Current Transformer Calculator
Calculate current transformer ratios, burden, accuracy class and sizing parameters for protection and metering applications in electrical systems.
Step 1: CT Specifications
CT Ratio Formula
CT Ratio = Primary Current / Secondary Current
Example: 1000A/5A = 200:1 ratio
Step 2: Application & Options
Common CT Standards
Metering CTs: 0.1-1.0 accuracy class
Protection CTs: 5P, 10P accuracy class
Standard Ratios: 100:5, 200:5, 400:5, 800:5, 1000:5, 1200:5, 2000:5
Current Transformer Results
Current Transformer Ratio
CT Type Comparison
| CT Type | Accuracy Class | Typical Burden | Application |
|---|
Current Transformer Formulas
CT Ratio = Ip / Is
Where:
• Ip = Primary Current (A)
• Is = Secondary Current (A)
• Burden = Is² × Zb (VA)
• Zb = Burden Impedance (Ω)
Common Standards:
• IEC 60044-1: Instrument Transformers
• IEEE C57.13: CT Requirements
• ANSI C12: Metering Standards
Example Calculation
Example: 1000/5 CT for Metering
Primary Current: 1000A
Secondary Current: 5A
CT Ratio: 1000/5 = 200:1
Burden: 15 VA
Secondary Impedance: 15/(5²) = 0.6Ω
Accuracy Class: 0.5 for revenue metering
Safety Factor: 20% above rated current
This CT can measure up to 1200A primary
while maintaining 0.5% accuracy.
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