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Limiting value of ratio error is ?
2%
4%
5%
6%
5%
In instrument transformers, specifically Current Transformers (CTs), the ratio error is the difference between the actual current ratio and the marked ratio. According to IS 2705 standards, the limiting value for ratio error for measurement-grade transformers is typically set at 0.5%.
In instrument transformers, specifically Current Transformers (CTs), the ratio error is the difference between the actual current ratio and the marked ratio. According to IS 2705 standards, the limiting value for ratio error for measurement-grade transformers is typically set at 0.5%.
RatioError=IpтАЛKnтАЛIsтАЛтИТIpтАЛтАЛ├Ч100% тАФ where KnтАЛ is the rated transformation ratio, IsтАЛ is secondary current, and IpтАЛ is primary current.
The ratio error exists because a portion of the primary current is utilized to provide the magnetizing force and core loss components required for the CT's magnetic circuit. This creates a deviation between the ideal transformation ratio and the actual transformation ratio defined by the turns ratio, expressed as a percentage of the rated current.
Ratio error is primarily caused by the magnetizing current component required for flux generation in the core.
This error varies with the secondary burden and the magnitude of the primary current.
The 0.5% limit is the standard accuracy class for conventional metering CTs used in power systems.
Higher precision (0.1% or 0.2%) is required for laboratory or high-accuracy billing applications.
Ensures accuracy of revenue metering in power systems.
Provides a standardized metric for quality control of current transformers.
Increases the cost and physical size of the CT due to higher permeability core requirements.
Ratio errors can lead to cumulative errors in large-scale energy accounting systems.
Energy billing and revenue metering.
Indicating instruments and protective relay systems.
Power system load monitoring.
Accuracy class defines the maximum allowable percentage ratio error at the rated current.
The error is influenced by the core material properties and the number of secondary turns.
C is correct тАФ The standard limiting value of ratio error for many commercial grade current transformers is defined as 0.5% at rated primary current.
Always check the burden rating of a CT when evaluating its ratio error, as exceeding the rated burden significantly increases the error beyond the 0.5% limit.