4 FM quick reads on backup power
1. 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.
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.
UPS Offers Protection Against Common Power System Faults
Generators can offer facilities and their operations long-term protection in the event of an interruption of service, but they cannot offer protection against many common faults in power systems. Facilities can achieve that level of protection only with an uninterruptible power supply (UPS). While there are several different configurations for UPS, online systems are the most common.
An online UPS has three components: a charger/rectifier, storage batteries, and a power inverter. Incoming alternating current from the utility enters the charger/rectifier, which converts it to direct current. This direct current charges the batteries and supplies power to the inverter, which converts the direct current back to alternating current. In systems that provide power for loads in the event of extended outages, a generator typically is connected to the batteries.
The UPS offers the advantage of supplying power to the loads continuously, no matter what happens to the utility power. But the benefits of a UPS go beyond the ability to continuously supply power. The process of taking alternating current from the utility and converting it to direct current and back to alternating current also eliminates most power disturbances, including noise, transients, and voltage fluctuations.
Managers specifying a UPS to protect facilities and systems need to be certain it is sized properly for the load it is designated to protect. They at least must be sure to size the UPS so it can provide 150-200 percent of the connected load. This spare capacity protects the UPS from additional power loads while the equipment is starting, and it allows room for growth.
Managers also need to properly size the batteries in the UPS to provide the desired runtime in the event of a power loss. For some applications, the UPS only needs to provide power long enough to allow an orderly shutdown of connected equipment.