Releasers with electro-hydraulic retarders as an effective alternative for short circuit and overcurrent protection

Abstract

It is known that circuit breakers (CBs) installed in distribution cabinets (DCs), better known as “enclosed circuit breakers”, depending on the execution, are designed for: - protection against emergency states of grids: overvoltage and short circuit (s/c) or voltage drop below the permissible level (circuit breakers installed on the grid do not always provide protection against voltage reduction); - protection of AC motors, as well as for combined installation with other electric devices (CBs can service by grid sections as well as separate motors if CBs are used to operate the wound-rotor motor or starting devices, they must include voltage drop protection); - to be used as disconnectors for supply and trunk networks. Overcurrent protection is done by a bimetallic plate, while an electromagnetic releaser provides s/c protection. The main features inherent in this technical solution of overcurrent protection include: - relative dependence on ambient temperature; - inability to quickly switch on again after the CB is triggered; - unstable time-current characteristics of the CB. National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute” and «E.NEXT Ukraine» offers an alternative solution for the design of CB protection elements, which is an integrated overcurrent and short circuit protection at the same time in the form of a releaser with an electro – hydraulic retarder. A releaser with an electro-hydraulic retarder triggers the СB actuator, which breaks the contact group of the CB when the current exceeding the set maximum permissible value (s/c or overcurrent) is passing through electrical equipment. The main part of this releaser is an electromagnet, whose coil is connected in series with working contacts in the circuit of the operating current.