A standby generator system, often referred to as a generator set or "genset," is a self-contained unit that combines a prime mover (a mechanical engine, typically diesel or natural gas) and an electrical generator (an alternator). These components are mounted together on a common base to form a single piece of equipment. Its primary purpose is to supply electrical power independently of the electric utility, most commonly during a power outage, making it a cornerstone of emergency and backup power systems in critical facilities like data centers.

A. passive: This term applies to electrical components that do not produce energy (e.g., resistors, capacitors), which is the opposite of a generator's function.

C. active: While a generator is an active source of power, "active generator system" is not a standard industry term for the described physical assembly.

D. software: This term refers to computer programs and is entirely unrelated to physical hardware for electrical power generation.

1. U.S. Department of Energy, Federal Energy Management Program (FEMP). (2009). O&M Best Practices Guide for Standby Generators, Release 3.0, Chapter 2, Page 2.1.

The document states: "A standby generator set (genset) is the combination of an internal combustion engine and an electrical generator (alternator) that are coupled and mounted on a single frame." This directly supports the definition in the question.

2. Geng, H. (2014). Data Center Handbook. John Wiley & Sons, Inc. Chapter 10.3.1, "Standby Generators," Page 211.

This academic and professional handbook describes the system: "A standby generator system consists of a prime mover, an alternator, a cooling system, and a control system... The prime mover and alternator are coupled and mounted on a steel frame to form a generator set, or genset."

3. Iowa State University. (n.d.). Courseware for ABE 471/571: Electric Power and Electronics. Module: Standby Power. Section: "Components of a Standby System."

The course material explains: "The generator set, or 'genset', is the heart of the standby system. It consists of an engine mechanically coupled to an AC alternator, both of which are mounted on a common base."