By the end of this chapter, you will be able to:
Mastering these skills will help you confidently handle batteries and cells in real electrical projects, ensuring safety and reliability in your trade.
Three phase power supply forms the backbone of modern electrical distribution systems, delivering efficient and reliable power to diverse sectors across Kenya. Understanding its principles and configurations equips diploma-level graduates with essential knowledge to manage, troubleshoot, and optimize electrical systems in environments ranging from county referral hospitals to large retail complexes. This chapter explores the fundamental concepts of three phase power generation and the common methods of connecting three phase supplies, enabling students to apply these principles in various professional fields.
The generation of three phase power involves producing three alternating currents that are equal in frequency and amplitude but phase-shifted by 120 degrees. This method provides a steady and balanced power flow, essential for industrial and commercial applications where consistent energy supply is critical. In Kenya, institutions like county government offices and universities rely on three phase power to operate heavy machinery, air conditioning systems, and computer labs efficiently.
Three phase alternating current (AC) consists of three sinusoidal voltages of equal magnitude and frequency, each displaced in time by one-third of a cycle or 120 degrees. This phase displacement ensures that at any instant, the sum of the instantaneous voltages equals zero, providing a balanced system. The continuous power transfer in three phase systems reduces pulsations common in single-phase systems, making it ideal for powering sensitive equipment in hospitals and banks.
The generation of three phase voltage is achieved by rotating a coil within a magnetic field or rotating a magnetic field around stationary coils arranged at 120 degrees apart on the stator of a generator. This mechanical rotation induces electromotive forces (EMFs) in each coil, producing three sinusoidal voltages separated by 120 electrical degrees. For example, at a university power plant, the rotor’s mechanical energy, often from steam or hydro turbines, is converted into electrical energy in this manner.
Three phase power generation offers several advantages over single phase systems, including:
In Kenya, three phase power is supplied at a standard frequency of 50 Hz, with typical line voltages of 415 V between phases and 240 V between phase and neutral. Adhering to these standards ensures compatibility of equipment and safety in various sectors such as educational institutions and financial firms. Deviations from these standards can cause equipment malfunction or damage, underscoring the importance of proper system design and maintenance.
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Create a free accountThis chapter explored the fundamental principles of three phase power generation, explaining how three separate alternating currents are produced with a phase difference of 120 degrees to ensure efficient power delivery. It detailed the two primary types of three phase power supply connections, star and delta, highlighting their structural differences and implications for voltage and current in electrical systems. The chapter also covered essential calculations related to three phase power supply connections, enabling accurate determination of power, voltage, and current in both star and delta configurations. Measurement techniques for three phase power supply were examined, focusing on the one wattmeter, two wattmeter, and three wattmeter methods, each suited to different system conditions and load types. These methods provide practical means to assess power consumption and system performance in three phase circuits. Understanding these concepts is crucial for effective design, operation, and maintenance of electrical power systems in various industrial and commercial settings.
Type: Individual
| Tools & Equipment | Materials |
|---|---|
| Insulated screwdrivers | Three phase synchronous generator model 415 V, 50 Hz |
| Multimeter | Three phase load bank (resistive) |
| Connecting leads | Three phase voltage and current meter set |
| Switching board with isolator | |
| PPE (Safety gloves, goggles, safety boots) | |
| 3-phase model mounting board (500mm x 400mm) |
| S/N | Item | Quantity |
|---|---|---|
| 1 | Three phase synchronous generator model 415 V, 50 Hz | 1 Pc per Candidate |
| 2 | Three phase load bank (resistive) | 1 Pc per Candidate |
| 3 | Three phase voltage and current meter set | 1 set per Candidate |
| 4 | Connecting leads (4 mm2, red, yellow, blue, black) | 5 m per Candidate |
| 5 | Switching board with isolator | 1 Pc per Candidate |
| 6 | Instruction manual and circuit diagram sheet A4 | 1 Pc per Candidate |
| 7 | PPE (Safety gloves, goggles, safety boots) | 1 set per Candidate |
| 8 | Insulated screwdrivers | 1 Pc per Candidate |
| 9 | Multimeter | 1 Pc per Candidate |
| 10 | 3-phase model mounting board (500mm x 400mm) | 1 Pc per Candidate |
| Items to be Evaluated | Marks Available | Marks Obtained | Comments |
|---|---|---|---|
| TASK 1: Setup and demonstration of three phase power generation model | |||
| Wore personal protective equipment (gloves, goggles, boots) (Award 2 marks if all PPE worn correctly, else 0) | 2 | ||
| Listed and prepared all necessary tools and materials (Award 3 marks if all tools/materials listed and ready) | 3 | ||
| Connected the three phase synchronous generator model as per circuit diagram (Award 5 marks for correct and safe connections) | 5 | ||
| Connected the load bank correctly to the model (Award 4 marks for correct load connection) | 4 | ||
| Installed and connected the voltage and current meters properly (Award 3 marks for correct meter installation) | 3 | ||
| Used the isolator switch correctly to power the model (Award 3 marks for correct use of isolator switch) | 3 | ||
| Demonstrated operation by showing voltage and current readings on meters (Award 5 marks for clear demonstration and explanation) | 5 | ||
| Explained the principles of three phase power generation during demonstration (Award 5 marks for accurate and clear explanation) | 5 | ||
| Performed safe disconnection and housekeeping after demonstration (Award 3 marks for safe shutdown and clean working area) | 3 | ||
| Sub-Total | 33 | ||
| PRODUCT CHECKLIST | |||
| Model setup matches provided circuit diagram with correct wiring and connections (Award 5 marks if wiring and connections are correct and neat) | 5 | ||
| Operating readings show balanced three phase voltages approximately 415 V ±5% (Award 4 marks if voltages are balanced within tolerance) | 4 | ||
| Current readings show load current as per load bank rating (Award 3 marks if current readings correspond to load) | 3 | ||
| Mounting board is neat and components fixed firm and level (500mm x 400mm) (Award 3 marks if components are firmly fixed and neat) | 3 | ||
| Sub-Total | 15 | ||
| GRAND TOTAL | 48 | ||
Type: Individual
| Tools & Equipment | Materials |
|---|---|
| Lug Crimping Tool | 3-phase Induction Motor 415 V, 50 Hz |
| Electrician Toolkit (Screwdrivers, Pliers, Side Cutter) | 3 Phase Isolator 415 V AC |
| PPE (Gloves, Goggles, Safety Boots) | PVC singles R/B/Y/G cable 4.0 mm2 |
| Cable Clips | Labels/Tags |
| Cable Fork Lugs | |
| Vertical Wooden Installation Board 1m x 1m |
| S/N | Item | Quantity |
|---|---|---|
| 1 | 3-phase Induction Motor 415 V, 50 Hz | 1 Pc per Candidate |
| 2 | 3 Phase Isolator 415 V AC | 1 Pc per Candidate |
| 3 | PVC singles R/B/Y/G cable 4.0 mm2 | 4 m per Candidate |
| 4 | Labels/Tags | 1 set per Candidate |
| 5 | Cable Fork Lugs 4.0 mm2 | Enough per Candidate |
| 6 | Lug Crimping Tool | 1 Pc per Candidate |
| 7 | Electrician Toolkit (Screwdrivers, Pliers, Side Cutter) | 1 set per Candidate |
| 8 | PPE (Gloves, Goggles, Safety Boots) | 1 set per Candidate |
| 9 | Cable Clips 12 mm | 1 pkt per Candidate |
| 10 | Vertical Wooden Installation Board 1m x 1m | 1 Pc per Candidate |
| Items to be Evaluated | Marks Available | Marks Obtained | Comments |
|---|---|---|---|
| TASK 1: Preparation and Safety | |||
| Wore appropriate personal protective equipment (gloves, goggles, safety boots) (Award 2 marks for correct PPE worn, 0 if not) | 2 | ||
| Listed and assembled all required tools and materials (Award 3 marks for complete and correct tools and materials) | 3 | ||
| Ensured clean and safe working area before commencing work (Award 1 mark for good housekeeping) | 1 | ||
| Observed correct colour coding for three phase cables (R-Red, Y-Yellow, B-Blue, G-Green Earth) (Award 2 marks for correct colour code observed, 0 if incorrect) | 2 | ||
| Sub-Total | 8 | ||
| TASK 2: Connection and Labelling | |||
| Connected the three phase cables correctly to the motor terminals (Award 5 marks for correct and secure connections) | 5 | ||
| Connected the three phase cables correctly to the isolator terminals (Award 5 marks for correct and secure connections) | 5 | ||
| Used cable lugs and crimped securely without damaging cables (Award 4 marks for proper lug crimping and cable handling) | 4 | ||
| Fixed cables neatly on the installation board using cable clips at correct spacing (~150 mm) (Award 3 marks for neat cable fixing and correct clip spacing) | 3 | ||
| Correctly labelled each terminal and cable according to phase and earth (Award 3 marks for clear and correct labelling) | 3 | ||
| Sub-Total | 20 | ||
| TASK 3: Testing and Final Checks | |||
| Performed continuity test on all connections (Award 4 marks for proper continuity test and result) | 4 | ||
| Performed insulation resistance test (Award 4 marks for proper insulation test and result) | 4 | ||
| Verified polarity and phase sequence (Award 4 marks for correct polarity and phase sequence) | 4 | ||
| Ensured final connections are firm and no loose wires (Award 3 marks for firm and safe connections) | 3 | ||
| Performed good housekeeping after completion (Award 2 marks for cleaning the work area and proper tool storage) | 2 | ||
| Sub-Total | 17 | ||
| PRODUCT CHECKLIST | |||
| Finished installation board with correctly connected and labelled three phase terminals; cables fixed neatly; dimensions 1000 mm x 1000 mm verified (Award 15 marks for accuracy of connections, neatness, and correct labelling and dimensions) | 15 | ||
| Sub-Total | 15 | ||
| GRAND TOTAL | 60 | ||
At the start of this chapter we promised you would be able to:
Tick each one you can genuinely do.
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