Relay Setting Calculations & Coordination

What this covers

• Overcurrent and earth fault — pickup, time multiplier and curve selection for phase and earth elements, including directional and sensitive earth fault where required.
• Differential protection — bias characteristics, inrush and CT saturation restraint for transformers, generators, motors and busbars.
• Distance protection — zone reach, timing and teleprotection scheme settings for transmission lines.
• Coordination study — time-current curve plots across each protected path from source to load.
• CT and VT verification — checking that instrument transformer ratio, class and burden actually support the settings applied.
• Arc flash interaction — reviewing where settings drive incident energy, and where maintenance switching or zone-selective interlocking helps.

What you receive

• Setting calculation report with the assumptions and fault data used
• Relay setting sheets in a format ready to load into the device
• Time-current coordination curves for every path studied
• CT saturation and burden check calculations
• A record of any coordination compromises and why they were accepted

Standards and references

Calculations are prepared against IEC 60255 and the IEEE C37 series, with fault levels derived to IEC 60909 or ANSI/IEEE C37.010 depending on the project basis.