I use ADE7878A to develop our product. I measure the each phase current by different CTs (50A/5A,100A/5A, 400A/5A). These CT are standard product in market. So I want to fix the hardware design to match these CTs. The limit voltage of Ixn/IxP input is +/-0.5Vp-p in ADE7878A. How to design the burden resistor to match different CT??
Sorry to say that, different CTs have different transfer function, so you can get different voltage input to ADE7878A. In general, we don't need to change the sensors in meter application, so the CT and circuit won't be changed in the meter. You need to consider the dynamic range with specified error, if you use different CTs, error range cannot be guaranteed. Thank you very much.
Thanks, your information.
The secondary output of different CT is same to 5A. Is it not possible use same design in burden resistor??
You are right, the secondary output is same like 5A, but the dynamic range should be different to first input. You can use the same burden resistor with different CTs, choose the max range like 400A/5A. Then when you change to other CTs, the output should not beyond 5A. But you need to calculate the error with different CTs and make the final decision. Thank you very much.
we are designing the new product. This product is 3 phase 4 wire meter using ADE7878A. The meter connect the CTs which secondary current output is 5A . The CTs have different range (e.g. 400/5A, 200/5A....60/5A). When the meter connect 400A/5A CT, we will set the CT ratio to the system. If CT change to 200A/5A, we will set another CT ratio to system. So I want to fix the Hardware design. The CT ratio could be changed by software.
I would like to know how to calculate the burden resistor in the 5A secondary output?
Any suggestion? or reference design?
Take 400A/5A as an example, when you input 400A, you get 5A. Then choose the burden resistor value X ohms. So the differential voltage after the CT will be 5*X V. You can change to Peak to Peak value or rms value. Ensure the differential voltage not beyond the full scale ADC input range. If your max output is 5A, you should use the burden resistor calculated with 5A. Thank you very much.