Multipole phase shift torquemeters now measure shaft power to 0.1% accuracy in R & D applications, and to 1.0% when designed for permanent installation, both at confidence levels of 95%.
The total installed power to date is 2 million kW, and over 2 million hours have been logged with good reliability. They are in service at speeds up to 90,000 RPM and powers of 50MW.
The paper outlines ways of ensuring credibility, and describes typical designs for R & D use, and for permanent installation. It concludes that the application problems are largely those of transmission engineering.