Electrical Engineering MCQ Question on carbon brushes are preferable to copper brushes because Carbon brushes are preferred in DC Machines to Copper Brushes because: Carbon brushes reduce armature reaction Copper brushes have high resistance Carbon brushes reduce sparking None of these Correct answer: 3. Carbon brushes reduce sparking Explanation: Carbon brushes are preferred in DC … Read more
The demand factor of power station having connected load of 45 MW and Maximum demand of 20 MW is: 0.2 0.307 0.44 2.25 Correct answer: 0.44 Explanation: The formula for Demand factor is: Demand Factor = Maximum Demand / Connected Load DF = 20 MW / 45 MW = 0.44
The supply frequency of a 4 pole induction motor having a synchronous speed of 1800 RPM is: 50 Hz 60 Hz 120 Hz 240 Hz Correct answer: 2. 60 Hz. Explanation: The basic formula for Synchronous Speed of machines is: From this we obtain:f = P * Speed / 120 = 4 * 1800 / … Read more
The correct formula for Synchronous Speed in Electrical Motors: ηm = 120 * fe * P ηm = 120 * fe / P ηm = fe * P / 120 ηm = 120 * P / fe Correct answer: 2. ηm = 120 * fe / P Formula for Synchronous Speed:
The mechanical speed of magnetic fields can be related to the electrical frequency and pole number by the formula: ηm = 120 * fe * P ηm = 120 * fe / P ηm = fe * P / 120 ηm = 120 * P / fe Correct answer: 2. ηm = 120 * fe … Read more
The stator of 3-phase Induction motor generates which type of magnetic field: Rotating Steady Any of these None of these Correct answer: 1. Rotating The stator of the 3-phase Induction motor produces a rotating magnetic field.
A 2-speed Squirrel cage induction motor has a lower speed of 1400 RPM. The other speed will be: 700 RPM 1980 RPM 2800 RPM 3675 RPM Correct answer: 3. 2800 RPM Explanation: Multispeed winding motors have stator windings that be reconfigured to obtain a different number of poles. The low-speed winding is wound for more … Read more
The efficiency of a 75 kVA Transformer having power factor 0.85 at full load will be: (Other data Full load Cu losses: 900 W, Iron loss: 600 W) 95.75 96.83 97.25 98.05 Solution: Full load output = kVA * PF = 75 * 0.85 = 63.75 kW Full load losses = 1200 W + 600 … Read more
In auto-transformer, the power from primary to secondary is transferred: Conductively Inductively Both of these None of these Correct answer: 3. Both of these
The type of transformer which does not provide electrical isolation: Potential transformer Current transformer Distribution transformer Auto-transformer Correct answer: 4. Auto-transformer Auto-transformer is the type of transformer that doesn’t provide electrical isolation. In an autotransformer, there is a direct physical connection between the primary and the secondary circuits, so there is no electrical isolation in … Read more