Breaker Relay Settings Calculator

Back to Tools

This calculator provides guidance for setting protective relays for various electrical equipment, including transformers, Motor Control Centers (MCC), Power Control Centers (PCC), and motors. It aligns with common practices and standards from IEEE and IEC, assisting engineers in preliminary relay coordination.

Disclaimer: This tool provides preliminary settings for guidance only. Actual relay coordination requires a detailed system study, short-circuit analysis, and specialized software to ensure proper protection and selectivity. Always consult relevant standards and qualified engineers for final settings.

Equipment Details

Equipment Type

Voltage Rating (kV)

Rating (kVA / kW)

System Grounding Type

Potential Transformer (PT) Primary (V)

Potential Transformer (PT) Secondary (V)

Current Transformer (CT) Details

CT Primary (A)

CT Secondary (A)

CT Burden (VA)

CT Accuracy Class

Motor Specific Parameters

Power Factor (PF)

Efficiency (%)

Motor LRA Multiplier

Motor Start Time (s)

Thermal Time Constant (min)

Thermal Curve

Stall Protection Pickup (xFLC)

Stall Protection Time (s)

Undercurrent Pickup (%FLC)

Undercurrent Time (s)

Neg. Seq. Overcurrent Pickup (%FLC)

Neg. Seq. Overcurrent Time (s)

Starts/Hour Limit (ANSI 66)

Restart Inhibit Time (min)

Thermal Alarm Pickup (% of FLC)

Locked Rotor Trip Time (s)

Motor Ground Fault Type

Motor Ground Fault Pickup (A)

Motor Ground Fault Time (s)

Transformer Specific Parameters

Transformer Impedance (Z%)

Inrush Current Factor (xFLC)

HV CT Primary (A)

HV CT Secondary (A)

LV CT Primary (A)

LV CT Secondary (A)

Transformer Vector Group

2nd Harmonic Restraint (% of Diff Current)

5th Harmonic Restraint (% of Diff Current)

Overexcitation Pickup (V/Hz)

Overexcitation Time Delay (s)

Low-Set Differential Pickup (%FLC)

Low-Set Differential Time Delay (s)

Unrestrained Differential Pickup (xFLC)

Unrestrained Differential Time (s)

Restricted Earth Fault (64R) Pickup (A)

Restricted Earth Fault (64R) Time (s)

Relay Details

Type of Relay

Relay Application

IDMT Curve Type

Time Dial Setting (TDS)

Instantaneous Time Delay (s)

Coordination Time Interval (CTI) (s)

Dropout Ratio (%)

Advanced Relay Parameters (Numerical Relays)

Reset Time Factor

Harmonic Blocking (% of Fundamental)

CT/VT Supervision (60)

Breaker Failure (50BF/62BF) Time (s)

Auto-Reclosing (79) Stages

Auto-Reclosing (79) Dead Time (s)

Sync-Check (25)

Sync-Check Voltage Diff (V)

Sync-Check Angle Diff (deg)

Under Voltage (27) Pickup (V)

Under Voltage (27) Time (s)

Over Voltage (59) Pickup (V)

Over Voltage (59) Time (s)

Under Frequency (81U) Pickup (Hz)

Under Frequency (81U) Time (s)

Over Frequency (81O) Pickup (Hz)

Over Frequency (81O) Time (s)

Directional Element (67/67N)

Directional Characteristic Angle (deg)

Directional Polarizing Quantity

Relay Setting Guidance

Calculated Relay Settings

Setting Parameter	Calculated Value	Unit	Notes