Electrical

Question 1

How do you measure the charge of a lead acid battery?

Answer 1

Use correct PPE according to SDS
Use a hydrometer to check the specific gravity
Full = 1.25-1.28
Empty = 1.1

Question 2

What is a battery?

Answer 2

A battery is a DC power storage device made of electro-chemical cells used to provide DC electrical power

Question 3

Why is ventilation important in a battery room?

Answer 3

To prevent buildup of hydrogen

Question 4

Name one publication that deals with the storage of batteries

Answer 4

COSWP Ch20

Question 5

Tell me about secondary batteries (rechargeable batteries)
Types
Uses
Precautions

Answer 5

• Secondary batteries are rechargeable
• Types - Lead acid, Alkaline, Lithium-ion, Nickel-Cadmium
• Uses - Emgcy gen starting, UPS, emgcy lighting, lifeboat starting, radios
• Precautions - Ensure adequate ventilation & lighting, no smoke or flames, use EX rated tools, correct PPE, eye-wash and medical stations nearby, batteries properly stored as per COSWP Ch20, do not universally use tools for different battery types to prevent mixing acids & alkalines

Question 6

Why do we need batteries?

Answer 6

They are used onboard as a backup power supply for essential consumers, where in case of main power failure, they are fed from an emergency source of power
(During time between blackout and emergency generator startup)

Question 7

What does a battery UPS cover?

Answer 7

Nickel-Cadmium UPS Batteries will keep essential systems online such as:
• Navigation systems (radar, ECDIS, navigation lights, gyro repeater),
• Fire detection
• PMS & MAS/IAMCS
• PA & General Alarm
• WTD
• some CCTV
• Emergency steering control
• ECR computers.
• Communications (GMDSS)

Question 8

Battery checks

Answer 8

Check condition and tightness of the cable and battery terminals, nuts and intercell connectors

Question 9

Can lead-acid cells and and alkaline cells be stored together?

Answer 9

No they should never be stored together.
There is a risk of rapid electrolyte corrosion to metalwork and damage to both batteries.

Question 10

Checks on motor when running/starting up? (Already in service (no overhaul))

Answer 10

Earth cables
Loose covers
Condition of fan for damage and dirt

Question 11

Paralleling generators

Answer 11

• PPE, tag out book
• Engine local
• Engine checks (Pre-heat, CW, LO, Start Air, FO, turning gear) turning gear then slow turn, close indicator cocks.
• Start and monitor locally off-load and turn to remote
• Go to ECR, have SOP at hand
• Switch to manual, select incoming generator, turn on meters, start generator.
• Observe Voltage and frequency rise
• Voltage should be equal
• Adjust frequency down to 59Hz then up to 61Hz then back to 60 Hz to prove control
• Turn on synchroscope
• Adjust governor to get a slow clockwise rotation on synchroscope
• Close breaker at 5 to 12
• Bring the new generator load up slowly while decreasing load on other
• Balance out the load
• Wait and monitor
• Once satisfied, put back on auto and turn off synchroscope or else it will overheat of run continuously

Question 12

What does a synchroscope measure? And what happens if you try to parallel out of phase?

Answer 12

It measures the phase difference. The engine will try to ‘jump’ to that phase and it will cause catastrophic damage to the engine

Question 13

Main switchboard safeties

Answer 13

• Circuit breaker
• Fuses - will melt if current is high
• Overcurrent trip - trips after an extended period to allow for preferential trips to activate but it will trip instantly if the overcurrent is large.
• Reverse power trip - stops motoring
• Under voltage trip
• Under frequency trip
• Overspeed trip (mechanical & electrical)
• Preferential trip - trips equipment in a sequential order starting from non-essential equipment to prevent overloading
• Rubber mats
• Rescue hook

Question 14

Taking generator off load

Answer 14

Before stopping a gen make sure that the load is small enough for one gen to handle.
-Put the selector from auto to manual of gen that going off.
-Use governor to control speed so you can slowly reduce load.
-Monitor the parameters, the frequency will automatically maintain 60hz.
-Once gen has reached 5-10% load level, open the circuit breaker by turning ACB control to open.
-Readjust speed to 60hz
-Check gen that is running is maintaining speed.
-Let gen run idle to cool down.
-Stop engine by turning control knob to stop on switchboard.
-Isolation - close start air, drain start air, open indicator cocks, engage turning gear

Question 15

How do we find the source of an earth fault on the switch board?

Answer 15

Inform chief + ETO
We should go through each piece of machinery one by one turning them off and on again and check each time to see if the fault is resolved. Start with galley, laundry, AC, deck machinery but seek permission from each department prior to switching off.

Question 16

How to do current draw test on motor

Answer 16

Motor has to be live
Extra precautions must be taken
PPE
Check SMS
Insulated tools
Risk assessment
Permit
PPE
Rubber mat
Extra person
Recovery hook
Test with clamp meter round each phase

Question 17

How a three phase induction motor works?

Answer 17

3 phase is supplied to the motor and creates a rotating magnetic field in the stator windings
This field cuts through the rotor bars, inducing and EMF according to Faraday’s law of induction
This creates another magnetic field in the rotor which interacts with the rotating stator magnetic field to produce a torque and the rotor effectively starts ‘chasing’ this magnetic field

Question 18

Explain preferential trip and reverse power trip

Answer 18

• Preferential trip will trip machinery in a sequential order from the least essential systems such as galley, laundry , AC to most essential systems.
This is to reduce the load on the switchboard if the generator overloads to take it back to a safe level and preventing the generator from tripping entirely.
Usually in 3 stages with a short time period of even as little as 5 seconds between eachother.
Will trip galley, laundry, AC & some deck machinery first

• Reverse power trip prevents the generators from becoming motors and drawing the power from the board, causing a potential blackout and damage to the prime mover. Can happen when a generator is not taking on enough load. try

Question 19

What is an AVR

Answer 19

• An automatic voltage regulator is designed to monitor the output voltage of the generator and compares it to the set value.
• It then adjusts the level of excitation current supplied to the rotor of the generator to adjust the magnetic field, adjusting the output voltage.

Question 20

How a DG actually produces power (How an alternator produces DC)

Answer 20

• The prime mover rotates the crankshaft at a fixed RPM controlled by the governor. • This rotating shaft acts as the rotor inside the alternator which has excitation windings.
• The AVR supplies controlled DC to these windings while they rotate and this creates a rotating magnetic field which cuts through the stator windings, inducing an EMF (Faraday’s Law).
• This induced EMF causes an AC current to flow in the stator windings and this AC is converted to DC using a rectifier within the alternator.

Question 21

What is Faraday’s Law of Induction

Answer 21

A change in magnetic field will induce a current in an electrical circuit and the induced EMF is directly proportional to the rate of change of magnetic flux through the circuit.

Question 22

How to do continuity test and IR test

Answer 22

Pre-testing
• PPE
• LOTO
• Insulated tools
• Prove testing device works
• Prove dead on V setting
• Prove testing device works
• Take picture or note of terminal connection arrangement and remove them

• Continuity test - set to ohms - sends 1-3v DC through to test that the current flows with low resistance from A to B. Beeping or reading close to 0 indicates continuity.
• Insulation resistance test - set to 500v DC setting for 440v , 220v = 250v DC setting
Min reading 1 Mega Ohm.

Question 23

What can cause an earth fault?

Answer 23

Short circuit, water ingress, overheating, loose connections

Question 24

You try to start a motor and it is not starting, what do u do?

Answer 24

PPE
LOTO
Inform Duty (bridge if propulsion motor)
Insulated tools
Consider permit
Prove multimeter on testing unit
Prove motor dead
Prove multimeter on testing unit again
Could be blown fuse - check with multimeter
Check the terminal connections
Try to spin the motor manually, can uncouple the pump and motor to try spin each freely

Question 25

Advantages of high voltage

Answer 25

• Lower current for the same power P=IV • High torque for propulsion • Smaller and Lighter equipment • Smaller cables • Better efficiency (due to lower current, less copper losses, reduced winding temps -> longer insulation life • Enables use of variable speed propulsion (azipods) which with LV would require massive current and cabling

Question 26

What do you do if there is an earth fault?

Answer 26

• Call the ETO + investigate with him using on-off method • Try the non-critical equipment first: - Call galley and ask them if you can switch off supply to galley - Try laundry next - Anywhere that could be exposed to moisture • If this does not work, inform chief that you have to start switching off supply to more critical equipment.

Question 27

You have to replace/overhaul a motor due to SW ingress

Answer 27

Inform chief and duty watchkeeper Check spare parts Risk assessment + PTW PPE + Insulated tools LOTO the motor Prove Test Prove (proving dead) Take picture of terminal connections then disconnect and tape them off Unbolt and take out using correct lifting techniques and certified + inspected lifting equipment (LOLER regs) Take to workshop and disassemble Clean windings with Electro-Solv (Clean other parts with FW if the motor was flooded/contaminated with SW) Dry & Revarnish windings Reassemble & put back in Continuity & IR test Can also current draw test on load.

Question 28

Electrical motor starting methods

Answer 28

Motors usually use 6x the normal operating current when starting so we can use various starting methods to reduce this. Direct on-line = normal 6x Star-delta Soft start Auto-transformer

Question 29

What is the safe limit for current?

Answer 29

5mA which is roughly 50v AC & 120v DC

Question 30

Types of electrical tests & faults

Answer 30

• Continuity test - checks how current flows from one point to another in an electrical circuit by placing a small voltage across a chosen path (phase to phase, phase to earth) • Insulation resistance - to test the condition of the conductor insulation, helps to detect earth faults or short circuits • Short Circuit - due to double break in insulation, allowing a path between phases and creating a large current • Earth fault - when current finds an unintended path to earth h

Question 31

Motor safeties

Answer 31

Fuses Overload protection Earth connection

Question 32

HV Safety Devices

Answer 32

HV Rubber mats HV Rescue hook HV Circuit breakers HV Switchboard interlocks HV Spider Arc-flash suit/PPE