I am working on a power meter project where I want to measure an AC current using a shunt resistor. After research, I found that the use of this resistance is rarely. Is it possible to know the reason for this and what are the other possible solutions? This was my first project idea, where I used a current transformer. now I thought of the shunt resistor but I read about the problem of isolation. is there any solution to replace the current transformer with the shunt resistor without getting the problem of isolation
The resistance can be very small, because we have simple means to amplify those small signals accurately - the modern op-amp is a marvel of engineering in that regard.
The reasons are related. We desire:
Low burden voltage - that's the voltage drop across the shunt. An ideal current measurement device has zero resistance. Practical ones try to approach that ideal, so the shunt has low resistance so it doesn't affect the circuit it's placed into very much. We care that the circuit doesn't suffer from the voltage drop.
Low dissipated power - shunts have non-zero temperature coefficient, so as they heat up from burden power (burden voltage x current), their calibration conductance changes (Amperes per Volt). Low burden voltage aids in lowering the dissipated power. As some power dissipation is inevitable, the higher power shunts use various techniques for temperature compensation, e.g. special alloys, temperature sensors, etc.
what are the other possible solutions?
Current transformers work for AC current sensing and offer inherent isolation, especially useful when the voltages and/or currents involved are very high,
Magnetic field sensors, typically Hall sensors, but also fluxgate sensors for higher accuracy applications, measure the magnetic field produced by the current flowing through the conductor. Those can be used in both AC and DC applications.
What ends up being used depends on the needs of the application: safety requirements, thermal budget, market acceptance, sensitivity, linearity, noise level.