4 FM quick reads on generators
1. Meters Offer Greater Opportunities For Energy Efficiency
Regular testing, maintenance, exercising, and inspection can help keep standby generators ready to perform when needed.
For optional standby generators (not required by life-safety code), critical loads supported by the generator system typically include data center and call center equipment such as UPS systems, cooling, phone systems, and desktop equipment (computers, etc.).
For emergency standby generators (required by life-safety code), critical loads supported by the generator system typically include emergency lighting, fire alarm systems, fire pumps, and elevators. Life-safety generators are also sometimes used to additionally support optional loads, such as data centers; however, in this case the life-safety loads take precedence over the optional loads.
Good design, quality equipment, trained operating personnel, commissioning, regular inspections and exercising, preventative maintenance, trained service support, and performance testing are all key to reliable performance.
Standby generators should be regularly serviced by, and under a 24/7 service agreement with, a qualified local service organization. Preventive maintenance (PM) service must be performed on schedule. Even OEM and qualified service organizations can become lax about PMs; it's up to the owner to ensure that these contractual requirements are performed or to hold the service organization accountable.
Unless your local utility regularly serves up power failures (of more than a few seconds), an exercising program is required for standby generators. It is standard practice to set ATS or switchgear controls for automatic engine starting and running at no load (no ATS transfer) for about 30 minutes; this is done as often as weekly but no less frequently than monthly. Exercising can be manually initiated as well. If automatically initiated, it's a good idea for operators to be present onsite observing normal performance.
2. Reliable Power Must Be Maintained In Critical Systems
It might not be economical for most facilities to collect detailed data about motors and drives to populate a CMMS, so the next best approach is to create a plan managers can use consistently when making repair-or-replace decisions. The plan should address such questions as:
How large is the motor or VFD?
What does the motor or VFD serve?
About how old is the motor or drive?
What is the component's expected service life?
What is known about the maintenance history?
For small motors, it is generally most economical to simply replace the motor. For large motors used in some institutional facilities or campuses, the most cost-effective decision can be to repair or rebuild both small and large motors. The key is to estimate when the cost of repair and current levels of maintenance exceed the cost of replacement.
If a manager does not know the installation date of the motor or drive, the next step is to estimate the date by determining the installation date of the parent asset and comparing the visual appearance and any wear on the motor or drive to the parent asset. For example, if a chilled-water pump was installed when the building was constructed and the motor looks to be the same age as the pump, it might be safe to assume the motor and the pump are the same age. Asking the maintenance technicians who have been at the facility for the longest time about the history also can be especially valuable.
Whether or not to repair VFDs will depend on their condition. VFDs are electronic, so they have fewer moving parts that can fail. But if the drive has truly failed — if its control panel no longer functions, for example — the general practice is to replace it.
3. Reliable Power Must Be Maintained In Critical Systems
The failure of a backup power system in an institutional or commercial facility could cause the loss of productivity, revenue and even human life. As a result of these high stakes, maintenance and engineering managers must ensure they provide a reliable flow of power to support critical systems and equipment, especially in emergencies.
In many facilities, a standby generator system supports crucial life-safety systems, such as egress lighting and fire alarm, that enable occupants to safely evacuate a building. In health care facilities, these systems also support essential life-support and other equipment.
In facilities with critical computer and technology loads, uninterruptible power supplies (UPS) are part of the standby power-distribution system. These systems include auxiliary equipment, such as transfer switches and fuel tanks.
But even modern facilities that are designed according to codes to provide backup power systems with appropriate levels of redundancy will have a high probability of failure if technicians do not properly test and maintain these essential systems.
It is important that technicians address all system components both individually and as a system. Standby power systems typically contain cooling, fuel, battery/charging, engine, and distribution subsystems, which all have their own unique testing and maintenance requirements.
Among the most common causes of failure in generator and UPS distribution systems are these:
- Incomplete system commissioning that fails to identify installation or control-logic errors
- Equipment not returned to proper operational state after testing, maintenance or alarms
- Generator failure to start, due to old, discharged or poorly maintained batteries
- Battery charger breaker turned off
- Low fluid levels or fluid leaks
- Exhaust system failure due to wet stacking, or running generators under low load that causes the accumulation of carbon particles, unburned fuel, oil and condensed water in the exhaust system
- Insufficient reserve of fuel or deteriorating fuel quality
- Operational failure of ventilation louvers.
4. Determining Optimal Start Time Delays For Generators
The standby-generator start-time delay programming adjustment is driven by a number of factors.
Opinions range from 0.5 seconds to 30 seconds. One concern is that the majority of utility power bumps last less than 3 seconds. Therefore you can have quite a few unnecessary engine starts with start programming set for less than 3 seconds.
The short power bumps typically result from utility re-closers that automatically open and close quickly in an attempt to "shake loose" a problem on the lines, such as tree branches, animals, etc. Re-closers are often programmed by the utility to open and re-close quickly a couple times, resulting in power bumps of 1 second or less, then to remain open up to about 3 seconds on the third and typically final attempt. The fourth time a re-closer opens it typically stays open for many minutes or longer (awaiting manual intervention).
Another concern is that many times the utility fails, then returns, and almost immediately fails again. A generator start timer (typically located in the ATS or generator switchgear) will typically reset when power returns. For UPS backup energy storage, the recharge time is typically 10 times longer than the discharge time, so rapid short utility bumps can cumulatively draw down short-term storage (a very real concern for flywheel UPS systems). Multiple 3 to 10 second utility power failures within a short duration can leave a UPS flywheel too depleted to provide ride-through time.
Most engineers recommend programming generator start time delay settings in the 3 to 5 second range. If utility power is down for more than several seconds it will probably be down for several minutes or hours, so you might as well start your engines. It's best not to challenge UPS batteries any longer than necessary and risk the chance of a UPS failure. The longer a data center runs with no cooling while waiting for generator power, the greater the risk of the data center overheating. However, starting the generator for every light flicker takes its toll on equipment, with impacts on reliability, maintenance, and environmental emissions.
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