ABB REL 356

ABB REL 356 Current Differential Protection
4-3
Measuring Elements and Operational Logic
Figure 4-3. Operating Characteristic
External fault
For an external fault, the currents will be 180° out of phase and of equal magnitude:
4.14.107.0
2
0180
180
−=−=−
⋅=+=+=
=°∠+=+=
°∠=
R
ESOP
ITLITLITLITRITLRES
ITLITLITRITLOP
ITLITR
which, of course, is less than OTH which is a positive value (settable 0.00 – 3.98).
Internal fault
For an internal fault, the currents will be practically in phase:
where OTH should be selected so that minimum internal fault current will produce trip.
Communication Channel Options
REL356 is available with eight different communication interfaces:
· 9600 bps audiotone
· British Telecom audiotone
· 56/64 kbps direct digital
· 56/64 kbps 820 nm multi-mode fiber
· 56/64 kbps 1300 nm single mode fiber, short reach
· 56/64 kbps 1300 nm single mode fiber, medium reach
· 56/64 kbps 1300 nm single mode fiber, long reach
· 56/64 kbps direct digital with G.703 interface
()() OTHITRITLITRITLITRITLRESOP
ITRITLRES
ITRITLITRITLOP
ITLITR
≥+=+−+=−
+=
+=+=
∠≅∠
3.07.07.0