IL01906001E
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Instructional Literature
Effective: May 2005
Page
3
Arcflash Reduction Maintenance Switch
Application and Installation
1.3 Example Calculation
The following is a calculation example for a 1600 A circuit breaker
with a 1600 A sensor. The time current graph (Figure 2) shows
the circuit breaker settings before and after the Arcflash Reduc-
tion Maintenance Switch installation.
In this example, the following power system conditions exist:
Bolted fault current through the reductive
device to fault location
= 40.00 kA
Arcing fault current calculated using
IEEE Std. 1584
TM
-2002 = 19.98
kA
85% of arcing fault current per
IEEE Std. 1584
TM
-2002
= 16.98 kA
Running load current through circuit breaker
= 1.12 kA
Transient motor in-rush current through breaker
(6 × 1.6 × 480 A)
= 4.80 kA
Total running load + transient motor in-rush load = 5.92 kA
Setting choices for the RS are: 2.5 ×, 4.0 ×, 5.9 ×, 7.6 × or
9.8 × rating plug value with a pickup tolerance of
±
10%.
1. Setting 9.8 × 1600 A =15.68 kA± 10% =pickup range of
14.11 to 17.25 kA.
2. Setting 7.6 × 1600 A =12.16 kA± 10% =pickup range of
10.94 to 13.38 kA.
3. Setting 5.9 × 1600 A =9.44 kA ± 10% =pickup range of
8.50 to 10.38 kA.
4. Setting 4.0 × 1600 A =6.40 kA ± 10% =pickup range of
5.76 to 7.04 kA.
5. Setting 2.5 × 1600 A =4.00 kA ± 10% =pickup range of
3.60 to 4.40 kA.
In this example, there are two appropriate setting choices (either
5.9 [R3] × or 7.6 [R2] ×). Either of these settings are above the
total plus transient load (5.92 kA) and below the minimum arcing
current (16.98 kA). Either of these settings reduces the incident
energy from 10.7 to 2.2 cal/cm
2
(refer to the Table 2).
Table 2. Example Calculations for All RS Positions.
Note:
* Arcing current low tolerances (85%) used.
REDUCTION
SETTING
BUS
kV
REDUCTIVE
DEV.
BOLTED
FAULT
kA
REDUCTIVE
DEV.
ARCING
FAULT
kA
TRIP /
DELAY
TIME
sec
ARCFLASH
BOUNDARY
in. (mm)
WORKING
DISTANCE
in. (mm)
INCIDENT
ENERGY
cal/cm
2
NFPA70E
PPE
CLASS
INACTIVE
0.48
40.00
19.98
0.24
106 (2692)
24 (610)
10.7
Class 3
[R5]
0.48
40.00
19.98
0.05
37 (940)
24 (610)
2.23
Class 1
[R4]
0.48
40.00
19.98
0.05
37 (940)
24 (610)
2.23
Class 1
[R3]
0.48
40.00
19.98
0.05
37 (940)
24 (610)
2.23
Class 1
[R2]
0.48
40.00
19.98
0.05
37 (940)
24 (610)
2.23
Class 1
[R1]
0.48
40.00
16.98
0.24
94 (2388)
24 (610)
8.97
Class 3*
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