Electric Motors & Transformers by Hand: Turns Ratios, Equivalent Circuits, Voltage Regulation, Efficiency, DC Motor Speed & Torque, Induction Motor Slip, Power Flow & Motor Energy Costs

What you'll build

What you will be able to do

Each lab ends with a concrete result that you build yourself and the checker confirms, cell by cell.

• Take six fictional transformers on Ashgrove's test bench and work out the turns ratio, the secondary voltage and current, the primary current, the apparent power on both sides and the load resistance as the supply sees it.
• Reduce a fictional 50 kVA transformer to one resistance and one reactance, express its impedance in per unit, and work out the voltage drop and the voltage regulation for five loads – lagging, leading and half load – with real and imaginary parts in separate columns.
• Split the losses of a fictional 100 kVA transformer into a fixed core loss and a copper loss that grows with the square of the load, compute the efficiency from ¼ to 5/4 load, find the load of maximum efficiency and the all-day efficiency of a daily load profile.
• Run a fictional DC motor through a load test: armature current from torque, back-EMF, speed in rpm, a chart of the drooping speed–torque line, the starting current at standstill and the series resistor that limits it.
• Read six fictional induction-motor nameplates and work out the synchronous speed from poles and frequency, the rated slip, the frequency of the rotor currents and the speed at the present part load.
• Follow 18.6 kW of electrical input through a fictional induction motor stage by stage – stator losses, air-gap power, rotor copper loss, mechanical power, friction – to the shaft, then compute speed, torque and efficiency and chart the power at each stage.
• Compute the torque of a fictional induction motor over a slip table from a simplified equivalent circuit, chart the torque–slip curve, find the slip and size of the maximum torque in closed form and estimate where the rated load torque line crosses the stable part of the curve.
• Price four options for a fictional 22 kW fan motor over its yearly duty cycle: keep the old motor, buy a more efficient one, or add a variable-speed drive that uses the cube law of fans – yearly kWh, cost, investment and payback.