Civil Engineering Reference
In-Depth Information
required. In most areas of the country, a second power feed from the serving electric
utility can serve as a standby power source. However, unless the facility is extremely
large, or a convenient second primary feed is available, the capital cost for this will
be prohibitive. The other general form of standby power is on-site power generation.
There are code definitions of standby power that describe auxiliary power systems:
emergency power, legally required standby power, and optional standby power. Emer-
gency power requires the power to be available and on-line within 10 seconds. Legally
required standby power is required to be available and on-line within 60 seconds.
Optional standby power does not have any time constraints. Chlorine scrubber facilities
usually require emergency power. All other facilities would normally fall under legally
required or optional standby power.
Standby power generation usually takes the form of an engine-driven generator
using either diesel, natural gas, or liquid petroleum gas (LPG). The most common and
least expensive is a diesel engine-driven generator. Units are available for indoor or
outdoor installation. Usually the generator is connected to the facility electrical system
using an automatic transfer switch that will automatically start the generator and trans-
fer load to the generator upon loss of utility power, return to utility power when it is
restored, and stop the generator.
Fuel storage for diesel-powered generators can be provided by underground or
aboveground tanks or by tanks built into the base of the generator.
If underground fuel storage is required, the cost of the diesel engine-driven gen-
eration system will be increased substantially and an alternate fuel, such as natural gas
or LPG, if available, may be more cost-effective. Above-grade diesel fuel storage is
cost-effective and can be accomplished with standard equipment. Tanks built into the
base of the generator are common and provide up to about 24 hours of operation in
storage. If the generator is to be installed indoors, the in-base fuel storage capacity
may be limited by code and an outdoor tank may be required. The local fire authorities
should be consulted when planning indoor fuel storage. The selection of generator fuel
(diesel, natural gas or LPG) should consider the following:
Cost of unit
•
Availability of the fuel under emergency conditions
•
Fuel storage requirements and costs
•
Air quality requirements and codes
•
An alternative power system is the use of engine-driven equipment, usually a pump,
using either natural gas or diesel as a fuel source. The engine-driven pump may be
direct-driven, or operated through a right-angle drive, with an electric motor used to
normally power the pump.
SUPPORT SYSTEMS
There are a number of support systems to be considered in design of water facilities.
Many are code requirements and will vary from location to location. This section will
serve as a checklist of items to consider. Local code authorities should be consulted
during design for particulars.
