IEEE PES/IAS Joint Chapter July Technical Presentation Meeting Basics of solar phenomena & How transformers react and handle events

Transcription

1 Topic and abstract Geomagnetic disturbances Events associated with GMD have been known and studied in power systems since the 1960 s. Early events pre dating the AC power have been recorded to the 1850 s. This technical meeting of the joint Maine Chapter of the IEEE PES/IAS will educate attendees on: Basics of solar phenomena How transformers are impacted and react to GMD events GMD impact on the power system Impacts of GMD in Maine Mitigation technologies Craig L Stiegemeier; Transformer Remanufacturing & Engineering Services; IEEE PES/IAS Joint Chapter Meeting Geomagnetic disturbance impact on transformers and the power grid is forbidden without ABB s prior written consent. 1

2 Geomagnetic disturbance impact on transformers and the power grid Topics reviewed Geomagnetic disturbances (GMD) and mechanism of generation of geomagnetically induced currents (GIC) Effects of GIC on power transformers Recent significant GMD events Effects of GIC on power systems Developing a plan Evaluating the GIC capability of a power transformer Fleet assessment of GIC susceptibility Grid resiliency / mitigation Slide 3 Slide 4 Mechanism Of Generation Of GIC Geomagnetically Induced Currents is forbidden without ABB s prior written consent. 2

3 Geomagnetic disturbance (GMD) Strong solar flare activities => Sends plasma beams to earth Changes the magnetic field of Earth => GMD By NASA Slide 5 Solar cycle by sun Sunspot count Occurs on an average of 11 year cycle (prediction is still difficult) Source: NASA Reported: Worst recorded in 1859, called Carrington Event Reports of strong GMD in 1921 Slide 6 is forbidden without ABB s prior written consent. 3

4 Detection/prediction of solar storms Slide 7 Movies should be screened in the grey area as featured here, size proportion 4:3. No titles should be used. ABB Inc Slide 8 is forbidden without ABB s prior written consent. 4

5 Mechanism of generation of GIC Change of earth s magnetic field => Voltage in transmission circuits Transmission line / Power transformers / Ground Fraction of a volt to several volts / km Ground currents flow into neutrals of power transformers Magnitude of GIC in a transmission circuit is a function of: Magnitude & orientation of GMD, location on earth, proximity to large bodies of water, resistance of the soil, and direction / height / length of the transmission line Highest for > 500 kv Transmission K Scale Slide 9 GIC Effects on Power Transformers Factors that determine the magnitude of GIC Affected location on Earth is dependent on location & timing of the sun activity A significant Sun-spot activity may, or may not, mean high GIC in a particular location on Earth Magnitude of GIC is a function of location on earth, resistance of the soil, direction, height, and length of the transmission lines 500 kv and 765 kv transmission lines travelling long distances are the most susceptible to higher levels of GIC Based on above, only specific power grids or parts of a power grid would be susceptible to high levels of GIC Slide 10 is forbidden without ABB s prior written consent. 5

6 History of recent significant GMD events March 13, 1989: Highest recorded GIC level in recent history for North America Short duration peaks of Amperes / phase in GSU s at PSE&G s Salem Generating station Slide 11 Effect of DC on Power Transformers Slide 12 is forbidden without ABB s prior written consent. 6

7 DC flux density shift in transformer cores Flux Density, Tesla Flux Density vs Phase angle (20 Ampd DC) Bm, AC 1.6 Bm, (AC+DC) DC flux = N I DC / R Phase Angle, Degrees Slide 13 DC causes part cycle saturation of the core DC Shift AC + DC B AC Time I Im AC Im AC+DC Time Non linearity of the core material limits core from fully saturating Slide 14 is forbidden without ABB s prior written consent. 7

8 Magnetizing current pulse caused by DC/ GIC Exciting current, % of Load Cuurent 40% 35% 30% 25% 20% 15% 10% % Exciting Current - 1 phase transformer - 20 Amps DC High Peak pulse One per Cycle Small mean width 1/8 th 1/12 th of Cycle RMS = % of peak 5% 0% Degrees Slide 15 % I mag of 1 phase Transformer under effect of DC Per Phase Currents Slide 16 is forbidden without ABB s prior written consent. 8

9 VAR consumption vs. magnitude of GIC 18 Fundamental Inductive MVAR Drawn by Transformer vs GIC % Fundamental MVAR GIC, Amps/Phase Utilities should use this data to plan their VAR resources during GMD events Slide 17 VAR consumption vs. magnitude of GIC (2) % MVA Rating GIC, Amps/Phase Utilities should use this data to plan their VAR resources during GMD events Slide 18 is forbidden without ABB s prior written consent. 9

10 Current harmonics associated with DC / GIC 6% Harmonic Spectrum of Magnetizing Current under different levels of GICs % Harmonic Amplitude (% of Rated Load Current) 5% 4% 3% 2% 1% Idc = 25 Amps/Phase Idc = 50 Amps/Phase Slide 19 0% Harmonic Frequency, Hz Utilities use this data to optimize protection during GMD events GIC Effects on Power Transformers DC flux path in different core types Core Form, 3 phase, 3 limb Core Form, 3 phase, 5 limb Shell Form, 3 phase, conventional Shell Form, 3 phase, 7 limb Core / Shell Form, 1 phase Slide 20 3 Phase, 3 Limb cores require much higher magnitudes of DC to saturate compared to all other core types Other core types are basically equivalent, other design factors are more relevant is forbidden without ABB s prior written consent. 10

11 Transformer core types core form 3-phase, 3 limb 3-phase, 5 limb Slide 22 Transformer core types core form 1-phase, 3 limb 1-phase, 4 limb Slide 23 is forbidden without ABB s prior written consent. 11

12 GIC Effects on Power Transformers Modelling of transformer cores with DC 3 phase, 3 limb core 1 phase, 4 limb core Considered DC Flux Ftc Fcc1 Fcc2 Tank Fy = Fs By = Bs Hy = Hs Fm Bm Hm Considered AC + DC flux Core Fc Fcw top Fa Fw Fs Bs Hs outer loop I - Fw Bw Hw I + inner loop only 1/2 considered I + I - Lh L Fcw bot Fcb1 Fcb2 Ftb Ls Due to Symmetry only 1/2 of the core is considered Lm 3 phase, 3 limb Cores: DC return flux through air & tank All other Core Types: DC flux flows within core Slide 24 Effect of DC/GIC on core loss and core noise Increase in core loss / noise level is significant even at low levels of DC Noise increases in level and also in frequency content Typically, 120 / 240 / 360 / 480 Hz => Much higher > 480 Hz GIC (A/Phase) Core Loss Increase Core Noise level Increase (db) % % % % % % % 46.7 Slide 25 is forbidden without ABB s prior written consent. 12

13 Thermal effects of DC A high magnitude pulse of magnetizing current High magnitude of leakage flux, rich in harmonics Higher I2 R and eddy current losses in windings & structural parts Increase is low because of low RMS value Some of the core flux flows outside the core Causing higher windings, tie plates, and tank losses Core saturation => significant change in leakage flux pattern => High winding circulating currents in some designs Slide 26 Effect of DC on winding hot spot temperature 124 Winding Hot Spot Temperature vs Time, 1-Phase Transformer 122 Wdg Hot Spot Tempt, Degree C Idc = 50 Amps Idc = 30 Amps Idc = 20 Amps Time, Minutes Slide 27 is forbidden without ABB s prior written consent. 13

14 Effect Of GIC On Power Transformers Slide 28 Signature / profile of GIC GIC, AmpsADC Low / moderate magnitudes of GIC sustained for several hours; interrupted by short duration / high peak pulses hr signature of GIC Slide 29 is forbidden without ABB s prior written consent. 14

15 Effect of GIC on winding hot spot temperature 124 Winding Hot Spot Temperature vs Time, 1-Phase Transformer 122 Wdg Hot Spot Tempt, Degree C Idc = 50 Amps Idc = 30 Amps Idc = 20 Amps Time, Minutes Actual temperature rise is much lower for the short duration of high GIC peaks For a 2 minute duration: Rise is 3, 4, and 6 C for GIC of 20, 30, and 50 Amps Slide 30 GIC Effects on Power Transformers Injection of 75 Amps DC into 370 MVA and 550 MVA, 735 kv, 1 phase transformers, by IREQ Slide 31 is forbidden without ABB s prior written consent. 15

16 GIC Effects on Power Transformers Injection of 75 Amps DC into 370 MVA and 550 MVA, 735 kv, 1 phase transformers, by IREQ Slide 32 Temperature rises in structural parts & tank are moderate even after applying 75 A DC (75 times the Excitation Current) for an hour No damage resulted in either transformer GIC Effects on Power Transformers Characteristics of GIC A base current of several Amps or 10s of Amps High magnitudes of peak GIC of short duration (1-2 minutes) Fig 4.8 in Meta-R-319 Report by J. Kappenman Slide 33 is forbidden without ABB s prior written consent. 16

17 GIC Effects on Power Transformers Per phase GIC wave-form used for thermal calculations Idc 400 Amps 400 Amps 20 Amps 20 Amps 20 Amps (0,0) Time, Minutes Slide 34 GIC Effects on Power Transformers Winding hot spot rise due to GIC in a single-phase transformer 160 Winding Hot Spot Temperature vs Time 140 Winding Hot Spot Tempt, Degree C C rise due to 20 Amps 35 C rise in the 2-minute duration of the GIC pulse Drops back to original temperature in 4 minutes Duration of Temperature pulse is too short to cause winding damage Temperatures & durations << allowed by IEEE for emergency overload Same is true for structural parts of the transformer Time, Minutes Slide 35 is forbidden without ABB s prior written consent. 17

18 GIC Effects on Power Transformers Measured Temperature rises in windings & structural parts due to DC 1 phase at HQ, 75 Amps DC for 20 minutes 3 phase, 5 limb at FINGRID using 50, 100, 150, 200 Amps DC for intervals of 30 minutes each Tokyo Elec., Toshiba, Hitachi, and Mitsubishi, tested large models of core form and Shell form transformers with DC equivalent to Amps / phase for full size transformers for minutes. Measured from C temp rises in mainly structural parts No damage observed in windings or major insulation Again, because of its short duration, GIC would cause much lower temperature rises and no insulation damage / loss of life Slide 36 History of Recent Significant GMD Events Slide 37 is forbidden without ABB s prior written consent. 18

19 History of recent significant GMD events March 13, 1989 Base GIC of 20 Amps / phase interrupted by short duration pulses of 80 Amps / phase in GSU s at PSE&G s Salem and Hope Creek generating stations Significant overheating of series LV connection of an old shellform transformer caused by high circulating currents Transformer taken out of service a week later because of significant gassing Less overheating of others of same design transformers in the area with continued operation Some gassing / tank paint discoloration of a number of transformers in northeast of USA An 8 hr. blackout of the HQ system Due to tripping of Capacitor banks / SVC s; causing system instability High VAR demand initiated response Slide 38 History of recent significant GMD events Sweden / Oct. 31, 2003 Report of very strong GMD storm; 3 phase / 5 limb / 400 kv transformers were subjected to 330 Amps GIC in the neutral 20 min. black out / system instability caused by tripping of 130 kv line Low level gassing in the transformers; indicating Minor overheating S. Africa: Nov. 03 June 04 A few transformers had significant winding damage Moderate levels of GIC Coincided with winding failures caused by Copper Sulphide Slide 39 is forbidden without ABB s prior written consent. 19

20 Evaluation of Susceptibility of A Fleet of Power Transformers to Effects Of GIC Slide 40 Evaluation of total susceptibility of transformers to effects of GIC To determine which transformers: Are susceptible to damaging overheating Are susceptible to core saturation and only moderate overheating Have low level of susceptibility to either effects of GIC Are not susceptible to effects of GIC Total susceptibility to effects of GIC is determined by: Transformer design based susceptibility GIC level based susceptibility Slide 41 is forbidden without ABB s prior written consent. 20

21 Results of GIC susceptibility study on large power transformer fleet > 500 kv Slide 42 Orange: Susceptible to both core saturation and possible damaging winding and/or structural parts overheating Yellow: Susceptible to core saturation and only moderate overheating Green: Low susceptibility to both core saturation and overheating Blue: Not susceptible to core saturation or overheating Benefit of fleet GIC susceptibility evaluation Allows utilities to focus their mitigation / studies efforts For transformers identified to be susceptible to core saturation Utilities could request manufacturers to provide data on the additional VAR consumption and current harmonics as a function of the level of GIC the transformer would be exposed to For transformers identified to be susceptible to possible damaging overheating Utilities could request manufacturers to provide data on the thermal Capability of these transformers Slide 43 is forbidden without ABB s prior written consent. 21

22 Evaluation of GIC Capability of Transformer Designs Slide 44 Approach / Definition 45 Combinations of load current and GIC current for which the hot spot temperatures of neither the Windings nor structural parts would exceed certain temperature limits To limit loss of life of solid insulation Avoid formation of gas bubbles Slide 45 is forbidden without ABB s prior written consent. 22

23 Approach / Temperature Limits 46 For low / moderate level Base GIC, the hot spot temperature limits recommended by IEEE / IEC loading Guides to be used for long duration overloading of transformers, are used Windings: 140 ºC Structural parts: 160 ºC (IEC & IEEE) For high peak, short duration GIC pulses, the hot spot temperature limits recommended by IEEE / IEC Loading Guides to be used for short duration Emergency overloading of transformers (< 30 minutes), are used Windings: 160 ºC Structural parts: 180 ºC (IEC) Windings: 180 ºC Structural parts: 200 ºC (IEEE) Slide 46 GIC capability of a large 1 phase transformer Slide 47 is forbidden without ABB s prior written consent. 23

24 GIC impact on power transformers Summary Transformer designs susceptible to damaging windings overheating are those where core saturation changes the leakage flux pattern This change in the flux pattern results in very high levels of winding circulating currents The PSE&G Salem transformer is an example of one of these designs GIC fleet assessment studies help utilities identify transformers that require magnetic & thermal evaluations; reducing risk of blackouts and possible thermal issues in some old design transformers For many technical reasons, DC testing of power transformers in the factory is of little benefit and little relevance to actual operating conditions and is also unnecessary Also, DC testing of transformers on the power Grid for partial verification of some calculations may be okay, but the cost is very high and the test would be performed at no load Slide 48 GIC impact on power transformers Summary Because of the nature of GIC signature, the majority of large power transformers would not fail thermally, even under high GIC levels Therefore, months / years of blackouts (as predicted by some,) is not realistic The effect of the increased VAR consumption & current harmonics on the power system, and its components, is the most significant consequence of GIC This is even more true for high levels of GIC It is important to evaluate this effect Slide 49 is forbidden without ABB s prior written consent. 24

25 Grid GIC studies Topics Simplified analysis VAR consumption due to GIC and effects Voltage and reactive power control Transformer saturation and harmonics effects FERC required GIC studies Slide 50 Simplified analysis Increased transformer VAR can be expressed as: Q = I 2 X Voltage drop along a line: V = I X line Power transfer: P Max =V 1 V 2 Sin(δ 12 ) / X line As Q, I, V, V 1 and / or V 2 and P max Thus, stability may become a concern Slide 51 is forbidden without ABB s prior written consent. 25

26 VAR consumption vs. magnitude of GIC 18 Fundamental Inductive MVAR Drawn by Transformer vs GIC % Fundamental MVAR GIC, Amps/Phase Utilities should use this data to plan their VAR resources during GMD events Slide 52 Examples of voltage instability caused by imbalanced VAR support New York Power Pool September 22, 1970 French system December 19, 1978 Florida system December 28,1982 Northern Belgium August 4, 1982 Swedish system December 27, 1983 Southern Florida 1985 Japanese system July 23, 1987 Western France 1987 Hydro Quebec blackout (GIC) March 13, 1989 Southern Finland August 1992 Western Systems Coordinating Council (WSCC) Region 1996 Slide 53 is forbidden without ABB s prior written consent. 26

27 Voltage instability Examples Reactive Power in the News (New York Times, Sept. 26, 2003) Experts now think that on Aug. 14, northern Ohio had a severe shortage of reactive power, which ultimately caused the power plant and transmission line failures that set the blackout in motion. Demand for reactive power was unusually high because of a large volume of long-distance transmissions streaming through Ohio to areas, including Canada, than needed to import power to meet local demand. But the supply of reactive power was low because some plants were out of service and, possibly, because other plants were not producing enough of it. NERC - Minutes Board of Trustees (February 23, 2012) I.9 Conclusions The most likely worst case system impacts resulting from a low probability GMD event and corresponding GIC flow in the bulk power system is voltage instability caused by a significant loss of reactive power support simultaneous to a dramatic increase in reactive power demand. The lack of sufficient reactive power support was a primary contributor of the 1989 Hydro Québec GMD induced blackout. During the geomagnetic disturbance, seven static SVC s tripped off line within 59 seconds of each other, leading to voltage collapse of the system 25 seconds later. Slide 54 Voltage and reactive power control Requires the coordination work of transmission and distribution disciplines. Typical needs are to: Forecast the reactive demand and required reserve margin. Plan, engineer, and install the required type and location of reactive support. Maintain reactive devices for proper compensation. Recommend the proper load shedding scheme, if necessary. Provide and maintain monitors to ensure accurate data. Slide 55 is forbidden without ABB s prior written consent. 27

28 Typical voltage control devices Shunt capacitors Series capacitors Shunt reactors Synchronous condensers SVC (static var compensator ) STATCOM (Static Synchronous Compensators) Slide 56 Current harmonics associated with DC / GIC 6% Harmonic Spectrum of Magnetizing Current under different levels of GICs % Harmonic Amplitude (% of Rated Load Current) 5% 4% 3% 2% 1% Idc = 25 Amps/Phase Idc = 50 Amps/Phase 0% Harmonic Frequency, Hz Slide 57 is forbidden without ABB s prior written consent. 28

29 Magnetizing current harmonics vs. magnitude of GIC 9 Amplitude of harmonics in % of Rated Current % Amplitude of Harmonics First Harmonic Third Harmonic Fifth Harmonic Seventh Harmonic Nineth Harmonic Eleventh Harmonic Second Harmonic Fourth Harmonic Sixth Harmonic Eighth Harmonic Tenth Harmonic GIC - Amps/Phase Utilities use this data to study effect on their power system equipment Slide 58 Possible harmonics effects on power systems Possible amplification of harmonic levels resulting from series or parallel resonances. Might damage equipment. Increase equipment losses and thus the thermal stress. Interfere with protective relays; Capacitor bank and SVC tripping may occur. The 2nd order harmonic could cause transformer differential relay miss- operation. The 3rd order harmonic may cause some line differential relay miss- operation. Generator overheating and tripping may occur. Interference with metering devices, control and communication circuits, and with sensitive electronic equipment. Increase in equipment noise and vibration. Slide 59 is forbidden without ABB s prior written consent. 29

30 Harmonics effects Examples March 13, 1989 blackout of the Hydro Québec (HQ) system initiated from tripping of seven SVC s. October 30, 2003 Sweden blackout was initiated by GIC saturation of large power transformers which resulted in large amount of harmonics. The tripping occurred due to GIC saturation of transformers which caused large components of 2 nd, 3 rd and 4 th harmonics in voltages and currents at the SVC locations. The 3 rd harmonics content caused tripping of a 130 kv line which cascaded into the blackout. Slide 60 FERC REQUIRED GIC STUDIES AND ANALYSIS Slide 61 is forbidden without ABB s prior written consent. 30

31 FERC Order 779 In May 2013, FERC issued Order 779 which directs NERC to submit reliability standards that address the impact of GMD on the reliable operation of the bulk-power system Stage 1 operating procedures Stage 2 detailed assessments (planning studies) Standards project (GMD mitigation) began in June 2013 Slide 62 TPL 007 summary Requires a GMD Vulnerability Assessment of the system for its ability to withstand a benchmark GMD event without causing a wide area blackout, voltage collapse, or damage to transformers, once every five years. Applicability: Planning Coordinators, Transmission Planners Requires a Transformer thermal impact assessment to ensure that all high-side, wye grounded transformers connected at 200kV or higher will not overheat based on the Benchmark GMD Event. Applicability: Generator Owners, Transmission Owners Slide 63 is forbidden without ABB s prior written consent. 31

32 Screening criterion, recommended by NERC, for Thermal Assessment of Power Transformers Originally > 15 Amps / phase for reference GMD storm Upon technical input from 5 major transformer manufacturers, it was recently changed to > 75 Amps / phase Slide 64 GIC effects Slide 65 is forbidden without ABB s prior written consent. 32

33 Studies needed for GIC concerns Geo-electric field determination DC system modeling GIC calculation Calculation of transformer reactive power absorption and harmonics Planning type studies with added reactive power absorption, considering contingencies. Conduct harmonics studies and determine the effects Identify limit violations and system issues Conduct thermal assessment of a portion of transformer fleet Determine mitigations and study their effects Slide 66 Available means of mitigation Alerting Monitoring / measurements Simulations and evaluation of risk Increasing robustness of network Increasing robustness of protection Proper operating procedures during a storm Installation of appropriate GIC blocking devices if needed and feasible Slide 67 is forbidden without ABB s prior written consent. 33

34 Geomagnetic disturbance impact on transformers and the power grid Summary The specific transformer design influences the impact of GMD/GIC events on a given transformer Only a small number of transformers are vulnerable to significant overheating when subjected to high levels of GIC All types of transformers place demands on the grid in terms of magnetizing current and reactive power demand, as well as the generation of harmonics The most significant impact of GIC is its effect on the stability of the power grid Slide 68 is forbidden without ABB s prior written consent. 34