Write CSS OR LESS and hit save. The backup protection is provided as the main protection can fail due to many reasons like, Failure in circuit breaker In the event of failure or non-availability of the primary protection some other means of ensuring that the fault is isolated must be provided. The design of the back-up protection needs to be coordinated with the design of the primary protection and essentially it is the second line of defense after the primary protection system. If primary protection fails to act, the. Your email address will not be published. The current is measured at various points along the current path, e.g., at source, intermediate locations, consumer end..The tripping time at these locations are graded in such a way that the circuit-breaker/fuse nearest the faulty part operate first, giving primary protection. The protection provided by the protective relaying equipment can be categorized into two types as: a) Primary protection b) Back-up protection. Back-up protection is the name given to a protection which backs the primary protection whenever the primary protection failed to operate during fault condition. Examples of the former are differential protection and frame leakage protection, and of the latter current time graded protection and distance protection. Some features of design and manufacture which make relays inherently reliable are high contact pressures, dust free enclosures, well braced joints and impregnated coils. Save my name, email, and website in this browser for the next time I comment. Selectivity is absolute if the protection responds only to faults within its own zone, and relative if it is obtained by grading the settings of the protections of several zones all of which may respond to a given fault. The central coordinating station receives information about the abnormal conditions through high frequency carrier signals. Whenever the Battery voltage reaches abnormal condition the DC tripping relay works in order to protect the other protective equipment’s relay coil. The backup protection provides the back up to the main protection whenever it fails in operation or its cut out for repairs. The relay R4 operates the circuit breaker at D and isolate the faulty section. Your email address will not be published. If one of the components in any part of the-system fails, (e.g. c) Trip supplies to the two protections should be separately protected (fuse or MCB). The stored program in digital computer determines the correct switching operation as regard severity of faults, system stability etc. 4 SCB Configurations, What is an Electrical Fuse? The back-up protection by definition is slower than the primary protection system. © Listenlights.com created and maintained by. Failure is not confined to protective gear but may also be due to breaker defects. Example: Restricted Earth Fault, Differential protection etc. This ideal is rarely attained in practice. Local back-up protection is achieved by protection which detects an un-cleared primary system fault at its own location and which then trips its own circuit breakers, e.g. Back-up protection systems should, ideally, be completely separate from the primary systems. DC tripping voltage system is mainly used in sensitive equipment like alternator control circuit and protective circuit, high voltage Power transformer protective circuit, turbine control panel etc. The backup protection is provided as the main protection. The speed of response will often depend on the severity of the fault, and will generally be slower than for a unit system. Operation of the back-up protection will be, of necessity, slower and will result in a greater proportion of the primary system being lost. Time Graded, Protection systems in successive zones are arranged to operate in times that are graded through the sequence of, so that upon the occurrence of a fault, although a number of protection. Breaker Backup protection: Separate circuit breakers is used for both protections in the same station. Protection Systems in which selectivity is relative are non-unit systems. As shown in figure above, if a fault occurs then. A station battery usually provides the circuit breaker trip current. The backup protection comes into play only when the primary protection … – Breaker Back-up: Different breakers are provided for main and back up protection, both the breakers are being in the same station. Sometimes for simplification, the backup protection has a low sensitivity and operated over a limited backup zone. we respect your privacy and take protecting it seriously. 2.Dakshata U. Kamble. the. Write CSS OR LESS and hit save. On assembly direct handling of components should also be avoided as far as possible. can fail due to failure of one of the components in the protective system such as a relay, auxiliary relay. Your email address will not be published. The failure of the primary protection … Protection Systems which in principle are absolutely selective are known as unit systems. DC Ammeter : Construction, Working and Temperature Compensation, What is Shunt Capacitor Bank? respond, only those relevant to the faulty zone complete the tripping function. Referring to the figure, the tripping time at station C, B and A are graded such that for a fault beyond C breaker at C operates as primary protection. Also the backup relays should be coordinated with the primary relays. [wp_ad_camp_1] The speed of response will often depend on the severity of the fault, and will generally be slower than for a unit system. A relay should be able to distinguish between a fault and an overload.