Presentation to WECC TSS May 8, 2015 Standpipe Synchronous Condenser and South-Central Wyoming Voltage Coordination Presentation to WECC TSS May 8, 2015

Introduction PacifiCorp customers in South-Central Wyoming system have been exposed to unacceptable voltage performance on a number of occasions. To remedy this issue, PacifiCorp is implementing several system improvements, including a new 65 MVA synchronous condenser at Standpipe substation, relocation of an existing 31.7 MVAr shunt reactor to Standpipe, installation of a new 25 MVAr shunt capacitor at Latham substation, implementation of droop control at area wind farms, and implementation of coordinated shunt device control at numerous substations.

Wyoming 230 kV System

South Central Wyoming Wind Dunlap 111 MW Seven Mile 118.5 MW Foote Creek 135 MW High Plains 127.5 MW

Dave Johnston Area Generation Windstar Area Wind 537.5 MW DJ 795.8 MW Windstar area generation: Glenrock – 237MW, TOW – 200 MW, Three Buttes – 100.5 MW

Voltage Performance Wind generation interconnected on the DJ to Point of Rocks 230 kV line tends to flow west (away from DJ). The Platte to Standpipe 230 kV line acts as a funnel for area generation, and sees the highest line flows in the region. Flow above 475 MVA is possible under maximum wind conditions. Flow on this line segment is directly correlated with wind generation output from Foote Creek, High Plains, Seven Mile, and Dunlap, and line flow can vary significantly with wind generation output.

Voltage Performance (ctd.) As generation output in the area varies, line load fluctuates above and below the surge impedance load of the line, resulting in large, relatively slow voltage swings.

Voltage Performance (ctd.) THE PERFECT STORM: High voltages are seen in the area when the DJ to Difficulty line is open in conjunction with low wind conditions. The DJ to Difficulty outage results in an approximately 200 mile-long, radial, lightly-loaded 230 kV line. During low wind conditions, area wind farms have little or no regulating capability. With the tie to DJ open, there is very little short-circuit MVA.

Standpipe Project To remedy voltage issues in the region, PacifiCorp is implementing several system improvements under the Standpipe project, including the following: Installation of a new +65 / -40 MVAr synchronous condenser at Standpipe substation. Relocation of an existing 31.7 MVAr shunt reactor to Standpipe. Installation of a new 25 MVAr shunt capacitor at Latham substation Implementation of droop control at area wind farms Implementation of coordinated shunt device control at Latham, Platte, Miners, and Standpipe. Decommissioning of the Foote Creek DVAR and implementation of power factor control of the shunt caps at Foote Creek.

Standpipe Synchronous Condenser Several dynamic reactive device technologies were investigated for Standpipe, including Static VAr Compensators (SVC), Voltage-Sourced Converters (STATCOM), and Synchronous Condensers. The synchronous condenser was selected based largely on technical criteria The Wyoming 230 kV system is heavily shunt compensated, and voltage instability was a concern with an SVC installation. System inertia relative to transfer levels (stiffness factor) in the region is very low. To date, STATCOM installations on the PacifiCorp system have not proven reliable, and difficulties were encountered procuring a STATCOM. The voltage swings in the region tend to be relatively slow, therefore speed of the device was not a significant factor.

Standpipe Synchronous Condenser There are several advantages of a synchronous condenser for this application. The condenser is a rotating machine, and adds inertia to the system. Control of the device is relatively simple and is not impacted by system configuration or future system upgrades. Linear output characteristic. Very few power quality issues. Voltage drop from starting was a concern; however a pony motor will be utilized to start the device. Coordination with local area wind farms can be managed with droop settings. There are also disadvantages associated with a condenser Losses Maintenance requirements Losses are mitigated to some extent by selecting a 6 pole machine – 1200 RPM rotation reduces windage losses. Maintenance reduced with brushless design. Compromise in machine speed.

Standpipe Condenser Dynamic Expansion The Miners shunt capacitor and Standpipe shunt reactor will be utilized to expand the available dynamic capacity of the condenser. The scheme will utilize the shunt devices to bias the synchronous condenser output to a value near the center of its dynamic capability (+15 MVAR). As the Standpipe synchronous condenser has a continuous output capability between -40 MVAR and +65 MVAR, the bias point at +15 MVAR will effectively provide +/-50 MVAR of available reactive capability to respond to system voltage fluctuations.

Standpipe Condenser Dynamic Expansion The Miners and Standpipe shunt devices will be controlled by the condenser as follows:

Wyoming Shunt Device Coordination Latham 1x25 MVAr Cap

Wyoming Shunt Device Coordination Platte 2x25 MVAr Cap 2x27 MVAr Cap

Wyoming Shunt Device Coordination Miners 1x27.6 MVAr Cap

Wyoming Shunt Device Coordination Standpipe 1x31.7 MVAr Reactor 65 MVA Condenser

Wyoming Shunt Device Coordination Foote Creek 6x5 MVAr Cap 3x6.67 MVAr Cap

Wyoming Shunt Device Coordination Shunt devices at Latham and Platte will be controlled locally utilizing coordinated switching setpoints and time delays. Shunt devices at Miners and Standpipe may be set to control local voltage utilizing coordinated switching setpoints and time delays; however their primary mode of operation will be the condenser dynamic expansion scheme. Shunt devices at Foote Creek will be controlled to minimize VAr exchange to the 230 kV system, with 34.5 kV voltage supervision.

Wyoming Shunt Device Coordination Shunt devices will be controlled utilizing a dual-band control philosophy.

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