Highset Overcurrent And Switch On To Fault Protection; Stub Bus Protection; Tripping Logic For Phase Overcurrent Protection; Current And Time Delay Settings For The I>3 Element - GE MiCOM P40 Agile Technical Manual

P44x/EN AP/Hb6
(AP) 5-96
I phase
I 1>
I 2>
Figure 65: Tripping logic for phase overcurrent protection
I>3 Highset Overcurrent and Switch on to Fault Protection
The I>3 overcurrent element of the P442 and P444 relays can be Enabled as an
instantaneous highset just during the TOR/SOTF period. After this period has ended, the
element remains in service with a trip time delay setting I>3 Time Delay. This element would
trip for close-up high current faults, such as those where maintenance earth clamps are
inadvertently left in position on line energisation.
The I>3 current setting applied should be above load current, and > 35% of peak
magnetising inrush current for any connected transformers as this element has no second
harmonic blocking. If a high current setting is chosen, such that the I>3 element will not
overreach the protected line, then the I>3 Time Delay can be set to zero. The remote source
should not not be sufficiently strong to cause element pickup for a close-up reverse fault.
If a low current setting is chosen, I>3 will need to discriminate with local and remote distance
protection. This principle is shown in Table 8: .
I>3 Current Setting
Above load and inrush
current but LOW
HIGH, ≥ 120% of max. fault
current for a fault at the
remote line terminal and
max. reverse fault current
Table 8: Current and Time delay settings for the I>3 element
Key:
As the instantaneous highset trips three pole it is recommended that the I>3 Time Delay is
set ≥ tZ2 in single pole tripping schemes, to allow operation of the correct single pole
autoreclose cycle.
I>4 Stub Bus Protection
When the protected line is switched from a breaker and a half arrangement it is possible to
use the I>4 overcurrent element to provide stub bus protection. When stub bus protection is
selected in the relay menu, the element is only enabled when the opto input Stub Bus
Isolator Open (Stub Bus Enable) is energised. Therefore, a set of 52b auxiliary contacts
(closed when the isolator is open) is required.
tI1>
Instantaneous Function After
TOR/SOTF Function TOR/SOTF Period
Yes - sensitive. Time delayed backup
protection.
Yes - may detect high Instantaneous highset
current close-up faults. to detect close-up
faults.
MiCOM P40 Agile P442, P444
Trip
No trip
tI2>
Time Delay Required
Longer than tZ3 to
grade with distance
protection.
I>3 Time Delay = 0.
(Note #.)
Application Notes
t
P0483ENa