Page 224 - Sustainable On-Site CHP Systems Design, Construction, and Operations

Electrical Design Characteristics and Issues 197

and equipment specifications. The utility will likely monitor the installation process
and if the design or equipment selection varies from approved conditions it may trigger
another utility (and often regulatory agency) review and approval process. As one can
imagine, this has impacts to schedule and budget. Another potential schedule impact is
the pretesting which requires temporary (and extensive) paralleling between the CHP
generator and the utility. Special agreements will likely be necessary and the time taken
to reach these agreements must be accounted for.
There are two separate stages to the construction process which ensures a suc-
cessful switchgear installation in a CHP facility—equipment certification and com-
missioning. Although it may be a requirement that certification occurs at a third-party
independent facility, equipment certification is most often done at the switchgear
manufacturing facility. Just as there are multiple components in a piece of switchgear,
there are multiple types of certification. One possibility is that each of the components
has been certified, and then all of the components are combined and tested as an
assembly. In this case, the switchgear is certified when it leaves the factory as a complete
system, and the CHP design engineer and facility owner can trust necessary settings
have been confirmed.
Another type of certification entails testing all of the components and evaluating
that each of them performs its particular function. Then, the components are assembled
as per a previously tested protocol which has proven the components will work together.
In this case, however, it will be more critical that the connections and settings are tested
and verified in the field. This testing is a major part of the commissioning process. With
either method, the switchgear used in a CHP installation will almost certainly require
special certification by a nationally recognized testing laboratory (NRTL) for intercon-
nection with the utility.
Commissioning testing will be the final step in the installation process to assure
the facility owner that the switchgear will operate as the CHP electrical design
engineer has intended. Of course, during the installation it is to be expected that
qualified experienced CHP system contractors run interim tests after each stage of
the installation, in order to catch and correct issues long before construction is com-
plete. However, a final testing program will need to be specified which satisfies the
owner and the utility that the switchgear works as intended, under both normal
conditions and fault conditions. This testing program must be specific enough to
note specific components to be tested in each step. For example, the commissioning
specification might note a specific relay or disconnect which will have to operate to
ensure an overvoltage condition on a particular downstream feeder does not propa-
gate to other feeders; that over voltage condition would be simulated as part of the
commissioning process.

Sample System Diagram
There are many possible connection configurations when CHP facilities interconnect
with a utility. These are dependent on the type of CHP generator, the size of the CHP
facility, the particular requirements of the serving utility and the type of utility distri-
bution system. What follows, for reference, is one typical example of the protection
between utility and CHP facility, and the additional protections typical for engine-
driven generators.