SECTION
10-
Type SST Overcurrent Trip Device
The SST is a solid-state, direct-acting, self-powered trip
device system. The SST system consists of the SST pro
grammer unit, current sensors, and a flux shifter trip de
vice. Fig.
57
shows a block diagram of the system.
1 0.1 PROGRAMMER UNIT
Fig.
58
shows a typical SST programmer unit. The pro
grammer unit provides the comparison basis for overcur
rent detection and delivers the energy necessary to trip the
breaker. It contains the electronic circuitry for the various
trip elements. Their associated pickup and time delay ad
justments (set-points) are located on the face plate. De
pending on the application, programmer units may be
equipped with various combinations of Long Time, Short
Time, Instantaneous and Ground Fault trip elements. See
Table
7
for available ratings, settings and trip characteris
tics. Adjustments are made by removing the clear cover
over the face plate, unscrewing (counter-clockwise) the
set-point knob, moving the set-point along the slot to the
new setting, and screwing the set-point knob in. Once all
adjustments are made, install the clear cover to the face
plate.
The SST programmer units can be optionally equipped
with trip indicators (targets). These are pop-out, me
chanically-resettable plungers located across the top of
the programmer's front. Units with a ground fault element
employ three targets: from left to right, the first is for over
load, the second for short circuit (actuated by the short time
and instantaneous elements) and the third for ground fault.
The latter is omitted on units without ground fault.
•
FIG. 57 - SST BLOCK DIAGRAM
OVOI.CWI
I TAIIGET
I
I
I
I
I
1 -
CIM:IIIT
I TMW
I
Each target pops out when its associated trip element
operates to trip the breaker. After a trip, the popped target
must be reset by hand. However, neglecting to reset does
not affect normal operation of any trip element or prevent
the breaker from being reclosed.
The programmer unit is mounted to the lower right of the
breaker as shown in Fig.
59.
The bracket attached to the
top of the programmer, see Fig.
58,
engages with a bracket
mounted to the underside of the breaker's front frame.
TABLE
7
SST TRIP CHARACTERISTICS
X
• Trip Ratinr
in Ampere.
•Sen.or Tap
Bnaker
Frame
-
- -
- - - -
-
- - -
SIZe
Type
(Amperes)
(
Sen.or
)
Am.,.re
Tapt
100. 1 50. 225. 300
AKR-30
800
- or -
300. 400. 600, 800
300. 400. 600. 800
AKR-50
1 600
- or -
600. 800. 1 200. 1 600
800, 1 200.
AKRT-50
2000
1 600, 2000
CD
Pitkup
toler
ante
11
� �
@
Pic:kup
toltnnte is
�
1 0'\
SST
PROGRAMMER ADJUSTMENT RANGE
(Set
Pointa)
Lonr Time
Short Time
GROUND FAULT
Instantaneous
Pic:k
<D
(•L)
Time
Pic:kup
Time
Pickup
Pickup
Time
Delay
®
Delay
®
®
Delay
(
Mult1p ..
)
Band
@
(
Multip ..
)
Band
@ (
Multiple
) (
Multiple
)
Band
@
or
X
(Sec:onds)
or L
(Sec:onds)
or L
or
X
(Sec:onda)
3, 4, 5.
.4, .5, .6,
6, 8, 10 IL)
.8. 1 .0.
1 .2 (X)
Maximum
Maximum
Maximum
.6
. . 7.
8.
22
-or-
0.35
4, &, 6,
0.30
.9, 1 .0.
lntermed.
lntcrmed.
8, 10, 12
(L)
.25, .3, .4,
lntermed.
1 . 1 ( X )
10
1 .7&, 2,
0.21
.&, .6,
0.16&
2.2&, 2.!i,
.7
(X)
MUiimum
3, 4
(Ll
Minimum
Minimum
4
0.09&
0.065
.2, .25, .3,
.4, .&,
.6 (X)
®
Tame delay shown at
60()'\
or lonl time pickup s.ettinl
(6L),
It
lower limit of band.
@
Time delay shown at lower limit of band.
45
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