H‑Infinity

When large motors start, they draw 5–8 times their rated current. This surge can cause significant voltage dips that affect other equipment, exceed breaker trip thresholds, or simply prevent the motor from reaching operating speed. Our dynamic motor analysis models the complete starting sequence — across-the-line, star-delta, auto-transformer, or soft starter — to verify successful operation.

01What is Dynamic Motor Analysis?

Dynamic motor analysis (also called motor starting study) simulates the transient behaviour of induction and synchronous motors during the starting period — typically 2–10 seconds for large machines. We model:

Motor Torque-Speed Curve

Breakdown torque, pull-up torque, and pull-down torque characteristics at various voltages and frequencies.

System Voltage Profile

Terminal voltage during starting to verify it stays above minimum thresholds (typically 80–85% of rated).

Acceleration Time

Time to reach full speed — critical for motors driving fans, pumps, and compressors where extended acceleration can cause overheating.

Current Inrush

Locked-rotor and accelerating currents to verify breaker and cable ratings.

02Why Motor Analysis Matters

Large motor starting is one of the most common causes of system disturbances during commissioning and restart after outages:

▸Excessive Voltage Dip — Motors drawing too much current can drop voltage below 80%, causing contactors to drop out, PLCs to reset, and lights to dim noticeably.
▸Failure to Accelerate — If load torque exceeds motor breakdown torque, the motor stalls, draws locked-rotor current indefinitely, and trips on overload.
▸Thermal Damage — Repeated failed starts or excessive acceleration times degrade motor insulation and can cause winding failures.
▸Generator Overload — On islanded systems, simultaneous motor starting can overwhelm generators and cause frequency/voltage collapse.

03Our Approach

Our motor starting analysis uses detailed equivalent circuit models and time-domain simulation:

1. Motor & Load Modelling

Extract equivalent circuit parameters from manufacturer data or test results. Model load torque profiles (constant, square, linear) and inertia (GD²).

2. Starting Method Selection

Evaluate across-the-line, star-delta, auto-transformer, soft-starter, and VFD starting methods to find the optimal trade-off between inrush current and torque.

3. Time-Domain Simulation

Simulate the complete acceleration curve (torque vs. speed, current vs. time, voltage vs. time) to identify problematic regions.

4. Multiple Motor Starting

For complex plants, model sequential or simultaneous starting of multiple large motors to assess cumulative impact.

04Scope of Motor Analysis

Our comprehensive motor starting assessments include:

▸Single Motor Starting — Full acceleration curve, voltage dip at PCC, thermal stress assessment.
▸Multiple Motor Sequencing — Optimised start sequences to minimise simultaneous inrush currents.
▸Recovery Analysis — Motor self-starting behaviour after voltage dip恢复 (restoration) to ensure critical loads restart within acceptable timeframes.
▸Starter Type Recommendation — Based on analysis, recommend optimal starting method for each motor.

05Standards & Compliance

✓IEEE 45 — Electrical Systems on Ships

✓IEEE 300 — Rotating Machine Starting

✓IEC 60034-27 — Starting of Rotating Machines

✓API 610 — Centrifugal Pumps

06Why H-Infinity

Motor starting analysis sits at the intersection of electrical design and mechanical engineering. Our team brings experience across oil & gas, mining, water treatment, and commercial construction — understanding the operational constraints that make certain starting methods impractical. We deliver not just simulation results but clear recommendations on starter selection and start sequencing.

Dynamic Motor Analysis