Effects of Voltage Sags on Industrial
Equipment
Mark Stephens, PE
Manager
Industrial Studies
Electric Power Research Institute
942 Corridor Park Blvd
Knoxville, Tennessee 37932
Phone 865.218.8022
mstephens@epri.com
Voltage Sag Test Equipment:
Porto-Sag
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2
Versions of the Porto-Sag
30 Amp Units
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100 Amp Units
3
200 Amp Units
Porto-Sag Software Interface
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4
Utility/Equipment Interface:
Voltage Sags
• Most Important Power Quality Variation Affecting Sensitive
Equipment
• Characterized by Magnitude (here, 50% of Nominal) and
Duration (here, 4 Cycles, 1 Cycle = 1/60 sec)
Duration (4 Cycle)
1
0.5
0
0
1
2
3
4
5
-0.5
-1
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Magnitude (50% of nominal)
5
6
7
8
Example Equipment Tolerance Curve
Programmable Logic Controller, 78%
15-20 events
120 Vac DPDT Relay, 75%
24 Vdc Instrument Power Supply, 70%
10-15 events
9.2 cycles
5-10 events per
site per year
37 cycles
0-5 events per
site per year
2 cycles
Percent of Nominal Voltage %
Sag Rate Probabilities vs Equipment System Test
Time (cycles)
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Voltage Sag Impacts on
• PCs
• Electronic Lighting
• Relays and Contactors and Motor Starters
• DC Power Supplies
• PLC Based Control Systems
• Variable Frequency Drives
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Switch Mode Power Supply Voltage
Sag Tolerance (100% Load)
All Power
Supplies At
100% Load.
Source: EPRI System Compatibility Task 2 Final
Report:Performance and Design Evaluation of Switch-Mode Power
Supplies - AC Interface Issues, July 1995.
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13 Power Supplies Models in
Sample Data Set
Standard Deviation: 2.65
Cycles, 9.27 %Vnom
Dell Dimension 8250
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Compaq Deskpro 2000
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HP Netserver LP1000r
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Impact on Lighting
PQ Issue:
Some HID metal halide
lamp/ballast systems are
prone to blackouts due to
voltage sags from the normal
operation of large electric
loads.
Restart times may take as long
as 10-15 minutes.
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Improving Immunity of
Metal Halide Lamps
• Use magnetic-regulator ballast to
increase metal halide lamp immunity to
sags
• For critical lighting applications install
non-HID lighting such as tungsten
halogen or use UPS
• Isolate lighting systems from sagcausing loads
• Consider installing instant-restrike metal
halide lamps
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13
Percent of Nominal Supply Voltage
Susceptibility of
HPS Lamps vs Age
80
60
40
Non-Regulating Ballast
Auto-Regulating Ballast
20
Magnetic-Regulating Ballast
0
New Lamp
0
Old Lamp
6,000
12,000
18,000
HPS Lamp Age (Hours of Use)
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24,000
Relays, Contactors & Motor Starters
• Relays
– Auxiliary device to switch control circuits, large
starter coils and light loads
• Contactors
– Electromagnetically operated switches that provide
a safe and convenient means for connecting and
interrupting power circuits
• Starters
– Same function as contactors but also provides
overload protection
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15
Finding the Weakest Link
Main
Contactor
2 cycles,
43%
Contactor
2 cycles,
49%
EMO Relay
(next gen)
0.5 Cycles,
78%
EMO
Relay
1 cycles,
52%
EMO Relay
1 Cycle
45%
EMO Relay
0.5 cycles,
61%
Not Shown:
EMO Relay 1 Cycle, 38%
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Voltage Tolerance Curve:
Ice Cube Relay
AB 120V AC Relay Ride-Through Curve
% of nominal V oltag
100
80
60
40
20
0
0
10
20
30
40
Cycle
What happens during a voltage sag down to 50% of nominal
for 5 cycles ?
3
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Voltage Tolerance Curve:
Small Contactor
Cutler Hammer NEMA Size 1 Starter
Ride-Through Curve
% of nominal
Voltage
100
80
60
40
20
0
0
10
20
Cycle
What happens during a voltage sag down to
50% of nominal for 5 cycles ?
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30
Hard-Wired Motor Control Circuits
3 WIRE CONTROL WITH FUSED
CONTROL CIRCUIT TRANSFORMER
AND CONTROL RELAY
3 WIRE CONTROL WITH FUSED
CONTROL CIRCUIT TRANSFORMER
L2
L1
L1
M
CR
PRI.
1
PRI.
FUI
1
FUI
XI SEC X2
STOP
2
START
M
L2
XI SEC X2
M
3
OL
STOP
GROUND
2
START
3
M
CR
GROUND
CR: AB 120V AC ‘Ice-Cube’ Relay
M: Cuttler Hammer Nema Size 1 Starter
Which Circuit is more susceptible to voltage sag ?
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OL
Emergency Off (EMO) Circuit
(Simplified)
Q1. What happens if the EMO relay or Main
Contactor are extremely vulnerable to voltage sags?
Q2. What if the plant voltage is low?
Q3. What if the transformer rated output voltage does
not match the relay and contactor?
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Impact of MCR
Notes:
1.0 Digital Meter
Jumpers must be
set for 120VAC.
What happens
when an
operator hits the
E-Stop?
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Industrial Load Bank
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Composite Voltage Sag Ride-Through of
General Purpose Relays
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DC Power Supplies
• DC Power Supplies Used for
– Instrumentation
– Control Voltage
– PC Power
– PLC P/S Power
– DC Relays,
Contactors,Motor Starters
• PQ Performance Varies based
on topology and loading
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Switch Mode Power Supply Voltage Sag Tolerance
(100% Load)
All Power
Supplies At
100% Load.
Source: EPRI System Compatibility Task 2 Final
Report:Performance and Design Evaluation of Switch-Mode Power
Supplies - AC Interface Issues, July 1995.
© 2009 Electric Power Research Institute, Inc. All rights reserved.
25
13 Power Supplies Models in
Sample Data Set
Standard Deviation: 2.65
Cycles, 9.27 %Vnom
Relative Power Supply Response at 100% Loading
Ride-Through for
Single-Phase Voltage
Sags
Curve Represents
when DC output
begins to deviate more
than 5% from normal
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Programmable Controllers
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PLC Fundamentals Block Diagram
SYSTEM INPUTS
PROCESSOR
PB
SYSTEM
OUTPUTS
PLC MEMORY
AND
CONTROL
PROGRAM
C
R
LS
POWER SUPPLY
EXTERNAL POWER SOURCE
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MS
CR
SOL
Arrangement of Remote I/O Racks
Remote I/O
Local I/O
Communication
Power
Input
Remote I/O
Communication
Input
Output
Processor
Power
PLC
Output
Master PLC
Hopper
On/Off
Control
Motor
Programming Unit
Pushbutton
Drum
Sensor
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AC Powered PLC Power Supply
From Typical PLC Literature:
“
”
What that means to you:
- Oversensitive Power Supply
- Customer Process Shutdown due to voltage Sags
What can be done about this?
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PLC System Wiring (Typical)
E-Stop
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PLC Test Results – Response 1
PLC Shuts down based on incoming AC Voltage before
Control System is affected.
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PLC Test Results – Response 2
PLC Shuts down on based on power supply DC Bus Voltage.
What happens if PLC has fewer I/O Cards?
What happens if PLC has more I/O Cards?
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Effect of Voltage Sags on Adjustable Speed Drives
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AC PWM Drive
INPUT
SECTION
ENERGY
STORAGE
SECTION
Rectifier
Diode Bridge
DC Bus
Capacitor
800
OUTPUT
SECTION
IGBT
Inverter
800
700
600
600
600
400
200
0
-200
500
400
300
65
70
75
80
85
Time (mS)
Source Voltage
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0
60
0
-400
-600
100
-600
200
-200
200
-400
-800
60
Voltage (V)
Voltage (V)
Voltage (V)
400
65
70
75
80
85
-800
60
65
70
75
80
85
Time (mS)
Time (mS)
DC Bus Voltage
35
Motor Input Voltage
Example Response of ASD to Short Interruption
A Two-Cycle Interruption
Motor Current
ASD Input Voltage
0
10
20
30
40
Cycle
50
60
0
10
30
40
Cycle
50
60
50
60
Motor Speed
ASD DC Bus Voltage
ASD
20
Motor
0
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10
20
30
40
Cycle
36
50
60
0
10
20
30
40
Cycle
Voltage Sag Impact on ASD
dc Link
Rectifier
Inverter
Inverter
dc Bus
Voltage
660V
420V
trip level
Drive Trips on Undervoltage
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Induction
Motor
Example Drive 1
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Example Drive 2
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Example Drive 3
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Why Do ASDs Trip During Single-Phase
Voltage Sags?
•
VSI AC Drive During Normal Operating Conditions
•
(Van = 100%, Vbn = 100%, Vcn = 100%)
DC Bus Voltage (in Volts)
DC Bus Voltage
Bridge Rectifier Output
700
600
500
400
300
200
100
0
0
0.005
0.01
Time (in Seconds)
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0.015
0.02
Why Do ASDs Trip During Single-Phase
Voltage Sags?
•
VSI AC Drive During a Single-Phase Sag
•
(Van = 100%, Vbn = 100%, Vcn = 0%)
DC Bus Voltage (in Volts)
DC Bus Voltage
Bridge Rectifier Output
Trip Level
700
600
500
400
300
200
100
0
0
0.005
0.01
Time (in Seconds)
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0.015
0.02
Line-Side and Motor-side Contactors
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ASD Enable Signal
Contact on
120 V AC relay
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Latched Start/Stop Control
(3-Wire Control Scheme)
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What About Your Plant?
Active Demo Using EPRI’s Power Quality
Investigator Software
PQ Investigator
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PQ Investigator
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