Regarding Power Factor and Power Measurement Accuracy Using CT on CT Secondary with ADE7880

Dear All,

Thanks for all your support.

 we currently developing a three-phase power quality monitoring device based on the ADE7880 energy metering IC. The system measures voltage, current, power factor, active power, reactive power, and harmonic components using current transformers and voltage dividers connected to the ADE7880 inputs. 

 In some industrial installations, we encounter situations where a current transformer (CT) is already installed on the power line and is being used by an existing metering system. For practical and safety reasons, we may not be able to install another CT directly on the primary conductor. In these cases, we are considering measuring the current by connecting a second CT to the secondary output of the existing CT. We have tested this method and were able to measure the current successfully using this technique. However, we would like to clarify the following regarding power measurements: 

1. When using this CT-on-CT configuration, will the power factor, active power, and reactive power measurements from the ADE7880 still be accurate? 

2. Since two CTs are involved, there may be additional phase shift introduced in the current signal. Could this affect the power factor and power calculations inside the ADE7880? 

3. Is it possible to compensate for this effect using the ADE7880 phase calibration registers (APHCAL, BPHCAL, CPHCAL)? 

4. What design changes or calibration steps would you recommend to obtain accurate power factor, active power, and reactive power measurements when using this measurement technique?

Our main goal is to understand whether this method can provide reliable power quality measurements, and what adjustments may be required in the hardware or calibration process to achieve correct results. 

Additionally, we have another question regarding voltage measurement. In high-voltage industrial systems, a Potential Transformer (PT) is often used to step down the system voltage to a standard lower voltage level. If a PT is used to convert high system voltage to a lower voltage suitable for measurement, can the ADE7880 measure this voltage accurately when the PT secondary is connected to the voltage input circuit through a resistor divider? Are there any specific design considerations or calibration steps recommended when measuring voltage through a PT?