Dynamic Arc Flash Reduction System

www.usa.siemens.com/mcc
Dynamic Arc Flash Reduction System
and its application in motor control centers
White Paper
Author:
Pablo Medina
Product Manager, tiastar MCC
Executive Summary
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. In response to safety
needs and to fulfill these standards, Siemens has developed new technologies to address
the issue of arc flash, and help mitigate its risk. This paper will explore the capabilities of
the Dynamic Arc Flash Sentry (DAS), 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 parameters (A and B), that allow the operator to switch back and forth from a normal
operating mode to a maintenance mode. The maintenance mode (Parameter B) reduces the
instantaneous trip setting of the WL main 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
A white paper issued by: Siemens.
© Siemens Industry, Inc. 2013. All rights reserved.
White paper | Dynamic Art 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 breaker
and numerous feeder 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-5
20 A
BUS-8
4
BUS-7
kV
PNL
12 5 k VA
0.
2
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 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.
A white paper issued by: Siemens.
© Siemens Industry, Inc. 2013. All rights reserved.
White Paper
|
Dynamic Arc Flash Reduction System
|
3
July 1, 2009
White paper | Dynamic Art Flash Reduction System
This MCC configuration will serve as the basis for this
example. To properly coordinate the breakers controlled in
the MCC with the main 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.
.5 .6 .8 1
1000
700
500
400
300
2
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 breaker.
Figure 2 shows the TCCs of 4 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
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
BL-2
Siemens (Std)
LXD6
Frame = 600A(500-600T)
Trip = 600
Inst = 3 (3800A)
BL-1
Siemens ETU 776 L(SIG)
Frame = 1600(I^2T)
Plug = 1600
Cur Set = 1 (1600A)
LT Band = 15 sec
STPU = 6510 (6510A)
ST Delay = 0.32
STPU I²t = Out
Inst = 65000A
200
100
70
500
400
300
200
100
70
BL-4
Siemens (Std)
HFD6
Frame = 250A(225-250A)
Trip = 225
Inst = Fixed (1800A)
50
40
30
20
20
10
10
7
7
5
4
3
5
4
3
2
2
BL-5
Siemens ETU 776 L(SIG)
Frame = 800(I^2T)
Plug = 800
Cur Set = 0.8 (640A)
LT Band = 5 sec
STPU = 4000 (4000A)
ST Delay = 0.097
STPU I²t = Out
1
.7
.5
.4
.3
1
TIME IN SECONDS
TIME IN SECONDS
50
40
30
3 4 5 6 7 8 9 10000
1000
700
.7
.5
.4
.3
.2
.2
.1
.1
.07
.07
.05
.04
.03
Normal Operation
Parameter A
.05
.04
.03
.02
.01
.5 .6 .8 1
.02
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
CURRENT IN AMPERES X 10 AT 480 VOLTS
FigureMode
2 – TCC of Parameter A – Normal Operating Mode
Figure 2. TCC of Parameter A – Normal Operating
A white paper issued by: Siemens.
© Siemens Industry, Inc. 2013. All rights reserved.
.01
3 4 5 6 7 8 9 10000
White paper | Dynamic Art Flash Reduction System
As you can see in Figure 2, the WL breaker is selectively
coordinated with the devices downstream from it. The WL
main has a typical instantaneous trip time of 0.32 seconds
at 65kA. The next step is to run an arc flash hazard analysis
across the system to determine the calculated risk of
working on this MCC. By inducing a fault, the arc flash
boundary, the incident energy, and proper personal
protective equipment (PPE) can be calculated based on
IEEE 1584 and NFPA 70E standards.
Figure 3 shows the conditions that appear at the MCC
when a fault is sent to the bus in MCC1. The incident
energy is calculated to be 24.4 cal/cm2 and a PPE level #3.
This level of PPE would require the qualified personnel to
wear flame resistant clothing and equipment, as well as
an arc flash suit, all with a minimum arc rating of 25.
Hazard/Risk
category
0
1
2
3
4
As the PPE level increases, the material can become
increasingly bulky and hot, leading to uncomfortable
work conditions for any personnel. This figure 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.
So how can we resolve this problem? The goal would be
to reduce the arc flash risk by lowering the amount of
incident energy of the system. This is done by reducing
the clearing time of the fault, which then makes a safer
environment. This solution lies in Dynamic Arc Flash
Sentry Technology.
Clothing description
Nonmelting, flammable materials (i.e., untreated cotton,
wool, rayon, or silk, or blends of these materials) with a
fabric weight at least 4.5 oz/yd2
Arc-rated FR shirt and FR pants or FR coverall
Arc-rated FR shirt and FR pants or FR coverall
Arc-rated FR shirt and pants or FR coverall, and arc flash
suit selected so that the system arc rating meets the
required minimum
Arc-rated FR shirt and pants or FR coverall, and arc flash
suit selected so that the system arc rating meets the
required minimum
Required minimum arc
rating of PPE [cal/cm 2]
N/A
4
8
25
40
Table 1. Protective Clothing Characteristics from Table 130.7(C)(11), NFPA 70E, 200
MCC BUS
112.7” AFB
24.4 cal / cm² @ 18"
#3 @ 18”
Siemens HFD6
250/225
Siemens LXD6
600/600
Figure 3. Art Flash in Parameter A
Siemens 1600L
1600/1600
Figure 3 – Arc Flash in Parameter A
A white paper issued by: Siemens.
© Siemens Industry, Inc. 2013. All rights reserved.
Siemens 800L
800/640
White paper | Dynamic Art 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
.5 .6 .8 1
1000
2
dual protection capability of the ETU776 trip unit
previously mentioned. So, lowering the instantaneous
trip settings of the WL 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
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
700
500
400
300
200
3 4 5 6 7 8 9 10000
1000
700
BL-1
Siemens ETU 776 L(SIG)
Frame = 1600(I^2T)
Plug = 1600
Cur Set = 1 (1600A)
LT Band = 3 sec
STPU = 6510 (6510A)
ST Delay = 0.32
STPU I²t = Out
Inst = 10000A
BL-2
Siemens (Std)
LXD6
Frame = 600A(500-600T)
Trip = 600
Inst = 3 (3800A)
500
400
300
200
100
100
70
70
50
40
30
50
40
30
BL-4
Siemens (Std)
HFD6
Frame = 250A(225-250A)
Trip = 225
Inst = Fixed (1800A)
20
10
10
7
7
5
4
3
5
4
3
2
2
BL-5
Siemens ETU 776 L(SIG)
Frame = 800(I^2T)
Plug = 800
Cur Set = 0.8 (640A)
LT Band = 5 sec
STPU = 4000 (4000A)
ST Delay = 0.097
STPU I²t = Out
1
.7
.5
.4
.3
1
.7
.5
.4
.3
.2
.2
.1
.1
.07
.05
.04
.03
TIME IN SECONDS
TIME IN SECONDS
20
.07
Maintenance Operation
Parameter B
.05
.04
.03
.02
.01
.5 .6 .8 1
.02
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
CURRENT IN AMPERES X 10 AT 480 VOLTS
Figure 4. TCC of Parameter B – Enhanced Safety
Mode
Figure
4 – TCC of Parameter B – Enhanced Safety Mode
A white paper issued by: Siemens.
© Siemens Industry, Inc. 2013. All rights reserved.
.01
3 4 5 6 7 8 9 10000
White paper | Dynamic Art 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
breaker. The TCC for Parameter B is displayed in Figure 4.
As can be seen, the WL main overlaps the WL feeder 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.
In this example, only the instantaneous pickup was
reduced between Parameter A and B, keeping all other
trip unit and main breaker settings the same. When an
electrical fault is applied to the MCC1 bus in Parameter B,
the difference can be seen.
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.
It also shows a reduction in the required PPE level to #1.
The arc flash boundary is reduced to 27.2 inches away
from the MCC.
MCC BUS
27.2” AFB
3.0 cal / cm² @ 18"
#1 @ 18”
Siemens 1600L
1600/1600
Siemens HFD6
250/225
Siemens LXD6
600/600
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.
Figure 5 – Arc Flash in Parameter B
A white paper issued by: Siemens.
© Siemens Industry, Inc. 2013. All rights reserved.
Siemens 800L
800/640
White paper | Dynamic Art 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 breaker, with the instantaneous pickup being reduced.
This greatly reduces the incident energy of a potential arc
flash and creates a safer environment.
By switching from Parameter A to B, the DAS allows a
temporary overlapping of the main breaker with a feeder
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 1 second, this value is still well below the
instantaneous pickup of the main circuit breaker at 10kA.
.5 .6 .8 1
1000
700
2
CURRENT IN AMPERES X 10 AT 480 VOLTS
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
BL-2
Siemens (Std)
LXD6
Frame = 600A(500-600T)
Trip = 600
Inst = 3 (3800A)
This leads to the second and more realistic point of
understanding the temporary overlap of the main breaker
with a feeder. 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 can not 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.
.5 .6 .8 1
1000
2
CURRENT IN AMPERES X 10 AT 480 VOLTS
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
700
3 4 5 6 7 8 9 10000
1000
700
BL-1
Siemens ETU 776 L(SIG)
Frame = 1600(I^2T)
Plug = 1600
Cur Set = 1 (1600A)
LT Band = 3 sec
STPU = 6510 (6510A)
ST Delay = 0.32
STPU I²t = Out
Inst = 10000A
BL-2
Siemens (Std)
LXD6
Frame = 600A(500-600T)
Trip = 600
Inst = 3 (3800A)
200
200
100
100
100
70
70
70
50
40
30
50
40
30
20
20
20
10
10
10
10
7
7
7
7
5
4
3
5
4
3
5
4
3
5
4
3
100
70
50
40
30
BL-4
Siemens (Std)
HFD6
Frame = 250A(225-250A)
Trip = 225
Inst = Fixed (1800A)
2
2
BL-5
Siemens ETU 776 L(SIG)
Frame = 800(I^2T)
Plug = 800
Cur Set = 0.8 (640A)
LT Band = 5 sec
STPU = 4000 (4000A)
ST Delay = 0.097
STPU I²t = Out
1
1
20
2
BL-5
Siemens ETU 776 L(SIG)
Frame = 800(I^2T)
Plug = 800
Cur Set = 0.8 (640A)
LT Band = 5 sec
STPU = 4000 (4000A)
ST Delay = 0.097
STPU I²t = Out
1
200
50
40
30
BL-4
Siemens (Std)
HFD6
Frame = 250A(225-250A)
Trip = 225
Inst = Fixed (1800A)
2
500
400
300
1
.7
.7
.5
.4
.3
.5
.4
.3
.2
.2
.2
.2
.1
.1
.1
.1
.07
.07
.07
.05
.04
.03
.05
.04
.03
.02
.02
.7
.5
.4
.3
.05
.04
.03
Normal Operation
Parameter A
.02
.01
.5 .6 .8 1
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
.01
3 4 5 6 7 8 9 10000
CURRENT IN AMPERES X 10 AT 480 VOLTS
.7
.5
.4
.3
.07
Maintenance Operation
Parameter B
.01
.5 .6 .8 1
.05
.04
.03
.02
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
CURRENT IN AMPERES X 10 AT 480 VOLTS
Figure 6. Parameter A and Parameter B comparison
Figure 6 – Parameter A and Parameter B comparison
A white paper issued by: Siemens.
© Siemens Industry, Inc. 2013. All rights reserved.
TIME IN SECONDS
200
TIME IN SECONDS
500
400
300
BL-1
Siemens ETU 776 L(SIG)
Frame = 1600(I^2T)
Plug = 1600
Cur Set = 1 (1600A)
LT Band = 15 sec
STPU = 6510 (6510A)
ST Delay = 0.32
STPU I²t = Out
Inst = 65000A
TIME IN SECONDS
500
400
300
500
400
300
TIME IN SECONDS
3 4 5 6 7 8 9 10000
1000
700
Even with multiple devices and other loads running, a very
high current spike would need to exist in order to trip the
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.
.01
3 4 5 6 7 8 9 10000
The Dynamic Arc Flash Sentry has been available in low
voltage switchgear for some time. It has recently become
available in Siemens new Arc Sentry 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.
2) EasyPower 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 Work
place. 2009 Edition.
6) ”Dynamic Arc-Flash Sentry” by Ray Clark. Siemens
Technical Journal.
Siemens Industry, Inc.
3333 Old Milton Parkway
Alpharetta, GA 30005
www.usa.siemens.com/mcc
All rights reserved. All trademarks used are
owned by Siemens or their respective owners.
A white paper issued by: Siemens.
© Siemens Industry, Inc. 2013. All rights reserved.
Originally published 2009.
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