What is the red color marked block in the attached figure ?

[Walter Roberson]

Is a higher resolution image of that available ?

[Yangyadatta Tripathy]

This is as higher resolution I can find.

Answer 1

[Walter Roberson]

I was able to determine that the blocks that are feeding into there are Voltage sensors, which output a numeric (Simulink) signal, not an electrical signal.

It is pretty difficult to tell, but the block just might be a Mean block: https://www.mathworks.com/help/physmod/sps/powersys/ref/mean.html which would output the mean of the input over one cycle of a given frequency.