ABB Switzerland Ltd REG 316*4 1MRB520049-Uen / Rev. F
3-90
The function determines the power direction by measuring the
phase-angle of the current in relation to the opposite phase-to-
phase voltage. Which current is compared with which voltage
can be seen from the following table.
Current input Phase-to-neutral voltage Calculated voltage
I
R
U
S
, U
T
U
ST
= U
S
- U
T
I
S
U
T
, U
R
U
TR
= U
T
- U
R
I
T
U
R
, U
S
U
RS
= U
R
- U
S
The voltage measurement automatically compensates the group
of connection of the v.t’s. For example, the phase-to-phase val-
ues are calculated for Y-connected v.t’s (v.t. type UTS), while the
input voltages are used directly for delta-connected v.t’s (v.t.
type UTD).
Delay
The delay enables the protection to be graded with other time-
overcurrent relays to achieve discrimination. Its setting is thus
chosen in relation to the timer settings of upstream and down-
stream protective devices. The zone of protection covered by
this overcurrent protection extends to the next overcurrent pro-
tection device.
Should in the event of a fault in the next downstream zone, the
protection for that zone fail, this protection function takes over
after the time set for “Delay” and clears the fault as backup.
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