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Systems Engineering – Unit 3 Revision Study Guide
Electrical & Energy Systems
1. The Engineering Process & Systems Thinking
1.1 The Engineering Process Stages
You must know the sequence and purpose of each stage:
1. Investigate & design
2. Plan
3. Produce a solution
4. Test and diagnose
5. Evaluate and report
6. Modify and improve
Once a system is built, the next stage is always “Test and diagnose”.
1.2 IPO Diagrams (Input–Process–Output)
Used to analyse and explain systems.
Example: Home Security Alarm
• Inputs: Motion sensors, door switches, keypad input
• Process: Microcontroller compares input to programmed logic
• Outputs: Alarm siren, alert light, SMS notification
Be ready to label inputs, processes, and outputs clearly.
2. Energy Sources & Sustainability
2.1 Renewable vs Non-Renewable
• Renewable: Solar, wind, hydro, tidal, biomass, geothermal
• Non-renewable: Coal, oil, gas, nuclear (alternative but not renewable)
Geothermal energy comes from heated groundwater.
2.2 Advantages & Disadvantages (Exam Favourite)
Wind Power – Advantages
• Renewable
• Zero greenhouse emissions during operation
• Low operating cost
• Scalable
• Reduces fossil fuel dependence
Coal Power – Disadvantages
• High CO₂ emissions
• Non-renewable
• Air pollution
• Thermal inefficiency
• Environmental damage
You will be asked to:
• Compare energy sources
• Justify one over another
• Give an opinion with reasoning
3. Energy Transformations
Know energy chains in order:
Examples
• Wind turbine:
Kinetic → Mechanical → Electrical
• Hydro power:
Potential → Kinetic → Mechanical → Electrical
• Solar PV:
Radiant → Electrical
4. Efficiency Calculations HIGH PRIORITY
4.1 Formula
Efficiency=
Useful output energy
Total input energy
× 100%
4.2 Combined Efficiency
Multiply efficiencies as decimals:
Example:
• Solar panel: 40% → 0.40
• Battery: 80% → 0.80
0.40 × 0.80 = 0.32 = 32%
Combined efficiency = 32%
5. Electrical Fundamentals
5.1 Current Types
• AC (Alternating Current): Household power, wind turbines
• DC (Direct Current): Batteries, solar panels
5.2 Frequency & Period
1
𝑓 =
𝑇
• Australia mains electricity = 50 Hz
• Direction changes 50 times per second
Example:
• Period = 0.005 s
𝑓 = 1 ÷ 0.005 = 200 Hz
6. Power, Work & Energy Calculations
6.1 Power
𝑊
𝑃 =
or𝑃 = 𝑉 × 𝐼
𝑡
Example:
• 1,000,000 J in 50 s
𝑃 = 1,000,000 ÷ 50 = 20,000 W
6.2 Work
𝑊 = 𝐹 × 𝑑
Example:
• 2000 N × 10 m = 20,000 J
7. Batteries & Electrical Storage
7.1 Series vs Parallel
• Series: Voltage adds
• Parallel: Capacity (Ah) adds
Example:
• 4 × 12 V batteries in series = 48 V
7.2 Battery Runtime
Total energy
Time (h)=
Power of load
8. Circuit Theory
8.1 Ohm’s Law
𝑉 = 𝐼 × 𝑅
8.2 Resistance
• Series:
𝑅𝑇 = 𝑅1 + 𝑅2 + 𝑅3
• Parallel:
1
1
1
=
+
𝑅𝑇
𝑅1
𝑅2
8.3 Capacitors
• Series: inverse rule
• Parallel: add values directly
9. Electrical Components & Symbols
You must identify:
• Resistor
• Variable resistor (potentiometer)
• Capacitor
• Cell / Battery
• LDR (light-dependent resistor)
• LED
• Diode
• Thermistor
• Switch types: SPST, SPDT, DPDT
LED does not detect light
LDR, phototransistor do
10. Transformers
Formula
𝑉 𝑠
𝑁 𝑠
=
𝑉 𝑝
𝑁 𝑝
Example:
• 40 primary, 800 secondary
• Input = 240 V
𝑉 𝑠 = 240 × (800 ÷ 40) = 4800𝑉
Used to step up voltage → reduce current → reduce power loss
11. Power Transmission
Why Voltage Is Stepped-Up
• Reduces current
• Minimises power loss as heat
• Improves efficiency
• Allows thinner cables
• Enables long-distance transmission
12. Power Electronics
Rectifier
• Converts AC to DC
H-Bridge + PWM
• Technique: Pulse Width Modulation (PWM)
• Purpose: Convert DC into simulated AC & control motor speed
13. Semiconductors
• Doping: Adding impurities to silicon
• Creates diodes and transistors
• Enables controlled current flow
14. Safety & Standards
Before using 230 V power tools: Must have a current electrical safety tag
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