Download ReadingTCCs and OCPD open time

4/18/2012
Some of these slides excerpted from
Chapter
1
OVERLOAD EXAMPLE
Normal current flows for an alternating 60-hertz circuit.
When an overload occurs, the magnitude of the current increases.
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2
SHORT‐CIRCUIT CURRENT: SYMMETRICAL
The fault is symmetrical when the current has a wave shape that has equal
magnitudes above and below the zero current axis.
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SHORT‐CIRCUIT CURRENT: ASYMMETRICAL
The fault is asymmetrical when the current has a wave shape that has
unequal magnitudes above and below the zero current axis.
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4
BOLTED FAULTS: THREE‐PHASE
Bolted fault condition represents solid connection
Three-phase bolted faults typically result in the highest level of fault current.
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5
ARCING FAULTS – THREE PHASE
480Y/277 V

3 / 4W
Solid Grd
A
B
C
N
Ground
2
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THREE‐PHASE ARCING FAULT
A three-phase arcing fault 0.02 seconds after a screwdriver
touched phase-to-ground
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7
TIME CURRENT CHARACTERISTIC CURVES
•
Understanding how OCPDs respond to various levels of
overcurrent (from light overloads to high level short-circuit
currents).
•
How to read time
time-current
current curves (TCCs) of an OCPD
OCPD.
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8
TIME CURRENT CHARACTERISTIC CURVES
• For 100A fuse,
different overcurrent
scenarios
• The following slides
will illustrate each
scenario
i on a ti
timecurrent curve
E
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TIME CURRENT CHARACTERISTIC CURVES
Understanding the TCC
• TCC for 100A Class J fuse (dark
solid line labeled)
• Logarithmic scales, not linear
• Horizontal axis: current axis
(amperes)
• Vertical axis: time axis (seconds)
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TIME CURRENT CHARACTERISTIC CURVES
Scenario A
Normal
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TIME CURRENT CHARACTERISTIC CURVES
Scenario B
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TIME CURRENT CHARACTERISTIC CURVES
Scenario C
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TIME CURRENT CHARACTERISTIC CURVES
Scenario D
Threshold of current-limiting range ≈ 1500A
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TIME CURRENT CHARACTERISTIC CURVES
E
Scenario E
Current-limiting
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5
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TYPICAL CLEARING TIMES FOR LV FUSES
Considerations for Fuse Clearing Times
• Maintenance generally not issue
• Can vary by fuse UL class
• Can vary by amp rating
• Can vary by vintage
16
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BRANCH CIRCUIT BREAKERS
Three Types Branch Circuit CBs
• MCCBs
• ICCBs
• LVPCBs
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17
MCCB FRAME SIZES AND AMPERE RATINGS
Molded Case Circuit Breakers
F Frame
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K Frame L Frame
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TYPICAL CB OPENING TIMES
2002 IEEE 1584 Guide for Calculating Arc Flash Hazard
Qualifier: LV CBs with instantaneous trip
EXAMPLE: 200A THERMAL MAGNETIC MCCB
1000
10
2
3 4 5 6 7 89 100
2
CURRENT IN AMPERES AT 480 VOLTS
3 4 5 6 7 89 1000 2 3 4 5 6 7 89 10000 2
3 4 5 6 7 89 100000
1000
700
700
500
400
300
500
400
300
200
200
100
100
70
70
50
40
30
50
40
30
TIME IN SECONDS
S
20
20
10
10
7
7
5
4
3
5
4
3
2
2
1
1
.7
.7
This is for
IT = 10X
.5
.4
.3
.2
TIME IN SECONDS
S
Carry Current
Continuously
.5
.4
.3
.2
.1
.1
.07
.07
.05
.04
.03
.05
.04
.03
.02
.01
.02
10
2
3 4 5 6 7 89 100
2
3 4 5 6 7 89 1000 2
3 4 5 6 7 89 10000 2
3 4 5 6 7 89 100000
.01
CURRENT IN AMPERES AT 480 VOLTS
160A
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EXAMPLE: 200A THERMAL MAGNETIC MCCB
1000
10
2
3 4 5 6 7 89 100
2
CURRENT IN AMPERES AT 480 VOLTS
3 4 5 6 7 89 1000 2 3 4 5 6 7 89 10000 2
3 4 5 6 7 89 100000
700
500
400
300
1000
700
190 s
500
400
300
200
200
100
100
70
70
50
40
30
50
40
30
20
10
10
7
7
5
4
3
5
4
3
2
2
1
1
.7
.7
This is for
IT = 10X
.5
.4
.3
.2
TIME IN SECONDS
S
TIME IN SECONDS
S
20
.5
.4
.3
.2
.1
.1
.07
.07
.05
.04
.03
.05
.04
.03
.02
.01
.02
10
2
3 4 5 6 7 89 100
2
3 4 5 6 7 89 1000 2
3 4 5 6 7 89 10000 2
3 4 5 6 7 89 100000
.01
CURRENT IN AMPERES AT 480 VOLTS
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600A
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EXAMPLE: 200A THERMAL MAGNETIC MCCB
1000
10
2
3 4 5 6 7 89 100
2
CURRENT IN AMPERES AT 480 VOLTS
3 4 5 6 7 89 1000 2 3 4 5 6 7 89 10000 2
3 4 5 6 7 89 100000
1000
700
700
500
400
300
500
400
300
200
200
100
100
70
70
50
40
30
50
40
30
20
10
10
7
7
5
4
3
5
4
3
2
2
1
1
.7
.7
This is for
IT = 10X
.5
.4
.3
.2
.1
.5
.4
.3
.2
.1
.07
.07
.05
.04
.03
.05
.04
.03
0.018s
.02
.01
TIME IN SECONDS
S
TIME IN SECONDS
S
20
10
2
3 4 5 6 7 89 100
.02
2
3 4 5 6 7 89 1000 2
3 4 5 6 7 89 10000 2
3 4 5 6 7 89 100000
.01
CURRENT IN AMPERES AT 480 VOLTS
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10,000A
TYPES OF OCPDS – CIRCUIT BREAKERS
•
2000A CB with:
o short-time delay
and
o instantaneous override set at
12X
•
When MCCBs and ICCBs have
short-time delays, an
instantaneous override is
necessary to protect the CB.
0.23s
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DIFFERENT TYPES OF CBS
• CB curve on the right is a low
voltage power circuit breaker
equipped with a short-time
delay and no instantaneous
trip.
• CB curve on left has an
instantaneous trip.
0.18s
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NJATC Code and Practices 3 Workbook Lesson 4 - Types of OCPDs—Circuit Breakers
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10
2
700
3
3 4 5 6 7 89 100
2
500
400
300
Restraint
signal
1
CURRENT IN AMPERES AT 480 VOLTS
3 4 5 6 7 89 1000 2 3 4 5 6 7 89 10000 2
2
3 4 5 6 7 89 100000
1200A
500
400
300
200
200
400A
100
70
100
70
50
40
30
50
40
30
20
20
175A
Restraint
signal
TIME IN SECONDS
10
2
7
10
7
5
4
3
5
4
3
2
2
1
1
.7
.7
.5
.4
.3
.5
.4
.3
.2
3
CB3 Trips
Instantaneously
X Fault Here
1000
700
.2
0.40s
.1
.07
.05
.04
.03
.1
.07
.05
.04
.03
.02
.01
TIME IN SECONDS
1000
1
.02
10
2
3 4 5 6 7 89 100
2
3 4 5 6 7 89 1000 2
3 4 5 6 7 89 10000 2
3 4 5 6 7 89 100000
.01
CURRENT IN AMPERES AT 480 VOLTS
When there is a fault on the loadside of CB3, CB3 opens instantaneously and
sends a signal to CB 2 and CB1 to hold off (short-time delay).
TYPICAL OPENING TIMES FOR SOME CIRCUIT BREAKERS
150A (F Frame, Thermal Mag): 0.02 sec or less in instantaneous range
400A (J & K Frame, Thermal Mag or Elect Trip)
0.02 sec or less in instantaneous range
(Short time delay available up to instantaneous override of 10X)
Zone selective interlocking available 400A frame and above (0.04
sec.)
600A (L F
Frame, Th
Thermall Mag,
M
El t Trip
Elect
T i or Optimum
O ti
Trip
T i Unit)
U it)
0.02 sec or less) in instantaneous range (typically 10X max)
(Short time delay available up to instantaneous override of 10X)
1200A (N Frame, Elect Trip)
0.03 sec or less in instantaneous range (typically 8X max)
(Short time delay available up to instantaneous override of 8X)
2500A (R Frame, Elect Trip)
0.05 sec or less in instantaneous range (typically 10X max)
(Short time delay available up to instantaneous override of 10X)
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TYPICAL OPENING TIMES FOR SOME CIRCUIT BREAKERS
Current Limiting Circuit Breaker (Both Types):
(Current-Limiting CB must be tested, listed, and marked as such)
100A Current-R-Limiter (Slot motor design):
0.03 cycles or less
1/2 cycle or less about 20,000A or more
400A Current-R-Limiter (Slot motor design):
0.03 cycles or less
1/2 cycle or less about 30,000A or more
100A Tri-Pac (fused limiter design):
0.017 cycles or less
1/2 cycle or less about 7000A or more
400A Tri-Pac (fused limiter design):
0.017 cycles or less
1/2 cycle or less about 10,000A or more
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TYPICAL OPENING TIMES FOR SOME CIRCUIT BREAKERS
Insulated Case Circuit Breaker (SPB w/Digitrip Unit):
w/short time delay - Up to 30 Cycles, until to instantaneous
override.
w/instantaneous
/i t t
override
id - 0.05
0 05 sec (3 cycles)
l )
Instantaneous override:
400-800:
25kA
1200:
35kA
1600-3000:
35-51kA
4000-5000:
65-85kA
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©2011
TYPICAL OPENING TIMES FOR SOME CIRCUIT BREAKERS
Low Voltage Drawout Circuit Breaker (DS w/Digitrip Trip
Unit):
w/out Instantaneous Trip - Up to 30 Cycles, depending
upon the short time delay setting.
w/Instantaneous Trip (no short time delay): 0.07 sec
(between 4-5 cycles)
w/fused limiter (DSL): half cycle or less (in current limiting
range, fault would need to be approx 12-15 times limiter
rating)
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TYPICAL OPENING TIMES FOR SOME CIRCUIT BREAKERS
Considerations for CB Opening Times
• Depends on condition of maintenance
• Can vary by manufacturer
• Can vary by type
• Can vary by frame size
• Can vary on options and settings
• Can vary by vintage
• Older circuit breakers may be slower operating
designs (even if CB is in original operation condition)
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