I think you should read thepaper below.

In general, a PMU measures the electrical waves using GPS for time synchronisation. The devices are installed at the begin as well as the end of a line and send both signals to a Wide Area Measurement System (WAMS). The WAMS compares the signals and determines the phase difference. So it is possible to determine the complex voltage vector respectively the system state.

http://ieeexplore.ieee.org/xpl/articleDetails.jsp?tp=&arnumber=1556966&sortType%3Dasc_p_Publication_Year%26queryText%3D.QT.Phase+Measurement+Unit+.QT.

PMU  is consists of filters,Analog to digital converters,Receivers,PLL.Usually it measures waves and all the mesurements are synchronised and time stamped.Calculates signal magnitude and angle called phasor.

Usually an unknown signal passes through filters ,converters and then estimators and receivers and during the process,PMU configuration is able to extract the above said informations.

A phasor measurement unit (PMU) or synchrophasor is a device which measures the electrical waves on an electricity grid, using a common time source for synchronization. A PMU can measure 50/60 Hz AC waveforms (voltages and currents) typically at a rate of 48 samples per cycle (2880 samples per second for 60Hz systems). The analog AC waveforms are digitized by an Analog to Digital converter for each phase.

https://www.eiseverywhere.com/file_uploads/b9c0cedfe296b5347ce0877fbfac3753_PMU_Relay_Schoolcopy.pdf

http://www.eng.buffalo.edu/Research/BEST/Teaching/EE611/Phasor_Measurement_Unit.pdf

PMU-Phasor measurement unit consists of  an Anti Aliasing Filter,A/D Converter,GPS unit,PLL oscillator, Microprocessor unit,Modem- Transmitter etc. checkout the block diagram of PMU. For the sampled analog input signals, it estimate the states out of it and time signals are tagged.The time stamp is an 8-byte message consisting of a 4 byte S.O.Cand a 3 byte FoS and a 1 byte time quality indicator as per  IEEEC37.118 /IEEE C37.224

Through an Remote terminal unit informations are exchanged to Station PMU's later ThroughTCP/IP Protocols the communication is held. The data get stored  for further processing at PDC .

 For further details Refer the author Phadkeand his findings.

The traditional technique are too bulky and iterative in nature for system power flow measurement. The new technique of Phasor Measurement Unit is now applied for measurement of bus voltage and current. The state estimator by use of full weighted least square is nonlinear in nature, but with PMUs and traditional technique it will improves the accuracy of the measurement with minimum use of the iteration process.

https://www.researchgate.net/publication/310006226_GAMS_Code_for_Optimal_PMU_Placement

Code GAMS Code for Optimal PMU Placement

Thank you so much Dr. Alireza for shedding the light and sharing the materials.

 synchrophasor  units(PMU) are installed at remote end in power substation.They are connected to CTs(curent transformer)  and PTs (potential transformer).Line current and voltage are directly fed to these devices.Inside PMU, it has filter circuit, sampling circuit , time synchronised signal(from GPS) and processing  unit. Before processing the input signal for estimating its phasor value, it is filtered and sampled to overcome the problem of aliasing and leakage .Through suitable algorithm like FFT, IpDFT, SDFT or parametric approaches its phasor estimation is performed. Estimated phasor value consist of magnitude , phase , frequency and rate of change of frequency  of input signal .These set of information are sent as frames(40/60 frames per second) through different communication channels to PDCs (Phasor Data Concentrators).PDC is connected to several PMUs in a region .They concentrate the data collected from different PMUs and send to control centre for taking the necessary control action.

Hello Salah Eldeen Gasim Mohamed,

A brief overview of the operation of PMU and WAM is available at the 3rd book in the following list

https://www.researchgate.net/profile/Mohamed_EL-Shimy/publications?pubType=book

Some advanced applications of them are available at the 2nd book in the above list, and the following article

Article Stability-based minimization of load shedding in weakly inte...

A phasor measurement unit (PMU) is a device used to estimate the magnitude and phase angle of an electrical Phasor quantity like voltage or current in the electricity grid using a common time source for synchronization. Time synchronization is usually provided by GPS and allows synchronized real-time measurements of multiple remote measurement points on the grid. PMUs are capable of capturing samples from a waveform in quick succession and reconstruct the Phasor quantity. The resulting measurement is known as a synchrophasor. These devices can also be used to measure the frequency in the power grid. A typical commercial PMU can report measurements with very high temporal resolution in the order of 30-60 measurements per second. This helps engineers in analyzing dynamic events in the grid which is not possible with traditional SCADA measurements that generate one measurement every 2 or 4 seconds. Therefore, PMUs equip utilities with enhanced monitoring and control capabilities and are considered to be one of the most important measuring devices in the future of power systems. A PMU can be a dedicated device, or the PMU function can be incorporated into a protective relay or other device.

Phasor Measurement Unit (PMU)

A device (mostly microprocessor based) which reports the magnitude and phase angle of an analog and /or derived phasor with respect to the global time reference, as per the synchrophasor standards ( IEEE 1344, IEEE C37.118).

The PMU is a devise in which you can measure 50/60 Hz AC waveforms ,it convert the later into three parts phasor(Amplitude+phase)+the frequency.

Samples the continuous voltage or current signal.

Uses Discrete Fourier Series (DFS/DFT) method to compute the magnitude and phase of the signal.

Calculate magnitude and phase for each phase of the 3-phase quantity