Multifunctional microcontroller-based protection unit for switchgear of terminal users

Aiming at the incoming line switchgear cabinet characteristics of 12 kV distribution network terminal substation and main unit, this paper presents a multifunctional digital protection set of terminal user switchgear based on 16-bit microprocessor. The power of the protector is supplied by itself from the CT. Based on thermal cumulate principles, a rapid and high precision inverse-time phase-sequence over-current protection is implemented. Three stages phase-sequence current and zero-sequence current protection can be implemented. Main circuit phase-lack fault and CT wire-break fault can be identified by the current signs and values. Fault current recording is displayed by liquid-crystal and current curve diagram can be transmitted to PC and therefore analyzed. It can communicate with other protection apparatus based on CAN field-bus. Test results show that time duration and current operating value precision are less than 2%, and the functions of the protection device are reliable.