Steps to selecting and troubleshooting generators
This column continues where
we left off last month, with advice
about choosing and using equipment
BY DAN POPP
One of the first things to do in sizing a generator set is to figure out specifically what the project involvesOne of the first things to do in sizing a generator set is to figure out specifically what the project involves
One of the first things to do in sizing a generator set is to figure out specifically what the project involves
One of the first things to do in sizing a generator set is to figure out specifically what the project involves. This may seem obvious, but on many occasions we have encountered a “boiler plate” specification that does not fully fit the application. What is the minimum generator loading? An underloaded generator will fail prematurely due to excessive carbon build up and non-optimal engine operating temperatures.
What if the supplied loads allowable voltage and frequency dip? If the equipment can only sustain a 15% voltage dip and the system is sized for 30% voltage dip, the supplied equipment powered by the generator may not work, or worse, be damaged. Is the system going to be used for emergency situations only, or will it be for continuous prime power use? Standby applications usually do not have an “overload” capability.
Once the project specifics are verified, we need to identify the equipment the generator set will power. When non-linear loads are present, such as UPS systems, VFD’s, certain types of non-incandescent lighting, etc., it may be necessary to oversize the alternator in an effort to offset the total harmonic distortion these types of equipment produce. Less than 15% distortion is a good number to shoot for–the lower the better, but this number is affected by the equipment the generator will be powering, so, be aware of it on the front end!
When THD issues arise, they ultimately play havoc with the generator’s ability to maintain a steady state output voltage. Underloaded UPS systems and power factor correction devices can also affect the voltage output from the voltage regulation system, as the voltage regulator will attempt to compensate for a leading power factor situation. PME/PMG style alternators are considered standard fare for these applications. versus a self-excited arrangement, as the voltage regulator will be that much more isolated from the effects of high amounts of THD. Imbalanced loads, large motor loads, peak loads, etc., also play a large part in the generator sizing equation. Again, today’s available sizing programs can account for these variables in great detail.
Properly sequenced load steps are another factor that can affect generator sizing. If a system does not have to meet the requirement to pick up 100% of the load upon the initial transfer, then the generator expert may be able to adjust the generator sizing based on the project’s motor starting requirements. By sequencing them in such a way that the largest motor starts first, we effectively reduce the starting requirements the generator system will see as subsequent loads come online. The generator system can actually be REDUCED in capacity when sequencing is allowable. Customers love the cost savings and the generator expert looks like the hero.
After the system is sized correctly and installed, someone needs to maintain it. Load bank testing, routine maintenance protocols and manufacturers maintenance schedules, when adhered to, will insure your hard-earned customer is happy with your services and their emergency power investment for years to come. Remote monitoring has become a great way to offer a service to your customers by selling them a peace of mind in that the generator is under constant “supervision” by the generator expert they count on. NFPA and Joint Commission accreditation testing can also be a constant revenue stream for the generator expert and give them access to organizations that specify emergency power systems as a requirement for operation.
A comprehensive testing and preventive maintenance program will reduce preventable failures and raise the uptime percentage of the customer’s generator system. Generator failures can result from several common maintenance issues. Some of the most common:
Starting-system issues: EGSA and other bodies associated with generator set standards report about half of emergency generator set failures are due to battery and battery system related problems. Choosing the correct battery and maintaining it properly can prevent the majority of battery failures. Assuring the charger is operating correctly and maintaining equalization on the cells is paramount.
Poor fuel quality: Fuel-related issues are the second most common failure point in emergency generator systems. This can be from poorly maintained diesel fuel storage tanks clogged with algae and bacteria growth to natural gas system issues from improperly sized gas meters, pressure regulators and fuel lines. Diesel fuel polishing is another potential service offering in the generator expert’s service arsenal
Process control issues: Control issues are typically wrung out and addressed during commissioning, but with the sophistication of today’s paralleling, load shedding and utility interfacing controls and complicated software programs used to control them to an exacting degree, unforeseen issues can and do arise when the situation is less than ideal. A solid monthly testing program, like those specified by the NFPA and Joint Commission, will find and eliminate sequence-of operation errors and resolve them before an emergency arises.
Inadequate loading during test cycles: Insufficient loading causes wet stacking and accelerated wear of critical engine components. Generators will last longer if they run at higher a temperature, which ideally means loading the generator to at least 60 percent or more of rated load. Running diesel generators at no to low loads can cause carbon build-up on internal engine components, unburned fuel accumulation in exhaust systems and degradation of fuel injectors, engine valves and turbochargers.
Engine sub assembly item failures: Engine sub assembly items are on the engine and generator, such as water pumps, fuel pumps, cooling systems/radiators and charge air coolers. One of the highest failure items in this category are the systems block heaters. The block heaters maintain the engines coolant temperature approximately up to 100 degrees above the ambient temperature to facilitate cold weather starting and control accelerated wear from immediate loading by helping maintain normal operating temperature tolerances in the engine.
A properly sized and maintained generator system will allow the generator expert to shine for years to come because it will work when the customer needs it and with a little work up front will help facilitate what we all want to achieve – happy customers, referral business and increased profitability from becoming the “go-to-guys.” BXM
Dan Popp is with PM Technologies, LLC, a service provider for Lucas County that will expand to Dayton this year.