An AVR regulates excitation to control terminal voltage, but its power source affects how much excitation remains during motor starting, faults, harmonics and voltage dips. PMG is not merely a premium label and does not replace correct sizing or protection.
Define transient loads, nonlinear content, fault protection and voltage recovery first. Then select shunt, auxiliary-winding or PMG excitation and verify data for the exact alternator and AVR.
1. Understand what this decision changes
The AVR regulates but is not an unlimited energy source
It senses terminal voltage and controls field current, while excitation source, exciter and magnetic capacity still set the limits.
Excitation supply during a voltage dip matters
Large load steps or faults depress terminal voltage; an independent or reinforced source can maintain excitation and fault current better.
Loads and protection define the requirement
Motors, UPS systems, rectifiers, harmonics and selective protection require separate checks of dip, waveform and sustained fault current.
2. Inputs to confirm before procurement
Do not make a PMG yes-or-no decision before collecting load and protection data.
- Largest motor starting kVA and allowed voltage dip
- UPS, VFD and rectifier capacity and harmonics
- Fault current and duration required by protection
- Voltage recovery and steady regulation criteria
- Exact alternator, AVR and excitation arrangement
3. How the main options compare
| Option or parameter | Where it fits | What must be verified |
|---|---|---|
| Shunt-powered AVR | Conventional systems with moderate transients and defined loads. | Starting dip, fault behavior and nonlinear-load limits. |
| Auxiliary-winding or reinforced excitation | Projects needing improved transient and fault support. | Manufacturer design, forcing ceiling and test curves. |
| PMG-supplied AVR | Large motors, nonlinear loads or explicit fault-current and recovery needs. | PMG-AVR combination, complete-set match and protection study. |
4. The most common decision errors
Common mistakes
- Reducing alternator size just because PMG is fitted
- Confusing steady AVR accuracy with load-step performance
- Ignoring engine-speed dip during voltage recovery
- Specifying only the brand, not AVR and excitation models
Voltage transients are produced by engine, governor, alternator, excitation and load together.
5. What the technical specification must state
The specification should state at least
- Exact alternator, AVR and excitation models
- Steady regulation and load-step recovery criteria
- Fault-current multiple and duration
- Nonlinear-load and harmonic limits
- Excitation limiters, sensing and protection
Require curves and test methods for the selected model, not generic brochure claims.
6. How to verify and make the final decision
Verification and acceptance
- Check AVR, PMG, exciter and wiring identification
- Perform planned motor-start or load-step tests
- Record minimum voltage, recovery and frequency
- Verify protection fault response under a safe method
- Review waveform and temperature with nonlinear load
PMG is justified by defined transient and fault-current needs; ordinary loads do not need complexity for its own sake.
Use manufacturer data, complete-set transient testing and protection studies to prove the final choice.