How to specify an industrial generator set

Start with the operating duty

Standby, prime, and continuous ratings are not interchangeable. A standby set supports emergency or outage operation. Prime service expects extended operation with varying load. Continuous service is intended for long duration operation at a relatively steady load. The manufacturer rating definition and the expected annual operating profile must agree.

A unit selected only from the building peak can be wrong in either direction. Oversizing can create poor diesel loading and unnecessary cost. Undersizing can produce voltage dip, frequency instability, slow motor acceleration, or an inability to accept the required load step.

Describe the real load

Provide the running kW and kVA, largest step load, motor starting method, UPS or variable frequency drive content, harmonic profile, load sequencing, and future capacity. The alternator may need to be selected around transient response or fault clearing rather than steady state kW.

• Largest motor horsepower and starting method
• UPS, rectifier, VFD, data center, or other nonlinear loads
• Maximum acceptable voltage and frequency dip
• Single step or sequenced load acceptance
• Required redundancy such as N+1

Coordinate the electrical package

Voltage, phase, frequency, wire configuration, grounding method, breaker rating, interrupting requirements, neutral treatment, and connection arrangement belong in the RFQ. Low voltage and medium voltage packages can require very different alternators, breakers, terminations, and protection.

Controls should be coordinated with the ATS or paralleling system. Clarify remote start, annunciation, communications protocol, building management integration, protective relaying, metering, and remote monitoring before the controls are priced.

Account for the site

Ambient temperature, altitude, indoor or outdoor installation, sound limit, wind and seismic criteria, corrosion exposure, radiator arrangement, ventilation, exhaust routing, and service clearance influence the package. Fuel selection also affects permitting, runtime, storage, maintenance, and emissions strategy.

Define proof before purchase

State the required submittals, drawings, calculations, factory testing, witness testing, certifications, warranty, startup, training, and field load bank testing. Require the proposal to list included items, exceptions, and assumptions instead of relying only on a model number.