Eaton Cutler-Hammer Digitrip 3000 Instructions For Installation, Operation And Maintenance page 29

I.B. 17555C
Fig. 3-3 Sample Electronic Trip Curves
Ground Fault Protection
The ground fault protection function can be a composite
of the ground: 1) inverse time overcurrent curve shape,
pickup, and time, 2) short delay pickup and time, 3)
instantaneous pickup. Its curve shape is independent of
the phase curve. There are two differences between Dig-
itrip 3000 phase and ground functions: 1) Inverse time
overcurrent time multiplier values for the ground function
of the thermal curves are for (1 x I
x 2) The short delay settings are more sensitive and can
be set from (0.1 x I ) to (11 x I
n
portion of the curve in a horizontal direction and the time
portion of the curve in a vertical direction is similar to
phase inverse time over-current, short delay and instan-
taneous functions previously described. Therefore,
ground fault curve movement is not graphically illustrated.
Refer to Table 2.3 for the available ground fault settings.
When programming ground fault protection, keep in mind
that if "NONE" is selected, the ground fault protection is
disabled. Even if the ground fault protection is disabled, a
detectable ground current will still be displayed.
Effective November 1999
) while the phase is (3
n
). Movement of the pickup
n
Characteristic Curve Reminders
As previously mentioned, combining protective capabili-
ties is a matter of coordination. The effects of one selec-
tion should always be evaluated against other selections
to determine if the overall desired result is obtained. For
this reason, keep in mind the following Digitrip 3000
selection possibilities and relay design features when
programming the unit to closely coordinate with system
protective needs:
1. When "NONE" is selected as a setting, the associ-
ated tripping function is disabled.
2. When "NONE" is selected for the Phase Instanta-
neous Setting, a Phase Discriminator option is
offered.
3. The internal design of the Digitrip 3000 Protective
Relay is such that the Short Delay Time setting might
take precedence over the Inverse Time Overcurrent
Time. This is graphically illustrated in Figure 3-8.
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