer ratio calculator:
The CT Ratio to Current Calculator is used to convert a primary to a secondary or secondary to a primary current with a known current transformer ratio. It provides proportionality in the current scaling of measurement, protection, and metering systems of power networks.
CT Conversion formula:
The Ratio of CT to Current Calculator assists in calculating the ratio of primary to secondary current in a Current Transformer (CT). CTs have electrical applications in measurements, metering, and protection. The CT ratio (e.,g. 1000/5) indicates that with 1000A through the primary, 5A through the secondary.
The calculator will immediately determine the unknown value by entering the known CT ratio, along with primary or secondary current. It is necessary to make sure that meters, relays, and the protection circuits provide the correct readings. This calculator is easy to use to size, test, and validate the CT and is thus an important tool to electrical engineers and technicians involved with monitoring substation or industrial equipment.
⚡ Work & Installation (Input → Output):
To use this tool, enter the CT ratio (e.g., 200/5) and one current value — either primary or secondary. The calculator computes the corresponding current using the proportional formula:
\[ \frac{I_{P}}{I_{S}} = CT_{ratio} \]
During installation, connect CTs correctly to protect measuring devices from high currents. The secondary winding typically provides 1A or 5A to meters or relays, while the primary monitors high current through the conductor. Correct ratio selection ensures safety and accuracy in current measurement.
Testing & Final Adjustments:
The method of testing a CT can be described as a method of testing the primary current by applying a known current through the primary and measuring the secondary current. Compare the ratio obtained to the ratio calculated to ascertain the correctness. Check polarity, Wiring integrity, a nd CT burden rating in case of deviations. Tune metering equipment to the actual CT ratio. Periodic testing provides sound protection, relay operation, and also eliminates the possibility of under- or overcurrent misreadings. The CT secondary must always be shorted during maintenance to prevent high-voltage buildup. Correct current measurement is sustained through proper testing and adjustment, and faults are guarded against on connected devices.
Frequently Asked Questions - CT Ratio To Current Calculator:
What is a CT ratio to current calculator?
It calculates the primary or secondary current based on a current transformer ratio.
What does a CT ratio of 100/5 mean?
It means 100A in the primary produces 5A in the secondary circuit.
How to calculate secondary current?
I_secondary = I_primary × (CT_secondary / CT_primary).
How to find primary current?
I_primary = I_secondary × (CT_primary / CT_secondary).
Why are CTs used?
They reduce high current to measurable values for meters and protection relays.
What is the standard CT secondary current?
Usually 1A or 5A, depending on system requirements.
Can CTs measure both AC and DC?
CTs are designed for AC current measurement only.
What affects CT accuracy?
Burden resistance, saturation, and connection polarity can affect readings.
How do I test a CT?
Inject known current and compare measured secondary current with expected ratio.
Why must CT secondary be shorted during maintenance?
To prevent dangerously high voltages from developing when open-circuited.
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