How to Read CT Current Transformer Nameplate Details

How to Read Current Transformer Nameplate Details:?

Current Transformers are nothing but a step up transformer which is used to find out the primary current of the circuit. Current transformers reduce high voltage currents to a much lower value typically 1 A or 5 Amps and used to monitor the actual electrical current flowing in an AC transmission line by using an ammeter. Different types of current transformers are generally manufactured. In this we are going to see how to read or understand current transformer’s nameplate details. Lets start…

Refer the CT Nameplate details:

Current transformer name Plate Details
Current transformer name Plate Details

CT Ratio: 100/5-5 A

CT ratio means the currant transformation ratio, here the CT contains Single primary current and dual secondary current output. 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.

Learn More:   Relationship of Frequency Vs KVA Output or Rating of Transformer

Voltage level: 12/28/75 kV

The voltage level means the rated operating voltage of the current transformer. The first form 12kV is the rated voltage under normal steady operation, the second value 28kV means the CT can be operated at 28kV for 1 minutes at 50 Hz Frequency and the third value 75kV means the CT’s maximum withstand able impulse voltage.[wp_ad_camp_1]

IS 2705/1992:

IS 2705/1992 means the CT manufactured and tested as per Indian Standard procedure section 2705/1992.

Burden: 5VA/5VA

The maximum allowable apparent power from the CT is called Burden. Here 5VA is the maximum limit of the current transformer’s output. These data are used to protect the Current transformer from overloading. The 5VA/5VA means both the core can be loaded upto 5 Volt Amp.

Class: PS 5p10, 0.1

Class means the percentage CT error value when you calibrate the CT with the standard CT. Class are calculated by

This is the only data differential metering CT and protection CT. Protection CTs are generally marked as PS class- Protection Special.

Learn More:   What is Percentage Impedance & Calculate Percentage Impedance?


  • 5p –percentage of error value accuracy class.
  • 10 means the accuracy limit factor.

What is accuracy limit factor:

Ratio between the over current to rated current is called accuracy limit factor. It is important for the PS class CT. If the current exceeds the 10 times of its rated current, the CT accuracy class may get change.

Manufacture details:

Here we can get the CT manufacture name, for feature spare procurement.



Please enter your comment!
Please enter your name here