Load Flow and Motor Starting Studies
Load flow and motor starting studies answer the questions that show up after commissioning if nobody asked them first: will the voltage hold at the far end of the plant under full load, and will the largest motor start without dragging the bus down far enough to drop contactors elsewhere?
Load flow and motor starting analysis
Steady-state voltage at every bus under realistic loading, not connected-load arithmetic.
Transformer and feeder loading against nameplate, identifying where capacity is genuinely constrained versus where it only appears to be.
Voltage drop against CEC limits, and power factor at the service.
Spare capacity assessment — useful input when you are deciding whether an expansion needs a service upgrade or can be absorbed.
Motor starting analysis
Voltage dip at the motor terminals and across the rest of the bus during start.
Acceleration time against the driven load, confirming the motor will actually get up to speed within its thermal limit.
Comparison of starting methods — across-the-line, soft start, VFD — where the dip is unacceptable.
Effects on sensitive loads elsewhere in the facility, including contactor drop-out and VFD undervoltage trips.
Typical triggers
Adding a large motor to an existing plant. Retrofitting pumping or compression capacity. Persistent unexplained trips on start. Utility complaints about flicker. A facility expansion where the question is whether the existing service can carry it.
Deliverables
A sealed report with the modelled cases, the loading and voltage profile at each bus, and the conditions under which limits are exceeded.
Voltage drop results at the worst-case bus for each operating scenario, checked against CEC limits and against equipment tolerance, which is often the tighter of the two.
Motor starting results giving the voltage dip at the motor terminals and at neighbouring buses, starting time against the motor thermal limit, and whether contactors and undervoltage relays will hold through the start.
Where a direct-on-line start does not pass, a comparison of the practical alternatives — reduced voltage, soft start, variable frequency drive, or a supply change — with the trade-offs stated.
The ETAP or EasyPower model file.
Common questions
My motor starts fine today. Why model it? Because the question is rarely whether it starts, but what else drops out when it does. A dip that the motor tolerates can still trip a drive, drop a contactor or reset a control system on the same bus.
How much voltage dip is acceptable? There is no single number. Contactors typically drop out somewhere around 70 to 80 percent of rated voltage, drives ride through far less, and lighting flicker becomes a complaint long before anything trips. We model against the equipment you actually have rather than a generic threshold.
Do I need this for a small motor? Not usually on a stiff service. It matters when the motor is large relative to the supply — a common case on rural feeds, on generator supply, and on any site where the transformer was sized for the load rather than the starting duty.
Can you model generator supply? Yes, and it is where motor starting studies earn their keep. Generator source impedance is far higher than a utility source, so a start that is unremarkable on utility power can be the sizing case for the generator.