Synchrophasor Implementation to Establish Dynamic Line Rating Paired with Adaptive Distance Relaying Protection
By Chris Postma
Methods have previously been developed using synchrophasors to aid in the measurement of transmission line constants for use in protection settings. This paper seeks to further these elements by incorporating three phase line constants calculated with synchrophasor data. These calculated values can be used to adjust the directional protection to maintain accurate settings based on the available thermal capacity of a given transmission line. This approach can be used to track not only the variation of line constants with MVA loading and varying weather conditions, but also the modulation of line capacity due to the impact of atmospheric conditions.
By directly tracking the line constants the available line transfer capacity can be determined while taking account of potential loading imbalance between phases. The author’s hope for this assessment method is twofold, first, that it can be implemented in existing synchrophasor installations to provide a metric for monitoring transmission element stressing. This implementation was determined to be particularly useful in areas where wind resource penetration was constrained due to static thermal line ratings. Second, to provide adaptive protection of the element as its thermal loading varies due to operating in a dynamic environment.
Adaptive distance relaying accounts for the impact of thermal loading on line impedance and helps to prevent unnecessary tripping events due to protection settings based on static line characteristics. To test this implementation two relays with Phasor Measurement Unit (PMU) capabilities were driven using forced outputs from an Omicron CMC 353 relay test set. The Omicron was used to simulate increases and decreases in thermal loading. These events represent various loading conditions on a transmission line, which were used to show line constant modulation due to changes in system demand and ambient weather conditions. The synchrophasors were provided to a Real Time Automation Controller (RTAC) for processing to validate the method. RTAC values were used to switch relay protection settings groups to reflect real time modulation of transmission line constants.
This paper was presented at the 5th Annual PAC World Americas Conference 2018 in Raleigh, North Carolina