Hitachi Mining, a part of Hitachi Construction Machinery, has introduced AC drive in rigid dump trucks. The EH3500AC is powered by a Cummins 16-cylinder, QSK50 Tier II compliant turbo diesel, developing 1491kW at 1900rpm and driving through axle-mounted Hitachi AC traction drives.
Fully loaded, the EH3500 weighs 500 tonnes with a payload of 360+ tonnes. The truck is powered by two AC traction motors, which propels the gargantuan to a speed of over 55KPH. The motors also function as electric brakes bringing the 3.6 metre wheels to a safe stop without the use of mechanical brake pads.
AC drives start-off with a basic 6-7% higher efficiency over DC drives of comparable size, allowing faster travel speeds while reducing diesel fuel consumption.
Using the same drive concept as a diesel electric locomotive, the EH3500 AC’s 3500HP diesel engine powers an AC alternator. Constant voltage DC from this alternator is transformed by an inverter into variable frequency AC, which in turn supplies the two AC electric motors installed in the rear axle of the truck. The output frequency and voltage of the inverters are controlled to provide precise motor torque and speed.
In retard, the inverters generate electric power by slowing down the motors. Braking choppers, connected to the inverters, channel that power straight into a power resistor grid that continuously dissipates the energy until the truck reaches standstill. The smooth braking action is like driving a car, but without mechanical brake wear.
AC traction drives are the logical solution for today's higher payload and performance requirements
- AC traction drives are better than DC drives
- Their reliability has been proven in locomotive, excavator, and industrial drives
- They meet high torque at low speed and high speed requirements
- AC traction drives are virtually maintenance free
- Higher AC drive efficiency reduces fuel/oil costs
- Special control reduces brake, engine and tyre wear
The EH3500 is suitable for open-pit mining because of its compatibility with harsh Australian environment.