System voltages classes can be classified into three:
- Low Voltage – System voltage which are less than 1000 V
- Medium Voltage – System voltage equal to or greater than 1000 V and less than 1,00,000 V(1000kV).
- High Voltage – System voltage greater than 1,00,000(100kV).
The application of this voltage classes:
- Low Voltage : This class of voltage is used for supply for utilization equipment(generally non industrial), majorly residential loads.
- Medium Voltage: This class of voltage is generally supplied for distribution transformer, which steps down the medium voltage to low voltage to supply utilization equipment. Medium voltage below 13.8 kV are often used to supply large motors
- High Voltage: This class transmit large amount of electric power from one substation or main transmission substation located mean generating station to another transmission substation and further it will step down to medium voltage and distributed.
The above voltage class classification are as per IEEE 141 standards.
Voltage Classification as per IEC 60038
The Voltage Classification as per IEC 60038 used in a power system transmission and distribution are as follows:
- Low Voltage – upto 1000V
- dium Voltage – 1000V to 35kV
- High Voltage – 35kV to 230 kV
- Extra High Voltage – above 230 kV.
Voltage Classification as per Indian Electricity Rules
As per the Indian Electricity Rules the following voltage classification:
- Low Voltage: upto 250V
- Medium Voltage: 250 – 650V
- High Voltage: 650V – 33000V
- Extra High Voltage: above 33000V
The two main parameter of electric power supply are “Voltage” and “frequency”, which are not same around the regions. considering single phase 230 V and 50 Hz are mainly followed in Aria, Africa, Europe etc. and while in America they use 120 V with 60 Hz frequency. Different voltage levels and frequency combinations are used in different regions.
While the difference between 230 V and 120 V single phase, 120 V is adopted in indent to minimize the risk of electric shock, even though the conductor size is resistance loss for 120 V is high compared to 230 V.