Facility Connection RequirementsMay 1, 2005
Structural strength criteria shall comply with applicable industrial standards such as “Design of Latticed Steel Transmission Structures” (ANSI 10, published by ASCE), “Manual of Steel Construction” (published by American Institute of Steel Construction Inc.), or Building Code Requirements for Structural Concrete (ACI-318, published by American Concrete Institute).
I. M. Ratings
All facility equipment ratings shall be in accordance with NEPOOL Capacity Ratings Procedure which is posted on the ISO-NE webpage.
All circuit breakers and other fault interrupting devices shall be capable of safely interrupting fault currents for any fault they may be required to interrupt. Application of circuit breakers shall be in accordance with ANSI/IEEE C37 standards.
I. N. Reliability and System Security
FPL-NED designs and operates its transmission system to meet all applicable ISO-NE, NEPOOL, NPCC and NERC Planning and Operating Standards. The planned transmission system with its expected loads and transfers must be stable and within applicable ratings for all category A, B, and C contingency scenarios1 The effect of category D contingencies on system stability is evaluated when changes are planned in the transmission system. The design of new transmission connections should take into account and minimize, to the extent practical, the adverse consequences of category D contingencies
System and generator stability is to be maintained for normal clearing of all three phase faults. A normally cleared fault is assumed to last six cycles (0.1 seconds) for circuit elements protected by three cycle breakers. This provides approximately one cycle margin for slower than expected fault clearing. For circuit elements protected by two cycle breakers, a normally cleared fault is assumed to last five cycles.
The power system must be stable for single line to ground faults with the failure of a protection system component to operate. This includes clearing of a system fault with the simultaneous failure of a current transformer, protective relay, breaker, or communication channel. Three phase faults with the failure of a protection system component to operate are to be considered in all design alternatives with adverse consequences to system stability minimized.
FPL-NED transmission circuits are protected with primary system relays that provide no intentional time delay when clearing faults for 100% of a line. A second high-speed relay system with communications and no intentional time delay is required if a failure of the primary system can result in instability when a fault is cleared by time delay backup protection. This can be the case for an end of line fault on a short line combined with a failed relay. Likewise, two
1 NERC Planning Standards, Table 1