L Questions Flashcards
How can you reduce the output voltage of a transformer?
reduce the number of turns in the secondary windings
How to change rotation of a 3 phase motor?
Swap 2 phases with each other,changes direction of the rotating magnetic field.
each phase peaks at a different time (sine wave)
Importance of earth bonding straps?
So any enclosure (cabinets,metal boxes,motors) containing electricity that may be touched by personnel is earthed to the ship to reduce lethal shock hazard.
What do you know about High Voltage?
- Where voltage exceeds 1000v AC or 1500v DC
- Voltage large enough to cause injury or death
*Documentation involved
**
* PTW
* SFT (sanction for test)
* LOA (Limitation of access)
* SS (switchng schedule)
What equipment have battery backups & why?
- Compasses
- Diesel engine starting
- RICE
So when main supply fails you can maintain 24v DC supplies so ship can still manuver & navigate.They are constantly being charged
On Load fuse testing
Using fluke mit420/continuity test
- Load connected & on
- Test across each fuse
- If the fuse is blown it will go through the fluke
- If fuse is good it will go through fuse
- Good = very low ohms
- Bad=>1000k ohms
Off load fuse testing
Continuity
- Load off
- Fluke becomes the load
- Put one lead on motor side of fuse then put the other lead on the other phases
- Good= if the circuit is complete
What is the half split method?
When you split a circuit in half to narrow down the location of a fault
Continuity test
- Check for Continuous circuit or if it is open
- DEAD TEST
- Set to Ohms
- Close switch
- Closed circuit=small resistance 10-50 Ohms
- Open circuit= Greater than 1000kOhms
Non contact test
- Check no short circuits
- DEAD TEST
- Remove load
- Test phase to phase
- Inject 500v
- Good=1M ohms or higher
- Bad=0.01Mohm
Insulation resistance test
- Ensure no short circuit between circuit & earth
- Power isolated
- Test between Phase and earth
- Inject 500V
- Good = higher than 1Mohm
