bbstract -Charge comparison is a new transmission line protection system.It compares local and remote quantities of charge, using a bi-directional communications channel. Charge comparison is a form of current differential relaying. Traditional current differential relaying schemes have three critical communications-related problems: protection lost if the channel fails, large channel capacity required, and precise channel delay compensation required. In large measure, charge comparison overcomes these three communications-related problems.Kevwords -Charge comparison, Current differential relaying, Transmission line protection, Digital communications.
The angular performance of a nano-angle generator (NANGO) developed at Diamond Light Source has been characterised using a dual-beam laser interferometer designed and built at the National Physical Laboratory (NPL). NANGO is a flexure-based, piezo actuated device which generates milli- to sub-nano-radian angles for the calibration of metrology instruments used to test the quality of synchrotron X-ray mirrors and angular nano-positioning stages at Diamond. The NPL interferometer provides traceability for small angle measurements made by NANGO. An uncertainty budget has been developed for measurements over a 50 nanoradian range. In closed-loop, using feedback from the NANGO’s angle encoder, for the first time we show that 1 nanoradian steps made by NANGO are measurable by an external metrology device. The 200 kHz acquisition rate of the NPL angle interferometer also reveals new dynamic information about NANGO’s angular motion. The NPL interferometer demonstrates that NANGO in open-loop can make: distinct steps of 500 picoradians; sinusoidal oscillations at 0.4 Hz with an amplitude of 125 picoradians; or 1 nanoradian oscillations at 40 Hz. Traceability to the SI though National Metrology Institute instrumentation for NANGO will provide enhanced accuracy for a wide range of angle metrology applications at Diamond, including inputs to deterministic polishing techniques for the creation of next-generation X-ray mirrors and dynamic characterisation of nano-positioning stages.
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