Stabiliser is the Automatic Voltage Regulator which receive a fluctuating AC Voltage of low or high amplitude and delivers constant output voltag ±190 or ±0.5 % on demand.
2.
How will I select Stabiliser / Powercon Rating?
You will need to check the rating of the equipment to protected. Such rating are normally available to be protected. Such rating are normally available on Machine or on Load in Amp. or KVA. Otherwise you will need to consult the manufacturer of the equipment or take a measurements.
It is always recommended to measure the loads in True RMS value.
Second, you have to know about the Input - source Voltage fluctuations during day and night times.
In brief you have to select the Input Voltage window and the power consumption of your appliance with safety margins.