Transcript Power Surges Causes, and Effects in a Residential Environment

POWER SURGES & THEIR
CAUSES AND EFFECTS IN
A RESIDENTIAL
ENVIRONMENT
Presented to the SFPE
January 13, 2014
Paul McCoy, P.E.
A Little About Me…
• Paul McCoy is a graduate of IIT - Electrical Engineering
• Licensed Professional Engineer in State of Illinois
• Former senior executive at ComEd
• Included close relationships with the Fire Service both in Chicago and suburban
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areas
Co-developed the ComEd Safety Village
Established first-in-nation outfitting of workforce with fire-retarding clothing
Worked extensively with the MABAS structure
Extensive “hands on” work with all classes of electrical equipment, controls and
system protection technology including trouble analysis, system analysis and project
commissioning on equipment from 480 to 765,000 volts
Includes extensive understanding of the effects of electrical contact and the human
body
• Extensive operations, operational analysis, commissioning,
and energy policy experience
• Co-founder of several industry organizations
• Currently a director or principal with several companies
Today’s Agenda
• What is a “power surge”?
• Caused by nature
• Caused by the utility or within the end-user environment
• Why are some dangerous and what causes this?
• Is there a “signature” that can be rapidly recognized?
• What kind of damage is caused?
• What should a first responder look for?
• Assessing risks
• Can they be mitigated?
• Wrap-up and questions
OK, So What Is a Power Surge?
• An elevation in service voltage
• Can be a short-lived “spike” or a series of same
• Generally lasting just a few thousandths of a second
• Longer-lived voltage elevation caused by utility equipment failure or
mis-operation
• Lasting for sizeable fractions of second or longer
• Generated from inside the home
Volt-Amp-Ohm Relationship
Surges Caused by Nature
• Lightning is the only common natural cause
• Characterized by an almost instantaneous rise in voltage
of short duration
• The steep rise in voltage (far faster than normal utility frequency)
can cause some bizarre things to happen
• It’s a function of packing substantial energy into an extremely short time
• Stories are legend about the effects on structures, electrical
equipment and humans
• All utilities protect themselves (and us) from the vast
majority of damage – but nothing is perfect
• A big factor is exactly where the lightning strike occurs
• Effects dissipate rapidly with distance so usually affects just a few
homes or businesses (per strike)
Lightning Characteristics
• Total flash duration:
• Number of strokes/flash:
• Stroke duration:
• Interstroke interval:
• Current:
• Total charge transfer:
200 - 300 ms
3–5
50 - 70 µs
60 ms
50 – 300 kA
20 – 200 C
109 – 1010 J
• Total flash energy:
• This is total cloud to ground energy
• A fraction of this is delivered to what is “struck” on the ground
Energy Causes the Damage, Not the
Voltage (Keep Remembering This)
• 4 kJ equals the energy in one gram of TNT
• 1 MJ will easily melt one pound of steel
• 2 MJ will easily vaporize that same pound of steel
Surges From the Utility Network
• Caused by switching
• Capacitors (devices that control voltage)
• Maintenance
• These are generally harmless in the context of what we are
concerned about in this discussion
• Can also be caused by your “neighbors”
• Starting and stopping of their air conditioners, etc.
• Industrial processes like welding, large air compressors, elevator
motors, and on and on
• These are also generally harmless in the context of today’s
discussion (but can be really irritating)
• Then there is the category of sustained elevated voltage,
which can cause substantial damage
Components of the Grid: Overview
Source: www.nerc.com
• The “grid” can be broken down in to four main components:
Generation, Transmission, Distribution, and Load
• This diagram is a basic overview, but does not truly illustrate the
HIGHLY interconnected nature of the transmission system.
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A Typical Local Substation
A Large In-Line Distribution Line
Regulation Installation
Some Distribution Examples
Sustained Elevated Voltage
• Voltage above normal.
• Significantly above-normal voltage will cause real
damage!
• While voltages don’t reach lightning-strike levels, the total energy
available at the home service entrance is actually considerably
larger and of longer duration
• This is almost always caused by the utility if you are a
residential customer
How Does This Happen?
• Failure of voltage regulation devices and/or controls at the
substation or on the distribution line
• Can lead to over-voltages of 10-20%
• Can cause premature appliance failure
• Can cause overheating of end-use equipment
• Or it can occur when a power line of higher voltage
contacts a line below it of lower voltage (hardware failure)
• This can raise the lower voltage line to that of the higher voltage
line for fractions of a second or longer
• This can produce voltages double or more of normal
• Internal home damage can be immediate and widespread
• “Signature” – multiple homes/businesses with damage all
at the same time
Damage That Can Occur
• Anything electronic
• If lucky, limited to power supply
• Appliances
• Control panels and compressor/motors
• HVAC
• Controls, motors, contactors
• This damaged equipment can be the source of fires if the
enclosure doesn’t contain hot material
Damage That Can Occur, Cont.
• Extremely high voltage can also cause:
• Exploding light bulbs
• Destroyed surge protectors (both plug-in and whole-house)
• Energy being dissipated is beyond rating
• Destroyed plug-in timers and dimmer switches
• Sparking outlets
• All of these have the potential to cause fire, especially if
they are near/under curtains, bedding, on rugs, under
upholstered furniture.
• Except in extreme cases, relatively modern house wiring
and the main panel will fare the best (modern wiring is
rated at 600 volts)
If You Are a First Responder
• After obvious checks for smell/smoke
• Check electronics
• Surge protectors
• Timers/dimmers
• Unless smell/smoke indicate, metal-enclosed appliances,
other metal-enclosed utilization equipment and the
main/panel may be best left to the end of your “sweep”.
First Responder Checks
• In particular look for “hidden damage”
• The bottom of surge protectors
• Hidden timers
• If any bulbs have “popped” check all the closets, crawl spaces, etc.
for any potential incipient fires
• If the house is without power, check the main panel
• If the main breaker is tripped, don’t close it without an internal
check of the main panel by someone qualified
• Evidence of wiring, main panel, outlet or wall switch
damage should be cause to require a detailed check of
house wiring and other equipment by someone qualified
• I’d have everything checked anyway (includes the entire HVAC
system)
Mitigation Measures
• For utility-induced extended high voltage there is no fool-
proof mitigation
• Surge protectors can help, but cheap ones provide little or no
protection
• Whole-house protection helps a lot.
• Can be pricey
• Be prepared for the protection to sacrifice itself to save the house
equipment – so how it is installed/mounted is important
• Here, again, you get what you pay for
• Still need point-of-use surge protection
Whole House Protection
Point-of-Use Surge Protection
• Coordinates with the whole-house unit (which has a
higher voltage clamping rating)
• Think of these working as a “waterfall”
• Adds additional energy dissipation capability
• This is a case of “you get what you pay for”
• Higher cost units usually have higher energy dissipation ratings (up
to 3500 Joules)
• What many don’t know is that surge protectors have an
expiration date (generally about 5-7 years from date of
purchase) – it’s stamped on the back
• Every surge they “clamp” takes life from the unit
• Top-of-the-line whole house units have replaceable
energy dissipation surge blocks
Conclusion
• Instances of extended high voltage are rare
• But when they occur significant damage is possible
• Damage is reduced with a good electrical installation and
quality surge protectors (whole-house and point-of-use).
In these events expect the service-entrance surge
protector and point-of-use surge protectors to sacrifice
themselves.
Thank You!
Contact Info:
[email protected]