Alternator is a very a crucial part on ship providing power on board for machineries and personal use. So its maintenance and electrical safeties are of top priority. Regular checks and maintenances are done on alternator for proper functioning of it . The maintenance checks done on alternator are mentioned below –
- Prime Mover is stopped and locked off
- Generator circuit breaker is locked off i.e auto start is isolated .
- Put tag ” Men at Work”
- Check /Inspect windings for sign of damage , loose connection of terminals .
- Check for moisture and oil contamination .
- Remove oil and dust from winding , use vacuum cleaner
- We should inspect insulation resistance by doing open insulation test (two phase should not short circuit), close insulation test (there is continuity in the phase conductor ) and earth test of motor (no connection of phase and motor body )
- Check Pedestrial bearing lubrication ( Oil level )
- Check air gap between rotor and stator (0.3mm)
- Check the space heater working .
- Check for any loose connection (rotating polyphase rectifier .)
- Check the governor excitation system such as AVR, thyristors ,diodes for proper operation and tightness of connection in terminal.
For Slip Ring Alternators
- Check the rotor slip rings and check that carbon brushes have free movements in their boxes .
- Record the brush pressure by using spring type balance , a pull of about 1-1.4 kg is recommended .
- If the brushes have shortened it will result in sparking , replace with correct size and bend them to the curvature of slip rings .
What are the Alternator Safeties
Over current instantaneous trip
Setting – In 2-10 times rated generated current for 0.2 to 1 sec .
Under Voltage/Over Voltage
UV setting – 0.8* rated generated voltage , OV setting- 1.2* rated generated voltage
Over frequency /Under frequency
OF setting- 62Hz , UF setting – 58 Hz
Reverse power Relay
This is must for generators intended for parallel operations .Setting — 5-10% of rated power (time 0.5- 3 sec)
Over current Inverse time Relay
Setting — 0.7 – 2 times rated generator current (time 1- 10 sec)