Dynamic Scheduling FERC Order 888 defines dynamic scheduling: which is the electronic transfer of the time-varying electricity consumption corresponding to a load or the time-varying generation associated with a generator from one control area to another. Dynamic scheduling moves the control requirements associated with one (or more) physical entity from one control area to another.
Dynamic Scheduling For example, in the Southwest, four control areas use their Hoover rights for regulation. WAPA receives every 4 seconds (normally 2-4 seconds) from four different control areas request for timevarying amount of generation (up to their contractual allocations). WAPA aggregates the four requests and sends the total to the control system and Hoover Dam. DS has application for both load and generation. Generation applications have higher DS than load
ACE Where: NI A F A β I ME = NI S F S ( NI NI ) 10β ( F A Dynamic Scheduling S A F actual and scheduled net interchanges actual and scheduled frequencies frequency bias setting (MW/0.1Hz) meter error correction factor S ) I ME ACE was required to cross 0 at least once every 10 minutes(a1). Average ACE (energy imbalance) should be within Ld (0.2-0.5% of peak demand) every 10 minutes (CPS1&CPS2)
Dynamic Scheduling Portion of ACE Dynamically allocated L d (0.2-0.5% of peak demand, e.g. BCH Ld ~ 50 MW)
Dynamic Scheduling How to determine the maximum DS? A quick search of the subject yielded no available methodology! There are two possible approaches: Steady-State (powerflow based). A series of snap shots, less accurate in capturing dynamic interaction Time domain (longer term transient analysis). AGC and other controls can be modeled. Requires dynamic data,specially for switchable shunts, ULTCs, ACE- AGC model, SPS, etc.
Dynamic Scheduling Amount of Dynamic Scheduling may be restricted due to: TTC (voltage/transient security limits) Ramp rate (e.g. 100 MW/min) Frequent switching of shunts Frequent Arming/Disarming of RAS Etc.
Dynamic Scheduling Voltage Schedule and Shunt Switching: The 500 kv system voltages should be generally maintained at 525 kv. In general, 550 kv is the upper continuous limit acceptable on any 500 kv bus, 570 kv is acceptable for up to 5 minutes. During heavy transmission loadings voltages should be maintained in the 525 kv to 535 kv range to minimize losses and increase stability margins. During lighter loadings voltages should be reduced to 520 kv, or lower if practical, to reduce VAR generation from the lightly loaded transmission. Sequentially timed tripping of most 500 kv circuits at voltages between 570 kv and 585.
Dynamic Scheduling Voltage Schedule and Shunt Switching: Sub Min kv Max kv Min p.u. Max p.u. CBN 530 547 1.06 1.094 CK5 515 545 1.03 1.09 ING 530 545 1.06 1.09 MSA 515 540 1.03 1.08 KLY 525 540 1.05 1.08 CUSTER * 515 540 1.03 1.08 MONROE * 525 550 1.05 1.10 ING 239 243 1.037 1.054 MDN 238 243 1.035 1.057 * From BPA s KVSCHED08_24Mar08.xls
Dynamic Scheduling Possible Remedial Schemes to Address DS problems: SVCs Other FACTS devices (e.g. STATCOM) Considering AUTO RAS arming Etc.
Summary of 2008 DS Limit Study With the addition of large amounts of wind generation in the Pacific Northwest it is expected that the need for regulation and other ancillary services will increase in the coming years. It is possible that BC could help meet part of this demand. However, the transmission between BC and the Pacific Northwest would need to support higher levels of Dynamic Schedules. Currently, the Northern Inter-tie Dynamic Scheduling limit is 300 MW. In a 2008 study the voltage issues related to increasing DS limit on the Northern Inter-tie to 750 MW were explored.
Summary of 2008 DS Limit Study The study was designed to: Assess the impact of up to 750 MW of DS on regional voltages during Summer Heavy Load Hour (HLH) conditions for North-South with full PSE generation, and for South-North with light PSE generation; Assess the relative performance of possible system reactive reinforcements in BC; Test a study methodology to quantify the impact of mid-term dynamic phenomena such as DS. The simulations were performed using the Voltage Security Assessment Tool (VSAT) of Powertech s DSATools TM
Furthermore, the sensitivity of the results to all switched shunts and ULTC controls was examined when reactive reinforcement was assessed. Reactive reinforcement in the form of continuously controlled Static VAr Compensator (SVC) was examined at four different locations, namely, Ingledow and Meridian 500 and 230 kv buses. No reinforcements were investigated on the US side Summary of 2008 DS Limit Study The switched shunt controls, as well as Under Load Tap Changers (ULTC) were locked at first; subsequently the AutoVar controls at MDN230 and ING230 were turned on to find out if any reactive switching was required and how the key bus voltages changed.
Summary of 2008 DS Limit Study It was assumed that increases in the Northern Inter-tie DS limit would be staged in small increments of up to 100 MW. These were grouped into six stages: Stage 1: 50 MW BCTC-NWE & 200 MW BCTC-CAISO Stage 2: 100 MW BCTC - BPA plus Stage 1 Stage 3: 100 MW BCTC - BPA plus Stage 2 Stage 4: 100 MW BCTC - Washington plus Stage 3 Stage 5: 100 MW BCTC - Portland Area plus Stage 4 Stage 6: 100 MW BCTC - BPA plus Stage 5
Summary of 2008 DS Limit Study BC - US Additional Flow 800 600 400 200 0 Stage 6: Profile A 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Minute (Note: DSmax = 512.5 MW due to diversity in schedules.) BC - US Additional Flow 800 600 400 200 0 Stage 6: Profile B 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Minute
Summary of 2008 DS Limit Study Future DS commitments would likely have different maximum ramp rates. Consequently, for the purposes of this study some ramp rates were assumed. Two potentially stressed profiles were developed to try and quantify how the ramp rates could be factored into the time-stepped power flow studies. Profile A results from each DS ramping continuously at its maximum ramp rate (i.e., Saw-tooth Profile). Profile B results from each DS ramping to its limit at its maximum ramp rate, holding there until every other DS in that stage has reached its corresponding limit, and then all ramping back in the opposite direction to their other limit (i.e., Max-Min Profile).
Summary of 2008 DS Limit Study CKY500 500. 530.94 kv 50045 MDN230 230. 50018 240.31 kv ING230 230. 240.58 kv 50183 0.0 MDN T1 12.6 51175 122.3 MDN T3 12.6 51182 0.0 ING T4 12.6 50588 0.0 ING T2 12.6 51190 ING T5 12.6 51208 0.0 MDN500 500. 524.87 kv 50047 0.0 CBN500 500. 523.96 kv 50860 533.67 kv 50703 NIC500 500. 50194 ING500 500. 524.60 kv -279.1 0.0 NLY230 230. 50784 237.15 kv 0.0 1008 MW -168 MVAr 992 MW -167 MVAr 300 MW -24 MVAr 40323 CUSTER W 500. 526.81 kv NLYPHS 230. 50822 238.89 kv Case 1:Summer HLH 2300 MW N-S ALIS 40749 752.6 MONROE 500. 545.61 kv 40145 239.00 kv BOUNDARY 230.
Summary of 2008 DS Limit Study Case 1: Summer HLH 2300 MW N-S ALIS PV Plot for Stage 6 of Profile B Without Shunts Switching.
Summary of 2008 DS Limit Study Case 1: Summer HLH 2300 MW N-S ALIS PV Plot for Stage 6 of Profile B With Shunts Switching.
Summary of 2008 DS Limit Study Case 1: Summer HLH 2300 MW N-S ALIS PV Plot for Stage 6 of Profile B Without Shunts Switching.
Summary of 2008 DS Limit Study Case 1: Summer HLH 2300 MW N-S ALIS PV Plot for Stage 6 of Profile B With Shunts Switching.
Summary of 2008 DS Limit Study
Conclusions of 2008 DS Limit Study DS study up to 750 MW for a wide range of conditions/scenarios Worst case: All Lines In Service with 2300 MW of N-S transfer Northern Inter-tie DS exacerbated potential voltage stability problems around Custer and Ingledow Maximum increased switching frequency: 16 on/off per hour With 1900 MW S-N flow: No switching up to 750 MW DS SVC examined at ING500, MDN500, ING230, MDN230: