It is a value of the instantaneous value of the voltage and even the direction continuously changing with time. At its maximum, it is 220 times the root number (1.414x220 = 311 volts), and when it is the smallest, it is minus 311 volts (in this case, the voltage is reversed), and the zero crossing is changed from large to small. At this point intersects the horizontal axis).
When describing an electrical system, it is common to describe its voltage, current, resistance (or impedance). You can describe an electrical system from the perspective of a radio signal (if you are doing an analog radio communication system), you can also The angle of electricity describes an electrical system (this is the initial entry point for students and textbooks). At this point, you use the RMS value of voltage and current instead of the instantaneous value mentioned above.
The validity of the RMS value refers to what effect this electricity actually has on your diesel generator (or how much equivalent heat is generated for the resistance in the later test), so the RMS value is the basic electrical system description. Value, and it is usually used only to describe the alternating current