Tractor Power Generator

Tractor power is matched by a rule of thumb of roughly 1.5–2 hp per 1 kVA of generator output. An 18 kVA unit therefore calls for about 27–36 hp, a 27 kVA unit for about 41–54 hp, and headroom matters because the tractor has to hold PTO speed constant under full load. The second condition is shaft speed: a generator built for 540 rpm must never be driven at 1000 rpm. The third is the lifting capacity of the three-point linkage, since units above 20 kVA weigh several hundred kilograms.

The difference lies in the source of drive and in running costs. A tractor generator is an alternator, a gearbox and a control panel, so at 18 kVA it weighs distinctly less than an engine-driven set of the same rating and costs a fraction of the price. There are no oil or filter changes, and no fuel ageing in a tank through 6–12 months of standstill. The trade-off is dependence: without a running tractor the machine does nothing, and it cannot be wired into an automatic transfer switch.

Output frequency is a direct function of shaft speed, so revolutions are set before any load is connected and locked with the hand throttle. On a 540 rpm shaft the gearbox spins the alternator to 3000 rpm, which gives 50 Hz; a deviation of 5% downwards already means about 47.5 Hz and overheated electric motors. The frequency meter on the generator panel is the reference — if the reading drops below 49 Hz under load, raise engine speed or shed part of the load.

An 18 kVA set delivers about 14.4 kW of real power at a power factor of 0.8, enough on a farm for a milking parlour, a milk cooler, barn ventilation and water pumps at once. The limiting factor is not total consumption but inrush current: induction motors draw 3–7 times rated current at start-up, so the largest load is always started first. Connecting to a building installation requires a changeover switch isolating the mains, fitted by a qualified electrician.