SECTION 1 0-Type SST Overcurrent Trip Device
The SST is a solid-state, d i rect-acti n g , self-powered trip
device syste m . The SST system consists of the SST pro
grammer unit, current sensors, and a flux sh ifter trip de
vice . Fig.
57
shows a block d i agram of the syste m .
1 0.1 PROG RAMMER UNIT
Fig.
58
shows a typical S ST programmer u n it . The pro
grammer u n it provides the com parison basis for overcur
rent detection and delivers the energy necessary to trip the
b reaker. I t contai ns the electronic c i rc u itry for the various
trip elements. Their associated pickup and time de lay ad
j u stments (set- poi nts) are located on the face plate . De
pending on the application, prog rammer u n its may be
equipped with various combi nations of Long Time, S hort
Time, I nstantaneous and G round Fault trip elements. See
Table
7
for available ratings, setti ngs and trip characteris
tics. Adj ustme nts are made by removing the clear cover
over the face p late, u nscrewing (counte r-clockwise) the
set- point knob, moving the set-po int along the slot to the
new setting, and screwi ng the set- point knob i n . Once all
adjustme nts are made , install the clear cover to the face
p late .
The SST prog ram mer un its can be optionally eq u i p ped
with trip i ndicators (targets ) . These are pop-out, me
chanical ly-resettable plungers located across the top of
the prog rammer's front. U n its with a ground fault element
e m ploy three targets: from left to right, the f i rst is for over
load, the second for short circuit (actu ated by the short time
and instantaneous elements) and the t h i rd for ground fault.
The latte r is om itted on un its without ground fault.
8
t
�- - - - --
OVERLOAD
I TARGET
I
I
I
I
I
I
SHORT
lciRCUIT
I TARGET
I
FIG. 57 - SST B LOCK DIAGRAM
Each target pops out when its associated trip element
ope rates to trip the breaker. After a tri p, the popped target
must be reset by hand. However, neglecti ng to reset does
not affect normal operation of any trip element or prevent
the breaker from being reclosed .
The prog rammer unit is mou nted to the l ower 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
mou nted to the underside of the breake r's front frame.
TAB L E 7 SST TRIP CHARACTERISTICS
X • Trip Rating
in Amperes
• Sensor Tap
Frame
- - - - -
-
- - - - -
Breaker
Size
Type
(Amperes)
(
Sensor
)
Ampere
Taps
100, 1 50, 225, 300
AKR-30
800
- or -
300, 400, 600, 800
300, 400, 600, 800
AKR-50
1600
- or -
600, 800, 1 200, 1600
800, 1 200 ,
AKRT-50
2000
1 600, 2000
CD
Pickup tolerance is ±.. 9%
@
Pickup tolerance is ±.. 1 0%
S ST PROGRAMMER ADJUSTMENT RANGE (Set Points)
Long Time
Short Time
GROUND FAULT
Instantaneous
Pick
(D
(•L)
Time
Pickup
Time
Pickup
Pickup
Time
Delay
®
Delay
®
®
Delay
(
Multiple
)
Band
@
(
Multiple
)
Band
@)
(
Multiple
) (
Multiple
)
Band
@
of X
(Seconds)
of L
(Seconds)
o f L
of X
(Seconds)
3, 4, 5,
.4, .5, .6,
6, 8, 10 (L)
.8, 1 .0,
1.2 ( X )
Maximum
Maximum
Maximum
.6, .7, .8,
22
-or-
0.35
4, 5, 6,
0 . 30
I
.9, 1 .0,
Intermed .
lnt..rmed .
8, 10, 12 ( L )
.25, .3, . 4 ,
Intermed.
1 . 1 ( X )
1 0
1 . 75, 2 ,
0.21
.5, .6,
0.165
2.25, 2.5,
. 7 (X)
Minimum
3 , 4 ( L )
Minimum
Minimum
4
0.095
0.065
.2, .25, .3,
.4, .5,
.6 ( X )
@
Time delay shown a t 600% of long time pickup setting ( 6 L ) , a t lower limit of band.
G)
Time delay shown at lower limit of band.
45
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