hv sytem in ships

High voltage on ships

General Power Systems

• Majority of merchant ships have a 3-phase3 wire, 440 V insulated neutral earthpower systems

• •This power system falls in the category ofLV and meets the power demands ofmedium capacity motors up to 200 kW

• When large loads are connected to the LVsystem the magnitude of current flowbecomes too large resulting in overheatingdue to high iron and copper losses

• P = VI CosФ• Copper loss =I² R [kW]

Losses in Electrical Systems

Copper Losses in electrical cables and machine windings.Hysteresis Loss in magnetic cores.Eddy current loss in conductors and cores.All these losses are current dependent and rise to very high levels in LV machines for large power ratings

Benefits of H V Power Systems• Ships with large electrical loads now operate at high• voltage of 3.3-6.6 kV• Such high voltage reduces the magnitude of current and

thus lowers iron/copper/eddy current losses and alsoresults in a cooler motor operation

• Low current flow reduces conductors size and hence lowers cost of electrical equipmentPower transmission more efficient with low lossA 6 MW motor load at 440 V and 0.8 pf will require SB fault level to be of 90 kA and cable full load current of 3300 A

• Same power system at 6.6 kV, needs SB fault level of only 9 kA and cable full load current of 220 A

• Flexibility of power system layout• Prime Mover-Generator units can be located

at convenient location away from thepropellers

• Propulsion motor can be located at the astern below the water surface

• This results in shorter shaft and reduced vibration

• Load Diversity• –A set of prime movers can meet the demand of

propulsion as well as ships electrical load• –Prime movers can be operated at economical speed

at all times• –Propulsion load can be regulated to meet emergency

electrical load without adversely affecting the shipspassage time

• Ease of Control• With advancement in power electronics fine speed

regulation of ac motors has become common practice

Typical Marine HV Systems• 3.3 kV•6.6 kV•11 kV• Principal Components of HV System• By generating electrical power at 6.6 kV instead

of 440 V, distribution and switching power about 6 MW becomes easy

•-Main Generators•HV Switch Board•HV Cables•HV Transformers•HV Motors (2-12 MW)

Typical HV Equipment Rating

Main SB= 6.6 –11 kV, Bus Cap =1250A•Cargo SB = 6.6 kV, Bus Cap =1250 A•Ballast Pp Motor = 6.6 kV, 330 – 2000 kW

HD Copm = 6.6 kV, 770 kW, 3560 rpm•Bow Thrusters = 6.6 kV, 3 MW,•Transformer = 3400 kVA, 6600/450 V•Reefer Transformer = 6600/450 V,

Typical HV Power System

HV/LV Power Supply system

Propulsion Plant Layout

HV Propulsion Power System

Concept of Electrical Propulsion

Typical EL Propulsion

HV Voltage Shipboard System• A) Bus bars:• •Made from high conductivity copper having sufficient

cross section such that max temp rise is 45K•All bare areas are coated, plated with tin to protect against corrosion•Color markers provided to distinguish between phases

• B) Phase Arrangement (view from front panel):• •Phase R (Red): Left Top Front• •Phase Y (yellow )• •Phase T (Blue) Right Bottom Rear

• C) Earthing:• •For earthling the switchboard to the vessel’s hull, earthling bars

and terminals are provided through out cubicles.• •All incoming and outgoing circuits are provided with switch of

earthing and short circuiting for maintenance purpose.

• D) Characteristic• •Rated voltage : 7.2kV• •Service Voltage: 6.6kV• •Rated Frequency: 60 Hz• •Rated insulation : 20 kV RMS (one minute)

•Protection Degree : IP32•Busbar Current: 1250 A

H V ship board system

1 Unit of 6.6 kV Diesel Generator (3450 kW)2 Units of 6.6 kV Turbo Generator (3450 kW)1 Unit of 440 V Emergency Generator (550 kW)Battery Supply1 bank of 24V dc ship’s battery1 bank of 24 V dc Radio Battery- GMDSS Console

Consumers• Consumers ranging from:

6.6 kV- Cargo Pumps, Ballast pumps, HD Compressors440V- Most of machineries in E/R such as Main Sea Water Circ.

• Pump, Central Fresh Water Cooling Pump, etc220V- Power outlets, lighting, navigation equipments, etc110 V dc- Control circuit for MSB24 V dc- Navigation Equipments

SWITCHBOARDS ARRANGEMENT

• Consists of:•High voltage main switchboard•High voltage cargo switchboard•Low voltage main switchboard•Low voltage cargo switchboard•Emergency switchboard•Group starter & Individual Panels

PROTECTION SYSTEM FOR DG & TG

• Protection being provided for the DG and TG to avoid any unsafe• occurrences.• •Basically the protection is done by a protection device known as• HIMAP and provided at MSB.

•Type of Protection•Under Voltage- setting at 60% / 2 seconds (3960 KV)•Over Voltage- setting at 110% / 5 seconds (7260 KV)•Reverse Power- setting at -10% / 10 seconds (-345 KW)•Instantaneous-•STD setting at 250% (942A)•Instantaneous setting at 1000% (3770A)•Long Time Delay setting at 110% (415A)•Earth Fault

OVERCURRENT SETTING FOR BUS TIE, CSB ANDTRANSFORMER

STD LTD• BUS TIE 200%, 0.7S 100%, 30S

• CSB 250%, 0.57S 100%, 30S

• HV Trans. 300% ,0.57s 105% , 60s

MOTOR PROTECTION

• Protection provided •Over current•Earth fault•Phase fail•Motor Protection provided by independent relay•Low current•High current•Arc fault

HV MSB• The operation could be in manual or auto. However, it is always to

be kept in• auto since control is done from IAS.

All necessary mimics and controls are being provided inside IAS.Manual operation is as per normal low voltage switchboard where indication light, breaker control, meters. Governor control, etc being provided on the switchboard.

• Generators are being protected by a device known as HIMAP. All protection settings are being set inside the HIMAP.

• Vacuum Circuit Breakers (VCB) are being used for the bus tie and generator Panels.

• Vacuum combination Contactors are being used for the ballast and cargo pumps

HV CARGO SWITCHBOARD

• Cargo switchboard is equipped with soft starter for the cargo pumps.

• By pass switch is provided in order to start by direct on line.

• Soft starter panels are provided for each port and starboard cargo switchboard.

• Facility to simulate the cargo pumps is possible. This is done by disconnecting the breaker and removing the low current relay. This is done prior to discharge port

POWER GENERATION• Generator particulars: Maker: Nishishiba Electric, Type: Brushless

Excitation System, Voltage: 6600V Output: 3450KW rated Current: 377A Frequency:60Hz, Full Load Speed: 1800RPM, Rotor Type: Salient Type, Protection:IP55

• •A dc current is applied to the rotor winding which produces a rotor magnetic field. The rotor is then turned by prime mover producing a rotation of magnetic field. This magnetic field induces a three phase set of voltages within the stator windings, the dc current is set at 5.6A by maker.

• •A brushless exciters are used to supply this dc current. A brushless exciter is a small ac generator with its field circuit mounted on the stator and its armature circuit mounted on the rotor shaft.

• •The three phase output of the exciter generator is rectified to direct current by rectifier circuit, also mounted on the shaft and then fed to the main field winding (rotor winding)

• By controlling the small dc field current of the exciter generator, it is possible to adjust the field current on the main field or rotor winding.

• To make the excitation of generator completely independent of any external power sources, a small pilot exciter known as PMG is included in the system.

• The PMG is actually a small ac generator with permanent magnets mounted on the rotor shaft and a three phase winding on the stator. It produces power for the field circuit of the exciter which in turncontrols the field circuit of the main machine.

PROCEDURE OF MEGGERING THE CARGO PUMP

• The switchboard is designed with many interlock keys. Therefore, knowing the steps are essential:

• A) ensure the cargo pump is in stop condition.• B) Turn the key and disconnect the breaker by using handle.• C) Turn the other key to enable the handle for mechanical earthing

switch to be inserted.• D) Turn the mechanical earthing switch to earth the breaker• E) Take the key and bring it to rear side• F) Turn the key to open the bottom compartment• G) While the compartment is in open condition, turn the key off and

bring back to front panel to disable the mechanical earthing• H) Confirm that the pump has no residual potential by using

potential detector.• I) The meggering can be done as usual for the pumps

HV Safety

• Precautions before work on HV:• Safety wearing must be used before proceeding to job.

•Isolate power•Test HV live-line tester to prove its proper functioning.•The circuit on which work is to be carried out, must be tested and proved dead by an HV live-line testing equipment.•The circuit to be earthed down by connecting with hull.•Issue EPTW.•Minimum two people should work together.

• Safety precautions associated with operation of high voltage system:• Before start of work an Electrical Permit to Work must be issued.

EPTW is prepared and approve by the authorized officer.The copied permit signed by the responsible person usually has at least 5 sections with the first stating the work to be carried out.

• The next section is a risk assessment declaring where isolation and earthing has been applied and where danger/caution notices have been displayed then the permit is signed as authorized by the Chief Electrical Officer or Chief Engineer.

• In the third section, the person responsible for the work (as named in section• one) signs to declare that he/she is satisfied with the safety precautions and• that the HV circuit has been isolated and earthed.• Section four relates to the suspension or completion of the designated work.

The last section cancels the permit with a signature from the authorizing officer.The EPTW is valid only for 24 hours.

Marine Electrical HV Propulsion System

• Overall power train efficiency with EP is around 87-90%.• Employment of permanent magnets in electric generators

and motors as well as general advances in semiconductortechnology may improve this figure to around 92-95% in thenear future.

• Electrical transmission will consist of three basic energy conversions:

• -From (rotating) mechanical energy into electrical energy: E- generator

• -From electrical energy into (rotating) mechanical energy: E-motor• -Some form of fixed or controlled electrical conversion in between:

power converter

Structure of a combined powerplant for ships

Shuttle Tanker Electrical Lay out

FPSO Electrical lay out

HV CIRCUIT BREAKERS

Air Circuit Breakers•Oil Circuit Breakers•Air-ballast Circuit Breakers•Gas (SF6- Sulphur Hexafluoride) Circuit Breakers

•Vacuum Breaker

Future electrical ship• Future HV ships systems at sea may require voltages up to

13.8 kV to minimize fault levels• It is therefore essential that all Marine Engineering

personnel are trained in safe working practices for thesevoltages.

• The Electrical officers of the near future must be fullytrained to carry out maintenance and defect rectificationon Medium Voltage (MV) systems.

• This will mean a considerable increase in the electrical content of all training.

• Training will also need to be given to non-technicalpersonnel to ensure everybody is aware of the dangersof these higher voltages.

Available systems