IEEE 1584 · Engineering
Motor Start Analysis
## Motor Start Analysis
What We Deliver
Questions a Motor Start Study Answers
Motor starting is the single most disruptive event a Peruvian facility's electrical system sees. Knowing the outcome in advance saves you from nuisance trips, stalled loads, and commissioning delays.
Voltage Dip Calculation
Time-domain simulation of terminal voltage during starting, verified against the 80% nameplate floor and bus-level limits for sensitive loads.
Starting Method Comparison
DOL vs reduced-voltage autotransformer vs soft starter vs VFD, each modelled in ETAP with cost and voltage-impact tradeoffs.
Generator Impact Analysis
Transient simulation of motor start on generator-only supplies where motor kVA exceeds 10-15% of genset rating.
Protection Coordination
Verify upstream breakers ride through starting inrush (5-7× FLA for DOL) without nuisance tripping.
Cable Sizing Verification
Check cable thermal ratings under starting current and voltage drop compliance per RM 111-2013-MEM installation codes.
Recommendation Report
Selected starting method with relay settings tuned to ride through transient, plus commissioning procedure.
How We Work
Our Process
Motor Data Collection
Gather motor nameplate, starting impedance, load inertia, and supply short-circuit data.
Load Flow Modeling
Build the ETAP model with current bus loading and utility fault contribution to represent real starting conditions.
Starting Simulation
Run time-domain simulation of direct-on-line start; iterate through soft starter, VFD, and reduced-voltage options if DOL violates limits.
Recommendation
Deliver sizing, settings, and commissioning plan with expected voltage dip and acceleration time per scenario.
Equipment Protection
Protect Downstream Loads From Motor-Start Transients
Voltage drops during motor starts affect everything on the bus — lighting, PLCs, drives, instrumentation. Modelling the transient protects the whole plant.
- Prevents motor stall and thermal damage from undersized supply
- Verifies 80% nameplate terminal voltage minimum during acceleration
- Eliminates nuisance upstream breaker trips during motor start
- Confirms sensitive bus voltage rides through within PLC and drive tolerances
- Provides OSINERGMIN-ready documentation for motor installation approval
Deliverables
Motor Start Report Contents
Every motor start report includes time-domain simulations, starting-current curves, voltage-recovery plots, and a clear go/no-go recommendation for direct-on-line start.
- 1Voltage vs time at motor terminals and every sensitive bus
- 2Current vs time from inrush through steady-state
- 3Motor and load torque-speed curves with acceleration margin
- 4Starter sizing and settings when DOL is not viable
- 5Recommendations for bus configuration during start
FAQ
Frequently Asked Questions
What is a motor start analysis?+
A motor start analysis is a time-domain simulation that predicts the transient electrical behaviour when a large motor is energized — voltage dip at terminals and across the bus, inrush current magnitude and duration, acceleration time to rated speed, and protection device response. The study determines whether the motor can start safely and what starting method is required.
Why do motors cause voltage dips?+
Induction motors draw 5-7 times their full-load current during starting because the rotor slip is 100%. This inrush current flows through source impedance — transformer, cables, generator — causing voltage drop at the motor terminals and every bus upstream. In Peruvian industrial facilities with weak supplies, the dip can exceed 20% and trip sensitive equipment.
When is a motor start study required?+
Before commissioning any motor larger than 30% of supply transformer kVA, before adding any motor to a generator-only supply where motor kVA exceeds 10-15% of generator rating, or whenever multiple motors start simultaneously. RM 111-2013-MEM requires that motor installations meet voltage tolerance limits, which a starting study verifies.
What is an acceptable voltage dip?+
Terminal voltage must stay at or above 80% of rated during motor acceleration — below this the motor develops insufficient torque to reach speed. Bus voltage should stay above 90% for sensitive loads like PLCs, VFDs, and contactors. Utility codes in Peru often limit voltage dip at the PCC to 3-5% for large motor starts.
How does a VFD help with motor starting?+
A variable-frequency drive ramps the motor up from low frequency, limiting inrush to near full-load current regardless of motor size. The VFD also controls acceleration time and torque profile. For motors where direct-on-line starting violates voltage dip limits, a VFD or soft starter is typically the most economical solution after a Carelabs study confirms the sizing.
Model Your Motor Start Before You Commission
Carelabs engineers deliver ETAP-based motor starting studies for industrial facilities across Lima, Arequipa, Trujillo, and Chiclayo
Request a Free Quote