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5/20/2018 Effects of Voltage Sags
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The effects of voltage sags
by
Terry Chandler
Power Quality Inc/Power Quality Thailand LTD
For IEEE Hong Kong Section
May 31, 2002
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Sags or Dips?
A decrease in the nominal voltage for ashort duration.
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Standards regarding Sags
IEC 1000-4-1/11 Measurement of sags
IEEE 1159 Monitoring of Sags
IEEE P1346
ANSI C84.1
IEEE 1100
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IEEE SCC 22
Short duration variations
2.1 Instantaneous
2.1.2 Sag(Dip) 0.5 to 30 cycles 0.1 to 0.9 pu
sags (dips) have a magnitude and
duration SCC is the standard coordination committee
of IEEE
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Accepted description
Sag is a IEEE term DIP is IEC term
Sag refers to % of decrease in Voltage
IE a 20% sag is a voltage decrease to 0.8 PU
DIP refers to % of voltage remaining
IE a dip to 80% is a decrease to 0.8 PU
Is the glass half full or half empty?
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Classifying Sags (Dips)
CBEMA
100%
1 day
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Classifying sags (dips) II
ITIC (New CBEMA)
unacceptableacceptable
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Cause of Voltage sags
Faults on the distribution system
User distribution system failure
User loads
Equipment malfunction
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Faults on the distribution
system
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User equipment that can
cause sags
Copiers and laser printers
Arc welders
Motor starting
Power saws
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Welder causes voltage sag
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Voltage sag from the utility
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Semi 47 Voltage sag standard
A new standard developed by the SEMI
organization members to define thedesired minimum equipment sensitivityto voltage sags
Similar to ITIC curve in the voltage sagdomain
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ITIC Semi 47
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ITIC Semi
47
50 ms 0.2 0.5 second
20 ms
| 0.5 sec | 10 sec
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Load sensitivity to voltage
sags
Motors
Contactors that
Small 50% sag shuts down 600 hp load
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Sag indications without a PQ
meter Lights blink
Motors slow down and return to normalspeed
Computers reboot unexpectedly
Automated equipment stopsunexpectedly
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Root cause of sensitivity
Automated
Equipment
Equipment
disconnect
Ac relay
Electrical contactor on the input power
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Process sensor
Automated Equipment
Equipment
disconnect
DC relay process
sensor
With voltage sags sends shut down signal
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Emergency shutdown circuitWith voltage sag sends shutdown signal
Automated
Equipment
Equipment
disconnect
Ac relay
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DC buss sag
DC relay
AC to DC
convertor
DC to AC
invertor
AC motor
DC buss
monitor
Electroniccontrol
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Voltage imbalance sensor
voltage
unbalance
relay
AC to DC
convertor
DC to AC
invertor
AC motor
Electronic
controlDC relay
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Improving voltage sag
immunity Relay settings
DC relays Switchmode power supply configuration
oversize power supply or capacitor
Dynamic sag corrector
Connect loads phase to phase
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Voltage sense relays
Upper and lower trip points
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Ride thru device
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Sag mitigation technologies
UPS
Standby
line interactive On-Line
Dynamic voltage restorer (DVR)
Voltage Regulator
Static transfer switch
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UPS Uninterruptible Power Supplies
Battery
On-line
Standby
Flywheel
Super conductor
Super Capacitor
Fuel Cell
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On-line UPS
Battery
system
input
harmonic
filter
LoadInverter
Bypass
Rectifier
Charger
System
bypass
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Rotary UPS
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Example of rotary
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DVR
Bypass
DVR Electronics
SS Shorting Switch Inverters,
Filters, Controls
Cap Energy Storage
Isolation Isolation
To Source To Plant
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Flywheel ups
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Example of flywheel UPS
Photo compliments of Beacon.com
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Standby UPS
Battery or Flywheel
More efficient than on -line
Output meets ITIC or Semi-47 standard
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Standby UPS
Main System Container
Isolation
Transformer
Static Switch
Critical
Load
Utility
Input
up to (8) Power M odules
CB2
Output
CB1
Input
CB3
Bypass
Battery
String Battery
Charger
Inverter
Bridge
System
Control
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Example of Standby UPS
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3 phase sag
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UPS output during sag
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Conclusions
Graph compliments of WWW.powerstandards.com
Voltage sags are the #1 Power Qualityproblem
The source can be from the utility orfrom internal loads, wiring, problems etc
Solutions can be very inexpensive or veryexpensive
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The bottom line
Voltage sags are an economic or $$ problem
It requires detailed PQ data to determine ifthe solution costs $100 or $10,000,000.