Gaurav Sharma John Hannah Vivekanand Sivaraman TIMING APPLICATIONS OF GPS High Energy Transmission with High Precision GPS Time Gaurav Sharma John Hannah Vivekanand Sivaraman Gaurav Sharma John Hannah Vivekanand Sivaraman

ABOUT BPA Bonneville Power Administration – Power Supplier in the Pacific North West. Serves Oregon, Washington, W Montana, and most of Idaho. 390 switching stations 16500 MW Power Capacity & 8600 MW annual delivery 181 Customers including industries and public utilities

Timing Applications in Energy Transmission Power generation and Power transfer Power Outages Disturbance Records Fault Location Real Time Phase Measurements Power Generation and Power Transfer: Scheduling. Power Outages: Maintenance Outages are scheduled. Disturbance Records: Records need to be time stamped. Billing: Price varies with demand – so billing is based on time Fault Location: discussion Now or later ???? Real Time Phase Measurements: discussion Now or later ????

BPA: Timing Techniques and Problems Central Time System Not enough accuracy for Fault locators signal subject to distortions High frequency pulse over Microwave for Fault Locators Used up a lot of available bandwidth Local Time Code Generators for remote stations Time code generator needs to be manually resynchronized every couple of months – no resetting at regular interval Radio reception from GOES or WWV GOES receivers off the correct time. GOES signal subject to interference and eclipses. GOES satellite system problems – repositioning - requires antenna repointing. Central Time: Synchronized to UTC. Uses IRIG-B time code over microwave for time to field locations. The MW pulse for FLAR: needed for higher accuracy (than can be provided for by IRIG-B time code). Local Time Code Generator: Required because distortions of MW signal are common and difficult to resolve – for distant stations Radio Reception from GOES and WWV Radio station: For distant stations. GOES: Geostationary Orbit Earth Satellite WWV: Radio Station, Fort Collins, Colorado

BPA: Timing Techniques Problems Possible Solution: GPS 1 microsecond accuracy Multiple satellite redundancy High Reliability BPA Lab Testing – showed high accuracy, precision and reliability in timing.

GPS Implementation in Central Time System New system - 3 primary sources, 1 voting switchover unit + Monitoring Systems Primary sources equipped with GPS receivers, each having an antenna and a power unit. 2 with battery back up. 1 has a rubidium oscillator in the event of GPS input failure. Improved Switching Tolerance (1 Microsecond level) (What is switching?) o Each source independently decodes time and frequency and generates a 1PPS signal and 1Pulse per 100 sec signal. Each monitors the 60Hz power system frequency with the GPS based reference. Computes the power system frequency and errors – output. o The switching unit compares the time, frequency and error signals. This unit designates one as a primary source and compares same set of signals from other two. If one unit is off by certain tolerance limit it is blocked – if the primary is blocked – switching designates another as the primary. The GPS system has allowed a low 1microsecond tolerance for switching.

GPS Implementation in Fault Location and Rectification When a fault occurs on a transmission line a high frequency wave propagates in both directions from the fault. Compare the arrival time at switching stations on the either side of fault for locating it. Problems with Old System: Synchronization pulse used a lot of bandwidth (expensive) over the analog microwave system Available to major stations only GPS Implementation: Initially, for the synchronizing the pulse to UTC only - Later, also as FLAR units Available to even minor and remote stations When a fault occurs on a transmission line a high frequency wave propagates in both directions from the fault. Compare the arrival time at switching stations on the either side of fault. Compare the arrival time at switching stations on the either side of fault. Since the accuracy of measurement is 1-micro second and the speed of wave is about the speed of light – the accuracy of determining the position is about a 1000 ft. This is the spacing between two high voltage transmission line towers, which is saying that the search is narrowed to a few transmission towers. Initially GPS receiver was used to synchronize the pulse to UTC. This allowed transmission of the pulse to a remote unit that was not covered by the microwave system. Now they use the GPS receivers as FLAR units in themselves. Wider coverage and cheaper installation. Plan to phase out the complete analog system in another 10yrs or so.

GPS Implementation in Phasor Measurements Phasor: a vector representation of a sinusoidal quantity that includes a magnitude and a phase angle. The power system in North America is a three-phase 60Hz sinusoid. Phase angle between two stations determines the power transfer between stations. Phasor observations used for monitoring. (Require 0.1 electrical degree accuracy for monitoring Or 5 micro-sec synchronization between monitoring units.) GPS used as precise timing source.(The accuracy of time measurement ~1 micro-sec). o  Phasor is a vector representation of a sinusoidal quantity that includes a magnitude and a phase angle. o The power system in North America is a three-phase 60Hz sinusoid. o Phase angle between two stations determines the power transfer between stations. The phase angle keeps changing according to the power being consumed in different ‘phases’. o  Phasor observations are used for monitoring. There is an optimal phase angle when maximum power transfer takes place. o  Require 0.1 electrical degree (at 60Hz 1 electrical degree = 46 microseconds) accuracy for monitoring => 5-microsecond synchronization between monitoring units. o GPS was used for precise timing source for the purpose of testing.

Conclusions Expensive upgrades and redundancies were avoided. GPS provided a comprehensive way for implementation of accurate timing system – no need for different timing system for every other system. Stood the tests for accuracy, reliability, coverage and cost.