Residual Sensing; Source Ground Sensing; Zero Sequence Sensing; Multiple Source/Multiple Ground - Eaton Cutler-Hammer Digitrip 1150 Instructions Manual

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be considered along with the manner and location in
which the circuit breaker is applied to the system. These
elements are discussed in Sections 2.3.3 through 2.3.6.
The Digitrip 1150 family uses three modes of sensing to
detect ground fault currents: residual, source ground, and
zero sequence (see Table 2.1). Magnum Circuit Breakers
can accommodate all three types except for 4-pole
breakers. The breaker secondary contact inputs B-6 and
B-7 are used to configure the breaker cell positions for the
three schemes. A jumper from B-6 to B-7 programs the
trip unit for either a source ground or zero sequence
configuration. Removing the jumper will program the unit
for a residual ground fault scheme. This jumper resides
on the stationary side of the switchgear assembly. In all
three schemes, the proper current sensor input is re-
quired on the external sensor input terminals B-4, B-5 of
the breaker secondary contacts.
Table 2.1 Digitrip Sensing Modes
Ground (Earth) Breaker
Fault Secondary
Sensing Method Contacts Req'd
Residual No Jumper
Source Ground Jumper B6 to B7
Zero Sequence Jumper B6 to B7
Note: This information applies to Trip Units with Ground

2.3.2 Residual Sensing

Residual Sensing is the standard mode of ground fault
sensing in Magnum Circuit Breakers. This mode utilizes
one current sensor on each phase conductor and one on
the neutral for a 4-wire system (shown in Figures 2.2
and 2.3). If the system neutral is grounded, and no phase
to neutral loads are used, the Digitrip 1150 with ground
includes all of the components necessary for ground fault
protection. This mode of sensing vectorially sums the
outputs of the three or four individual current sensors. For
separately-mounted neutrals, as long as the vectorial sum
is zero, then no ground fault exists. The neutral sensor
must have characteristics and a ratio which matches the
three internally-mounted phase current sensors. Available
types of neutral sensors are shown in Figure 2.4. Re-
sidual ground fault sensing features are adaptable to
main and feeder breaker applications.
CAUTION
IF THE SENSOR CONNECTIONS ARE INCORRECT, A
NUISANCE TRIP MAY OCCUR. ALWAYS OBSERVE
THE POLARITY MARKINGS ON THE INSTALLATION
DRAWINGS. TO INSURE CORRECT GROUND FAULT
EQUIPMENT PERFORMANCE, CONDUCT FIELD
Courtesy of NationalSwitchgear.com
Digitrip GF
Applicable Figure Sensing
Breakers Reference Element
Used
3 or 4 pole 2.2, 2.3, 2.5, 2.9 element R5
3 pole only 2.7 element R4
3 pole only 2.8 element R4
TESTS TO COMPLY WITH NEC REQUIREMENTS
UNDER ARTICLE 230-95(C).

2.3.3 Source Ground Sensing

Depending upon the installation requirements, alternate
ground fault sensing schemes may be dictated (see
Figures 2.6 and 2.7). The ground return method is usually
applied when ground fault protection is desired only on
the main circuit breaker in a simple radial system. This
method is also applicable to double-ended systems where
a midpoint grounding electrode is employed. For this
mode of sensing, a single current sensor mounted on the
equipment-bonding jumper directly measures the total
ground current flowing in the grounding electrode
conductor and all other equipment-grounding conductors.
In the CURRENT (protection) submenu, there is a setting
(EXT GND CT RATIO) that enable the proper scaling of
ground pickup and display of ground current if External
Ground CT is employed. This screen is presented when
jumper B-6 to B-7 is presented on a trip unit equiped with
GROUND. External Ground CT ratios of 10, 100, 200,
400, 800, 1000 A:1 and "none" setting are selectable, with
"none" defaulting to the plug In rating. With the correct
ratio selected the GF pickup settings are adjustable in
AMPERES.

2.3.4 Zero Sequence Sensing

Zero Sequence Sensing, also referred to as vectorial
summation (see Figure 2.8), is applicable to mains,
feeders, and special schemes involving zone protection.
Zero Sequence current transformers (4 1/2" x 13 1/2" [114
mm x 342 mm] rectangular inside dimensions) are
available with 100:1 and 1000:1 ratios. The EXT GND CT
RATIO setting described above is applicable for zero
sequence.

2.3.5 Multiple Source/Multiple Ground

A Multiple Source/Multiple Ground scheme is shown in
Figure 2.9. In this figure, a ground fault is shown which
has two possible return paths, via the neutral, back to its
source. The three neutral sensors are interconnected to
sense and detect both ground fault and neutral currents.
Call Cutler-Hammer for more details on this scheme.

2.3.6 Ground Fault Settings

The adjustment of the ground fault functional settings
2
(FLAT response or I t) is discussed in Section 4.2.1.8.
The effect of these settings is illustrated in the ground
fault time-current curve referenced in Section 9.
I.L. 70C1036H01
Effective 8/18/99