The desired performance of an FCL reflects where and how the utility wishes to use it. For example, one utility may wish to limit fault currents on its 138 kV transmission lines . Another may wish to limit faults on the low voltage side (e.g., 12 kV ) of its step-down power transformers. Each of the FCL designs, now being developed, will be well suited to some uses and less well suited to others. For example, an FCL whose design makes it comparatively large will be more easily located near a high voltage transmission line than in an urban substation which very little room left to house additional equipment. Another example, an FCL that takes minutes to recover after it has limited a fault will be better suited to places where faults currents are one time events than to places where faults reoccur each time the wind blows a tree branch to and fro.
Despite this variety in specifications, one should expect that all utilities will have a common set of concerns when each considers adopting an FCL for a specific use. These concerns follow:
1) first cost of FCL: purchase price, installation cost- the FCL must be less expensive than the equipment it is meant to protect
- utilities will try to identify places where one FCL protects many transformers
3) annual cost of FCL: operations and maintenance
4) reliability
- will the FCL perform when there is a fault?
- will the FCL insert impedance when there is no fault?
5) standby impedance (also known as “insertion impedance”)
6) nominal voltage - the design voltage of the line, usually quantified as the phase to phase difference in rms voltage.
7) nominal current - the line’s maximum rated current
8) unlimited fault current and amount by which that fault current is to be reduced - the unlimited fault current has no relation to the nominal current (e.g., at one site, the nominal current is 0.8kA while the unlimited fault current would be 63 kA)
9) speed of FCL’s response
10) duration of FCL’s response
11) speed of FCL’s recovery
12) size: footprint, height, weight
