1. Goshen Area Bus Reconfiguration
Presented by PacifiCorp Grid Operations

2. 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.

3. Why was load shed required?
NERC standard FAC 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

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

5. 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

6. 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

7. 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

8. 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

9. 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

10. Goshen 161 kV bus split

11. Goshen 161 kV bus split

12. 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

13. Risk to load

14. Risk to load

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

16. 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)

17. 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

18. 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

19. Questions