Phasor Measurement Unit

Today, I read about Phasor Measurement Unit (PMU). If you are familiar with alternating circuit theory, you should know what phasor is. But it is always good to refresh our memory, isn't it?

In ac circuit analyis, generally we use a voltage source, sinusoidal voltage source. Then we usually represent it using something like

v(t)= Vm sin (wt + d)

at time t=0, it is

v(0) = Vm sin (d).

The last one can be in short represented as a phasor with magnitude Vm/sqrt(2) and phase angle d. Hence, a phasor is an alternative representation of sinusoid signals. This ends our review about it.

Now, returning to PMU, it is a technology that enable power utility to have real-time synchronised phasor measurement unit. How can it be done? It is done by integrating digital signal processing, sensors, GPS and telecommunication technology. Sensors are used to sample voltage or current signals. DSP further processed it to find its fundamental frequency, amplitude and phase angle. With the help of GPS, measurements can have time stamp which provide us with synchronous measurements. Those are a very short introduction of how a PMU works.

Next, how is it useful for power engineer? Well, you know, when we are doing steady-state analysis of a power system, our state variables are voltage phasors at all buses. Once we know them, we can calculate other information such as, power flow, current, and line losses. The whole procedure of load flow calculation is to find them. The good news is those phasors can be directly measure using PMUs. Another possible application is to measured slow transient in power system caused by load variation. Those measurement can be used to verify relevant dynamic model of power system.

We can also have better information to predict future load or possible contingency.

Well now that you know a little about PMU, you might want to read more, don't you? Here are the list of reading materials related to this topic.

[1] Phadke, A.G.; , "Synchronized phasor measurements in power systems," Computer Applications in Power, IEEE , vol.6, no.2, pp.10-15, Apr 1993

doi: 10.1109/67.207465
URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=207465&isnumber=5308