32
Operations - Instantaneous Fault Protection
Adjustable Instantaneous Pickup
Adjustable Instantaneous Pickup
The Instantaneous Pickup adjustment is used to set the
current level at which the breaker will trip without an inten-
tional time delay. Non-delayed tripping, as a result of a severe
overcurrent condition, minimizes potential damage to electri-
cal systems and equipment. On Siemens Electronic Trip
Units, the Instantaneous Pickup adjustment may be set to
1.5, 2, 3, 4, 5, 6, 7, 8, 10, or 12 times I
r
.
Instantaneous Pickup
Instantaneous Override
On all trip units, an instantaneous override function has been
provided . It is set nominally at the short time rating of the
respective breaker frame size. This allows the breaker to ride
through high faults up to its short time capability; however, it
is self-protecting above these values.
Breaker
Frame Size
Short Time kA Rating
(.500 seconds max.)
800A
1200A
2000A
25
25
35
Discriminator Circuit (Making Current Release)
This circuit overrides the short time delay function should the
breaker attempt to close into a faulted system, tripping the
breaker instantaneously. The discriminator function is en-
abled for the first 6 cycles of current flow, after which normal
short time characteristics operate.
Instantaneous Override (Illustrated with Short Time Fixed
Delay)
Courtesy of NationalSwitchgear.com
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