Electricalreads

Testing Guidelines • Protection scheme shall operate correctly at critical time of fault in system and also it shall avoid tripping of healthy system/elements. Testing of Protection scheme is carried out for verification of scheme for intended operation and as confirmation of healthiness of protection scheme. • Protection engineers should have appropriate engineering skills with an emphasis on electrical power engineering with knowledge of communication and IT systems is also required. This provides the basic knowledge that is a prerequisite for understanding the principles and techniques of power system protection. However, recently recruited protection engineers will need further training and experience before they can be expected or allowed to work unsupervised in the field of protection. • Enhanced functionality of numerical protection devices based on microprocessor technologies lead to an increased number of setting parameters and the use of flexible products based on a man...

LINE  DIFFERENTIAL  PROTECTION Many transmission lines are now having OPGW or separate optic fiber laid for the communication. Where ever such facilities are available, it is recommended to have the line differential protection as Main-I protection with distance protection as backup (built-in Main relay or standalone). Main-II protection shall continue to be distance protection. For cables and composite lines, line differential protection with built in distance back up shall be applied as Main-I protection and distance relay as Main-II protection. Auto-reclose shall be blocked for faults in the cables. For Lines with length smaller than 10KMs having OPGW Communication link availability, shall have Line Differential Protection as both Main-1 and Main-2 and Distance Protection as backup function in both relays. ·       Current differential protection with line charging compensation. ·       Inbuilt distance protection capable of being inde...

Overvoltage Protection in Electrical Power Transmission Line • An overvoltage alarm (Ph-N as measurement mode) shall be set at 110% with delay of 0.5 Sec (220kV and 400kV Lines). For detection of any PT secondary circuit issue. (i.e. floating neutral condition) • Over voltage protection with two stage trip (Ph-Ph as measurement mode) shall be configured in 400 KV system only. It shall be configured in main-1 or main-2 distance protection schemes. • The low stage (Stage-1) shall be set in the range 110-112% (typical 110%) with the time delay of 4-7 Sec. However, time grading of 1-3 second may be provided between over voltage relays of double circuit lines. Longest time delay shall be checked with expected operating time of over fluxing relay of the transformer to ensure disconnection of line before tripping of transformer. • The high stage (Stage-2) shall be kept in the range 140 – 150% with time delay of 100-150 msec. • The overvoltage setting is to be kept same for transmiss...

For phase to ground faults, resistive reach should be set to give maximum coverage considering fault resistance, arc resistance & tower footing resistance. It has been considered that ground fault would not be responsive to line loading. ·      In case of phase to phase fault, resistive reach should be set to provide coverage against all types of anticipated phase to phase faults ·      In relays having quadrilateral characteristics, it shall have independent resistive reach settings for Phase to ground faults, and Phase to phase faults, ·      While setting resistive reach load encroachment possibility shall be considered.

About Electrical Power Transmission Line Protection The protection relaying of the transmission lines shall be designed to ensure that: • Faults on any part of the 220\400kV transmission line are detected by at least two high speed independent protection relays that have the capability of independently initiating fault clearance within the required time; • Protection scheme applied is adaptable and adequate for protection of the entire transmission line and provide backup protection for associated transmission line circuit end equipment and adjacent transmission lines if required; • Protection scheme is arranged to ensure no part of the primary system is unprotected; • Protection scheme is capable of independently tripping the circuit breaker(s) selectively to clear the fault within specified fault clearance times; • Protection for the 400/220 kV transmission lines shall be phase segregated and shall be capable of single pole tripping and Auto reclosing function. • Protecti...