Motor Starting Analysis

pandapower ANDES

Motor Starting checks voltage dip and loading when asynchronous motors start. Use the steady-state study for three snapshots (before / locked-rotor / after), or the dynamic study for a time-domain startup. Methods include DOL, soft-start, star-delta, autotransformer, and reactor. Overview: Motor starting guide.

Where to find it

Simulate → Motor Starting. Requires a subscription. Each motor needs locked-rotor current, R/X, and rated voltage set in the Motor dialog.

When to use

Voltage dip vs a limit (for example 10–15%) during DOL or soft-start
Comparing starter methods in steady-state
Start time and voltage recovery in dynamic mode

How to run

Place Motor elements and fill locked-rotor data.
Click Simulate → Motor Starting.
Choose steady-state or dynamic, the motors to start, and the starter method.
Run and review bus dip, branch loading, and (in dynamic mode) the time plots.

How the two study modes work

Steady-state (pandapower)

Before: motors to start are taken out of service; AC load flow gives pre-start voltages.
During: each starting motor is replaced by a locked-rotor PQ load. Starting current is \(I_{lr} = lrc\_pu \cdot I_n\), scaled by method factor \(k_m\) (DOL = 1, soft-start = \(I_{limit}/lrc\), star-delta = 1/3, autotransformer = \(tap^2\), reactor = \(1/(1+x_r)\)).
After: motors return at their loading; post-start voltages are computed.
Checks: dip % vs limit on every bus; branch loading during start vs thermal limit.

Dynamic (ANDES)

Network is mapped to ANDES; selected motors become Motor3 devices with u=0.
A Toggle connects each motor at \(t_{start}\).
TDS returns bus voltage, motor current, slip, and torque vs time; start time is when slip falls below threshold.
Soft-start in dynamic mode is approximated by scaling motor Sn so initial current ≈ \(I_{limit}\).

Input Parameters

Parameter	Description	Type	Options / typical values	Default
Calculation Mode	Steady-state voltage dip or dynamic ANDES startup	radio	steady, dynamic	steady
Motor(s) to Start	Which motors start in this study	select	All in-service motors, or one motor	All
Starting Method	Starter type (exact factors in steady-state; DOL / approx. soft-start in dynamic)	select	DOL, soft-start, star-delta, autotransformer, reactor	DOL
Soft-start Current Limit (p.u.)	Current limit as multiple of rated current	number	Typical 2–4	3
Autotransformer Tap (p.u.)	Starting tap for AT method	number	0.1–1.0	0.8
Reactor Reactance (p.u.)	Series reactor for reactor start	number	≥ 0	0.25
Max Voltage Dip Limit (%)	Pass/fail threshold for (V_before − V_during) / V_before	number	Typical 10–15	15
Max Branch Loading Limit (%)	Thermal check during start	number	Typical 100	100
Dynamic t_start / t_end	Motor connect time and simulation end (dynamic mode)	number	seconds	0.1 / 5

Results

SLD boxes: bus V before/during/after and dip % (green PASS / red FAIL); motor I_start and method
Results dialog: tables for motors, buses, branches; CSV download; Chart.js plots for dynamic mode
Summary: worst dip, voltage/thermal fail counts

Limitations and Considerations

Important notes:

Steady-state locked-rotor model is a snapshot, not a full torque–speed acceleration curve
Dynamic soft-start is an approximation (Sn scaling), not a thyristor softstarter controller model
Star-delta / autotransformer / reactor factors apply exactly in steady-state; dynamic mode uses DOL (or approx. soft-start)
No vendor-specific DSL controllers, synchronous-motor excitation start, or variable rotor resistance
Dynamic mode requires a network suitable for ANDES (synchronous generator / slack as for Transient Stability)

Technical References

Based on: pandapower load flow and motor element (lrc_pu, rx); ANDES Motor3 + Toggle for time-domain startup. Typical study outputs include voltage drop before/during/after start, start time, and grid loading.

Related: Motor element · Short Circuit · Transient Stability (ANDES)

Last updated: October 2026

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