A mining trolley wire locomotive that jumps to full speed the moment it is powered up is a serious safety and control issue that demands fast diagnosis. Below I explain the most common causes, clear troubleshooting steps, and practical fixes to bring the locomotive’s control system back to safe, predictable operation.
Common causes of sudden full-speed start
IGBT module breakdown (short circuit): The IGBT (insulated-gate bipolar transistor) modules in the traction inverter control current to the motors. If an IGBT fails short, the controller can lose the ability to limit motor drive and the locomotive may surge to full speed.
Speed-setting (speed-given) voltage too high: The speed command (given voltage) from the speed setter or potentiometer directly controls motor torque. If this signal is stuck or set too high at power-up, the locomotive will accelerate immediately.
Other electrical/control faults: Loose wiring, a failed trigger/driver board, or shorted feedback sensors can mimic the above behaviors and should be checked.
Safe immediate actions
Cut power and isolate the vehicle — remove supply before any inspection.
Tag and lock out the trolley power to prevent accidental re-energizing.
Alert operations and safety teams; do not attempt a live test without qualified electrical personnel.
Troubleshooting checklist
Visual and basic checks
Inspect control cabinet for burnt components, smell of ozone, or melted insulation.
Check fuses and visible wiring integrity.
IGBT inspection
With power isolated, perform diode and insulation tests on IGBT modules (or have a qualified technician do so).
Replace any IGBT showing short or inconsistent readings.
Speed setter and control signal
Measure the speed command (voltage) at power-up — it should sit at a safe idle reference.
Calibrate or replace the speed potentiometer / speed-giver if it reads high.
Control board & sensors
Check trigger/driver boards for blown components.
Verify encoder or tachometer feedback wiring is intact and providing correct signals.
Protection & firmware
Ensure drive protection settings (overcurrent, ramp rates) are correctly configured.
Update or reload controller firmware only per manufacturer guidance.
Preventive measures
Schedule regular preventative maintenance for the traction inverter and control systems.
Install surge protection and ensure good earthing/grounding to reduce transient damage to IGBTs.
Keep a maintenance log of control settings and repairs to trace recurring faults.
A reliable maintenance program and immediate corrective action — especially checking the IGBT modules and the speed-setting voltage — will help prevent repeated incidents of a mining trolley wire locomotive starting at full speed and will restore safe, controlled operation.
