Areva MiCOM P441, Technical Manual

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Application Notes P44x/EN AP/E33
MiCOM P441/P442 & P444 Page 77/220
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 9.
I>3 Current Setting Instantaneous
TOR/SOTF Function Function After
TOR/SOTF Period Time Delay Required
Above load and inrush
current but LOW Yes - sensitive. Time delayed backup
protection. Longer than tZ3 to
grade with distance
protection.
HIGH,
≥
120% of max.
fault current for a fault at
the remote line terminal
and max. reverse fault
current
Yes - may detect
high current close-
up faults. Instantaneous
highset to detect
close-up faults. I>3 Time Delay = 0.
(Note #.)
TABLE 9 - 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. Thus, a set of 52b auxiliary contacts (closed
when the isolator is open) are required.
P0536ENa
I>4 Element: Stub Bus Protection
Busbar 1
Busbar 2
Open isolator
V = 0
I > 0
VT
Protection's blocking using VTs
Stub
Stub
Bus Protection : I >4
Bus Protection : I >4
Although this element would not need to discriminate with load current, it is still common
practice to apply a high current setting. This avoids maloperation for heavy through fault
currents, where mismatched CT saturation could present a spill current to the relay. The I>4
element would normally be set instantaneous, t>4 = 0s.