Presentation on theme: "POWER SURGES & THEIR CAUSES AND EFFECTS IN A RESIDENTIAL ENVIRONMENT Presented to the SFPE January 13, 2014 Paul McCoy, P.E."— Presentation transcript:
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 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
Todays 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
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 Its 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:200 - 300 ms Number of strokes/flash:3 – 5 Stroke duration:50 - 70 µs Interstroke interval:60 ms Current:50 – 300 kA Total charge transfer:20 – 200 C Total flash energy:10 9 – 10 10 J 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 todays 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 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. 11 Source: www.nerc.com
Sustained Elevated Voltage Voltage above normal. Significantly above-normal voltage will cause real damage! While voltages dont 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 doesnt 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, dont 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 Id 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
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 dont know is that surge protectors have an expiration date (generally about 5-7 years from date of purchase) – its 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.
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