Generator Technical Knowledge — Advanced Power Systems
Advanced engineering topics for electrical engineers and power system designers. This guide assumes familiarity with basic generator operation.
Level 1: Power Factor Fundamentals
Power Factor (PF) = Real Power (kW) / Apparent Power (kVA). Inductive loads (motors, transformers) cause lagging PF. Capacitive loads cause leading PF. Most generators are rated at 0.8 PF lagging. A 100 kVA generator at 0.8 PF delivers 80 kW.
Level 2: Voltage Regulation & AVR
The Automatic Voltage Regulator controls excitation current to maintain output voltage within +/-1%. Regulation speed: modern AVRs respond in <50ms. Steady-state regulation: +/-0.5% from no-load to full-load. Transient response: voltage dip <15% for sudden load application, recovery within 1 second.
Level 3: Parallel Generator Operation
Requirements for paralleling: same voltage, same frequency, same phase sequence, same phase angle (at moment of connection). Synchronizing methods: manual synchroscope, automatic synchronizer, or dead bus closure. Load sharing: isochronous (all units share proportionally) or droop (frequency drops with load).
Level 4: Harmonic Distortion
Non-linear loads (VFDs, UPS, LED lighting, computers) generate harmonics. Total Harmonic Distortion (THD) should be <5% for generators. Harmonics cause: overheating of generator windings, voltage waveform distortion, neutral conductor overcurrent (triplen harmonics), AVR instability. Solutions: oversize alternator, use 2/3 pitch windings, install harmonic filters.
Level 5: Generator Protection Systems
- Overcurrent: 51/51V relays (inverse time overcurrent with voltage restraint)
- Differential: 87G (stator winding protection)
- Ground fault: 51G/64G (stator ground fault)
- Loss of excitation: 40 (field failure)
- Reverse power: 32 (motoring)
- Over/under frequency: 81O/U
- Over/under voltage: 59/27
- Synch check: 25 (prevents out-of-sync closure)