AC/DC generation
What energy conversion takes place in an electrical generator?
Mechanical energy is converted into electrical energy.
State Ohm’s Law in words.
The current in a circuit is directly proportional to the voltage and inversely proportional to the resistance.
What does the term “MEN” stand for?
Multiple Earthed Neutral.
What type of current does a single-phase induction motor operate on?
Alternating current (AC).
Before working on electrical equipment, what is the first safety step you must take?
Isolate the supply.
What component in a DC generator converts the alternating current produced in the armature into direct current?
The commutator.
What happens to the current if the resistance in a circuit increases while voltage stays the same?
The current decreases.
What is the main purpose of earthing an electrical installation?
To provide a safe path for fault current and prevent electric shock.
Name the two main parts of an induction motor.
The stator and the rotor.
What is the purpose of using a “lock-out and tag” procedure?
To prevent the circuit from being re-energised while maintenance is being carried out.
Why are slip rings used in an alternator?
To transfer the alternating voltage from the rotating armature to the external circuit.
Explain why fuses or circuit breakers are always placed in the active conductor.
So they disconnect the live supply and make the circuit safe if a fault occurs.
Why is the neutral conductor earthed at multiple points on the distribution network?
To reduce voltage rise on the neutral and provide protection against lightning or high-voltage flashover.
Why does a single-phase induction motor need an auxiliary or start winding?
Because a single-phase supply cannot produce a rotating magnetic field on its own, so the start winding provides initial torque.
Why must you test a voltage tester on a known live source before and after testing for dead?
To ensure the tester is working correctly and hasn’t failed.
Name one reason AC generation is preferred over DC generation for national electricity supply systems.
AC can be easily transformed to different voltages for efficient transmission.
What effect does connecting additional loads in parallel have on the total current drawn from a supply?
The total current increases because each additional load provides another path for current.
What could happen if the MEN link in a switchboard is missing or loose?
Fault protection may fail, and exposed metal parts could remain live, creating a serious shock hazard.
What is “slip” in an induction motor?
The difference between the synchronous speed of the rotating magnetic field and the actual speed of the rotor.
Name two personal protective items commonly used when testing or working on live equipment.
Insulated gloves and safety glasses (or a face shield).
Explain the relationship between the number of poles in an alternator and the frequency of the generated voltage.
The more poles an alternator has, the higher the frequency produced for the same rotational speed.
Why is it important that the neutral conductor is correctly identified and connected in a single-phase system?
To ensure correct polarity, proper operation of protective devices, and to prevent electric shock risks.
Explain the function of an earth electrode in an MEN system.
It connects the installation’s earthing system to the general mass of earth, stabilising voltage and providing a reference point.
Explain how a three-phase induction motor produces a rotating magnetic field.
The three currents are 120° apart in phase, creating magnetic fields that combine to rotate continuously around the stator.
If a portable appliance fails a safety test due to excessive leakage current, what must be done according to AS/NZS 3760?
It must be immediately removed from service and not used again until repaired or replaced.