IEEE Winter Meeting 2000, Singapore, 23-27 January 2000
Overview of voltage sag
mitigation techniques
Ambra Sannino
Department of Electrical Engineering
University of Palermo, Italy
Michelle Ghans Miller, Math H.J.Bollen
Department of Electric Power Engineering
Chalmers University of Technology
Gothenburg, Sweden
IEEE Winter Meeting 2000, Singapore, 23-27 January 2000
outline
• need for voltage sag mitigation
• mitigation through system improvement
• increasing equipment immunity
• installation of additional equipment
• conclusions
Ambra Sannino - University of Palermo, Italy
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IEEE Winter Meeting 2000, Singapore, 23-27 January 2000
today’s scenario
the need for power quality improvement
Factory
sensitive equipment
production lines
Automated factories use sensitive equipment
• power electronics (AC and DC drives)
• process-control electronics (computers, PLCs)
Faults in the power system can cause process interruptions
with associated costs due to loss of production, damaged
product and equipment, and other factors
Ambra Sannino - University of Palermo, Italy
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IEEE Winter Meeting 2000, Singapore, 23-27 January 2000
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different faults cause different sags
100%
Voltage
80%
50%
remote
MV networks
transmission
network
motor starting
local
MV network
fuses
interruptions
0%
0.1 s
1s
Duration
Ambra Sannino - University of Palermo, Italy
IEEE Winter Meeting 2000, Singapore, 23-27 January 2000
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from system faults to process interruptions
Faults in the utility power system:
• three-phase
• single-phase-to-ground
• phase-to-phase
Consequences at the PCC:
• voltage sags
• interruptions
Consequences on the process:
• equipment trip
• process interruption
Ambra Sannino - University of Palermo, Italy
IEEE Winter Meeting 2000, Singapore, 23-27 January 2000
improving power quality
for sensitive customers
system
improvement
mitigation
equipment
improvement of
equipment immunity
Ambra Sannino - University of Palermo, Italy
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IEEE Winter Meeting 2000, Singapore, 23-27 January 2000
mitigation through system improvement
critical factors:
improvements:
• frequency of events
• reducing the number of faults
• sag duration
• reducing the duration of faults
• sag magnitude
• changing power system layout
Ambra Sannino - University of Palermo, Italy
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IEEE Winter Meeting 2000, Singapore, 23-27 January 2000
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equipment sensitivity (1)
POWER
SYSTEM
~
~
~
SINGLE-PHASE
DIODE RECTIFIER
DC-DC
CONVERTER
DIODE RECTIFIER
low-power electronics
POWER
SYSTEM
INVERTER
AC drive
~
+
FIELD
WINDING
-
DC MOTOR
ARMATURE
WINDING
CONTROLLED
RECTIFIER
~
SINGLE-PHASE
DIODE RECTIFIER
DC drive
Ambra Sannino - University of Palermo, Italy
AC
MOTOR
IEEE Winter Meeting 2000, Singapore, 23-27 January 2000
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equipment sensitivity (2)
sag 70% magnitude, 100 ms duration
1
voltage [V]
0.8
0.6
0.4
0.2
0
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.2
time [s]
effect of a sag on a single-phase rectifier
Ambra Sannino - University of Palermo, Italy
IEEE Winter Meeting 2000, Singapore, 23-27 January 2000
equipment sensitivity (3)
sag 70% magnitude, 100 ms duration on phase C
250
voltage [V]
200
150
100
50
0
0.08
0.1
0.12
0.14
0.16
0.18
0.2
0.22
0.24
time [s]
effect of an unbalanced sag on a three-phase rectifier
Ambra Sannino - University of Palermo, Italy
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IEEE Winter Meeting 2000, Singapore, 23-27 January 2000
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improving equipment immunity
• low-power electronics: adding capacitance, improving the dc/dc
converter
• AC drives : adding capacitance, reducing the setting for the dc bus
protection
• DC drives: implementing proper control algorithms for adjusting
the firing angle of the devices according to changes in the input
voltage. Adding capacitance is not a viable option
Ambra Sannino - University of Palermo, Italy
IEEE Winter Meeting 2000, Singapore, 23-27 January 2000
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mitigation devices
• motor-generator set
• ferroresonance transformer
• electronic tap changer
• uninterruptible power supply
• static transfer switch
• series-connected voltage source converter
• shunt-connected back-up source
Ambra Sannino - University of Palermo, Italy
IEEE Winter Meeting 2000, Singapore, 23-27 January 2000
13
different sags require different solutions
100%
Voltage
80%
50%
remote
MV networks
equipment improvement
motor starting
transmission
network
local
MV network
fuses
system improvement
interruptions
0%
0.1 s
1s
Duration
Ambra Sannino - University of Palermo, Italy
IEEE Winter Meeting 2000, Singapore, 23-27 January 2000
14
conclusions
• mitigation of voltage sags requires careful inspection of
the characteristics of the process and of the nature and
origin of sag events
• the installation of mitigation devices (normally the only
choice for the customer) can be seen as a short-term
solution. The mitigation capability of these devices is mainly
limited by the energy storage capacity
• only improvement of system performance (for long, deep
sags) and of equipment tolerance (for short, shallow sags)
can solve the problem in the long term
Ambra Sannino - University of Palermo, Italy