Power Systems & Machines (Elec-A6) - Solutions & Help
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Next Technical Exam Sitting: May 11-15, 2020
Your exam is fast approaching. You might be working a job and have a family that needs your time. The last thing you want to do is spend $1,000 on a course to re-learn this material.
If that sounds like you, our Power Systems and Machines (Elec-A6) help is for you.
About: The power systems and machines exam is written nationally for electrical aspiring engineers. The code for this exam is:
- Electrical - 07-Elec-A6 (or you may see it like YY-Elec-A6, Elec-A6)
- Mechatronics - 16-Mex-B10 (or you may see it like YY-Mex-B10, Mex-B10)
Format: 3-hour long, closed book exam. Out of the seven questions that are asked in the exam, only five need to be attempted.
Dates written: The exam is offered twice every year in the months of May and December.
Approved aids: Since the course is highly computational, approved Casio or Sharp calculators are permitted.
After reviewing several previous exams, a question pattern emerges. Here is a summary of the different question types that you will typically face.
Q1. Transmission and Distribution
The first question tests your knowledge and your concepts about transmission line circuits. It is a numerical question. For instance, you may be asked to calculate the value of load current, power losses in the transmission line and source voltage in the given circuit. Your understanding of circuit analysis, network analysis, transmission line model, line impedance, transmission line impedance, load flow analysis, voltage magnitude and angle, active and reactive power, 2 port network and calculation of ABCD parameters will be tested here. Please refer the 2 port diagram below.
Supply end voltage =Vs
Supply end current =Is
Receiving end voltage = Vr
Receiving end Current = Ir
Q2: Single phase and Three Phase
The second question is a numerical problem regarding single phase and three phase circuit. You'll be tested on your knowledge of star and delta mode of connection, phase voltages and line voltages. You will be given a balanced three-phase, with parameters such as impedance between the source and the load, line to line voltages. You will be asked to calculate line current from the source, you could also be asked to draw a phasor diagram depicting the line currents without a power factor correction and with the power factor correction.
Q3: DC motors
You will be asked to calculate the output power, output torque and efficiency of the motor with given parameters such as voltage level, armature resistance, rotational losses, rotor speed in rpm and current through the windings. There could be an additional question which would ask you to calculate the total current consumed by the motor, operating speed and efficiency provided that mechanical load is added to the motor with given mechanical torque. The problems related to DC motors are solved with the following steps:
- Draw a circuit diagram with initial values.
- Write EMF equation and torque equation for initial conditions.
- For initial condition, some variable (like armature resistance, field resistance, load torque, armature applied voltage) will be changed and you will be asked to calculate new armature current, speed, etc.
- Variables to be calculated are assumed and emf equation and the torque equation for the new operating point are written again.
- You have 4 equations now – 2 corresponds to initial operating conditions and the other 2 corresponds to the new operating conditions.
- Take the ratio of the torque equations and ratio of back emf equations.
- Solve the unknown from the above equations.
The fourth question is also a numerical problem. It tests your knowledge on single phase 2 winding transformers and three phase transformer. You will be provided with the open circuit and short circuit test data, number of phases, kVA rating, voltage ratio and the frequency for the transformers. You will be asked to find parameters for open circuit test from LV side and parameters for short circuit test from HV side. You will be asked to draw the equivalent circuit of the transformer (i) referred to LV side and (ii) referred to HV side inserting all the parameter values. (Iii) full-load voltage regulation and efficiency of the transformer with power factor given.
Q5: Synchronous Motors, Generators and power factor
The fifth question consists of calculating supply current, power factor of source Vs and calculating complex power, real power and reactive power of the source. This also involves drawing phasor diagram, calculating mechanical power input to the generator rotor, per phase excitation voltage, armature current, total complex power delivered to the bus and generator power factor. You will be provided parameters such as the number of poles, the frequency of the motor, voltage, KVA rating of the motor with power factor, rotor torque, and synchronous reactance. Also, you could be asked to sketch the governor characteristics.
Q6: Induction Motors
This question specifically tests your knowledge on induction motors. You will be given the circuit with parameters such as frequency, voltage, number of phases, mode of connection (star or delta), values of R and X, line current and power factor. You will be asked to calculate developed torque, output power and efficiency of the motor.
Utkarsh Patel, MASc, P.Eng. is an experienced electrical engineer with specialization in power systems. He is working as an electrical engineer since last five years being electrical system owner and overseeing industrial power distribution systems. He holds P.Eng. in the Province of Ontario and is registered as a professional member of IEEE. He has published papers in IEEE journal and conferences.
The recommended textbooks for this exam are:
- Electric Machinery and Power System Fundamentals, by Chapman, Stephen. 2001 edition, McGraw Hill.
- Electrical Machines, Drives, and Power Systems, by Wildi, Theodore. 6th edition, Prentice Hall.
While we don't reference them in the course, owning one or both will give you more opportunities to re-learn the theory and practice questions from the textbook. It is not necessary to own them to take the course, but it might be a good idea as an additional resource for you.
Based on your education and experience, we've put together a few different options to help you out. If you are feeling confident in the material and believe you are knowledgeable on the exam topics, then a less expensive option may be best for you. For those who need more help and support, the more expensive packages would be recommended.
$399, $350, $250
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Includes the following: (depending on your package):
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(Date of exam(s) solved)
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