Resource-saving microprocessor-based reed switch current protection

Abstract

We suggest designing a cutoff and an overcurrent protection for 6–35 kV electrical installations with switchgear cubicles on the basis of reed switches and a microprocessor without current transformers. A reed switch is a small glass tube with plates inside, which contact under the action of the corresponding magnetic field. Two reed switches are mounted near each busbar inside a switchgear cubicle at a safe distance using specially designed structures. The magnetic induction which acts on them is determined by the Biot–Savart law with experimentally found coefficients. The effect of currents in neighboring electrical installations and in switchgear cubicle casings is taken into account. We have developed and describe here an algorithm of protection operation and a technique for selecting parameters and estimating protection sensitivity. Such protections are noise-resistant due to detection of short circuits by the third actuation of a read switch; they detect a failed component with the help of built-in diagnostics. The test diagnostics is performed by means of supplying current simultaneously to the control windings of two reed switches, and the functional diagnostics, by means of supplying current to them in turn. The efficiency of such protections is confirmed by the simulation results.