Effective 8/2006
Page 9
I.L. 66A7534H04
2.2 Low-Energy Trip Actuator
The mechanical force required to initiate the tripping action
of the circuit breaker is provided by a special low-energy
Trip Actuator. This device is located behind the molded
platform on which the Digitrip units are supported.
(See
Figure 1.2)
The Trip Actuator contains a permanent magnet
assembly, moving and stationary core assemblies, a
spring, and a coil. Nominal coil resistance is 25 ohms and
the black lead is positive. The circuit breaker mechanism
automatically resets the Trip Actuator each time the circuit
breaker opens.
When the Trip Actuator is reset by the operating mecha-
nism, the moving core assembly is held in readiness
against the force of the compressed spring by the perma-
nent magnet. When a tripping action is initiated, the low-
energy Trip Actuator coil receives a tripping pulse from the
Digitrip trip unit. This pulse overcomes the holding effect of
the permanent magnet, and the moving core is released to
upset the trip latch of the circuit breaker mechanism.
2.3 Ground Fault Protection
2.3.1 General
When employing a ground fault scheme, the distribution
system characteristics
(i.e. system grounding, number of
sources, number and location of ground points, etc.)
must
be considered along with the manner and location in which
the circuit breaker is applied to the system. These ele-
ments are discussed in Sections 2.3.2
through 2.3.4.
The Digitrip uses two modes of sensing to detect ground
fault currents: residual and zero sequence
(See Table 2.1)
.
The breaker’s secondary contact inputs B-6, B-7, that
were shown in Figure 1.6, are used to configure the
breaker cell positions for the two schemes. Having no
jumper from B-6 to B-7 programs the unit for a residual
ground fault scheme, while installing a jumper from B-6 to
B-7 programs the unit for zero sequence configuration. If
present, this jumper resides on the stationary side of the
switchgear assembly. The proper current sensor input is
required on the external sensor input terminals B-4, B-5 of
the breaker secondary contacts.
Figure 2.1 Zero Sequence Current Transformer
2.3.2 Zero Sequence Sensing
Zero Sequence Sensing, also referred to as vectorial
summation, is applicable to mains, feeders, and special
schemes involving zone protection. An optional CH Type-V
Zero Sequence current transformer
(See Figure 2.1)
, having
taps for 100A and 200A ratings is available for this
application. The torroidal sensor has a 4.8” I.D. (12.192cm)
with a 7.6” O.D. (19.304cm). Its style number
69C3016G01.
(See Figure 2.3 and Appendix C)
2.3.3 Residual Sensing
Residual is the standard operating mode of ground fault
sensing. This mode utilizes one current sensor on each
phase conductor
(See Figure 2.2)
. If the system neutral is
grounded, but no phase to neutral loads are used, the
Digitrip includes all of the components necessary for
ground fault protection. This mode of sensing vectorily
sums the outputs of the three or four individual CH Type-V
current sensors. Residual ground fault sensing features
are adaptable to main and feeder breaker applications.
Ground (Earth)
Fault
Sensing Method
Breaker Secondary
Contacts Req’d
Figure
Ref
Digitrip GF
Sensing
Element Used
Residual
No Jumper
2.2
element R5
Zero Sequence
Jumper B6 to B7
2.3
element R4
Table 2.1 Digitrip Sensing Modes
