Most gensets built in India use a brushless synchronous alternator with an automatic voltage regulator (AVR). Small portable sets sometimes use brushed or capacitor-excited alternators, which are cheaper and simpler but give less stable voltage.
The alternator decides how well the set handles motor starting, uneven loads and sensitive electronics, so it deserves as much attention as the engine.
Main alternator types
- Brushless self-excited alternators take excitation power from the main output through the AVR, and suit most general use.
- Alternators with an auxiliary winding or a permanent magnet generator (PMG) keep excitation steady during heavy motor starting and short circuits.
- Brushed alternators feed the rotor through slip rings and brushes, which need periodic replacement.
- Capacitor-excited single-phase alternators are common on very small sets and give rougher voltage control.
Features to specify
- Insulation class, with class H common on industrial alternators, and the temperature rise class it actually runs at.
- Ingress protection, often IP23 for alternators inside a canopy.
- Single-bearing or two-bearing design, which affects how the alternator couples to the engine.
- Winding pitch, because a two-thirds pitch winding reduces third-harmonic currents in the neutral.
- Copper or aluminium windings, which affect losses and size, as covered for motors in copper versus aluminium winding.
- Voltage regulation, stated as a percentage band from no load to full load.
Standards and checks
Genset alternators are usually built to IEC 60034-1 for rotating machines, and ISO 8528-3 covers alternators used in generating sets. Ask the builder which standard the alternator follows and for its test certificate. The certificate should show winding resistance, insulation resistance and a no-load and load test.
Check that the alternator rating matches the engine, because the two are often bought from different makers. A larger alternator on a smaller engine handles motor starting better. A smaller alternator than the engine can drive will overheat on full load. The nameplate data should agree with the set rating on the genset specification.
For voltage and frequency, confirm the alternator is wound for your market. A 50 Hz alternator run at 60 Hz needs a different voltage setting, and not every design allows it.
Questions to ask the builder
- Which alternator model and frame size is fitted to each set rating?
- Is the alternator made in-house or bought from a specialist maker?
- What voltage dip does the set show when your largest motor starts?
- Is the AVR standard, or is a digital AVR available for tighter control?
- Are anti-condensation heaters fitted for humid or standby sites?
- Will the alternator's test certificate carry the same serial number as the nameplate?
Next step
We check alternator nameplates, test certificates and wiring against the order before loading. To review the alternators in a supplier's sets, book a free sourcing review.