Electrical Science and Technology

"Ships on Seas"

The electrical equipment aboard ship is inspected and tested during the complete engine survey which occurs every four years.

Such a survey is prescribed under the Rules and Regulations for the Classification of the Ship (depending where your ship is registered)

The electrical survey guidance in this report is based on the periodical survey regulations of Lloyd’s Register of Shipping, London.

Other classification societies have their own rules which although similar to Lloyd’s,shouldbe consulted prior to an electrical survey.

Electrical equipment and services aboard ship must also meet the minimum standards by various national and international organization.

For UMS operation, a survey of the associated alarms, controls and fire detection is required.

For tankers/gas carriers and other ships transporting flammable cargo, an additional survey of all electrical equipment in hazardous areas is carried out during each docking survey and annual survey.

The surveyorwill require that main and emergency generators are clean, respond correctly to controls and load changes, and show stable operation when required to run in parallel with other generators.

 A visual check will be made for any obvious deterioration, abrasion, or cracking of the insulation around the end winding coils of the stator.

An insulation testto earth and between stator phase windings (if neutral point can be disconnected at the terminal box) should be carried out while the machine is still hot after running on load.

 Remember to disconnect all AVR equipment, instrument connections and generator heater supplies when testing for IR.Special attention to the contact surface of any commutatoror slip-rings is required.

Generator running test, on load, should confirm the proper operation of governor and AVR controls with correct voltage, frequency, and current values indicated on the generator control panels.

Governor droop (typically 4%)and its response to load changes must be within the declared specification for the prime mover/generator combination.

A visual examination of circuit-breaker in main, emergency and section boards will usually precede operational tests.

The surveyor will particularly check the condition of main, arcing, and auxiliary contacts for signs of wear, misalignment and overheating.

Arc chutes must be clean, free of arc debris and correctly aligned.

 Test on a circuit-breaker will include ‘close’ and ‘trip’ operations while in its ‘isolated’ position (i.e. not connected in circuit).Over-current trips are typically set for 125% of full load current with a typical time delay of 20 sec. but this can vary to suit the thermal capacity of the generator. 

 Switchboards and fittings

 An obvious survey requirement for any switchboard, section board or distribution board is that they are clean. This includes all internal surfaces as well as the external pane surfaces, instrument faces and control switches.

A thorough cleaning job on the inside of the main switchboard can only be safely carried out when the board is completely ‘dead’ (all generators stopped and prime movers locked OFF

 Feeder isolator blades and fuse holder contacts must be checked for any mechanical wear or damage due to overheating or arcing at the contacts.

Operational test on a main switchboard under this heading will focus on the synchronizing controls and generator protection relays such as reverse power and preferential load shedding trips.

Typical reverse power trip settings may be 10-15% of generator power rating, with a time delay of 3-5 sec. for a diesel drive.  

Question:

Would IR reading of 0.5 MΩ to earth be acceptable?

Answer:

Although a minimum of 1MΩ is generally specified for new equipment, Lloyd’s rules suggest that 0.1 MΩis acceptable. However, most surveyors would insist on at least 2kΩ/volt, i.e. 440kΩ, say, 0.5MΩ as a reasonable minimum value for a 440V generator. 

Question:

What is the point of earthingone end of a current transformer secondary winding?

Answer:

Should the insulation between primary and secondary breakdown, the secondary circuit can be raised to full primary voltage; e.g. 440V above earth which should damage the secondary insulation with a serious risk to personnel. By earthingone end of the CT, the circuit is ‘anchored’ to zero volts. As a bonus, the earth connection will allow such a fault to be detected on the earth fault monitor.

Question:

What are the functions of EPR or butyl and PSP or CSP?

Answer:

EPR or butyl rubber are good electrical insulators but are not mechanically strong or resistant to oil. This is why a sheath of PCP or CSP which is stronger and has greater oil and fire resistance is fitted around the inner insulation.

Please check your understanding on basic electrical engineering.

The author is a licensed engineer. He is an advocate of corruption awareness. He believe that thru awareness of the consequences of corruption--the community will be awaken and will not allow any form of corruption to engulf their very existence.