Transcript Impulsive Transients and Metal Oxide Varistors (MOVs)

Surge Protection Devices
By: Stelios Ioannou
George Bolos
Definition of Power Quality
• Power Quality is measured at end-user side.
• Good power quality: any electrical device at the
end-user side performs as expected and
intended.
• Poor power quality: If any electrical device
misbehaves as a result of fluctuations in voltage
waveform magnitude, frequency, harmonic
distortion, symmetry, or even discontinuity in
supply, then power quality is said to be “poor”.
Main Power Quality
Problems
•
•
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•
•
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•
Voltage Sags
Micro-Interruptions
Long Interruptions
Voltage Spikes
Voltage Swells
Voltage Unbalance
Harmonic Distortion
Power Quality Problems
Facts
Voltage
Variations, 11.0
Oscillatory
Transients, 49.5
88.5% of PQ Problems
are Caused due to
Transients.
Black-outs, 0.5
Lightning
Transients, 39.5
Source: REO, Power Quality Facts. Online Posting: www.reo.co.uk, March 21, 2005.
According to EPRI
(Electric Power Research
Institute):
• In 1999 power sags, surges and transients cost
US industry over $50B in downtime.
• In 2000 the figure doubled to over $100B.
• In 2001 related downtime doubled again to
$200B.
• By comparison, the 2 day NE USA blackout of
2003 is estimated to cost the
US economy $17B.
Transients and AC Power
Power line transient voltage levels can be in excess of 10kV
approximately compared with an office block in town which can expect
levels of 3kV.
IEEE Definitions of Transients (Std.4-1995)
Open-Circuit Voltage Waveform:
- Front Time: 1.2uS ± 0.36uS
-Decay Time (Duration): 50uS ± 10uS
Short-Circuit Current Waveform:
- Front Time: 8uS (+1uS, -2.5uS)
- Duration: 20uS (+8uS, -4uS)
Transients Impact On
Devices
Impact to Electronic Loads
Circuit Board Failure
Yes
-----
Yes
Data Transmit Errors
Yes
Yes
Yes
Memory Scramble
Yes
Yes
Yes
Hard Disk Crash
Yes
-----
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SCR Failure
Yes
-----
-----
Process Interrupt
Yes
Yes
Yes
Power Supply Failure
Yes
-----
Yes
Program Lock Up
Yes
Yes
Yes
Source: Dranetz handbook of Power Quality.
Surge Protection Devices
surge arresters, transient voltage surge
suppressors (TVSS)
– Surge Diverters
– Surge Suppressors
Technology Profiles
Surge Diversion
Surge Suppression
Power Line
Filter
Load
Load
Protector
Power Line
Surge Suppression Profile
Source: Zero Surge Inc., “Surge Removal Filters”. Online
Posting: www.zerosurge.com, March 21, 2005.
Surge Suppression
Waveforms
Attenuated Output.
Source: Zero Surge Inc., “Surge Removal Filters”. Online
Posting: www.zerosurge.com, March 21, 2005.
Surge Diverters
100mA
50mA
0A
-50mA
-100mA
-8.0V
-I(D2)
-6.0V
-4.0V
-2.0V
0V
2.0V
4.0V
V_V1
Ideal V-I Clamping Characteristics.
6.0V
8.0V
Surge Diverters Devices and
Applications
• Zener Diodes: Ideal clamping characteristics but
poor energy limitations.
• Crowbars: High energy capabilities, but power
follow problem.
• Metal Oxide Varistors (MOV): low stand-by
currents, high short-circuit current capabilities (α
diameter) , wide range of operating voltage (α to
thickness), energy is evenly distributed on the
volume of the MOV.
Surge Diverter Waveforms
MOV Clamps a 1000V Transient Voltage to 400V and a Current of 344A.
Common Question
Q: 400 volts let-through voltage, wouldn’t that
damage an electronic device operating at
120V?????
A:
• 400 volts is peak value, whereas 120VRMS (170V
peak).
• The duration of the let-through voltage is less
than 100 us.
CBEBA Curve
167 us
Comparison
Surge Diverters
Surge Suppressors
• Ground
Contamination.
• MOV is sacrificial
element.
• Attenuation of Data.
Surge Protection Devices
Classification And Certification
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Performance
Reliability
Mode of Suppression
Underwriters Laboratories Inc.
(www.ul.com)
Performance
• Class 1 products have suppressed voltage
ratings of 330 volts. Under specified test
conditions, at any transient voltage level,
their measured suppressed voltages are
330 volts or less.
• Class 2 products have suppressed voltage
ratings of 400 volts.
• Class 3 products have ratings of 500 volts.
Reliability
• Grade A products must be certified to have
passed 1000 surges of 6000 volts and
3000 amperes without failure.
• Grade B products must pass 1000 surges
of 4000 volts and 2000 amperes.
• Grade C products must pass 1000 surges
of 2000 volts and 1000 amperes.
Mode of Suppression
• Mode 1 products protect the ground by not
diverting surge energy to it.
• Mode 2 products contaminate the ground
wire.
Price Range
Surge suppressors (Class A, Grade 1, Mode 1):
• 7.5A: $125
• 15A: $169
• 20A: $249
Surge Diverters (Only Performance Data is available):
• Class A: approximately $30
• Class D: approximately $9.99