RELAY COORDINATION STUDIES EXECUTIVE SUMMARY
Relay coordination studies – It is a well-known fact that the power system is not completely free from failures/faults. The key here is to mitigate the consequences during the event of faults. Damage to equipment during a fault can be reduced by quickly isolating the faulty portion from the rest of the health system. The objective of the protection coordination study is to determine optimum settings for protection devices such that the protection system isolates the minimum possible faulty portion at the earliest possible to ensure a reliable power supply for the health system. The optimum settings ensure required sensitivity and selectivity that protect workers from harm as well. The software used for the protection coordination study is ETAP, DigSilent Power factory, PSCAD, and PSS/E. The protection coordination study involves protection devices from various manufacturers such as Siemens, ABB/Hitachi, GE, Schneider, and so on.
WHY RELAY COORDINATION STUDY?
• To determine the optimum settings for protective devices in the system such as relays, releases, breakers, etc to ensure that proper coordination is achieved.
• To analyze time coordination curves (TCC) to verify the coordination between upstream and downstream protection devices including fuses.
• To check the sequence of operation of protection devices for various operating configurations.
• To find out the fault clearing time.
• To verify the protection coordination of t existing plant especially when there is a change in the network connectivity or source fault level.
• To generate calculations and finalize the unit protection settings of a generator, line, cable, transformer, motor, reactor, and capacitor banks.
• As an input for the calculation of incident energy in Arc Flash Studies.
HOW RELAY COORDINATION STUDY? (METHODOLOGY)
• Collection of inputs (SLD, equipment parameters – Voltage kV rating, Power MVA rating, Impedance, System fault level, X/R ratio, relay details, protection schematics, etc.)
• Modelling in study software.
• Carry out the short circuit simulations for various system configurations (normal and contingency configuration)
• Generating TCC curves and determining the characteristics and optimum settings
• Verification of sequence of operation for different types of faults (3 Ph, SLG, L-L, L-L-N) at various locations.
• Generating relay setting tables/charts, relay settings soft file (parameterization) file.
• Submission of detailed report.
• Presentation of study findings.
OUTCOMES OF RELAY COORDINATION STUDY
• Detailed report explaining the input data, system configuration, observations, and recommendations
• Fault currents at various buses and branches in the system.
• Relay setting charts/tables with optimum settings
• Time coordination curves
• Sequence of operation
• Relay setting soft file
• Input to Arc Flash Study
REFERENCE
• IEEE 242 – Recommended Practice for Protection and Coordination of Industrial and Commercial Power Systems
• IEEE 3004 Standards: Protection & Coordination
• IEEE 399 – Recommended Practice for Industrial and Commercial Power System Analysis
• IEEE 241 – Recommended Practice for Electric Power Systems in Commercial Buildings
• IEC 60255 Measuring relays and protection equipment

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