Page 209 - Sustainable On-Site CHP Systems Design, Construction, and Operations

182 De s i g n

Additionally, careful planning and consideration must be given to safety issues of a
CHP system to ensure equipment vitality and personnel safety. From grounding and
bonding to relaying protection for system interconnection, every CHP system design
must take into account all opportunities to introduce safety and protection measures.
There are different ways to ground the electrical system, each with advantages and
disadvantages. Certain methods for electrical bonding are requirements of the National
Electric Code (NEC) and these are discussed later in greater detail.
As discussed in Chap. 2, CHP systems are utilized in a wide variety of facilities,
from industrial plants to health-care campuses to military installations. The various
users of the electrical power downstream of the CHP facility are not particularly inter-
ested in where their power originates; rather, users are more concerned that the power
is available when and where needed and that it is of high quality. The electrical design
of a CHP system, therefore, must plan for voltage spikes and sags, harmonics, power
interruptions, and other power quality issues that traditionally challenge large power
generating and distribution systems. Particular challenges in power quality design
arise due to the protection system effects with multiple relays causing additional power
surges. However, steps can be taken to ensure clean power into the distribution system
and are discussed later in this chapter.
Unless the facility is designed to always operate in “island mode” separate from the
electric grid, interconnection between the CHP facility and the local utility is a critical
part of a CHP system; as noted above there are many codes and standards governing
this interconnection. Often, power generated by a facility from their CHP system is
meant as a supplement to the power they purchase from the serving utility. This means
both power sources are typically feeding into the same downstream distribution sys-
tem at the same time. Under this condition, utility companies assume the risk that a
fault in a facility’s electrical system may propagate into the utility power grid unless
appropriate protection measures are put into place. Electrical designers of CHP systems
must work closely with the local utility company to ensure those protection measures
acceptable to the local utility are in place.
Finally, any CHP plant design and construction should have well-developed and
thorough systems start-up and commissioning plans. It is a necessity to ensure the
entire electrical distribution system is operating in its optimal condition, and strong
commissioning of a CHP project will ensure that the proper choices were made during
system design, equipment selection, and installation.
This chapter serves as a general overview of electrical design considerations for a
CHP facility. A separate book could be written about these electrical issues to capture
the detail each of the issues deserves. The last portion of the chapter includes a simple
example of an electrical system for a CHP facility and a list of resources, and an electrical
designer is encouraged to dig more deeply into the items covered in general detail in
this chapter.

Switchgear Design Considerations
Switchgear design for a CHP plant must account for two separate but equally impor-
tant items: distribution and control. Distribution of the electrical power generated by
whichever type of CHP generator utilized throughout the facility is at the heart of CHP
system. No matter what the reasons are for installing a CHP plant at a facility—base load
power, possibly standby power, isolated feed, peak shaving, or export—the switchgear