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Which of the following is usually not the generating voltage?
6.6 kV
9.9 kV
11 kV
13.2 kV
9.9 kV
Generating voltages in large power plants are standardized based on the physical size of the generator, thermal constraints, and insulation limits. Voltages like 6.6 kV, 11 kV, 13.2 kV, 15 kV, 18 kV, 22 kV, and 33 kV are standard industrial values, whereas 9.9 kV is not a recognized industry standard for AC synchronous generator output.
Generating voltages in large power plants are standardized based on the physical size of the generator, thermal constraints, and insulation limits. Voltages like 6.6 kV, 11 kV, 13.2 kV, 15 kV, 18 kV, 22 kV, and 33 kV are standard industrial values, whereas 9.9 kV is not a recognized industry standard for AC synchronous generator output.
P=3тАЛVLтАЛILтАЛcos╧Х тАФ Relationship between Power, Voltage, and Current in three-phase systems
The selection of generating voltage is governed by the P=3тАЛVIcos╧Х relation. As the power rating increases, voltage is kept at an optimal level to manage the current density within the stator windings, minimizing I2R losses and insulation thickness requirements. Non-standard values like 9.9 kV are avoided to ensure global availability of switchgear, transformers, and protection relays that are manufactured according to standard IEC or IS voltage ratings.
Generating voltages are standardized to facilitate equipment interchangeability.
Higher ratings (e.g., 22 kV, 33 kV) are used for very large capacity generators (e.g., 500 MW+).
Selecting non-standard voltages leads to higher capital costs due to custom-built transformers and switchgear.
The range of 11 kV to 33 kV is the most common for utility-scale synchronous generators.
Standardization reduces inventory costs for spare parts.
Ease of procurement for grid-connected switchgear and protective equipment.
Using non-standard voltage levels significantly increases the design complexity of bus ducting and excitation systems.
Thermal power plants
Hydroelectric stations
Nuclear power generation
In India, the most prevalent generating voltage for thermal power sets (e.g., 210 MW, 500 MW) is 15.75 kV, 21 kV, or 23.5 kV.
Option 9.9 kV is technically invalid for AC synchronization equipment and is never seen in commercial power system design.
B is correct тАФ 9.9 kV is not a standard voltage level used for AC synchronous generator output in power systems.
Remember that generating voltage selection is a trade-off between insulation cost (which increases with voltage) and conductor size/losses (which decrease as voltage increases).