Rated Voltage – Operating Voltage
- Rated Voltage: Is the voltage for which a cable or flexible cord is intended to be used or according to which it is designed to indicate certain service properties, tests and possible uses.
- Operating Voltage : Is the voltage occurring between the conductor of a power installation (or between conductor and earth ) in undistributed operation at a given place and at given time. The operating voltage permissible in continuous undistributed operation does not exceed the rated voltage by more than 15%.
- The cables and flexible cords may be used:-
- In three phase system in which the operating voltage is not higher than 1.15 times the rated voltage.
- In single phase A.C. and D.C. system with symmetrically balanced voltage to earth in which the operating voltage does not exceed 1.15 times the rated voltage.
- In single phase A.C. and D.C. system, with one line earthed in which under operating conditions, the voltage to earth does not exceed 1.15 x √ 3 = 0.66 times the rated voltage.
Voltage Drop
Voltage drop is normally only of importance for cables of voltage rating 600/1000 volt or below. It is stipulated that the voltage drop within the installation should not exceed a value appropriate to the safe functioning of the associated equipment in normal service. The requirement is deemed to be satisfied if the voltage between the origin of installation (usually supply terminals) and the fixed current using equipment does not exceed 4% of the nominal voltage on the supply, disregarding starting conditions. (Diversity can be taken into account when calculating the voltage drop).
- For balanced three phase A.C. circuit, the values relate to the line voltage.
- The following equation of the voltage drop is to assume the worst condition, i.e. where the phase angle of the load is equal to that of the cable.
- MV = Vd x 1000
_____________
I x L
Where MV = approximate voltage drop (MV /Amp/mets)
Vd = voltage drop » 4% voltage (volt)
I = current in ampere
L = route length in meters
|
