* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Available Information on Voltage Sags and Interruptions
Power factor wikipedia , lookup
Fault tolerance wikipedia , lookup
Electrification wikipedia , lookup
Audio power wikipedia , lookup
Electrical ballast wikipedia , lookup
Power over Ethernet wikipedia , lookup
Electric power system wikipedia , lookup
Current source wikipedia , lookup
Ground (electricity) wikipedia , lookup
Pulse-width modulation wikipedia , lookup
Immunity-aware programming wikipedia , lookup
Power inverter wikipedia , lookup
Variable-frequency drive wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
Three-phase electric power wikipedia , lookup
Schmitt trigger wikipedia , lookup
Opto-isolator wikipedia , lookup
Power engineering wikipedia , lookup
Amtrak's 25 Hz traction power system wikipedia , lookup
History of electric power transmission wikipedia , lookup
Power electronics wikipedia , lookup
Voltage regulator wikipedia , lookup
Power MOSFET wikipedia , lookup
Buck converter wikipedia , lookup
Surge protector wikipedia , lookup
Electrical substation wikipedia , lookup
Stray voltage wikipedia , lookup
Switched-mode power supply wikipedia , lookup
Alternating current wikipedia , lookup
TR41.7.4-03-02-001 STANDARDS PROJECT PN-3-3283-RV2, Environmental Considerations (Revision of TIA/EIA571-A) TITLE Proposal for AC Power Interruptions (Clause 4.3.1.3) SOURCE VTech Communications 2 Shannon Ct Howell, NJ 07731 CONTACT Stephen R Whitesell Phone 732 751 1079 Fax 732 751 0095 Email [email protected] DATE January 29, 2003 DISTRIBUTION TR-41.7.4 Abstract The criteria in Clause 4.3.1.3 of TIA/EIA-571-A require products to span a complete power interruption of 125 ms in duration, with the ability to span a 2000 ms duration identified as desirable. These criteria have little basis in reality since complete power outages lasting between 20 and 2000 ms are extremely rare. On the other hand, voltage sags with time durations in this range are quite common. New criteria are proposed that require the ability to withstand voltage sags to specified levels for given durations. Longer durations are required for less severe sags. These criteria are based on information resulting from a study of distribution system power quality conducted in the mid 1990s and on data gathered by the semiconductor industry. Copyright Notice: The contributor grants a free, irrevocable, non-exclusive license to the Telecommunications Industry Association (TIA) to incorporate text or other copyrightable material contained in this contribution and any modifications thereof in the creation of a TIA Publication; to copyright and sell in TIA’s name any TIA Publication even though it may include all or portions of this contribution; and at TIA’s sole discretion to permit others to reproduce in whole or in part such contribution or the resulting TIA Publication. This contributor will also be willing to grant licenses under such copyrights to third parties on reasonable, non-discriminatory terms and conditions for the purpose of practicing a TIA Publication that incorporates this publication. Disclaimer: This contribution has been prepared by VTech Communications (VTech) to assist the TIA TR-41 Engineering Committee or one of its sub-elements as noted above. It is offered as a basis for discussion and is not to be construed as a binding proposal on VTech. VTech specifically reserves the right to amend or modify the material contained herein, and nothing herein shall be construed as conferring or offering licenses or rights with respect to any intellectual property of VTech other than as provided in the copyright statement above. Intellectual Property Statement: The individual preparing this contribution is unaware of any patents or published pending patent applications, the use of which may be essential to the practice of all or part of this contribution when incorporated into a TIA Publication. 2 Current Criteria Clause 4.3.1.3, Power Interruptions, of TIA/EIA-571-A reads as follows: Equipment shall maintain the connections of established calls for all ac power interruptions lasting 125 ms or less. It is desirable that the equipment maintain connections over interruptions up to 2 seconds in duration. It is also desirable that other equipment functions (digit reception, supervision, attendant operation, etc.) be maintained during interruptions lasting 125 ms or less. Background on Power Distribution System Faults Power distribution systems have a tree-like structure. Higher voltage main distribution feeders give way to lower voltage local feeders and ultimately to the drop wires to individual homes and businesses. These feeders are usually equipped with both fusible links and “reclosers”. A recloser is a circuit breaker with a means of automatically re-closing the circuit after a predetermined time-out interval. A fault in one part of the system may or may not have an effect on the power delivered by other parts of the system. An open at some point in the system obviously affects everything downstream from it. A short may affect parts of the system downstream from it; it may also affect other nearby branches in the system structure. A good overview of voltage sags and interruptions is provided in Chapter 3 of Electrical Power Systems Quality by Dugan, et al.1 The following discussion is based on information from that chapter. It is first helpful to distinguish voltage sags as short duration events (typically 0.5 to 30 cycles) in which the rms voltage level is between 10% and 90% of its nominal value. An interruption occurs when the rms voltage drops below 10% of nominal. Momentary interruptions can be as short as 20 cycles, but are typically on the order of 2 to 5 s. In rare instances, transients on the power line can result in interruptions lasting for 1 cycle or less. Voltage sags and momentary interruptions are generally caused by short duration or self-clearing faults on the power distribution system. Sustained interruptions of a minute or more are usually caused by permanent faults that require corrective action by a repair crew. Consider the customer who is supplied by a feeder on which a fault occurs due, for example, to a falling tree limb. The customer will experience a voltage sag during the fault condition followed by an interruption when the circuit breaker opens (typically in 3 to 6 cycles). The breaker will typically remain open for 2 to 5 s and then re-close. If the fault condition has cleared (e.g., the tree branch has burned due to arcing and fallen off the feeder), power is restored to its nominal value and life goes on. If the fault is still present, the breaker will again open in a few cycles and the process will repeat. After the second or third attempt, the breaker may go into a slow trip mode in which it takes perhaps 30 cycles to open. If the fault still persists, the breaker may remain open. It is also possible that a high fault current during the slow trip mode will cause the fusible link to open. In either case, the customer experiences a permanent interruption until a repair crew can be dispatched to rectify the fault condition. A much more common condition for an individual customer is for a fault to occur on one of the many other feeders supplied by the same substation or even on the transmission line providing power to the substation. In this case, the customer will experience a voltage sag during the time the fault is actually on the system, but will have normal power restored as soon as the breakers open on feeder experiencing the fault. There is a possibility of a repeated sag in 2 to 5 s due to the re-closing of the breaker as described above. Given the large number of feeders supplied by a single substation, the probability that a given customer will experience one or two voltage sags due to a fault event is much greater than the probability of experiencing an actual interruption. Available Information on Voltage Sags and Interruptions The Computer Business and Equipment Manufacturers Association (CBEMA) first issued a curve in the late 1970s describing the percentage of nominal voltage vs. time that computing equipment should be able to tolerate without malfunctioning. This curve addressed voltage swells as well as sags. The Information Technology Industry (ITI) Council (successor to CBEMA) revised and republished the CBEMA curve in 1996 and again in 2000. Details of the revised curve are shown in Figure 1. 2 3 0.01 500 Cycles of 60 Hz Power 1.0 10 0.1 100 1000 Percent of Nominal Value 400 300 Prohibited Region 200 100 No Interruption in Function Region No Damage Region 0 0.001 0.003 0.020 0.5 10.0 Duration in Seconds Figure 1: ITI (CBEMA) Curve The Electric Power Research Institute (EPRI) conducted a distribution system power quality study in the mid 1990s that collected data at 277 sites across the U.S. for a period of 27 months. 3 The results of the study, including the complete measurement database, have been published in three volumes. 4,5,6 The average number of sags per year identified in the EPRI study are shown in graphical form in Figure B.4, Annex B, of IEEE Standard 1346-1998.7 This graph is reproduced in Figure 2. Contours for 5, 10, etc. sags per year are shown. These contour lines represent events having sag voltages at least as low as the percentage shown and durations of at least as long as the time shown. For example, there were on average five sag events to 65% of nominal voltage or less lasting for 200 ms or longer. Comparing Figures 1 and 2 suggests there may be several sag events each year not covered by the CBEMA curve. For example, the EPRI data shows an average of 10 sags per year to 70% of nominal voltage or less lasting for more than 100 ms and 5 sags to 45% of nominal voltage or less lasting for at least 100 ms. Equipment compliant with the CBEMA curve could be susceptible to these sag events. 4 Figure 2: Average Results from EPRI Distribution System Power Quality Study Concerns about sag events not covered by the CBEMA curve led the Semiconductor Equipment and Materials International (SEMI) organization to conduct their own study of the power quality delivered to 15 semiconductor manufacturing facilities. Data was collected on over 1000 voltage sag events, with 166 of the events (15.4%) found to be below the CBEMA curve. On average, each site experienced 5.4 sags per year that were below the CBEMA curve. The results of the study, the CBEMA curve and a modification to the curve adopted by the semiconductor industry in their own SEMI F47 standard are shown in Figure 3.8,9 This figure clearly shows a large number of sag events lasting for 4, 5, or 6 cycles below the CBEMA curve. CBEMA Curve SEMI F47 Modification Figure 3: Results of Semiconductor Industry Voltage Sag Study 5 Discussion Based on the available information, the existing criteria in clause 4.3.1.3 of TIA/EIA-571-A has little basis in reality. Momentary interruptions, when they occur, last for a minimum of 20 cycles (333 ms) and more typically for a period of 2 to 5 seconds. On the other hand, short duration voltage sags lasting for 4, 5, or 6 cycles (6 cycles = 100 ms) do frequently occur. Thus, applying the 125 ms criteria in clause 4.3.1.3 to voltage sags instead of to interruptions would give it validity. Requiring equipment to span sags to 50% of nominal voltage for durations up to 125 ms (7.5 cycles) would pick up the high-density events from the SEMI study falling below the CBEMA curve as shown in Figure 4. Continuing in a step-wise fashion by requiring products to span sags to 70% of nominal for 500 ms (30 cycles) and 80% of nominal for 1 s (60 cycles) picks up most of the longer duration high-density events in the SEMI study results. It is also consistent with the slope of the EPRI study shown in Figure 2. A second curve is proposed in Figure 4 as a desirable objective. It picks up most of the lower-density data points from the SEMI study by using thresholds of 40% of nominal voltage for 125 ms, 50% of nominal for 500 ms, 70% of nominal for 1 s, and 80% of nominal for 2 s. In all cases equipment is expected to operate continuously at 90% of nominal voltage. CBEMA Curve Proposed Requirement Proposed Objective Figure 4: Proposed Voltage Sag Requirement and Objective Proposal Change the title of clause 4.3.1.3 to “Short Duration Power Interruptions and Voltage Sags”. Replace the text of clause 4.3.1.3 with the following text and figure: Commercial ac power may experience transient voltage interruptions lasting for less than one cycle, short duration voltage sags lasting for several cycles, and momentary interruptions lasting on the order of two to five seconds. Figure N shows the transient voltage interruption and sag criteria for which equipment using commercial ac power is expected to operate. The criteria are expressed in terms of the percentage of nominal voltage as a function of time and equivalent number of cycles of ac power. A nominal utilization voltage of 115 VRMS shall be assumed when checking for compliance with these criteria. 6 Equipment in any normal operating state shall continue to operate for any voltage sag or interruption in the region of Figure N identified as Operation Required. It is desirable that equipment continue to operate for any voltage sag in the region of Figure N identified as Operation Desirable. Continue to operate in this case means the equipment shall not change state or lose any information during the voltage sag or interruption and shall continue to function normally afterwards. Note: Two or three voltage sags could occur in succession. Such sags would normally be separated by intervals of 2 to 5 seconds or longer. It is recommend that 5-second intervals be used when applying multiple sags for compliance testing. 20 Percent of Nominal Voltage Value 100 125 Time in ms 500 1000 2000 Operation Required 80 Operation Desirable 60 40 Operation Not Required 20 0 1 1.2 7.5 30 10 Cycles of 60 Hz Power 60 120 100 Figure N: Transient Voltage Interruption and Sag Criteria Equipment using commercial ac power is not required to operate during short duration voltage interruptions lasting for several seconds. However, such equipment shall not lose any stored information during the voltage interruption and shall continue to function normally afterwards. 7 References 1 Roger C. Dugan, Mark F. McGranaghan, and H. Wayne Beaty. Electrical Power Systems Quality. New York: McGraw-Hill. 1996. 2 Technical Committee 3 of the Information Technology Industry Council. ITI (CBEMA) Curve Application Note. www.itic.org/technical/iticurv.pdf. 2000. 3 Dan Sabin. Overview of the EPRI Distribution System Power Quality Project. www.electrotek.com/PROJECTS/DPQ/Dpq.htm. May 2, 2001. 4 Thomas E. Grebe, D. Daniel Sabin, and Mark F. McGranaghan. An Assessment of Distribution System Power Quality, Volume 1: Executive Summary. EPRI Report TR-106294-V1. Palo Alto, California. May 1996. 5 D. Daniel Sabin. An Assessment of Distribution System Power Quality, Volume 2: Statistical Summary Report. EPRI Report TR-106294-V2. Palo Alto, California. May 1996. 6 Daniel L. Brooks and D. Daniel Sabin. An Assessment of Distribution System Power Quality, Volume 3: The Library of Distribution System Power Quality Monitoring Case Studies. EPRI Report TR-106294-V3. Palo Alto, California. May 1996. 7 IEEE 1346-1998, IEEE Recommended Practice for Evaluating Electric Power System Compatibility with Electronic Process Equipment. July 21, 1998. Mark Stephens, John Soward, Dennis Johnson, and Jim Ammenheuser. “Power Quality Solutions for Semiconductor Tools, Part 2: Voltage Sag Immunity Standard and Testing Methodology,” Power Quality Assurance. www.f47testing.com/semi_documents/Semi_part_2_PQ_Magazine_Article.pdf. May/June 2000. 8 9 SEMI F47-0200, Specification for Semiconductor Processing Equipment Voltage Sag Immunity. December 15, 1999.