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BBC Distance relay

BBC Distance relay

BBC Distance relay

(OP)
Hi, I'm in need for some help, it's regarding an old distance relay of electromechanical type, BBC LI41b, see attached image. The protection relay will be exchanged with a newer one, not decided yet, because of age and no spare parts available.
I have managed to get hold of a data paper of a BBC LI41a, but i cannot properly grasp the settings, to transform them to a newer protection relay.

The starting element seems to be of overcurrent type and a setting of 5A.

Zone1: 120%, zone2:67%, zone3: 0% and zoneA: 67%.

The replica impedance setting is, cot fi=0,6 and tan fi=1 with a reach of 0,2 ohm/ph.
Is there a way to get this vector in a+bi form?
Isn't 0,2 ohm/ph with a angle of (cot fi = 0,6 => fi = 59 degrees) very low?

No k0-factor.

The transmission line is 980m AXKJ 3x1x300mm2 (underground) + 1150m FeAl 3x234mm2 (overhead).

Or is there a better way to protect this short line?, directional overcurrent relay?

Sincerly Fredrik ;)

RE: BBC Distance relay

I certainly wouldn't try to translate old relay settings into a new relay; I'd just apply today's criteria to the new relay. If the line is 0.2Ω and the minimum Zone 1 setting is 0.05Ω you should be fine, particularly if the VT is a wound transformer rather than a CVT.

RE: BBC Distance relay

(OP)
Thanks for your reply David, that I can agree on but still you have to base the new settings on something. Regarding the replica impedance vector, I have: 2,6 + 4,3j, which is the impedance of the line if my calculations are correct (below).

cot φ = 0,6 → φ = 59˚
cos 59 = r/0,2 → r = 2,6
sin 59 = x/0,2 → x = 4,3j

RE: BBC Distance relay

Right, you have to base the new settings on something; to me that would be raw data. I'd look up (or recalculate) the line data. I'd never assume that an old setting was correct. That 0.6 may have been a compromise setting; maybe you'd be better off with something else with a new relay, maybe not. But you'll never know if you just copy the old settings.

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