Quality Parameters of Electric Supply
Frequency is a global phenomenon, i.e., it is the same at all points of a grid which is operating in synchronous operation. Frequency is an indication of the balance among generation and load in a grid. If the generation closely matches the load, the frequency would be the nominal frequency, that is., 50 Hz. If generation is more than the load in a grid as an overall, the system frequency would be greater than 50 Hz. If generation is less than the load, the system frequency would be less than 50 Hz.
Voltage is a local phenomenon, i.e., it can be different at different points of the grid. Thus, the grid operator has to ensure in which the proper voltage profile is managed at all points of the grid. For ensuring proper voltage profile, capacitors or reactors are installed at various points in the grid. If it is observed that the voltage is low at a particular point in the grid, then capacitors are installed at in which point. Same, if voltage is observed to be high, as per the studies, then reactors are installed at that point. The basic reasons of these elements are to ensure in which the reactive power requirement of the load or transmission lines is met.
Besides this, there are also other voltage phenomena such as unbalanced voltage in the three phases, voltage dip and etc. Voltage unbalance in the grid could be caused because of the tripping of one of the phases of a transmission line or because of unbalanced load in the three phases emanating from the distribution systems or bulk loads. Voltage dip, instead, is a transient phenomenon caused through a transient fault or tripping of an element at a remote location of the grid. Stormy weather could also cause flashover among arcing horns, resulting in voltage dip.
Harmonics is recently becoming an issue in the modern world, because of a number of electronic devices linked in the grid as well as in the distribution system, that converts AC to DC by rectifiers or which chop an AC wave for voltage or current control. In the grid, harmonics are caused through HVDC stations that convert AC to DC and back from DC to AC. In the distribution system, harmonics are caused through power supplies and inverters through that power are supplied to computers and all household appliances using digital technology that have permeated our lives. For this, standards have been laid down in the Regulations for Technical Standards for Connectivity to the Grid. As per the provisions of these Standards, the limits for individual and total harmonics distortion have been given.