Installing a genset

Generator set installation involves lots of details, but don't overlook the broad concepts.

By Todd Riemann and Steve Resner, MTU Onsite Energy, Mankato, Minn. February 1, 2009

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The installation manual provided with a genset usually covers many aspects of an installation. A typical manual includes many pages of instructions, diagrams, checklists, and advisories (e.g., don’t use galvanized components or Teflon tape on fuel systems for diesel-powered units). Be aware, however, that some important design issues may not be addressed in the manual. For example:

Enclosure doors that became misaligned during shipping or installation must be adjusted to regain the proper fit and smooth operation they had when the unit left the factory.

There is a structural formula for determining the thickness of the inertia pad/mounting base.

There is a mechanical formula to ensure adequate airflow through the genset enclosure based on unit heat rejection and acceptable air temperature rise within the enclosure.

While it’s important to follow every pertinent point in the installation guide, it’s equally important to keep in mind the broad concepts of genset installation. We’ll look at those in a minute. But first let’s review some general safety information related to genset operation that can affect genset installation.

Electromechanical equipment, including generator sets, transfer switches, switchgear, and accessories, can cause bodily harm and pose life-threatening danger when improperly installed, operated, or maintained. Dangers, warnings, and cautions are outlined in the installation manual to alert the operator to special instructions concerning a procedure that may be hazardous if performed incorrectly.

These safety alerts alone cannot eliminate the hazards that they signal. Strict compliance with these special instructions and common sense operation are crucial in preventing major accidents. When working with gensets, observe all warnings found on the equipment. Ensure that warning labels are legible and not obstructed by dirt, grease, or other equipment. The genset manufacturer cannot anticipate every possible circumstance that might involve a hazard. Therefore, the warnings in the installation manual and on tags and decals affixed to equipment are not all-inclusive.

Follow all applicable codes

The first broad concept in generator set installation is code compliance. NFPA compliance is critical, and of the several NFPA codes, NFPA 110 has the broadest application to both standby and emergency gensets. NFPA 70, which covers such electrical components as conductors and raceways, also has broad application in genset installation. Agencies in each layer of government, from the federal government down to the township level, can impose their own additional codes.

UL 2200 certification is available on many models of gensets, which goes a long way to ensure code compliance. UL 2200 covers stationary engine generator assemblies rated 600 V or less that are intended for use in ordinary locations. “Ordinary” means applications other than hazardous (classified) locations, uninterruptible power supplies, and marine use, which are all covered under separate codes. Included in UL 2200 certification is virtually every part of a genset assembly including the fuel system, control panel, harnesses, design elements to provide protection from water intrusion, and so on. UL 2200 also addresses the engine, but most engine matters are related to emissions. Depending on power output, engines need to be certified as U.S. Environmental Protection Agency Tier 2, Tier 3, or Tier 4i compliant.

Consider the duty cycle

Another issue in genset installation is current and future duty cycle. Will the system be used for backup? Base load? Peak shaving? According to NFPA 110, the unit should be sized so that its running load is 30% of its capacity. If it’s less than that, the diesel engine runs inefficiently, resulting in “wet-stacking” where fuel enters the crankcase. Standby systems should run under load at least an hour each month as a preventive maintenance measure; that 30% minimum load should be observed during these monthly run cycles using temporary load banks, if necessary.

In some situations, the duty cycle can change over the product lifecycle. If a plant expansion or other change occurs, there are several ways to accommodate that increased demand. The original genset can be replaced with one of greater capacity. A second, parallel system can be added. The most cost-effective approach is to anticipate the need and install a unit of adequate capacity the first time, assuming that a larger system still meets the 30% load guidelines. Load banks, either temporary or permanent, can provide the 30% load until system gowth hits the 30% threshold.

Location, location, location

The generator set’s location is another important consideration. One detail that often gets overlooked is restricted access imposed by the nature of the facility. This is especially true at hospitals and jails. You don’t want service technicians to have to pass through a series of security checkpoints every time they leave the building to get a part from their truck. Siting the system for optimal access may not be an option on retrofits if the genset is inside the building and relocating it to a new, outdoor enclosure is cost-prohibitive.

The same limitations may be imposed when retrofitting with a new genset that requires more airflow than the system it replaces. Providing sufficient airflow for both combustion and cooling is crucial. Placing the genset outside helps. An inside location can pose a challenge, and the longer and more convoluted the required ducting is, the greater that challenge. A genset installed inside also can create problems with exhaust flow. Anything other than short, straight exhaust routing can cause problems such as excessive back-pressure or excessive condensation. Another key consideration for interior locations is the need to isolate the genset from other parts of the building with an occupancy barrier.

Whether the genset is located inside a structure or out, proper exhaust design is a crucial part of safety and performance. It takes several pages to cover the subject in various installation guides, addressing everything from the flexible section that isolates the exhaust system from engine vibration, to the screen mesh that keeps birds and rodents out of the exhaust stack, to keeping the exhaust outlet away from fresh air intakes. Exhaust design instructions are worthy of special attention as there are many opportunities for mistakes.

Proper feeding

Exhaust can be tricky, but there are plenty of opportunities for error on the intake side of the engine. Fuel system problems occur on gaseous gensets when engineers lose sight of two fundamental needs of the engine: volume and pressure. Problems can arise when the fuel supply is some distance from the engine. As with air flow and exhaust, the diameter of the line and the number of bends must be considered.

Depending on the proximity of the components and other factors, a diesel fuel system might have three components. There is a main tank, which must be sized for a certain number of hours at full load, depending on the needs of the customer. There may be a day tank to provide a ready supply of fuel at the injector pump. Day tanks are used when the engine pump does not have the necessary lift to draw fuel from the main tank. If the main tank is above the level of the injectors, the day tank is used to remove the fuel head pressure that would otherwise be placed on the engine fuel system components. If there is a day tank, there also will be a fuel oil transfer pump (auxiliary pump) to supply fuel from the main tank to the day tank.

Conclusion

One final point in installing a genset is the need for an effective preventive maintenance program. Gensets often suffer from the “out of sight” syndrome, and they remain out of mind until they fail to start, shut down due to overheating, or exhibit other performance issues. For some reason businesses often neglect their gensets. Several genset companies’ distributors do a fair number of retrofits to replace units that would still be in service had they received proper preventive maintenance.

How does this play into the process of coordinating a new install or retrofit? If you think preventive maintenance may be neglected, suggest that the owner enter into a service agreement with the distributor from the start. Keep in mind that neglect of a genset can result in liability issues in the event of a genset failure.

Armed with appreciation for the big picture, engineers can go back and read the installation manual—section by section, page by page, line by line. Remaining mindful of both the overarching concepts and the finer points will result in a trouble-free installation and a satisfied customer.