Generator PQ curve on HMI

A little out of my area of expertise, but I found this , might help....

https://www.semanticscholar.org/paper/User-P-Q-Diagram-as-a-Part-of-a-Synchronous-System-Vrazic-Viskovic/ed7bd83657ad5fffac838ba1a3034e40f51ca2a1

A lot depends on your HMI and the DCS/Controller.

I wrote a program to Display the efficiency of a dragline while digging. There were 300 lines of code that stored the instantaneous values of current vs voltage in a Modicon Quantum PLC, as the cycle was being performed. The HMI, a Citect, read the stored values and built up the display in both %, numerically and in Graphically.

With other PLC and HMI it would be possible as I have made a similar program in Citect to read out values from a Bailey infinet 90 and to do the same with the Citect reading from a Schneider Premium PLC.

Does this mean that an array of data is needed in the PLC first? I have the following generator data available to the HMI and PLC, Active Power, reactive power, power factor, voltage, and current. How can I make use of this data to produce a real-time performance plot for the active power, reactive power, and power factor?

The HMI is Emerson

You do understand that the PQ curve for the generator is a static curve, you just report where the generator happens to be operating on that curve. The generator manufacture will call it a reactive capability curve, and will limit it to normally 3 quadrants, very little is allowed if reactive is lagging, power system supplying excitation to the generator. There might be a family of curves depending on temperature of the windings.

Not 3 quadrants, my bad, really barely more than 1 quadrant, and generator receiving excitation from load system is called leading operation of generator, lagging generator operation supplies reactive Q to the load system.

Your green pointer 180 degree would be angled like an analog meter pointer, angle based on calculation of kVA & power factor, against the static meter range specified by the generator manufacturer.

Your pointer equation needs to be separated into separate segments, truncated as Rixter shows, perhaps masked by the static overlay to get around having to truncate the green pointer ray...

Kindly assist or give me some more insight on how it can be done.

As the figure supplied by Rixter shows, the Y value of the indicator is the real power output of the generator MVA positive or negative, the X value of your display array is the value of MVAR, which can be positive or negative. The limit you need to calculate at each operating point to decide if your current point exceeds or is less than the limit, to turn the indicator color from gray or green to red, depending on your situational awareness scheme for the HMI.

I would develop a set of equations regressed from operating points defined on the Reactive Capability Curve, you need 4 such limit equations, to describe the 4 segments.

For example, you calculate the current power factor, and decide that the equation for the limit is the one furthest to the right, power factor below 0.8, for example, if that happens to be the rated power factor. You then plot the X,Y pair, MVAR, MW, and use the inverse parabolic equation for the rightmost segment to decide if it is red or green or gray.

I would break up the curve between -MVAR and +MVAR into two equations, and if the operating point is at all to the left of the Y axis, I would turn the indicator blob Yellow, to show that we really don’t ever want to be operating to the left, caution is advised.

Active power is MW, reactive power is MVAR, both signed floats. MVA is (amps x volts x square root of 3) / 1,000,000, and Power Factor is MW / MVA also a signed float. The square root of the sum of MW squared and MVAR squared is also MVA, you may be able to use trig in your calculations, but I like to code at the simplest forms, for the next person as well as for me understanding it 2 months later.

(Depending on the size of your machine, kVA may be more appropriate)

Why?