Electricity supply systems 2
Electricity supply systems and voltages 2 - Power generation, transmission, transformer arrangements, voltage levels, losses, star and delta voltages and formulas - 12 questions from a bank of questions
Answer ALL questions. Look for any feedback given if you get an answer incorrect. Keep choosing an answer until you get it correct. CORRECT or INCORRECT answers are indicated at the TOP of the page. A score is given at the TOP of the page when the exercise has been completed. © K.Brown 2015
Which one of the following is a renewable energy source?
? wind power ? nuclear ? coal ? oil
Which one of the following is a fossil fuel?
? gas ? nuclear ? wind ? tidal
What is the voltage of the 'super grid' system of electricity transmission?
? 132kV ? 33kV ? 11kV ? 400kV
What is the voltage of the 'national grid' system of electricity transmission?
? 400kV ? 33kV ? 11kV ? 132kV
What is the voltage distributed to 'heavy industry'?
? 400kV ? 132kV ? 11kV ? 33kV
What is the voltage distributed to 'light industry'?
? 400kV ? 132kV ? 33kV ? 11kV
What is the voltage output of the secondary STAR winding to a domestic/light commercial installation?
? 11kV ? 33kV ? 400/230v ? 400v
How are voltage levels converted between power station and consumer?
? transformers ? power converters ? inverters ? voltage levels remain the same throughout
Why are transmission voltages so high?
? to reduce losses ? to supply large items of electrical equipment ? to increase current demand ? to ensure sufficient power during a power-cut
What voltage can be acquired from a transformer (DELTA) secondary 400v 3-phase (3-wire) supply?
? 230v ? 400v ? 230/400v ? 11kV
What voltage can be acquired from a transformer (STAR) secondary 400v 3-phase (4-wire) design?
? 230v ? 400/230v ? 400v ? 11kV
How is (phase) voltage derived from Line voltage?
? Vp = VL / 1.732 ? Vp = VL x 1.732 ? Vp = VL + 1.732 ? Vp = VL - 1.732
How is Line voltage derived from (phase) voltage?
? VL = Vp x 1.732 ? VL = Vp / 1.732 ? VL = Vp + 1.732 ? VL = Vp - 1.732
If many single-phase loads are installed unequally across the 3-phases and neutral, what is the likely result?
? only the neutral will be overloaded ? nothing, the system is balanced ? phases will be out of balance and conductors will be overloaded ? only the phases will be overloaded
Three-phase equipment such as motors and transformers do not always require a neutral connection to them, why is this so?
? because they are 'balanced' electrical machines ? because they do not require 230v AC ? because they are un-balanced electrical machines ? this statement is incorrect - they DO require a neutral connection
a 3-phase supply has a 'line voltage' = 250v, calculate the 'phase voltage'.
? 144v ? 750v ? 400v ? 234v
What is the typical generating voltage from a power station?
? 400kV ? 25kV ? 132kV ? 33kV