Virtual Lab | Numerical Protection of Induction Motor

Experiment Objective

To perform numerical protection of a three-phase induction motor. The simulation calculates rated current, CT secondary current, relay pickup levels, sequence quantities and operating time for different abnormal operating conditions.

Live Measurements

Rated current —

Actual current —

CT secondary —

✓ SYSTEM READY — NO TRIP

Three-Phase Phasor Diagram

Voltage / Current Phasors — 120° Phase Displacement

Phase A

Phase B

Phase C

Negative sequence

Numerical Protection System

Numerical Calculations

1. Rated Motor Current

I N = \frac{P}{\sqrt{3} \cdot V \cdot η \cdot cosφ}

—

2. CT Secondary Current

I s = I p \times \frac{CTs}{CTp}

—

3. Thermal Pickup — 49

I OL = \frac{K}{100} \times I N

—

4. Overcurrent Pickup — 50/51

I OC = \frac{K}{100} \times I N

—

5. Earth Fault Pickup — 50N/51N

I EF = \frac{K}{100} \times I N

—

6. Negative Sequence Pickup — 46

I 2 = \frac{K}{100} \times I N

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Inverse-Time Relay Characteristic

IEC-style inverse characteristic

Inverse characteristic

Pickup

Operating point

Three-Phase Current Waveform

Phase currents with 120° displacement

Protection Pickup Comparison

Protection Decision

Element	Pickup	Measured	Decision
49	—	—	—
50/51	—	—	—
50N/51N	—	—	—
46	—	—	—

Adjust the relay settings and run the simulation.

49	Thermal overload
50/51	Phase overcurrent
50N/51N	Earth fault
46	Negative sequence