Facility Connection RequirementsMay 1, 2005
Three source terminal interconnection configurations of transmission lines are to be avoided within the FPL-NED transmission system. This is due to problems associated with protective relay coverage from infeed, sequential fault clearing, outfeed or weak source conditions, reduced load flow, and automatic reclosing complications. Extensive studies are necessary to evaluate all possible implications when considering three terminal line applications.
Some new connections to the FPL-NED transmission system may require one or more FPL-NED transmission circuits to be looped through the new facility. The design and ratings of the new facilities and the transmission loop into them shall not restrict the capability of the transmission circuits or impair FPL-NED contractual transmission service obligations.
Long taps to feed connected load directly tied to a transmission line are to be avoided. This presents coverage problems to the protective relay system due to infeed. Power line carrier signals can also be lost due to odd quarter wavelength sections.
Any new interconnection configuration should be designed in such a way so as to minimize the likelihood that FPL-NED would be prohibited from taking an FPL-NED transmission facility out of service for just cause. FPL-NED shall not be forced to open a transmission facility for an adjacent interconnected generator or transmission line to obtain an outage, other than during approved scheduled outage periods as such are coordinated with, and approved by ISO-NE or its designated Satellite Control Center, or in the case of an emergency. Manual switching or clearing electrical faults within the non-FPL-NED facility shall not curtail the ability of FPL-NED to transmit power or serve its customers.
Reliable station and breaker arrangements will be used when there are new or substantial modifications to existing FPL-NED substation(s). In general, transmission substations must be configured such that line and transformer, bus and circuit breaker maintenance can be performed without degrading transmission connectivity. This generally implies a breaker and a half or double breaker, double bus configuration. A ring bus may be used when a limited number of transmission lines are involved.
I. J. Grounding
Each interconnection substation must have a ground grid that solidly grounds all metallic structures and other non-energized metallic equipment. This grid and grounding system shall be designed to meet the requirements of ANSI/IEEE 80, IEEE Guide for Safety in AC Substation Grounding and ANSI/IEEE C2, National Electrical Safety Code. The transmission line overhead ground wire (OHGW) shall be connected to the substation ground grid.
If the interconnection substation is close to another substation, the two grids may be isolated or connected. Connected grids are preferred, since they are easier to connect than to isolate. If the ground grids are to be isolated, there may be no metallic ground connections between the two substation ground grids. There must also be sufficient physical separation to limit soil conduction. If the ground grids are to be interconnected, the interconnecting cables must have sufficient capacity to handle the fault currents, duration, and duty. FPL-NED must approve any