Electrical Loading Devices

Electrical distribution and common loading devices

Design Requirements • Electrical system which can provide the maximum load required (maximum reliability) • Electrical system that can distribute the needed capacity at the right proportion (continuation of supply) • Safe electrical system from overloading condition (adaptability to load variation) • Design which take weight, size and price in consideration

"system" evaluation • Is the apparatus enclosure appropriate for the location? • Is the fixture adequately grounded to reduce the shock hazard? -Is the fixture enclosure fire retardant and not surrounded by combustibles? • Will a fault in the fixture be safely cleared by the first upstream overcurrent device so that other parts of the electrical system are not needlessly affected? • If it is a vital safety system, is the failure indicated and an alternative or back-up provided? • Do the components go together?

• Capacity. Determining the number and size of generating sets needed for a vessel requires a careful analysis of the normal and maximum demands during various phases of operation, including at sea, maneuvering, and in port. • Also, any special or unique operational considerations should be addressed. It is the intent of the regulations to ensure all normal "ship's service" loads can be kept energized with the largest generator out of operation, and without use of the emergency generator. • It is not the intent of the regulations to ensure that the vessel can continue to perform an industrial function, such as drilling or dredging, with a generator in reserve.

Design Works: •

Load Identification – identifying the load by listing down all electrical equipment installed on board – air conditioning and refrigerated holds must be included – identify all the equipment rated or nominal kW

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Load Analysis – – – –

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Analysis the load and prioritizes its importance Determine its service factor which based on time used in 24 hours period Allowance for losses must also be included Determine the needed kW for all condition (sea, fishing, port, emergency etc)

Generator Sets Determination Wiring and Electrical Distribution Diagram Wiring Arrangements.

Design Requirements • • • • • • • • • • • • •

1. Mission 2. Scenarios 3. Key Roles 4. Key Task 5. User Characteristics 6. System Effectiveness machineries in emergency cases. 7. Operability 8. Crew Station and Interface Design9. User Acceptance 10. Survivability 11. Maintainability 12. Availability 13. Reliability 14. Safety and Health

The load analysis documents • • •

(a) Individual load factors used are reasonable. (b) Application of the load factors is reasonable and thorough. (c) Generating plant is adequate and in accordance with the applicable regulations. (2) Considerations. The load analysis should be prepared and evaluated with the following considerations in mind: • (a) Loads can be classified by various operating conditions such as port, anchor, sea, functional, emergency, maneuvering, or cold start. The load analysis will normally address only the normal sea load, maneuvering load and emergency load, unless special considerations for the safety of the ship require otherwise (e.g., at sea cargo transfer (functional)). • (b) A motor may be oversized for its attached load and thus not operate at its rated capacity. • (c) Formulas for the determination of load factors for major steam propulsion vessels may be found in SNAME T&R Bulletin 3-11, "Marine Steam power Plant Heat Balance Practices", Section 3.2.15.

The load analysis documents • • • • • •

(e) A single load factor for group loads may be assigned if they meet one of the following criteria: (1) Two or more loads operate with a definite relationship to each other (e.g., heating and air conditioning); (ii) When the relationship described in (i) above is not clear, but is known to exist (e.g., galley equipment); (iii) When low power loads in the same space can be assigned roughly the same load factors (e.g., radios and electronics). (f) Known load use data should always be used in lieu of demand factors, if available. (g) Power conversions and their efficiency should be considered (e.g. power factors, transformers, semiconductor controlled rectifiers (SCR's). Due to efficiency below 1.0, apparent connected loads may be increased due to the conversion equipment).

The load analysis documents •

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(h) Loads that are provided individual factors in the analysis should not be additionally assigned a group factor, and vice versa (e.g., 0.3 (individual factor) x 0.4 (group factor) 0.12 (final factor) (either 0.3 or 0.4 could be used, but not 0.12)). (i) Factors of zero (0) are assigned to equipment that is seldom used. (j) Factors of 0.9 and 1.0 are used where motors operate at full load for an extended period of time. (k) Any standby or duplicate units should be listed and assigned a factor of zero unless they are continuously idling. The primary unit should be assigned an appropriate factor, e.g., Steering pump #1, d.f.=0.9; Steering pump #2, d.f.=0.0 (Stby). (1) The development of standard load factors for given classes of vessels is encouraged, as time and experience permit. (m) Large equipment -- unusually large loads, as compared to the generating capacity -- should be assigned appropriate factors assuming that other non-essential loads are not operated simultaneously.

The load analysis documents • • • • • • • • • • • • • •

n) The load analysis should show that the generating plant is adequate to simultaneously carry the loads vital to the survival of the vessel in an emergency such as fire or flooding. These loads should include: (i) Steering; (ii) Vital propulsion auxiliaries; (iii) Ventilation; (iv) Communications; (v) Fire pumps; (vi) Alarms; (vii) Bilge pumps; (viii) Emergency lighting; (ix) Radar; and (z) Controls. (o) For unmanned machinery spaces, remotely operated emergency loads, such as bridge started fire pumps should be assigned a load factor of 1.0. (p) Automatically started equipment should be provided a load factor of 1.0 without regard for spinning reserve. (q) Special functional operations of the vessel, such as underway replenishment (a Military Sealift Command (MSC) Ship), dredging (a hopper dredge), and at-rig offloading (an offshore supply vessel) do not require one generator in reserve. Normal at sea operations such as cargo cooling (refrigerated ships) and liquid cargo recirculation (offshore supply vessels) do require one ship's service generator in reserve.

Electric Generating Capacity To simplify, these calculations help in determining the needed service factor for different kind of equipments and usage: • Service Factor, fs = 24 hour average operating load • Rated load • For motor driven auxiliaries; • fs = operating BHP x No of hours in use per day • Motor rated BHP 24 • Operating load in KW • (24 hours average) = 0.746 x fs x (motor rated BHP) x (no. of unit operating) • (motor efficiency) • For lighting, galley, heaters, electronics gears, etc • fs = operating KW x No. of hours in use per day • rated KW 24

Load Identification Tables are divided into several categories where each category consists of: • all the equipment which needs electricity in its region: • Lightening • Navigaton • Propultion • Auxiliary Which are accounted for under: • the quantity, • electrical load, • voltage • and even the service factor are included inside the table for easier analysis and calculation.

Lighting • In designing the electrical system for this ship, choosing the right illumination for the ship is also considered as one of the electrical designer’s job. • From the given load identification, the type of lighting varies from places and tasks. • Usually, navigational lights use a higher power type of light compared to the one used in cabins or wheelhouse. • Thus, it can be seen that the lighting power used by navigational lights are somewhat 80% higher than the one used inside the ship.

Lighting • •

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When choosing the illumination levels for any particular area, a few things should be taken into consideration such as: The installed lighting must provide a good illumination to ensure the safety of personnel, where machinery spaces should be well and adequately lit. Lighting should also be provided for escape routes and lifeboat embarkation area. The chosen lighting system must provide an adequate illumination for tasks required in that particular area. If possible, the lighting system must assist in the creation of an aesthetically pleasing environment which is very vital in accommodation and communal areas such as galley statutory regulations required that emergency lighting to be embodied in the general system which cover crews areas, alleyways, cabins, stairways and exist which will surely facilitate escape during emergency. Lighting are required be in :Lifeboat embarkation area, CabinsGalley, Wheelhouse, Engine Room

Generator Sets Determination This tabled under the following: Nominal W Appliance Factor Appliance W After the load identification and generating power calculations, if the power needed by the ship is around 28KW only. A 30KW generator is considered to be the best choice since it has the necessary power needed plus an extra 10%. Generator in general are usually sold in power of 5 meaning that it is easier to find a generator which produce 30KW instead of 28KW or 27.9KW making the 30KW more ideal choice for this ship.

Generator Sets Determination • After installing the needed generators, a switchboard is needed to provide for the control, protection paralleling or separating the service of generators. Bear in mind that for the installation of switchboard it needed to be: • At dry area and accessible from both front and rear • Should be located as far inboard as possible • An adequate amount or front and rear space for accessibility in term of operation and maintenance. • Close as possible with the associated generators sets. • Able to operate satisfactorily at 300 angle from any direction.