Synchrophasor Initiative in India - erldc

SYNCHROPHASORS - INITIATIVE IN INDIA JUNE 20124 CHAPTER 4: UTILIZATION OF SYNCHROPHASORS IN REAL TIMEPhase angle measurement is commonly used in auto synchronization of generating stations andcheck synchronization relays used at substations for closing of lines as well as during threephaseauto-reclosing. All these applications are at the local level. At control centre level thisanalogue value is normally not considered as measurable in SCADA system and hence doesnot form a part of the database. However SCADA technology does provides an estimate of therelative phase angle difference (with respect to a reference bus) through the State Estimator.The State estimator uses the SCADA inputs (analogue and digital measurands) to estimate thesystem state viz. node voltage and angle. SCADA data has limitations due to resolution, datalatency, updation time and data skewedness. Update time in the SCADA system is considerablylarge for visualizing and controlling the dynamics of power system. The synchrophasorstechnology overcomes the above limitations to a large extent and it has been found tosupplement the real time data available from SCADA/EMS. Two sets of displays are available;one set of displays with data from Historian and second set of displays with real time data fromPDC. Few customized displays have been prepared for the operators. Displays are presently ofthree types- tabular display, dial display and trend display.In control room the synchrophasor data has helped in improving/enhancing situationalawareness through real time monitoring of frequency, df/dt, angular separation and voltage. It ispossible to recognize the occurrence of transmission line tripping/ revival within a flow gate byobserving the step change in angular separation, step change in voltage magnitude, stepchange in line current (MW & MVAR). It is also possible to recognize the occurrence ofgenerator tripping by observing the frequency decline, increase in df/dt, change in angularseparation, decrease in voltage magnitude. Occurrence of load crash/ load throw off can beobserving sustained High frequency, sustained abnormal phase angle separation, SustainedHigh voltage. It also helps in subsystem synchronization during restoration by using standingphase angle separation and phase sequence.4.1 Visualization of grid frequencyA synchronous system is generally characterized by a same frequency at all nodes in steadystate as observed in SCADA/EMS.4.1.1 Case Study-1: Difference in frequency at different locations in NorthernRegionFigure 42 and 43 show the frequency profile recorded by PMU’s on 23 rd May 2010 and 3 rdJanuary 2011. The difference in the frequency at Vindhyachal, Kanpur, Dadri and Moga can beclearly seen from the synchrophasors data. All these four nodes are located far from each otherwithin the synchronous grid.POSOCO Page 55 of 143