Siemens Dynamic Arc Flash Reduction
System and its application in motor
control centers
The risk of Arc Flash is a growing concern within the electrical equipment
community and among both designers and workers. Current research shows that
up to 80% of reported electrical injuries are caused by an electrical arc1. This fact
has spawned new requirements and standards in governing documents, such as in
NFPA 70E and the NEC, which address the safety of workers, on and around
energized electrical equipment. Prior to the development of these standards,
Siemens understood the importance of mitigating arc flash risk for its customers.
This led Siemens to develop the innovative Dynamic Arc Flash Sentry (DAS). This
paper will explore the capabilities of the Dynamic Arc Flash Sentry, investigate an
example case, and show the benefits of this technology in motor control centers.
Siemens strongly recommends that all systems be de-energized when personnel
are working on electrical equipment. However, in some circumstances qualified
professionals may need to access and work near energized equipment. For
example, many troubleshooting operations, or work on critical applications, require
that power remain on to complete the task. This is where many accidents occur and
the risks and effects of an arc flash are the greatest. The Dynamic Arc Flash Sentry
system is designed to greatly reduce the risk of arc flash while maintaining
efficiency of the loads on the motor control center. These loads could include
motor inrush currents, and normal variance in motor operating amperage.
Siemens Dynamic Arc Flash Sentry Technology uses a dual function setting of the
ETU776 electronic trip unit when housed in the Siemens WL power circuit breaker.
The trip unit has two complete and independent set of parameters (A and B), that
allow the operator to switch back and forth from a normal operating mode to a
personnel protective mode. It should be noted that the parameters A and B can
be assigned to either the normal operating mode or personnel protective mode.
By setting the personnel protective mode to parameter A and the normal
operating mode to parameter B, a fail-safe is created because the system will
default to DAS-active in the event the DAS wiring is broken. However, throughout
this paper, normal operating mode will refer to parameter A and personnel
protective mode will refer to parameter B. The personnel protective mode
(Parameter B) reduces the instantaneous trip setting of the WL main circuit
breaker. By reducing the instantaneous region, the trip timing of the system is
controlled, and can be reduced to clear a fault much sooner than the original
operating time. This decreases the amount of energy available in an arc flash,
making the area surrounding the motor control center less susceptible to an arc
flash event.
A white paper issued by Siemens. ©2016
Siemens Industry, Inc. All rights reserved.
www.usa.siemens.com/mcc
White Paper | Dynamic Arc Flash Reduction System
Let’s look at an example of how the DAS can function to
increase safety and help mitigate the risks associated with arc
flash. We will use a sample system that is based on an actual
application in the field. This example was set up with aid from
ESA and their EasyPower software2 tool to help create the
motor control center layout and calculate the associated arc
flash energies. Figure 1 shows a typical motor control center
with a Siemens WL as a main circuit breaker and numerous
feeder circuit breakers controlling different functions
including motors, panels and other loads.
kV
UTIL-1
10 000 0 MVA
15 0 (X/R)
10 000 0 MVA
15 0 (X/R)
12
.
47
BUS-1
TX-1
15 00 kVA
12 .47 - 0 .48 kV
5. 75%
10-1/C-600 kcmil
CU, 100', [Conduit]
0.
4
8
kV
BUS-2
GEN-1
1. 25 MVA
15 %
21 %
0. 7%
0.
4
8
kV
BUS-3
4-1/C-600 kcmil
CU, 100', [Conduit]
4-1/C-5 00 k cmil
CU, 1 00', [Co nd uit]
ATS-1
MCC 1
8
0.
4
Siemens HFD6
25 0/2 25
Siemens LXD6
60 0/6 00
Siemens LXD6
60 0/6 00
kV
Siemens 1 600 L
16 00/160 0
MCC BUS
Siemens 8 00L
80 0/6 40
Siemens HFD6
25 0/2 50
Siemens HFD6
25 0/2 25
Siemens HEG
12 5/1 00
Siemens HFD6
25 0/2 25
Siemens HFD6
25 0/2 00
Siemens HFD6
25 0/1 50
PNL
PNL-5
20 A
12 5 k VA
BUS-8
0.
2
4
BUS-7
kV
PNL-4
1-1/C-4/0 AWG
CU, 50', [Conduit]
0.
48
kV
1-1/C-4/0 AWG
CU, 50', [Conduit]
0.
48
kV
PNL
12 5 k VA
1-1/C-2 AWG
CU, 50', [Conduit]
PNL-3
31 kVA
kV
L-6
40 0 k VA
1-1/C-1 AWG
CU, 100', [Conduit]
0.
48
kV
12 5 k VA
1-1/C-350 kcmil
CU, 100', [Conduit]
0.
24
kV
PNL
PNL-1
8
PNL
4-1/C-600 kcmil
CU, 50', [Conduit]
0.
48
kV
BUS-4
TX-4 _A
50 kVA
0. 48 - 0.2 4 k V
3%
0.
4
M-2
30 0 HP
In ductio n
16 .7%
1-1/C-4/0 AWG
CU, 50', [Conduit]
0.
48
kV
M-1
30 0 HP
In ductio n
16 .7%
BUS-6
2-1/C-4/0 AWG
CU, 100', [Conduit]
0.
48
kV
BUS-5
2-1/C-4/0 AWG
CU, 100', [Conduit]
0.
48
kV
TX-4
50 kVA
0. 48 - 0.2 4 k V
3%
PNL
PNL-6
31 kVA
L-2
75 kVA
L-1
75 kVA
Figure 1 – MCC Example One-line Diagram
Note: The 1600A main circuit breaker of the example is in an isolated section respective to the rest of the MCC. The incident
energy for this section will be as calculated using the upstream protective device and not the levels shown for the MCC bus.
2
A white paper issued by Siemens. ©2016 Siemens Industry, Inc. All rights reserved.
White Paper | Dynamic Arc Flash Reduction System
This MCC configuration will serve as the basis for this
example. To properly coordinate the circuit breakers
controlled in the MCC with the main circuit breaker upstream,
it is appropriate to analyze the time current curve (TCC)
to see the trip parameters for long time, short time, and
instantaneous trips. Typically in a motor control center, as
with MCC1 in Figure 1, there are numerous operating devices
present. The resulting TCC for this motor control center would
be cluttered and virtually unreadable. For this example,
we selected the three most relevant devices to display, that
will affect the coordination of the upstream circuit breaker.
Figure 2 shows the TCCs of four devices: a 600A Siemens
combination motor starter with a 600A Siemens LXD6 circuit
breaker, a 250A Siemens HFD6 circuit breaker, an 800A
Siemens WL800L, and the main device a 1600A Siemens
WL1600.
CURRENT IN AMPERES X 10 AT 480 VOLTS
2
3
4
5
6 7 8 9 10
2
3
4
5
6 7 8 9 100
2
3
4
5
6 7 8 9 1000
2
3
4
5 6 7 8 9 10000
1000
900
800
700
600
500
1000
900
800
700
600
500
400
400
300
300
200
200
100
90
80
70
60
50
100
90
80
70
60
50
40
30
TIME IN SECONDS
20
BL-1
Siemens LD
LXD6
Frame = 600A(500-600T)
Trip = 600
Inst = 3 (3800A)
10
9
8
7
6
5
40
30
20
10
9
8
7
6
5
4
4
3
3
2
2
BL-4
Siemens FD
HFD6
Frame = 250A(225AT)
Trip = 225
Inst = 4 (1700A)
1
.9
.8
.7
.6
.5
1
.9
.8
.7
.6
.5
.4
.4
.3
.3
.2
.2
BL-2
Siemens WL FS I 800L
ETU 776 L(SIG)
Frame = 800(I^2T)
Plug = 800
Cur Set = 0.8 (640A)
LT Band = 5 sec
STPU = 4000A
ST Delay = 0.097
ST Delay I²t = Out
Inst = 52000A
.1
.09
.08
.07
.06
.05
.04
.03
TIME IN SECONDS
BL-5
Siemens WL FS II 1600L
ETU 776 L(SIG)
Frame = 1600(I^2T)
Plug = 1600
Cur Set = 1 (1600A)
LT Band = 15 sec
STPU = 6510A
ST Delay = 0.32
ST Delay I²t = Out
Inst = 65000A
.1
.09
.08
.07
.06
.05
.04
.03
.02
.02
.01
.01
2
3
4
5
6 7 8 9 10
2
3
4
5
6 7 8 9 100
2
3
4
5
6 7 8 9 1000
2
3
4
5 6 7 8 9 10000
CURRENT IN AMPERES X 10 AT 480 VOLTS
Figure 2 – TCC of Parameter A – Normal Operating Mode
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3
White Paper | Dynamic Arc Flash Reduction System
As you can see in Figure 2, the WL circuit breaker is selectively
coordinated with the devices downstream from it. The WL main
circuit breaker will instantaneously trip within 50 milliseconds at 65
kA. The next step is to determine the arc-flash boundary and proper
personal protective equipment (PPE) needed. There are two
methods to determine this. The first method is the incident energy
analysis method based on IEEE 1584 calculations, which are used to
determine the arc-flash boundary and incident energy exposure.
Based on the incident energy exposure, the correct PPE can be
determined using Table H.3(b) in NFPA 70E, shown below as Table 1.
The second method is the arc flash PPE categories method. Table
130.7(C)(15)(A)(b) or Table 130.7(C)(15)(B) in NFPA 70E can be used
to determine the PPE category and arc-flash boundary required for
work on certain equipment. Table 130.7(C)(16) can then be used to
determine the specific PPE required for each PPE category.
It is important to note that either, but not both, methods can be
used on the same piece of equipment. For example, the incident
energy cannot be calculated and then used to select a PPE category
from Table 130.7(C)(16).
Table 1 below from NFPA70E 2015 edition shows the PPE required
for each PPE risk category.
Incident Energy Exposure
Protective Clothing & PPE
≤ 1.2 cal/cm2
Protective clothing, nonmelting (in accordance with ASTM F 1506) or
untreated natural fiber
Shirt (long sleeve) and pants (long) or coverall
Other PPE
Face shield for projectile protection (AN)
Safety glasses or safety goggles (SR)
Hearing protection
Heavy-duty leather gloves or rubber insulating gloves with leather protectors
(AN)
> 1.2 to 12 cal/cm2
Arc-rated clothing and equipment with an arc rating equal to or greater than
the determined incident energy
Arc-rated long-sleeve shirt and arc-rated pants or arc-rated coverall or arc
flash suit (SR)
Arc-rated face shield and arc-rated balaclava or arc flash suit hood (SR)
Arc-rated jacket, parka, or rainwear (AN)
Other PPE
Hard hat
Arc-rated hard hat liner (AN)
Safety glasses or safety goggles (SR)
Hearing protection
Heavy-duty leather gloves or rubber insulating gloves with leather protectors
Leather footwear
> 12 cal/cm2
Arc-rated clothing and equipment with an arc rating equal to or greater than
the determined incident energy
Arc-rated long-sleeve shirt and arc-rated pants or arc-rated coverall or arc flash
suit (SR)
Arc-rated arc flash suit hood
Arc-rated gloves
Arc-rated jacket, parka, or rainwear (AN)
Other PPE
Hard hat
Arc-rated hard hat liner (AN)
Safety glasses or safety goggles (SR)
Hearing protection
Arc-rated gloves or rubber insulating gloves with leather protectors (SR)
Leather footwear
Notes:
Table 1 - Guidance on Selection of Arc-Rated Clothing and Other PPE from Table H.3(b), NFPA 70E 2015
AS: As needed [in addition to the protective clothing
and PPE required by 130.5(C)(1)]
SR: Selection of one group is required by 130.5(C)(1)
4
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White Paper | Dynamic Arc Flash Reduction System
Figure 3 shows the conditions that appear at the MCC when a
fault is sent to the bus in MCC1. Using the incident energy
analysis method, the incident energy is calculated to be 24.4
cal/cm2. Table H.3(b) can then be used to determine the PPE
required to work on this MCC.
MCC BUS
112.7” AFB
24.4 cal / cm² @ 18"
#3 @ 18”
As the PPE requirements increase, the material can become
increasingly bulky and hot, leading to uncomfortable work
conditions for any personnel. Additionally, operators wearing
arc flash suits have to be specially trained, and periodically
re-certified to wear the equipment. Figure 3 also shows that the
arc flash boundary is 112.7 inches away from the MCC in every
direction. To have personnel working on or around this
electrical equipment can be extremely hazardous.
Siemens 1600L
1600/1600
Siemens HFD6
250/225
Siemens LXD6
600/600
Siemens 800L
800/640
Figure 3 – Arc Flash in Parameter A
So how can we resolve this problem? There are two significant
solutions to this problem, which can be used either
independently, or jointly, to provide redundancy. The first
alternative is to reduce the incident arc energy of the system, as
discussed in this document. The second alternative is the
tiastar™ Arc Resistant Motor Control Center, as described in
its own White Paper.
The first alternative, reducing the incident arc energy of the
system, is done by reducing the clearing time of the fault,
which results in a safer environment. This solution lies in the
patented Siemens Dynamic Arc Flash Sentry Technology.
A white paper issued by Siemens. ©2016 Siemens Industry, Inc. All rights reserved.
5
White Paper | Dynamic Arc Flash Reduction System
Instead of working under these conditions, the DAS allows
the flexibility for the worker to switch from the normal
operating settings of Parameter A, to the lower arc flash
energy settings of Parameter B. The goal is that when any
person is working on or near this equipment, the system will
be set to Parameter B. This is made possible by the dual
protection capability of the ETU776 trip unit previously
mentioned. So, lowering the instantaneous trip settings of
the WL circuit breaker ensures that the time it takes for an
electric fault to clear will be decreased, providing a safer
working environment. Let’s look at the second part of the
example.
CURRENT IN AMPERES X 10 AT 480 VOLTS
2
3
4
5 6 7 8 9 10
2
3
4
5 6 7 8 9 100
2
3
4
5 6 7 8 9 1000
2
3
4
5 6 7 8 9 10000
1000
900
800
700
600
500
1000
900
800
700
600
500
400
400
300
300
200
200
100
90
80
70
60
50
100
90
80
70
60
50
40
40
30
30
TIME IN SECONDS
20
BL-6
Siemens WL FS II 1600L
ETU 776 L(SIG)
Frame = 1600(I^2T)
Plug = 1600
Cur Set = 1 (1600A)
LT Band = 15 sec
STPU = 6510A
ST Delay = 0.32
ST Delay I²t = Out
Inst = 10000A
10
9
8
7
6
5
4
3
20
10
9
8
7
6
5
4
3
BL-4
Siemens FD
HFD6
Frame = 250A(225AT)
Trip = 225
Inst = 4 (1700A)
2
1
.9
.8
.7
.6
.5
2
TIME IN SECONDS
BL-1
Siemens LD
LXD6
Frame = 600A(500-600T)
Trip = 600
Inst = 3 (3800A)
1
.9
.8
.7
.6
.5
.4
.4
.3
.3
.2
.2
BL-1
Siemens WL FS I 800L
ETU 776 L(SIG)
Frame = 800(I^2T)
Plug = 800
Cur Set = 0.8 (640A)
LT Band = 5 sec
STPU = 4000A
ST Delay = 0.097
ST Delay I²t = Out
Inst = 52000A
.1
.09
.08
.07
.06
.05
.04
.03
.1
.09
.08
.07
.06
.05
.04
.03
.02
.02
.01
.01
2
3
4
5 6 7 8 9 10
2
3
4
5 6 7 8 9 100
2
3
4
5 6 7 8 9 1000
2
3
4
5 6 7 8 9 10000
CURRENT IN AMPERES X 10 AT 480 VOLTS
Figure 4 – TCC of Parameter B – Enhanced Safety Mode
6
A white paper issued by Siemens. ©2016 Siemens Industry, Inc. All rights reserved.
White Paper | Dynamic Arc Flash Reduction System
When switching from Parameter A to Parameter B, each of the
settings is kept the same in the motor control center, except
the instantaneous trip setting of the WL main circuit breaker.
The TCC for Parameter B is displayed in Figure 4. As can be
seen, the WL main overlaps the WL feeder circuit breaker in
the instantaneous region, which was lowered to 10kA, while
the other regions remain coordinated appropriately. This
provides another example of the flexibility of the ETU 776 trip
unit in the Dynamic Arc Flash system.
MCC BUS
27.2” AFB
3.0 cal / cm² @ 18"
#1 @ 18”
This system allows the user to alter the trip delay settings, as
well as long time, short time, and instantaneous pickup of
the ETU 776 trip unit. However, these changes are not
required and can be kept the same for simplicity reasons. In
this example, only the instantaneous pickup was reduced
between Parameter A and B, keeping all other trip unit and
main circuit breaker settings the same. When an electrical
fault is applied to the MCC1 bus in Parameter B, the difference
can be seen.
Siemens 1600L
1600/1600
Siemens HFD6
250/225
Siemens LXD6
600/600
Siemens 800L
800/640
Figure 5 – Arc Flash in Parameter B
The results of the arc flash hazard analysis show that the
incident energy has been reduced to 3.0 cal/cm2, which is
over an 8 times reduction in energy.
Based on the incident energy analysis method, this also
significantly reduces the amount of PPE required by Table
H.3(b).
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7
White Paper | Dynamic Arc Flash Reduction System
Now let’s compare the TCCs from Parameter A and B when
they are side by side, as shown in Figure 6. This clearly shows
that the only parameter that is changed is the main WL circuit
breaker, with the instantaneous pickup being reduced. This
greatly reduces the incident energy of a potential arc flash
and creates a safer environment.
CURRENT IN AMPERES X 10 AT 480 VOLTS
CURRENT IN AMPERES X 10 AT 480 VOLTS
2
3
4
5
6 7 8 9 10
2
3
4
5
6 7 8 9 100
2
3
4
5
6 7 8 9 1000
2
3
4
2
5 6 7 8 9 10000
1000
900
800
700
600
500
1000
900
800
700
600
500
400
400
300
300
5 6 7 8 9 10
2
3
4
5 6 7 8 9 100
2
3
4
5 6 7 8 9 1000
2
3
4
5 6 7 8 9 10000
1000
900
800
700
600
500
400
400
300
300
200
200
100
90
80
70
60
50
100
90
80
70
60
50
30
20
BL-1
Siemens LD
LXD6
Frame = 600A(500-600T)
Trip = 600
Inst = 3 (3800A)
10
9
8
7
6
5
4
4
3
3
2
BL-4
Siemens FD
HFD6
Frame = 250A(225AT)
Trip = 225
Inst = 4 (1700A)
1
.9
.8
.7
.6
.5
.4
.3
.3
.2
.2
BL-2
Siemens WL FS I 800L
ETU 776 L(SIG)
Frame = 800(I^2T)
Plug = 800
Cur Set = 0.8 (640A)
LT Band = 5 sec
STPU = 4000A
ST Delay = 0.097
ST Delay I²t = Out
Inst = 52000A
.1
.09
.08
.07
.06
.05
.04
.03
.1
.09
.08
.07
.06
.05
.02
.01
2
3
4
5
6 7 8 9 10
2
3
4
5
6 7 8 9 100
2
3
4
5
6 7 8 9 1000
2
3
4
BL-6
Siemens WL FS II 1600L
ETU 776 L(SIG)
Frame = 1600(I^2T)
Plug = 1600
Cur Set = 1 (1600A)
LT Band = 15 sec
STPU = 6510A
ST Delay = 0.32
ST Delay I²t = Out
Inst = 10000A
10
9
8
7
6
5
4
3
1
.9
.8
.7
.6
.5
.4
.3
.2
.2
BL-1
Siemens WL FS I 800L
ETU 776 L(SIG)
Frame = 800(I^2T)
Plug = 800
Cur Set = 0.8 (640A)
LT Band = 5 sec
STPU = 4000A
ST Delay = 0.097
ST Delay I²t = Out
Inst = 52000A
.1
.09
.08
.07
.06
.05
.03
.02
.02
.01
.01
4
1
.9
.8
.7
.6
.5
.3
.04
10
9
8
7
6
5
2
.4
.03
20
3
BL-4
Siemens FD
HFD6
Frame = 250A(225AT)
Trip = 225
Inst = 4 (1700A)
2
.04
5 6 7 8 9 10000
30
BL-1
Siemens LD
LXD6
Frame = 600A(500-600T)
Trip = 600
Inst = 3 (3800A)
20
1
.9
.8
.7
.6
.5
.4
40
30
20
10
9
8
7
6
5
2
40
40
30
TIME IN SECONDS
BL-5
Siemens WL FS II 1600L
ETU 776 L(SIG)
Frame = 1600(I^2T)
Plug = 1600
Cur Set = 1 (1600A)
LT Band = 15 sec
STPU = 6510A
ST Delay = 0.32
ST Delay I²t = Out
Inst = 65000A
40
100
90
80
70
60
50
TIME IN SECONDS
100
90
80
70
60
50
TIME IN SECONDS
4
200
TIME IN SECONDS
200
3
1000
900
800
700
600
500
.1
.09
.08
.07
.06
.05
.04
.03
.02
.01
2
3
4
5 6 7 8 9 10
2
3
4
5 6 7 8 9 100
2
3
4
5 6 7 8 9 1000
2
3
4
5 6 7 8 9 10000
CURRENT IN AMPERES X 10 AT 480 VOLTS
CURRENT IN AMPERES X 10 AT 480 VOLTS
Figure 6 – Parameter A and Parameter B comparison
By switching from Parameter A to B, the DAS allows a
temporary overlapping of the main circuit breaker with a
feeder circuit breaker. However, to fully understand this
situation, there are two main points to consider. First, to
maintain a reliable system and avoid nuisance tripping due
to normal operating currents in Parameter B, inrush currents
must be taken into account. In this example, a 1500kVA
transformer with a 480V secondary side and 5.75%
impedance has a typical full load current of around 1.8kA.
For the 300 HP motor running in our example, the full load
amperage is 361 amps, which gives a typical inrush current
of around 4700 amps.3 With a peak inrush current lasting
less than one second, this value is still well below the
instantaneous pickup of the main circuit breaker at 10kA.
Even with multiple devices and other loads running, a very
high current spike would need to exist in order to trip the
8
main. The reality is: if the system is designed correctly,
compromising of the coordination which causes issues such
as nuisance tripping should be extremely limited. In addition,
the trade off that is being made with a worker standing in
front of an energized motor control center should be worth
this concession.
This leads to the second and more realistic point of
understanding the temporary overlap of the main circuit
breaker with a feeder circuit breaker. Parameter B does
present an overlap of coordination; however the intent of this
system is to create a significantly safer environment when the
equipment is energized. Safety should be the primary
concern in the unique and unusual situation in which the
equipment cannot be de-energized. To address this issue, the
DAS provides the flexibility of the full range of settings to
create a safer environment for workers. In this way, the DAS
system provides a unique solution for the industry.
A white paper issued by Siemens. ©2016 Siemens Industry, Inc. All rights reserved.
White Paper | Dynamic Arc Flash Reduction System
The Dynamic Arc Flash Sentry has been available in low
voltage switchgear for some time. It is available in Siemens
Arc Resistant Motor Control Centers. This technology can also
be employed in Siemens switchboards and busway. Siemens
is listening to its customers and meeting the highest industry
standards. By offering a system that has the flexibility to
actually reduce the amount of arc flash incident energy
without forcing customers to choose reliability over safety,
the Dynamic Arc Flash System is addressing the difficult
challenges related to electrical worker safety.
References:
1 National
Technology Transfer, Inc. NFPA 70E/ Arc Flash:
Electrical Safety. Edition 3.1.
2EasyPower
Software. ESA.
3 "Inrush
Current of Standard and High Efficiency Motors." Siemens Industry Automation and Drive Technologies,
Service & Support. www.automation.siemens.com.
4 IEEE
Std 1584 -2002.
5 NFPA
70E: Standard for Electrical Safety in the Workplace. 2015 Edition.
6"Dynamic
Arc-Flash Sentry" by Ray Clark. Siemens Technical Journal.
Siemens Industry, Inc.
5300 Triangle Parkway
Norcross, GA 30092
1-800-964-4114
www.usa.siemens.com/mcc
Order No. CCWP-DASMC-0616
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