PRactical Aspects Of Designing Safe And Compact Mv Switchgear Using “Air Core Ct”, “Resistor Voltage Divider VT” And Modern Intelligent Microprocessor Relays

Advancements in measurement and protection technology lead to the development of low-energy-analog (LEA) output signals in modern medium voltage switchgear design. Traditionally, medium voltage switchgear with rating 5kV-38kV uses iron cores, current transformers, and voltage transformers combined with the protective relays and metering equipment. With the new approach, iron core current transformers are replaced with LEA aircore-current-transformers (aCT), popularly known as Rogowski Coil, and voltage transformers are replaced with capacitive or resistive voltage divider (VD). IEC 61850 GOOSE and Sample Value communication technology available in modern intelligent microprocessor relays further improves the efficiency and reliability of protection and control schemes by better network communication and eliminating most copper wiring within the gear. With the apparent benefits of these advanced technologies, several specific areas of switchgear design improved. This paper discusses practical aspects and advantages of the new technologies and design considerations of an MV switchgear lineup, emphasizing conformance testing.