Advancement in Wide Area Monitoring Protection and Control Using PMU’s Model in MATLAB/SIMULINK ()
1. Introduction
The electrical power system is not a simple thing it’s a complex man-made system so it has many problems where as on the other end, it should reliable and supply electrical energy continuously without any interruption. There should be no blackout and outage [1]. The blackouts and especially infrequent outages is a combination of series of interrelated events. These series of events are hard to account even with modern powerful systems and can no longer be contained to the small portion of the system. Sometimes these small events or disturbances can be amplified to a system wide effect. Therefore for this purpose many techniques have been developed to survive the power system during disturbances and to continue its operation [2]. One recent developed technique which is used is WAMPAC with time synchronized measurement. It is a technique which transports the local information of selected areas to the remote location to work against the promulgation of vast disturbances. Presently, [3] the main technology used in it is PMUs and is the most precise and advanced technology. It gives information about the current and voltage Phasor, frequency and rate of change of frequency, this all information is synchronized with a high accuracy to a common reference time provided by GPS [4]. Its operation is based on mathematical measurement algorithms [5]. in an environment where the protected area is large, it would be very hard to design a protective or emergency control scheme based on fixed parameter settings As technology advances, the time frame of synchronized information has been steadily reduced from minutes, to seconds, milliseconds, and now microseconds. If only PMU measurements are used, there are also no complications from the use of both polar and rectangular values in the state estimation process, as would be done when including PMU measurements in traditional state estimators [6]. For example, one of the proposed applications of PMUs is their use on control for monitoring, alarm, and control operations [7].
This technology has been made possible by advancements in computer and processing technologies and availability of GPS signals. We are rapidly approaching an era where all metering devices will be time synchronized with high precision and accurate time tags as part of any measurement. To achieve the potential benefits, advancements in time synchronization must be matched by advancements in other areas. One example is data communications, where communication channels have become faster and more reliable in streaming PMU data from remote sites to a central facility. Improvements in instrument transformers (such as optical transducers) are important for the quality of the signals supplied to the PMU. A third area is in developing applications, i.e., software that operates on the data provided by the PMUs. Although academia, vendors, utilities, and consultants have developed a large number of methods and algorithms and performed system analysis and studies to apply the technology, like any other advanced tool, PMUs are good only in the hands of trained users. The technology exists today to bring the PMU information into the control centers located at remote area and present it to the operators in a graphical format. In this paper we discuss this advanced technology (PMUs) with the help of MATLAB simulation. We design this PMU model in MATLAB SIMULINK and then we installed this model in the start and end of transmission line in our sample simulation of a small power system in SIMULINK. This all is for testing of its testing valuation. Such application is made for the protection, monitoring and control of wide power system. And this paper also discusses our related research work to this subject.
In Figure 1 there is a transmission line, PMUs are installed on both ends of transmission line, these PMUs get data from CT and PT and then find the real time Phasor of current, voltage, frequency and rate of change of frequency, These Phasor are synchronized with respect to time provided by GPS, then transfer this data to the local PDCs, this data is then transferred to super PDC and then super PDC gives that data to data server.
2. Phasor Measurement Unit
[8] One of the most important measurement devices in Power systems is PMU. The PMU is capable of measuring the synchronized voltage and current phasor in a power systems. [9] The commercialization of the GPS with accuracy of timing pulses in the order of 1 microsecond made possible the commercial production of phasor measurement units. [10] PMU is considered to be one of the most important measuring devices in the future of power systems. The distinction comes from its unique ability to provide synchronized phasor measurements of voltages and currents from widely dispersed locations in an electric power grid. Simulations and field experiences suggest that PMUs can revolutionize the ways that power systems are monitored and controlled.
In this paper we introduce the PMU’s simulation in MATLAB and we integrated PMU in a simple power system. We derived the mathematical model and did simulation in MATLAB/SIMULINK.
PMU Mathematical Model
Following mathematical model is used to calculate the magnitude and phase angle of currents and voltages.
These equations are represented below:
(1)
Now for real part:
Now
(2)
(3)
Put Equations (2) and (3) in Equation (1)
For imaginary part:
(4)
(5)
(6)
Put Equations (5) and (6) in Equation (4) so
Now for magnitude and phase angle:
In this mathematical model we calculated real and imaginary part separately and then from it we calculated magnitude and phase
Figure 2 shows the PMU model which finds the Phasor of current, voltage, frequency and rate of change of frequency with respect to the GPS time. It gives us time synchronized measurement (this is the main advantage of PMU) angle.
3. Wide Area Modeling
Figure 3 shows our main simulation model where we have small sample power system; we have sub-system of generation and have two load areas consisting of domestic, commercial and industrial loads. These areas are fed by 500 kv transmission line. [11] In this power system we installed PMUs at both ends of transmission line and also in generation sub-system.
Figures 4-6 are the sub-system of load consisting domestic, commercial and industrial respectively.
4. Wide Area Monitoring
PMUs create a picture showing the stability status of the nodes in the monitored area. PMUs take this picture at the same reference time. Using real-time information from PMUs and automated controls to predict, identify, and respond to system problems; a smart grid can automatically avoid or diminish power outages, power quality problems and supply disruptions.
A Phasor network consisting of PMUs spread throughout the power system, PDC collect the information from PMUs and GPS time stamping can provide a theoretical accuracy of synchronization better than 1 microsecond. “Clocks need to be accurate to ±500 nanoseconds to provide the one microsecond time standard needed by each device performing SynchroPhasor measurement.” For 50 Hz systems, PMUs must deliver between 10 to 30 synchronous reports per second depending on the application. The PDC correlates the data, controls and moni-
tors the PMUs (from a dozen up to 60) .
In Figure 7 we have a current magnitude of phase c, current injection of line-1, current injection of line-2 and current injection of generator. Generator current is higher than line-1 and line-2 because at generator terminal we have 11 kv but at transmission line we have 500 kv. This all information of current magnitude is measured by PMU. We are measuring the current magnitude of all phases like this one. These all values of currents are real and time synchronized taken at the simultaneous time.
Figure 8 shows the voltage magnitude of phase c, voltage of line-1, voltage of line-2 and voltage of generator. Generator voltage is less than line-1 and line-2 because for transmission we step-up the voltage. This all information of voltage is calculated by PMU. We are measuring the voltage magnitude of all phases like this one. These all values of voltages are real and time synchronized taken at the simultaneous time.