Power System Protection Studies and Relay Coordination

Protective relays are to be designed to isolate the faulted portion of the system at the earliest, to prevent equipment damage and with minimum system disruption to ensure continuity of service to healthy portion of the network. When relays meant to protect specific equipments, transmission/distribution lines/feeders or primary zone do not operate and clear the fault in their primary protection zone, backup relays must act to isolate the fault, after providing sufficient time discrimination for the operation of the primary zone relays. The relays must also be able to discriminate between faulted conditions, normal operating conditions and abnormal operating conditions and function for the specific protection for which they are designed. Relay coordination calculation module must consider the operating characteristics of the relays, normal operating and with stand characteristics of the equipments and must determine the optimum relay settings to achieve the objectives stated. The parameters of the under frequency and under voltage relays can be set and their performance can be evaluated using detailed transient stability studies.

Protection system must also be designed to provide protection against thermal-withstand limits, motor stalling, negative sequence current with-stand limits, protection against abnormal frequencies, and protection against unbalance operating conditions as applicable to various equipments and operating situations.

Overcurrent Phase/Earth Fault Relays

• Overcurrent phase fault relays.
• Overcurrent earth fault relays.
• High set relay settings to ensure protection against primary zone faults.
• Coordination with maximum load current.
• Coordination with fuse characteristics.
• Coordination with maximum motor starting current and time.
• Coordination with transformer inrush current.
• Coordination with primary-back up pairs.
• Coordination with thermal withstand capabilities ([I-square]t = K characteristics).
• Coordination with safe stall limits for Motors.
• Automatic generation of TCC’s showing all relevant coordination.
• Automatic identification of primary and back up relay pairs.
• Provision for user defined back up relays for specific primary relays.
• Solution for multiple island networks.
• Multiple study cases for different network and source configurations in a single execution of the program.
• Built in libraries of commercial relays, IEEE and IEC characteristics.

Distance Relay Settings

• Zone setting calculations for zone 1 and 2.
• Zone 3 setting calculations based on inbuilt short circuit calculations.
• Settings for different commercially available relays.
• Different relay characteristics MHO , Polygonal , Lens , Circle , R/X Blinder, Offset characteristic.
• R/X diagrams.
• Solution for multiple islanded network in a single execution of the program.
• Solution for multiple study cases with different network configurations in a single execution of program.