3. It’s About Time! Nano Micro Milli Seconds Minutes Voltage Destructive Energy Transients TOV Swells Overvoltage
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5. Transient Surge Compared to Power Waveform 0° 90° 180° 270° 360° ~100 µSec One Cycle (16667 µSec)
6. Lightning strikes conductors directly. Lightning strikes the ground directly. Ground potential rise creates voltage differential in a radial direction from the strike. Cloud-to-cloud lightning electro-magnetically couples with conductors on the ground.
7. SPD Shunt Surges Away From Load Source Load CLAMPING VOLTAGE CLAMPING VOLTAGE SPD
8. It’s all about Ohm’s Law With SPD V = I X R Without SPD V = I X R V = Voltage on the Line I = Current on the Line R = Impedance of the building
9. It’s About Time! Nano Micro Milli Seconds Minutes Voltage Destructive Energy Transients TOV Overvoltage Abnormal OV
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13. It’s About Time! Nano Micro Milli Seconds Minutes Voltage Destructive Energy Transients TOV Swells Abnormal OV
14. IEEE Std 1100, 2005 Power Quality Disturbances Power Quality Event Time Range Above Nominal Voltage Range Over Voltage > 1 min 1.1 – 1.2 Swell 8 ms – 1 min 1.1 – 1.8 Temporary Over Voltage (TOV) 100 usec – 8 ms 1.8 – 2.0 Transient Surge 1nsec – 100 usec >1.2
15. … low MCOV selected by a wish to provide surge protection with low limiting voltage for loads perceived as needing such limiting voltage, but at a greater risk of destruction under TOV’s (Martzloff and Leedy 1989 [B219] TOV’s difficult to prevent in a power system, if not impossible !!!!
16. Reliability Chart for MOV’s Surge Current Impulse Duration (Microseconds) 1 2 10 10 2 10 3 10 4 10 5 10 6 Indef. Surge Current Rating Curves-20 mm MOV 20 microseconds 5000 microseconds
17. Test 1 – Apply 2 x Nominal Voltage to 120 / 150V MOV
20. Now that know how a simple SPD reacts to a TOV… --- should we install it inside our switch gear ??
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24. Arc Flash and TVSS Safety …… . In the United States, between five and ten times a day, an arc flash explosion occurs in electric equipment and the event sends a victim to a special burn center….. … . Of these burn victims, at least 1 will die as a result of the injuries received !!!! These statistics were compiled by CapSchell, Inc., a research and consulting firm specializing in preventing workplace injuries and deaths ARC FLASH IS A REAL DANGER
25. Suit Up for Servicing Integral SPD’s Every time you go into the Gear – Danger! Anytime a surge protection module, test board, alarm sensors or even a surge counter battery has to be replaced inside live equipment of an integrated Transient Voltage Surge Suppression (TVSS) device, it puts your people at risk unnecessarily.
26. How do you over come TOV and Swell impact on Service Entrance SPD’s ??? Question
37. Save Itself & Downstream Loads A = Pearson Current XFMR (301 X) B = Pearson Current XFMR (101) C = Pearson Current XFMR (1423) Applied Voltage: 213V (1.78 pu swell) Test Currents: 100A Power Factor: ≤ .1% SL2-150-120/208-3GY + TG150-120/208-3GY + Computer Selenium unit is situated closely to the swell source, the MOV is 200’ away Computer is 50 feet from MOV based SPD. * Ask for white paper Test 4408-N to be sent to you on your survey page PC SL2-150 TG150 200’ 50’ SOURCE
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Editor's Notes
Course outline – lightly review so engineers know what we are going to cover. All of the key ideas have one thing in common… Power Quality events that damage is greatly increased with time!
As this chart shows, Power Quality events are classified by how long they are being applied to the load. We have Transients which are 100 uSec or less, Temporary Overvoltages from 100uSec to 8 milliseconds, Swells from 8 milliseconds to 1 minute and Overvoltages greater then 1 minute. Our first area of discussion will be about Transient surges
Power Quality events in the United States has been studied extensively and much of that body of data has controlled the new IEEE release of information. This information has also led UL1449 to be recently updated to ensure surge protection devices fail in a safe manor.
The first power quality event we are going to talk about is the “Transient Surge” A Transient surge is described as any over voltage over 120% over nominal AC voltage that last less then 200 uSec’s. While looking at the transient at the timing of normal power( 60Hz), the transient appears as a quick pulse, but if you zoom in on that pulse you will see a complex waveform that has both Voltage & Current elements. On the slide here we are showing an example of a current surge of 8x20 usecs.
The most common form of lightning is cloud to cloud lightning. Lightning travels in a path more or less parallel to the ground and it does not strike the ground. Being of column of ionized plasma sometimes carrying tens or hundreds of thousands of amps and is capable of radiating an extremely powerful electromagnetic pulse. This pulse couples with virtually every object on the ground including conductors in the distribution system and even the ground itself which is conductive also. Conductive objects may include the power distribution systems, structural steel in buildings, and even the ground itself. Raceways and miscellaneous conductors inside of a building can be coupled to this magnetic pulse. Current flow results in any conductive object that is intercepted by this magnetic pulse and the surge is radiated in two directions from where it is coupled.
When a Surge Protection Device (used to be called Transient Voltage Surge Suppression TVSS device) is installed in the circuit correctly, it will provide a path of LEAST resistance to ground for the surge. Because a SPD has a “Turn On” voltage typically above 120% of line voltage it always allows a little bit of energy to sneak by to the load. This is called “Let Through” voltage. This should be as small as possible without having normal AC line activity to accidentally turn the SPD on.
Based on our last slide we show that a Surge Protection Device shunts the energy away from the load… how does that work? Well a building with NO surge protection has a power quality event happen with some type of transient or overvoltage event applied. As Voltage increases from the event, it means that surge current must also increase in direct ratio, because the building impedance stays the same. This means that the Load see’s both Overvoltage and a surge current element. When a Surge Protector is installed like previous slide We see that the voltage rises to a level to turn on the SPD. Once turned on the MOV device decreases its impedance to Neutral and Ground. The higher the surge current the MORE the impedance of the MOV is decreased… the net effect is that the voltage only goes up slightly. Obviously this concept only works if you stay INSIDE the design parameters of the MOV
We just looked at the quickest Power Quality events called Transient surges, Lets look at the other side of the spectrum called Over Voltages and Abnormal Over Voltages.
Underwriters Laboratory is broke up into two areas, Regulatory body directing minimum safety standards (which answers to the government) and their Testing Body, which like all Nationally Recognized Testing Labs, uses the UL documents to test for product safety. Other large Labs are ETC, CSA, VDE all are equally recognized by NEC an OSHA as a certifying body. Surge Protection Devices (SPD) safety document (UL 1449) have had a recently been updated and it primarily focused on how Surge protection fails in a safe manner. To eliminate blind spots in a protector designs all product was retested to two key tests. Expanded Overvoltage (2 times nominal voltage) and applied 4 different limited currents to the failed device to ensure it either stabilized its temperature safely or safely blew some sort of fuse and pulled itself safely offline.
Read above notes
Read above notes
We talked about the damages of transient surges and how SPD’s are used to divert that energy away from the load to ground. We also talked about Abnormal Over voltages which as the name applies, the Surge protection device need not have to survive but fail in a safe manner. Next we would like to talk about one of the most common power quality events called Temporary Over Voltages and Swells.
Power Quality experts (from Power Quality Show in Oct 2005) indicated that over the next 10 years the power grid is going to get worse over getting better and the most damaging power quality events will be Swells and TOV events. IEEE Emerald Book describes these disturbances as the following – review data on slide Key Take Away – The longer the event the more destructive energy available to hurt sensitive equipment
Point out that the Martzloff and Leedy paper is part of their handout. Cover key points on the slide
This is a copy from one of the MOV manufacturer spec sheet. All MOV manufacturers have a similar specification sheet. This sheet clearly shows that MOV’s life is directly related to the TIME a power quality event is applied. MOV’s are designed to supress transient surges and do a damn good job at it. But when MOV’s are exposed to Power Quality events above 100 uS they are stressed and degrade eventually fail in a shorted condition. This is why UL1449 changed its safety testing we just talked about. MOV’s fail shorted and if not properly fused will fail catastrohically.
As we mentioned this presentation is both discussion and laboratory. We will now randomly pick some MOV’s to be tested.
This test shows that when MOV’s are exposed to the all to common TOV, Swell or Overvoltage event, they become damaged. In this test we are simulating a Swell event. Swells are created from imbalances in the power lines caused by upstream short circuits and lightning surges effecting the capacitor banks.
As you can see here a Swell accidently turns on the MOV as determined by the voltage threshold set by the MOV’s Maximum continuous over voltage being appled
Read Notes The Gear guys are aware of this problem and that is why they are now de-emphasizing the integrated option and new product roll outs are focused back on external product. Will the Gear guys ever admit that integrated is a bad idea? No, because they have tens of thousands of product installed and to admit a bad idea opens them up to huge risk of negligence. IEEE took a stand and clearly indicated in the IEEE 1100 Emerald that integrated greatly increases the risk to collateral damage caused from product failure and arc flash.
Here is the a copy of the IEEE emerald book. This page is also copied in your hand outs
We know that MOV are the best surge protector for transient surges, but when exposed to swells and overvoltages, IEEE says they can fail catastrophically causing collateral damage through compromised insulation systems leading to Line to Line and Line to Ground faults. When you have a Line to Line or Line to Ground Fault you can trigger an uncontrolled event called “Arc Flash” How many of you in this room have had formal training on Arc Flash? How many of you know of a local Arc Flash event? Was anyone hurt? Well the CapSchell report indicates that of the many arc flash events that happen each day between 5 to 10 people are hospitalized. Of these people 1 in 5 die from the event. This is why OSHA has taken noticed and have applied safety requirements when working around both live and dead gear.
Even if the Switch Gear is shut OFF, the electrician MUST be suited up until he/she takes measurements on the bus validating that there is no power present. At that time they can down grade their outfit according to the risk. This means that everytime an electrician opens up a Switch board, MotorControl Panel, or Panel board to service the integrated TVSS they have to suit up according to OSHA.
When a Surge Protection Device (used to be called Transient Voltage Surge Suppression TVSS device) is installed in the circuit correctly, it will provide a path of LEAST resistance to ground for the surge. Because a SPD has a “Turn On” voltage typically above 120% of line voltage it always allows a little bit of energy to sneak by to the load. This is called “Let Through” voltage. This should be as small as possible without having normal AC line activity to accidentally turn the SPD on.
This chart shows a typical voltage / current curve performance for a Metal Oxide Varistor (MOV). Notice that as the current increases the let-through voltage also increases. As demonstrated in the Lab and by the MOV manufactures the MOV can wear out when subjected to multiple surge events over time or when exposed to swells. We call this protection ability to be able to handle power quality events like Transients, Swells and Overvoltages a Catastrophic Protector System or CaPS. When you connect a Selenium surge protector in parrallel with MOV’s we find that the resultant Hybrid gives us the best protection regardless of the Power quality event. The Selenium is well suited to handle the daily low current transient that tend to wear MOV’s down over time and also protect’s the MOV’s and loads against the slower acting overvoltages like TOV, Swells and Over Voltage events. When a transient surge is applied at high current we eventually see a handoff happen and the MOV takes over the work and suppresses against high energy transients caused by lightning.
Repeating our previous lab test, this test shows the Selenium to protect the MOV and Load even when significant over voltages are being applied.
For those of you that can’t see the MOV inside the demo, here is a photo of the set up.
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