Why are utilities hesitant to replace CTs/PTs?

The main difference between Rogowski Coils and CTs is that Rogowski Coil windings are wound over an air core (non-magnetic), instead of over an iron core. Therefore, Rogowski Coils are linear since the air core cannot saturate.

The mutual coupling between the primary conductor and the secondary winding in Rogowski Coils is much smaller than in CTs. Therefore, Rogowski Coil output power is small, so it cannot drive current through low-resistance burden like CTs are able to drive. Rogowski Coils can provide input signals for numerical relays that have a high input resistance; therefore, these devices must measure the voltage across the Rogowski Coil secondary output terminals. Relay manufacturers tend not to support technology since the signal processing required to extract the power frequency signal for applications in phasor-based protective relays and must be designed to accept these types of signals. There are other disadvantages to the Rogowski Coil as well, which include:

• The output of the coil must be pass through an integrator circuit to obtain the current waveform
• The integrator circuit requires a power supply of 3 – 24 Vdc
• It cannot measure dc current
• Sensitivity – compared with a CT, the Rogowski Coil has lower sensitivity due to the of a high permeability curve

Been out of the design and equipment selection game for a while now, but there is a few comments that I would have relating this technology from when I was there.  First, I think it comes back to application - this equipment is generally going to be used for metering, relaying, and instrumentation...each of which may have a different reason for trying new technology out.  I can also say the entry of optical equipment into the utility market was not the smoothest - there were many issues related to equipment design and accuracy of signal, so there is some early experiences that would lead one to question the reliability compared to traditional units.  We pull traditional wound units out of the field that test with the same accuracy that they were put in the filed with after 50-60 years - its a set and forget it technology, and although not perfect, the tiny amount of O&M related to those units over their lifetime is also a benefit.  Overall, I think if there is a use case and track record, most utilities are willing to try and pilot any newer technology - but it needs to have similar performance characteristics or greater benefits than those that have served us for 100 years.  Hopefully this helps...and for full disclosure, my knowledge base in this area is aged a bit.   

It could be as simple as the utility's culture. Many utilities hesitate to be the first one to try something new. There is no rush to become more competitive in a regulated market.