MIL-HDBK-1003/7
e) The cogenerator may be required to notify the company prior to each
start of energy delivery and interconnection to the utility system.
f) The utility may require that the cogeneration plant's scheduled
outage for maintenance coincide with periods when utility power system demand is low.
g) The utility may require a demonstration of reasonable reliability
of the cogeneration plant over the life of the contract.
h) The utility may require a contract specifying technical and
operating aspects of parallel generation.
21.5.2
Interconnection Equipment
21.5.2.1 Utility Standby Service. This arrangement requires a manual or automatic
throwover switch that will first disconnect the cogeneration electrical source from the
facility electrical load before connecting the facility electrical load to the electric
utility service entrance line.
21.5.2.2 Parallel Operation. This arrangement requires two manually operated
disconnect switches, one to disconnect or connect the cogeneration electrical source to
the facility electrical load and the other to disconnect or connect the facility
electrical load to the utility service entrance line. In addition to these switches,
meters for billing will be required and are usually supplied, owned, and maintained by
the electric utility. The manual switch for connect or disconnect of the utility
service from the facility electric load and cogeneration system electric source is
usually a mandatory contract requirement by the utility. The utility will further
require that this switch be under exclusive control of the utility, and that it must
have the capability of being locked out by utility personnel to isolate the utility's
facilities in the event of an electrical outage on transmission and distribution
facilities serving the cogenerator. The other manual switch or isolation device will
also usually be required by the utility contract to serve as a means of isolation for
the cogeneration equipment during maintenance activities, routine outages, or
emergencies.
The interconnection with the utility for parallel operation also requires
synchronizing controls for electrically synchronizing the cogeneration system with the
electrical utility system.
Line and Equipment Protection. Parallel operation introduces variables in
21.5.3
distribution line protection in that fuses and other sectionalizing devices may be
affected by generator contributions to fault currents. Line sectionalizing studies
should be made to verify correct operation of sectionalizing devices over the range of
conditions that could arise. Generators operating in parallel with the utility system
need protection against overload. To protect both line and cogeneration equipment in
the event of unacceptable fault, one protective relaying system is required to separate
the utility system from the cogeneration bus and another protective relaying system is
required to separate the cogenerator from the cogeneration bus. The required protective
relay functions are usually designated by the electric utility and the final design of
the complete protective relaying system must have the approval of the electric utility
prior to initial operation of the cogeneration system.
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