ECE4633 Assignment 1 Theory Q&A
2023
Describe the process for varying the amount of total or apparent power S (both real P
and reactive Q) that a
... [Show More] single 3-phase SG supplies to an infinite bus - ANS-1. Measure
the current and voltage values at the generator side and the bus side
2. Calculate the apparent power S by multiplying the voltage and current values
3. Evaluate the reactive power Q by determining the imaginary part of the apparent
power
4. Calculate the real power P by determining the real part of the apparent power
5. Modify the generators excitation voltage to increase or decrease the reactive power
Q being supplied to the bus
6. Modify the generators mechanical power output to increase or decrease the real
power P being supplied to the bus
7. Recheck the current and voltage values and repeat steps 2-6 until the desired
amount of apparent power S is achieved
Briefly describe the two types of rotors used in 3-phase revolving-field synchronous
generators. When and why is each type used? - ANS-1. Salient pole rotors: used in low
speed generators since their design tends to be short with a large diameter (used in
hydro-stations)
2. Cylindrical rotors: used in high/medium speed generators since they have a nonsalient pole design. This rotor type tends to be long with smaller diameter than the
salient pole design (used in gas, diesel, and thermal units)
What are the advantages of using a stationary armature in large 3-phase SGs? - ANS1. More practical since the AC power does not flow through slip-ring assemblies on the
rotor, but through solid electrical connections
2. Less maintenance than the rotating armature type
3. Easier to insulate the main windings (not subjected to centrifugal forces)
4. Adaptable to parallel operation and simple to synchronize and control
Describe the procedure to synchronize a 3-phase SG with an infinite bus using a
synchro-scope - ANS-1. Adjust the speed of the prime mover until the generator
frequency is equal to or slightly above the system frequency
2. Adjust the DC excitation until the generator voltage is equal to the system voltage of
the infinite bus
3. Check to ensure the phase sequences are the same
4. Observe the phase angle between the generator voltage and the bus voltage using a
synchro-scope or a 3-phase synchronizing switch
What are the limits that have to be considered when operating a 3-phase SG? - ANS-1.
Thermal limits set the maximum temperature rise and therefore the maximum power
loss in different parts of the SG
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