Goshen Area Bus Reconfiguration Presented by PacifiCorp Grid Operations

Pre-Contingency Load Shed Event December 4, 2013 Pre-contingency load shed required to prevent post-contingency violation on underlying 161 kV system for loss of 345 kV source into Goshen Since event, PacifiCorp has taken steps to prevent another pre-contingency load shed event.

Why was load shed required? NERC standard FAC-011-2 R2.1 Highest available facility rating cannot be exceeded for a credible outage at any time. Peak RC enforcing these standards, via Peak RC SOL Methodology To prevent NERC standards violation, amount of load in the Goshen area reduced to level where 161 kV system could serve remaining load, and stay within all facility ratings following contingency

Why was load shed required? Example from Peak RC Emergency Rating 4 Hour Rating Normal Rating

Preventing future load shed Short Term Solutions: Reconfiguring Goshen 345 kV bus (Completed) Procedure to serve Goshen area load radial off 345 kV source (Completed) Additional relay settings on 161 kV system (Completed) Splitting Goshen 161 kV bus to prevent complete loss of load (Completed) Long Term Solutions: Local Area Protection Scheme (Under study) Additional Transmission Capacity under study

Reconfiguring the Goshen 345 kV bus Goshen 345 kV bus had a weakness If one breaker out of service, single contingency could disconnect 345 kV source from 161 kV source December 4: Goshen CB 303 was out of service for critical maintenance Extensive engineering work performed to reconfigure the Goshen 345 kV bus, minimize risk to load Bus reconfigured: single breaker outage cannot remove both 345 kV sources

Radial load procedure Procedure calls for opening up 161 kV ties into Goshen 161 kV bus 3 operated by PacifiCorp, 1 by Idaho Power If 345 kV bus is lost, all load served out of Goshen lost Prevents pre-contingency load shedding Not automatic Trips all load in the area once a threshold has been exceeded

161 kV relaying In coordination with Idaho Power and Northwestern Energy, relay settings placed on 161 kV ties into Goshen area to protect 161 kV lines Relay settings open breakers if the elements are overloaded Prevents pre-contingency load shed Load can survive certain outage conditions versus radial procedure Automatic protection: load only lost if contingency occurs Still trips all load in the area once threshold exceeded, if contingency occurs

Each bus has own 345 kV transformer source Goshen 161 kV bus split Solution serves portion of the Goshen area load off east bus, leaves 161 kV ties, generation, some load on west bus Each bus has own 345 kV transformer source If one (or both) sources lost West bus served off the 161 kV ties East bus is lost Prevents total loss of Goshen area load

Goshen 161 kV bus split

Goshen 161 kV bus split

Risk to load Without bus reconfiguration, 100% of load served in the Goshen area at risk for an N-1-1 Preserves as much load as possible given current transmission system Next two slides show amount of load at Goshen at risk for radial and split bus configuration

Risk to load

Risk to load

Sectionalizing benefits Palisades loop and wind generation remain online Facilitates faster restoration Unilateral implementation Does not require complex relay logic

Load risk probability Now, 4 conditions need to occur simultaneously for load loss at Goshen Peak loading conditions Minimal generation Single 345 kV line out of service (maintenance, permanent fault) Additional 345 kV line suffering a permanent fault 1-2 can occur at same time, third is rare Prior to PacifiCorp’s actions, only 3 of these need to occur to trigger action (pre-contingency load shed)

Local area protection scheme Local Area Protection Scheme (LAPS) potential Will require redundancy and WECC RASRS approval Based on real-time system and loading conditions LAPS could determine required amount of load to shed for each system condition An appropriate amount of load selected for loss of 345 kV source

Additional system reinforcements 161 kV transmission capacity reinforcement Goshen-Sugarmill line scheduled to be re-conductored in November 2014 Additional 161 kV reinforcements under study

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