When selecting relays for bus protection, a major concern is the ability of the protective relaying scheme to restrain from tripping for close-in line faults. Tripping for bus faults, the reason for installing bus differential relaying, is less of a concern. During fault testing conditions, line circuit breakers, rather than bus sectionalizing circuit breakers or …
Surge arrester types and auxiliary equipment
Nearly 100 years ago, electrode gaps (rod, sphere, or pipe) were used to limit overvoltages on equipment (Sakshaug, 1991). Some of these systems, particularly pipe gaps, may still be in service today. However, the characteristic of gap sparkover voltage vs. surge front time does not match up well with the strength vs. front characteristics of …
Capacitor protection by surge arresters – ABB
Generally speaking, capacitor protection by surge arresters has been a difficult task before ZnO arresters became available. The high discharge currents and possible energies associated with an arrester operation at a capacitor bank heavily stressed the spark gaps in a SiC gapped arrester. The possible high energies could also result in overstressed SiC blocks. Once …
Applications and forms of differential relays
Differential relays take a variety of forms, depending on the equipment they protect. The definition of such a relay is “one that operates when the vector difference of two or more similar electrical quantities exceeds a predetermined amount. It will be seen later that almost any type of relay, when connected in a certain way, …
Whole-House Protection Strategy
No single SPD (Surge Protection Strategy) can protect all the equipment in a residence from all causes of electrical surges. Instead, a whole-house protection strategy, consisting of point-of-entry and point-of-use SPDs, is necessary to help guard against disturbances from inside and outside the home. A point-of-entry SPD is necessary to limit damage from electrical surges …
How residual current device (RCD) works?
The residual current device (rcd) is used to detect earth fault currents and to interrupt supply if an earth current flows. The main application is to prevent electrocution but RCDs can also be used to protect equipment, especially against fire. The earth fault currents that operate an rcd can range from 5mA up to many …
MiCOM P139 – Feeder Management and Bay Control
MiCOM P139 is a cost-effective one-box solution for integrated numerical time-overcurrent protection and control. The unit’s protection functions provide selective short-circuit protection, ground fault protection and overload protection in medium- and high voltage systems. The systems can be operated as solidlygrounded, low-impedance-grounded, resonantgrounded or isolated-neutral systems. The multitude of protection functions incorporated into the unit …
History of the development of busbar protection
Up to the mid 1930′s, no widescale efforts had been made to protect busbars on a unit basis. Also there was reluctance in arranging one protective equipment to cause simultaneous tripping of a large number of circuits. Before the British Grid System was built in the early 1930s, many undertakings ran isolated from adjacent ones, …
Distance Relays
Distance relays respond to the voltage and current, i.e., the impedance, at the relay location. The impedance per mile is fairly constant so these relays respond to the distance between the relay location and the fault location. As the power systems become more complex and the fault current varies with changes in generation and system …
