Industrial Applications, Drives and Automation Basics
What this domain tests
Industrial Applications, Drives and Automation Basics tests motor starters, variable frequency drives, load characteristics, PLC inputs/outputs, sensors and simple control logic used in pumps, fans, conveyors and compressors.
Core rules
- DOL starting suits small motors; star-delta reduces starting current but only for light loads; soft starters control voltage ramp; VFDs control frequency and voltage.
- VFD control is usually V/f for fan and pump loads. Ramp times, current limits and braking must be set for the load.
- Pumps and fans are variable-torque loads; power varies approximately with speed cubed. Conveyors are closer to constant torque.
- PLC inputs come from sensors and switches; outputs drive contactors, relays, solenoids or indicators. Logic must include interlocks and emergency stops.
Worked example
A 30 kW fan runs at 100% speed. Under affinity laws, reducing speed to 80% gives power ≈ 30 × 0.8³ = 30 × 0.512 = 15.4 kW, about half. This is why VFDs save energy on variable-torque fans, but the drive, motor insulation and cable must be suitable for harmonic and high-frequency effects.
Traps that cost marks
Using a contactor for frequent VFD output switching, ignoring the motor’s minimum speed and cooling, setting acceleration too fast and causing overcurrent, and assuming a sensor is faulty when the PLC input is miswired. Check common, supply and input polarity first.