MBrooke, et al
Definition:
Mho (Admittance) is the inverse of Ohm (impedance! And now, the rest of the story!
History
Early in the history of protection schemes, transmission line-protection was relegated to current-monitoring devices, i.e., instantaneous, time-overcurrent, directional-instantaneous, distance, etc! But, as lines grew longer and voltages higher, it became more difficult to implement the equations (based on impedance) with hardware (relays). Furthermore, fault-clearing times became intolerable as other systems, like radial feeders (which led to the 3-zone concept) and tapped-bus, were introduced! As early as the 30’s, protection schemes using “admittance-based” equations made it easier to implement with hardware! Additionally, fault-clearing times were improved to less than 1-cycle!
Today
Fuggedaboudit. It's all done by software!
Reason Against Re-wiring
The diagram submitted by MBrooke must not be changed! Each section, purported to be ‘miswired', are intentionally designed to energize the four-poles of a mini ‘2-phase motor’! Thus, sufficient torque is developed to actuate the trip-contact pertinent to the zone in which the fault occurs
Reference
“Silent Sentinels”, Messer’s J.L. Blackburn and G.D. Rockefeller, 1964 (Prof. Blackburn was my teacher and mentor)
(An aside, the cost of the book was $3.00 when I purchase it in school!)
Regard, Phil Corso
~RJ~