Load Bank Testing Stationary Generators in Buildings 5

[AKHou]

Should we continue to load bank test the emergency generators in our office buildings at 100% of name plate rating (per NFPA 110) even though the building's emergency power systems connected to the generator represent less than 80% of the generator's name plate rating. We understand the importance of eliminating wet-stacking but it seems wasteful - from an emissions aspect.

Why not load bank (for 2 hours annually) at 80% of rating?

 

[rbulsara]

The test requirement are to ensure readiness of emergency power system and it is not wasteful. I trust and hope that you are also performing required (and customary) weekly, biweekly or monthly operational tests

Rafiq Bulsara

http://www.srengineersct.com

 

[catserveng]

Two years ago had a customer, one of the major shipping companies in the USA, who lost one of their regional shipping centers when both emergency generators failed on overheating. It was a very hot summer day, the local utility asked the facility to get off line, the facility management agreed since they had a fully (they thought) operational standby system, after 40 minutes on line at about 85% load they lost first one then the other unit, leaving them dark. The units were 9 years old, regularly maintained by the local engine dealer, including a "less than 100% load test" every year.

The root cause was cooling system corrosion and partially blocked coolant passages. So why had the system failed in light of "regular maintenance". The cooling system was marginally sized for 100% load, as most standby systems are, during regular annual load tests at a lower load, no indication of overheating was noted since the only instrumentation for the cooling system is the jacket water outlet temperature, and regular load testing was performed in the winter. A slight upward trend in the jacket water temperature was noted over the previous two years, but not considered significant and not investigated further. In a normally operating cooling system at less than full load and in ambient conditions less than maximum, the engine cooling temperature regulators are controlling the engine temperature. What happened in this case (and many others)is this "reserve margin" went away over the years, and since the load testing was not requiring full cooling system capacity the problem did not become apparent until the worst possible time.

The facility saved money on 8 load bank tests by not testing at full rated load, the cost of the outage and subsequent damage and investigation far exceeded the monies saved. Oh and the insurance company ruled that the owner had not done his due diligence by not performing the "recommended testing" and so they bailed on the end user as well.

Sorry for the long winded story, but here are some facts that may help you in your decision.

This happens way more than it should, I saw these situations happen too often, for a combination of reasons, but cost savings and the desire to do the "green thing" were at the top of the list.

A standby system is typically low cost compared to other engine driven power systems, and it's rating and support systems are sized to give you what was sold and not much more (and sometimes not even what you really needed, like in the case of ambient temperature capability).

Your standby system is typically serviced by lesser experienced technicians. I'm not saying you're not getting good service, I'm saying you're likely getting what you're paying for. Most engine dealers are competetively bidding standby generator maintenance, and sending your top tech out to do monthly inspections and annual oil changes doesn't usually happen. If it starts, runs and doesn't exhibit anything out of normal parameters, it get's called good. The only time a senior tech gets involved is during more extensive testing or if a problem is noted.

Modern engines don't like to run lightly loaded, allowing them to get to the point of "wet stacking" means you are not allowing the engine to operate where it needs to, compromising reliability and performance, including emissions.

We've mostly covered the mechanical aspects, but the electrical side of the system, the generator, controls, circuit breaker and wiring also need to be qualified regularly to assure they perform as expected when needed as well.

Liability, you can look like a hero if you save money, reduce fuel consumption and emissions, but what happens to your process if your emergency system fails to perform as required? How will your management, local regulators and your insurance carrier all view your modified maintenace procedures?

My two cents worth, hope that helps.

Mike L.

 

[peebee]

What gives you the idea that NFPA 110 requires load testing to 100%? Am I missing something?

From NFPA 110-2010:
8.4.2 Diesel generator sets in service shall be exercised at least once monthly, for a minimum of 30 minutes, using one of the following methods:
(1)Loading that maintains the minimum exhaust gas temperatures as recommended by the manufacturer
(2)Under operating temperature conditions and at not less than 30 percent of the EPS nameplate kW rating
* * *
8.4.2.3 Diesel-powered EPS installations that do not meet the requirements of 8.4.2 shall be exercised monthly with the available EPSS load and shall be exercised annually with supplemental loads at not less than 50 percent of the EPS nameplate kW rating for 30 continuous minutes and at not less than 75 percent of the EPS nameplate kW rating for 1 continuous hour for a total test duration of not less than 1.5 continuous hours.