characteristics of transients voltages affecting equipment
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CHARACTERISTICS OF TRANSIENT
VOLTAGES AFFECTING CUSTOMER
EQUIPMENT
Presented at
TRANSIENT VOLTAGE SURGE SUPPRESSION
IN LOW VOLTAGE AC POWER SYSTEMS
Workshop
Santa Clara, California
May 12-13, 1992
Mark McGranaghan
ELECTROTEK Concepts, Inc
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Characteristics of Transient Voltages Affecting Customer Equipment, page 2
Electrotek Concepts, Inc.
OBJECTIVES
Provide examples of transient voltage characteristics
Identify important causes of transients in low voltage
systems
Identify impacts of transient voltages on equipment
Describe solutions to transient voltage problems
Note:
The information in this presentation was developed during
case studies sponsored by the Electric Power Research
Institute and Pacific Gas & Electric Company
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Characteristics of Transient Voltages Affecting Customer Equipment, page 3
Electrotek Concepts, Inc.
IMPORTANT CAUSES OF TRANSIENT VOLTAGES
Transients Initiated on the Utility System
Lightning
Capacitor Switching
Line/Cable Switching
Transformer Switching
Current Limiting Fuse Operation
Transients Initiated in the Low Voltage System
Capacitance Switching
Current Interruption (motors, etc.)
Power Electronics Operation
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Characteristics of Transient Voltages Affecting Customer Equipment, page 4
Electrotek Concepts, Inc.
LIGHTNING
Lightning transients are caused by a discharge of currentfrom the struck conductor or shield wire to ground.
The lightning stroke current as a very high rate-of-rise
(e.g. 1-10 microseconds).
A voltage transient results from the lightning stroke
current flowing through the surge impedance of the
transmission line - this will generally result in a flashover
or an arrester operation.
Example lightning stroke current:
-25
-20
-15
-10
-5
0
0 20 40 60 80 100 120 140
Current
(kA)
Time (uSec)
Lightning Stroke Current
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Characteristics of Transient Voltages Affecting Customer Equipment, page 5
Electrotek Concepts, Inc.
PROBLEM: LOW SIDE CURRENT SURGES CAUSED BY
LIGHTNING TRANSIENT
SOLUTION: LOW VOLTAGE MOV ARRESTERS ATTRANSFORMER SECONDARY AND AT
CUSTOMER SERVICE ENTRANCE
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Characteristics of Transient Voltages Affecting Customer Equipment, page 6
Electrotek Concepts, Inc.
CAPACITOR SWITCHING
Normal capacitor energizing on a power system is
characterized by a step change in the voltage followed by
a transient oscillation in the range 300-1000 Hz.
The magnitude of the transient should be in the range of
1.3-1.8 times the normal peak voltage.
Important parameters affecting this transient include:
Capacitor Size/Location
Switching Device Characteristics (Resistors,Reactors)
Size/Status of Other Capacitors
Short Circuit Capacity at the Substation/at the
Cap Bank
System Load Characteristics
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Characteristics of Transient Voltages Affecting Customer Equipment, page 7
Electrotek Concepts, Inc.
Normal capacitor energizing on the distribution system:
November 19, 1991 at 06:07:56 PQNode LocalRGE_BETAPhase A VoltageWave Fault
Trigger
0 10 20 30 40 50 60 70
-1.5
-1
-0.5
0
0.5
1
1.5
Time (mSeconds)
Max 1.094Min -1.280
Uncalibrated Data
Typical capacitor switching transient coupled to low
voltage system:
Voltage: Current:
April 26, 1992 at 06:15:56 PQNode LocalETKREALPhase C VoltageImpulse
Trigger
0 10 20 30 40 50
-150
-100
-50
0
50
100
150
Time (mSeconds)
Max78.25
Min-194.8
Volt-Seconds
912.8
BMI/Electrotek
April 26, 1992 at 06:15:56 PQNode LocalETKREALPhase C CurrentImpulse
0 10 20 30 40 50
-60
-40
-20
0
20
40
60
80
Time (mSeconds) BMI/Electrotek
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Characteristics of Transient Voltages Affecting Customer Equipment, page 8
Electrotek Concepts, Inc.
PROBLEM: MAGNIFIED TRANSIENTS AT CUSTOMER-
OWNED LOW VOLTAGE CAPACITOR
BANKS
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Characteristics of Transient Voltages Affecting Customer Equipment, page 9
Electrotek Concepts, Inc.
Capacitor switching transient on the distribution system:
CAPMAG> SRCA(Type 1)
0 20 40 60 80 100-60000
-40000
-20000
0
20000
40000
60000
Time (mS)
Max:Min:Avg:Abs:
RMS:
CF :FF :
48362.2-31823.418100.33182320232.8
1.572851.11781
Magnified transient at 480 Volt capacitor bank:
CAPMAG> MOVA(Type 1)
0 20 40 60 80 100-1000
-500
0
500
1000
Time (mS)
Max:Min:Avg:Abs:
RMS:CF :FF :
768.217-596.431258.266768290.9732.639421.12664
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Characteristics of Transient Voltages Affecting Customer Equipment, page 10
Electrotek Concepts, Inc.
These transients will often result in capacitor failures or failures
of electronic equipment.
Arrester energies are very high.
MOV arrester current:
CAPMAG> 480A- MOVA(Type 9)
0 20 40 60 80 100-2000
0
2000
4000
6000
8000
10000
Time (mS)
Max:Min:Avg:Abs:
RMS:CF :FF :
8138.62-4.100533.50978138449.82218.091613.4237
MOV arrester energy:
CAPMAG> MOVA(Type 9)
0 20 40 60 80 1000
500
1000
1500
2000
2500
3000
Time (mS)
Max:Min:Avg:Abs:
RMS:CF :FF :
2638.9802153.1126382378.251.109221.10456
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Characteristics of Transient Voltages Affecting Customer Equipment, page 11
Electrotek Concepts, Inc.
SOLUTION: LOW VOLTAGE CAPACITOR BANKS CAN
BE INSTALLED AS HARMONIC FILTERS TO
DETUNE THE CIRCUIT CAUSING
MAGNIFICATION
1.00
1.50
2.00
2.50
3.00
0 100 200 300 400 500 600
Voltage
(pu)
480 Volt Compensation Level (kVAr)
Compensation = Capacitors
Compensation = Filters
1500 kVA Transformer
3000 kVAr Switched Capacitor Bank
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Characteristics of Transient Voltages Affecting Customer Equipment, page 12
Electrotek Concepts, Inc.
PROBLEM: CAPACITOR SWITCHING TRANSIENTS
CAUSE NUISANCE TRIPPING OF ASDS
Transient Voltage at the 480 Volt Bus
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Characteristics of Transient Voltages Affecting Customer Equipment, page 13
Electrotek Concepts, Inc.
Drive Current:
DC Link Voltage in the ASD:
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Characteristics of Transient Voltages Affecting Customer Equipment, page 14
Electrotek Concepts, Inc.
SOLUTION: INPUT CHOKES OR ISOLATION
TRANSFORMERS ARE USUALLY
SUFFICIENT TO PREVENT DC
OVERVOLTAGES WITHIN THE ASD
600
700
800
900
1000
0 1 2 3 4 5 6 7 8 9 10 11
dcVolts
Choke Size (% on 10 kVA base)
Normal Operating Voltage
Typical Trip Level
3000 kVAr Switched Capacitor Bank
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Characteristics of Transient Voltages Affecting Customer Equipment, page 15
Electrotek Concepts, Inc.
PROBLEM: CAPACITOR SWITCHING TRANSIENTS
CAUSE FAILURE OF TAP SWITCHING
VOLTAGE REGULATOR/POWER
CONDITIONER
Transient at 480 Volt Service Entrance
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Characteristics of Transient Voltages Affecting Customer Equipment, page 16
Electrotek Concepts, Inc.
Input to Power Conditioner
Output of Power Conditioner
SOLUTION: SENSITIVE ELECTRONICS MUST BE
PROTECTED WITH APPROPRIATE SURGE
SUPPRESSION/FILTERING
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Characteristics of Transient Voltages Affecting Customer Equipment, page 17
Electrotek Concepts, Inc.
PROBLEM: CAPACITOR SWITCHING TRANSIENTS
MAGNIFIED AT OUTPUT OF ISOLATION
TRANSFORMER/FILTER COMBINATION
Many isolation transformer-type power conditioners
include a capacitor on the output to filter high frequency
transients. This capacitor can magnify capacitor
switching transients in the 300-1000 Hz range.
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Characteristics of Transient Voltages Affecting Customer Equipment, page 18
Electrotek Concepts, Inc.
LIPC Input Voltage Waveform:
LIPC Output Voltage Waveform:
SOLUTION: DO NOT USE THE CAPACITOR-TYPE
FILTERING WITH ISOLATION
TRANSFORMERS IN CIRCUITS
SUSCEPTIBLE TO CAPACITOR SWITCHING
TRANSIENTS
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Characteristics of Transient Voltages Affecting Customer Equipment, page 19
Electrotek Concepts, Inc.
TRANSIENTS CAUSED BY SWITCHING IN LOW VOLTAGE
SYSTEMS
Misoperation of Tap Switching Voltage Regulator
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Characteristics of Transient Voltages Affecting Customer Equipment, page 20
Electrotek Concepts, Inc.
Two different transients at 480 Volt locations close to
switched motor:
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Characteristics of Transient Voltages Affecting Customer Equipment, page 21
Electrotek Concepts, Inc.
Transient due to power electronics equipment current
interruption:
Transient caused by localized fault within customer
system and fuse blowing:
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Characteristics of Transient Voltages Affecting Customer Equipment, page 22
Electrotek Concepts, Inc.
Transients in a computer room that resulted in board
failures:
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Characteristics of Transient Voltages Affecting Customer Equipment, page 23
Electrotek Concepts, Inc.
Voltage Notching caused by Rectifier Switching:
Chokes or isolation transformers should be used in series
with phase controlled rectifiers (e.g. dc drives) to isolate
the notching transients from other loads.
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Characteristics of Transient Voltages Affecting Customer Equipment, page 24
El t t k C t I
Transients caused by switching operations within
customer facilities are characterized by high frequency
components.
These transients damp out quickly in the circuit.Significant protection can be obtained by using dedicated
circuits for sensitive loads.
Transient Voltage Surge Suppressors can be used to
protect sensitive loads being impacted by these
transients.
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