Dynamic Transfer Limits Study WIST Update 12/17/09 Brian Tuck, BPA

Purpose of Dynamic Transfer Limit Study Assess the operational impacts and cost-effectiveness of using dynamic transfers to support wind integration Reliability Concerns: No repeat of previous reliability problems resulting from rapid, continuous changes in power flow. Operational Concerns: Care must be taken to reasonably assure that system operators have the tools, skills, and information for real time operations. Joint Concerns: The wide impact of rapidly changing flows are likely to impact PNW systems adjoining BPA as well, possibly requiring greater coordination of procedures, voltage control, and other real-time activities by system operators of neighboring utilities.

Dynamic Transfer Limit Study Goals Effect of Variability and Uncertainty on Path Operation –What is “normal” variation? This study looks at how the system is operated and system security is maintained as the system varies in real-time. –How does continued development change the aggregate characteristics across critical paths? Dynamic Transfer Limitations for the Existing System –What impact can be tolerated and how does that translate into dynamic transfer limitations? –Identify limiting concerns and interactions –Develop a new performance criteria and method for analyzing dynamic transfer effects. –Develop a methodology for determining dynamic transfer limits across a path. Increasing Dynamic Transfer Capability –Evaluate operational improvements and system reinforcements that increase the available dynamic transfer capability across paths. –Identify upgrades and assess cost-effectiveness of implementation.

Limiting Concerns and Interactions Direct Effects Electrical parameters interact: MW, MVAr, kV, topology (X) -- Ohm’s Law –Voltage Sensitivity Measures and Criteria Voltage sensitivity will vary with path loading, area load, and reactive support from nearby machines. The allowed MW variation can be calculated for a given operating voltage range –Measuring Dynamic Reactive Support FCRPS Dynamic Reactive Support requirements Switching duty on reactive elements. Indirect Effects Electrical changes require Operator actions, or decisions, to take place –Real-time Control / manpower impacts RAS arming – impact varies with path loading System Operator visibility and situational awareness Nomogram Interactions

Establishing the Dynamic Transfer Limit Dynamic Transfer Limit (DTL) = –is the Variability our current systems can accommodate, –less an amount set aside to accommodate historical use, –less a margin for reliability DTL = (Variability Limit) – (Historical Use) – (Reliability Margin) “Historical use”: estimate of variability based on actual SCADA data across the path –SCADA is used where the historical use cannot be easily tied to specific arrangements for dynamic transfer –Using SCADA as of 11/09. Reliability Margin –Additional margin used to cover for uncertainties. –May vary with path

Calculating the Variability Limit Theory –Based on existing voltage stability fundamentals Optimization Methods –Optimization used to address simultaneous interactions –Automation to increase the number of scenarios and begin monitoring real-time cases

Using the PV curve to calculate System Variability Allowed voltage variability dV dP Dynamic MW Range

Why Optimize? There are multiple paths to study and they interact with each other –Wind generation in the Columbia Gorge will affect many paths such as COI, Idaho to NW and Montana to NW Bus voltages are impacted by different path flows Based on the current conditions one may want to restrict the amount of dynamic transfer. For example if the bus voltage is below the limit we do not want the dynamic transfer to pull the voltage further down. Different topology and system condition can change the dynamic transfer rating The goal is to maximize the Dynamic Transfer Limits for different paths

Optimization Problem Objective: Maximize the Dynamic Transfer Limits for different paths –Max(DT1, DT2,………) Same time the bus voltages within NW should not change more than –5 KV for 500 KV and 345 KV buses and –3 KV for 230 KV and 115 KV buses Any optimization technique can be used to solve the above problem

Objective Max ∑ DT i * DT i i = 1 to n paths Subject to ΔV k ≤ 5 KV for 500 KV and 345 KV buses k = 1, m buses (all the 500 KV and 345 KV buses) ΔV l ≤ 3 KV for 230 KV and 115 KV buses l = 1, p buses (all the 230 KV and 115 KV buses) Where DT i = Path i Dynamic Transaction Value ΔV k = Bus voltage change at bus k due to dynamic transfers Optimization Problem

Optimization Setup Heavy Winter Operations case POR-POD for 4 interconnections –NI: BCTC Hydro – LC Wind (JDA, MCN) –IPC: Hells Canyon – LC Wind –NWE: Colstrip – LC Wind –COI: LC Wind - NCAH W

Optimization Results

Historical Use of Dynamic Transfers Where are we starting from? Historically, the system has been operated in a fairly static manner –Moment to moment changes are typically very small Dynamic Transfer types –BCTC – CISO: dynamic transfers wheeled across the BPA system –Regulation for load following –NWPP Reserve Sharing –Accounting for small changes in generation at thermal plants Expanding the use of dynamic transfers to accommodate self-supply and other uses –New applications of dynamic transfers –Potential to vastly increase the number of dynamic transfers

North Of Hanford Existing Use Historical Variation calculated using archived SCADA values 99% of the time, the 5 min variation is less than 200 MW Flattens Quickly: 80% of the time dispatchers see less than 50 MW What point captures “historical variability”?

Northern Intertie Existing Use Using SCADA to estimate historical use is less applicable due to the existing dynamic arrangement and the radial nature of the path 99% of the time, the 5 min variation is less than 200 MW Situational Awareness Issue: 80% of the time dispatchers see less than 50 MW

- Example - North Of Hanford DTL DTL = (Studied Variability Limit) – (Historical Use) – (Reliability Margin) DTL = 500 MW – 200 MW – 100 MW = 200 MW –Dynamic Transfer Limit: 200 MW Outages or other system conditions could reduce the DTL, as real- time reliability concerns demand Normal Variability

Wind Historical Variations

Outstanding issues How will planned (1-3 years) wind projects effect dynamic transfers? –Complete analysis of wind project variability relationship to location and capacity. Establish DTL for all paths –Finalize methodology for variability limit and “historical use” –Complete analysis of light load scenarios (varations of load, generation pattern, outages, etc.) Continue development of the optimization tools and processes –Monitor and archive based on state estimator cases –Include reactive switching actions and dynamic reactive support in optimization Increasing the capability –Identifying locations that require additional support for dynamic transfers

-Appendix – Dynamic Transfer Definitions Many of these definitions cited are from the NERC Dynamic Transfer Guide

Dynamic Transfer Limit Definitions –Dynamic Transfer: A dynamic transfer contractually allows a resource to continuously ramp over a pre-determined range. It may be implemented as either a dynamic schedule, or a combination of pseudo-tie and dynamic schedule. –Dynamic Transfer Limit: The maximum allowed deviation of actual MW flow from schedule and the maximum continuous ramp rate allowed. –Dynamic Transfer Limit Methodology: A systematic, repeatable evaluation of the costs and capability to accommodate dynamic wheeling across the FCRTS –Dynamic Schedule: A dynamic schedule represents a power transfer between two separate Balancing Authorities. The real-time value associated with the scheduled power transfer is treated as the interchange schedule in the ACE equation. Like other schedules, a dynamic schedule is a reserved use of transmission. –Pseudo-Ties: A pseudo-tie is commonly used to represent generation or load remote to the controlling Balancing Authority, but assigned dynamically between balancing authorities. It is treated as actual interchange in the ACE equation. The operational and jurisdictional responsibility for the generation or load rests with the controlling Balancing Authority, as if the remote resource was connected within the controlling BA transmission footprint. The pseudo-tie provides a mechanism for control and shifting of ancillary service responsibility. It is not a reserved use of transmission.

Dynamic Transfer Limit Definitions –RAS: Remedial Action Schemes (in the NERC glossary, these are also known as Special Protection Schemes). Method of gaining transmission capacity through automatic post-contingency control actions (e.g. tripping generation, inserting capacitors, etc.) –SCADA: Supervisory Control and Data Acquisition. Used by Transmission Operations System Operators to monitor and control the transmission system. –WIST: Wind Integration Study Team. A component of Columbia Grid and Northern Tier Transmission Group that is providing technical peer review of the BPA Dynamic Transfer Limit Study. –RODS: Real Time Operations and Dispatch System. An accounting and control application that is used as a link between the Transmission Scheduling systems and the Automatic Generation Control application. –DSS: Dynamic Scheduling System. An application currently being supported and developed by the Joint Initiative participants. The DSS is intended to provide a common dynamic communication infrastucture and protocol that will allow participating entities to purchase or sell capacity and energy on a dynamic basis. –MVAR: The portion of electricity that establishes and sustains the electric and magnetic fields of AC transmission equipment. Reactive power is provided by generators, synchronous condensers, or capacitors and directly influences system voltage.