Monitoring of Angular Separation in Power system: Part 8 Synchrophasor measurement
Coming to the end of this angular separation monitoring article series, the last tool which system operator utilizes for measurement of angular separation is Synchrophasor data. However, prior to this, we already have a simplified view of the fact why direct angular separation measurement in a power system is not an easy task and complexity involved in transfer of this data to control center. The reason behind that is that you need to know the exact voltage phasors of distant locations and compare them with keeping one as a reference to get angular separation.?Collection of such highly granular information (one sinusoidal phasor is 20 ms for 50 Hz system) with time synchronization for comparison is a tough task. Look at the complexity of the overall process in the below figure.
This task can be simplified in form of Synchrophasor estimation. It is an estimation of phasor waveform over a period of time where the window over which it is estimated is synchronized with time stamping. Thus, the estimated phasor in the window will be a cosine wave with magnitude and angle with respect to the common reference used which is GSP time stamp. The estimation of phasor over a window reduces the amount of data significantly. And as the GPS time stamping will be available at all locations without any delay which will make common time reference available at all locations. This process is shown below.?
Now we need a device that can take input from CT/CVT at all locations in substations/plants and will use a phasor estimation algorithm over a fixed defined window length and utilize GPS time stamp to synchronize the estimation activity across all such devices in the power system. This device is called as phasor measurement unit (PMU). The various component of PMU device is described in below figure.
A brief history behind the phasor measurement unit is required to be quoted. How the improvement in computational process, instrumentation devices, communication technology and satellite technology has resulted in its development can be seen from the below attached figure.
Now coming to the point that if the PMUs are installed in various substations and they are estimating phasor then how the angular separation can be known to system operator.?The answer lies in Wide area measurement system (WAMS). ?WAMS system is basically comprised of field-located PMUs, Communication system (Optical fiber in general) from field locations to grid control center, a phasor data concentrator and analytical tools.
PMU sends the time-synchronized phasor data at a given reporting rate (25 Samples per second) in a standardized format as decided by IEEE C37.118 protocol. The same information is received via communication system by a phasor data concentrator (PDC) which decodes the time-synchronized data from various locations PMUs as per IEEE C37.118 format and arranges them with their time stamp. Thus, from PDC a complete snapshot of the grid at one time stamp can be known by system operators. Further, as all the voltage phasors of various substations at one timestamp are estimated using the same common reference signal so the angular separation between them can be calculated by subtracting their angles. This is shown in below figure.
PMU provides below shown information from various substations/power plants in time synchronized way. Further, the Synchrophasor data is also available at such a high rate thus providing system operators with a dynamic view of the entire power system. These characteristics of power system data available to system operators in real-time make it a powerful tool for monitoring. Multiple situational analysis visualization and tools can be developed over the high granularity data. Overall Synchrophasor data directly provide system operator with dynamic state measurement and operator can have adjacent as well wide area angle measurement for improving grid operation.
领英推荐
There is a multitude of references available to learn about PMU and WAMS.?You can visit website like NASPI, POSOCO, CIGRE, IEEE from where this information has been collected and shared.
With this, we complete the series of 8 articles on the Monitoring of Angular Separation in Power system. Links to old articles are provided below. Hope it helps us in learning about the practical aspects of power system operation.
Three angles of power system:
Monitoring of angular separation in power system part 1-7
Many thanks to my colleagues, mentors, seniors for helping us throughout this process and journey of learning in area of power system. Its our humble attempt to share some of experience learned during this continuing journey.
ASSISTANT ENGINEER TGTRANSCO
2 年Nice information Chandan Ji
Energy | CEA | Energy Efficiency |Design, Engineering| Energy Optimization
2 年Very useful article and series, insightful tool and info.Chandan Kumar
Former and founder CEO POSOCO, now Grid-India; Retd CPES India; FIEEE, FINAE, FNAE, FIE(I), Distinguished member Cigre, Distinguished Alumnus IIT KGP
2 年Thanks .Useful practical educational series on Angular Separation .....BTW power system representation and modelling could be either in Polar coordinate or Cartesian coordinate. It is because of easy handling of complex numbers by computers and absence of easy measurement of Angle that Cartesian dominated over Polar methods.I learnt Polar from Dr T N Saha at IIT KGP in 1973, later from the book by Stagg and Elabiad . Vintage Literature on Polar method techniques are very insightful , time to revise ....