Motors/Generators Flashcards
How does a brushless AC generator work?
A prime mover turns a shaft which in turn powers a high frequency generator via a belt driven by the rotating shaft. the HF gen provides 115v 1600hz 1 phase AC to the AVR which converts the voltage to 450V DC to the AC exciter, the rotor of the exciter provides AC to the rectified assembly which converts the current to DC which is then fed to the rotor of the generator creating a magnetic field across the stator. The stator then produces 450v AC 60hz 3 phase.
How does an AC motor work
The ac motor is comprised of two main components, the stator and rotor. The stator contains copper windings connected to 3 phases that create a rotating magnetic field. The squirrel cage stator is placed into the rotating magnetic field which causes it to rotate, the rotor is connected to a shaft which provides mechanical motion. The soul purpose of the AC motor is to change electrical energy into mechanical motion.
How does a DC motor work?
The DC motor has the same principles as the AC motor providing mechanical motion from electrical energy. The stator creates a magnetic field and the rotor is placed within that field, the rotor has copper windings which are connected to a current which when applied causes the rotor to rotate however the current must be reversed for it to continue rotating so a commutator is connected to the end of the rotor with brushes to reverse the current which reversed the magnetic field causing the rotor to continue rotating.
How does a basic AC single loop generator work?
Two poles induce a magnetic field with lines of force, a single loop armature is placed within the field and when rotated it cuts the lines of force creating an electrical current which the armature conducts. The armature loop is connected via slip rings and carbon brushes which transfer the current to a circuit providing single phase AC current. This concept converts mechanical motion to electrical energy.
How do you reduce the voltage using a transformer?
You reduce the number of secondary windings which decreases the voltage however it increases the current
How do you change the rotation of a 3 phase motor?
Change any two phases around
What is the importance of earth bonding straps?
To ensure that if personal is to touch any enclosed metals they won’t receive electrical shock as the enclosed metals such as motors are earthed to the ships hull, this massively reduces electric shock
What do you know about high voltage?
AC 1000v and DC 1500v, there are different states of HV onboard
HV LIVE - ship is able to produce, receive or supply HV
HV SAFE - compartment containing HV is isolated and safe to enter
HV DEAD - ship is not able to produce, receive or supply HV, all HV is isolated onboard
Describe an ON load test
Insert the fluke to either end of a fuse
The fluke is the lowest path of resistance, if the fuse is blown continuity will pass through the fluke and the light will turn on indicating a fault, if the light remains off then the fuse is good.
Describe an OFF load test
Remove the load and insert the fluke to the supply side of a fuse and to any other fuses return side. The fluke acts as the load so if continuity passes through the fluke and the light comes on then there’s no fault.
Describe a continuity test
close switch and switch GPTME to ohms, test between two phases, if low resistance shows then there is continuity however if it is >1000km then it’s an open circuit
Describe an earth continuity test
Using GPTME test between a phase and earth and if your GPTME reads above 0.1ohms then your earth is faulty
Describe a non contact test
Inject 500v between two phases with the load removed, any reading above 1Mo is a good reading, if it’s below 1mo then you have a short circuit
Describe a insulation resistance test
