What is current transformer rating?

Ratio. The CT ratio is the ratio of primary current input to secondary current output at full load. For example, a CT with a ratio of 300:5 is rated for 300 primary amps at full load and will produce 5 amps of secondary current when 300 amps flow through the primary.

What does current transformer ratio mean?

Definition: 1) The ratio of primary amps divided by secondary amps. 2) The current ratio provided by the windings of the CT. For example, a CT that is rated to carry 200 Amps in the primary and 5 Amps in the secondary, would have a CT ratio of 200 to 5 or 40:1.

What is class1 CT?

The class designation is an approximate measure of the CT’s accuracy. The ratio (primary to secondary current) error of a Class 1 CT is 1\% at rated current; the ratio error of a Class 0.5 CT is 0.5\% or less. Errors in phase are also important, especially in power measuring circuits.

How do you interpret CT ratio?

The CT ratio is the inverse of the voltage ratio. In this example, the voltage ratio is 1:5, so the CT ratio is 5:1. This means the current level is stepped down 5 times where, if the primary current is 200 amps, the CT output is 40 amps.

How is current transformer rating determined?

The rated power of the current transformer is the product of the rated load and the square of the secondary rated current and is quoted in VA. Standardised values are 2.5 – 5 – 10 – 15 – 30 VA. It is also permissible to select values over 30 VA according to the application case.

What are current transformers used for?

A Current Transformer (CT) is used to measure the current of another circuit. CTs are used worldwide to monitor high-voltage lines across national power grids. A CT is designed to produce an alternating current in its secondary winding that is proportional to the current that it is measuring in its primary.

How accurate are current transformers?

Current transformers must maintain 0.15\% accuracy from 5\% rated current through rating factor at rated burden. No accuracy is guaranteed at levels below 5\%.

What is class of accuracy in current transformer?

Accuracy Class of Current Transformer The accuracy class or simply class of measuring current transformer is 0.1, means the maximum permissible limit of error is 0.1\%, more clearly, if we try to measure 100 A with a 0.1 class CT, the measured value may be either 100.1 or 99.9 A or anything in between these range.

How do you read a CT nameplate?

CT Ratio: 100/5-5 A The ratio 100/5 means If the CT primary carries 100 Amps then the output of the CT secondary will be 5 Amps. The dual 5-5 A means the first core used for protection and second core used for metering purpose.