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Offshore VesselHigh Voltage Safety

IMCA SEL 031, IMCA M 217October 2012



A B The International Marine Contractors Association

(IMCA) is the international trade associationrepresenting offshore, marine and underwaterengineering companies.

IMCA promotes improvements in quality, health, safety,environmental and technical standards through the publication

of information notes, codes of practice and by other

appropriate means.

Members are self-regulating through the adoption of IMCA

guidelines as appropriate. They commit to act as responsiblemembers by following relevant guidelines and being willing to be

audited against compliance with them by their clients.

There are two core activities that relate to all members:

Competence & Training

Safety, Environment & Legislation

The Association is organised through four distinct divisions,each covering a specific area of members’ interests: Diving,

Marine, Offshore Survey, Remote Systems & ROV.

There are also five regional sections which facilitate work on

issues affecting members in their local geographic area –

Asia-Pacific, Central & North America, Europe & Africa, MiddleEast & India and South America.

IMCA SEL 031, IMCA M 217

www.imca-int.com/sel www.imca-int.com/marine

The information contained herein is given for guidance only and endeavours toreflect best industry practice. For the avoidance of doubt no legal liability shall

attach to any guidance and/or recommendation and/or statement herein contained.

© 2012 IMCA – International Marine Contractors Association



Offshore Vessel High Voltage Safety

IMCA SEL 031, IMCA M 217 – October 2012

1

Introduction ........................................................................................................... 1

2 Definitions .............................................................................................................. 2

3

What is Classed as High Voltage Onboard a Vessel? ........................................ 3

4 HV Equipment ....................................................................................................... 4

5 Advantages of High Voltage Supply over Low Voltage Supply ........................ 5

6 How Can Injuries Happen During Work on HV Equipment? ........................... 6

7 HV Safety Requirements ...................................................................................... 7

7.1

Training ..................................................................................................................................................................... 7

7.2 Risk Assessment ................ ................ ................ ................ ................ ................. ................ ................ ................ .... 7

8 Permit to Work System for HV Work ............................................................... 9

9 Additional Procedures to be Implemented for HV Systems .......................... 10

9.1 Sanction-to-Test System ................ ................ ................ ................ ................ ................ ................ ................ .... 10

9.2 Limitation of Access Form ................................................................................................................................ 10

9.3 Earthing Down ..................................................................................................................................................... 10

10 Safety Rules That Should be Implemented by Owners or Operators

with HV Equipment Onboard Their Vessels .................................................... 11

10.1 HV Enclosure Entry ............................................................................................................................................ 11

10.2 Work on HV Equipment ................................................................................................................................... 11

10.3 Earthing .................................................................................................................................................................. 11

10.4 General .................................................................................................................................................................. 11



IMCA SEL 031, IMCA M 217 1

1 Introduction

As the demand for electrical power increases on vessels, especially on

large offshore construction vessels with diesel electric propulsioninstallations, the supply current becomes too high for efficient and

practical use of the usual shipboard 3 phase voltage supply of 440 Volts

(V) AC.

To reduce the level of running currents and fault current levels it is

necessary to specify a higher system voltage for the higher power rated

equipment.

By generating electrical power at 440V from 3 x 1 megawatt, 0.8 power

factor diesel generator sets, each generator main cable and circuitbreaker has to handle a full load current of:

Power (W) = √3 x Voltage (V) x Current (I) x Power factor (Cos Ø)

W = √3 x V x I x Cos Ø

Which returns a current of: 1,000,000/√3 x 440 x 0.8 = 1,640 Amps

If a short circuit fault occurred on one of the outgoing feeder cables from the main switchboard then the

feeder circuit breaker would have to be rated to a potential fault current of approximately 65,000 Amps.

However, by generating electrical power at 6,600V (6.6kV) on the same system the full load current of each

generator is:

Current (I) = 1,000,000/√3 x 6,600 x 0.8 = 109 Amps

Also the fault current at the main switchboard would be as low as 4,500 Amps which, being considerably

lower, is more easily handled by the equipment.

In addition to the above, the power loss in an HV installation may be calculated by:

Power = Current² x Resistance (P = I²R)

This power loss is caused by the current flowing through the component resistance.

Therefore the power loss is reduced if the voltage is stepped up and thus it is always efficient to transmit

power at a higher voltage.

An example would be a bow thruster motor which may be of a smaller size if it is designed to operate on

6.6kV. For the same power, the motor would be of a smaller size if it is designed for 6.6kV when compared to

440V.

These are the major reasons why vessels have shifted towards high voltage systems.



2 IMCA SEL 031, IMCA M 217

2 Definitions

Additional earth An earth connection applied to apparatus after the application of a CME, normally

applied at the point of work if not already fitted with CME

Approved A type of form sanctioned for use by the DPA/superintendent/senior electrical

engineer

Authorised person (AP) An authorised person is appropriately trained and appointed in writing by the

superintendent/electrical engineer to carry out work as permitted by these rules

Caution notice A notice conveying a warning against interference with the apparatus to which it is

attached

Chief engineer Senior engineer onboard the vessel responsible for all vessel technical operations

and maintenance

Circuit main earth(CME)

An earth connection applied for the purpose of making apparatus safe to work onbefore a permit to work or sanction for test is issued and which is nominated on

the document

Competent person A competent person is appropriately trained and has sufficient technical knowledgeor experience to enable him to avoid danger. It is the duty of the authorised

person issuing a permit to work to satisfy himself that persons are competent to

carry out the work involved

Danger notice A notice calling attention to the danger of approach or interference with theapparatus to which it is attached

Dead At or about zero voltage and disconnected from all sources of electrical energy

Earthed Connected to the general mass of earth in such a manner as will ensure at all times

an immediate discharge of electrical energy without danger

High voltage (HV) A voltage exceeding 1,000 V AC

High voltage apparatus Any apparatus, equipment or conductors normally operated at a voltage higher than

1,000 V AC

Isolated The disconnection and separation of the electrical equipment from every source of

electrical energy in such a way that this disconnection and separation is secure

Key safe A device for the secure retention of keys used to lock means of isolation, earthing

or other safety devices

Limitation of access

(LoA)

A form issued by an authorised person to a competent person, defining the limits of

the work to be carried out in the vicinity of, but not on, high voltage electrical

apparatus

Live Electrically charged from a supply of electricity

Permit to work (PTW) A form of declaration signed and given by an authorised person to a competent

person in charge of the work to be carried out on or in close proximity to high

voltage apparatus, making known to him the extent of the work, exactly what

apparatus is dead, is isolated from all live conductors, has been discharged and

earthed and, insofar as electric hazards are concerned, on which it is safe to work

Safety lock A lock used to secure points of isolation, safety devices and circuit earths, being

unique from any other locks used on the system

Sanction for test (SFT) A form of declaration, signed and given by an authorised person to anotherauthorised person in charge of testing high voltage apparatus making known to the

recipient what apparatus is to be tested and the conditions under which the testing

is to be carried out

Designated person

ashore (DPA)/

superintendent / senior

electrical engineer

A senior electrical/mechanical engineer suitably qualified and appointed in writing by

the company to be responsible for compilation and administration of procedures forhigh voltage installations and operations




3 What is Classed as High Voltage Onboard a Vessel?

In marine practice, voltages below 1kV AC are considered LV (low voltage).

HV (high voltage) is any voltage above 1kV.

Typical marine HV system voltages are 3.3kV, 6.6kV and 11kV.




4 HV Equipment

The principal items of a high voltage vessel electrical system would be:

♦ the main generating sets;

♦ the main HV switchboards with associated switchgear, protection devices and instrumentation;

♦ HV cables;

♦

HV/LV step-down transformers to provide LV consumers;

♦ HV/HV (typically 6.6kV/2.9kV) step-down transformers supplying propulsion converters and motors;

♦ HV motors for main propulsion and thrusters;

♦ HV for significant equipment, cranes, ROVs, winches, etc.




5 Advantages of High Voltage Supply over Low Voltage Supply

Some of the major features of a high voltage supply on a vessel when compared with low voltage are as follows:

♦ HV systems have more extensive and complex networks and connections;

♦ Access to HV areas is strictly limited and securely controlled;

♦ Isolation procedures are more involved and switching strategies have to be formulated and recorded;

♦

Isolated equipment must be earthed down;

♦ Appropriate test probes and instruments should be used;

♦ Diagnostic insulation resistance testing is necessary;

♦ HV systems may be earthed neutral and use current limiting resistors;

♦ Special HV circuit breakers should be installed;

♦ Current magnitude and time is used for discrimination in protection/monitoring devices.




6 How Can Injuries Happen During Work on HV Equipment?

The most significant danger to any person carrying out electrical work is that they might suffer an electric

shock. Any contact of a part of the body with a live conductor will result in electric shock. There is also a riskof severe burn injuries resulting from arcing when conductors are inadvertently short circuited.

An HV electric shock will almost certainly lead to severe injury or death.

Factors likely to increase the risk of receiving an electric shock include the following:

♦ HV work onboard may be carried out in close proximity to a person(s) not familiar with HV hazards.

Therefore the area must be properly cordoned off from the surrounding work that may be going on anddanger notices well posted;

♦ There will be large areas of earthed metal that can be easily touched, increasing the possibility of electric

shock from an HV conductor;

♦ High voltage insulation testing (flash testing) can be particularly hazardous when several parts of the

equipment are energised for a period of time;

♦ Some equipment could be using water in its operation which can lead to an increased risk of injury. Ingeneral, water conducts electricity and reduces the resistance of the skin;

♦

The use of test instruments when taking measurements of high voltages can increase the risk of injury ifthey are inadvertently used without the earth (protective) conductor connected. This can result in the

enclosure of the instrument becoming live at high voltages;

♦ High voltage equipment will store energy after disconnection. For example, on a 6.6kV switchboard a fatal

charge may still be present on the equipment hours or even days later;

♦ If during maintenance an HV circuit main earth (CME) is removed from the system, it must not be worked

on, as the HV cabling can re-charge itself to a high voltage (3-5kV) from induced voltages from nearby liveHV cabling.




7 HV Safety Requirements

7.1 Training

The 2010 Manila Amendments to the International Convention on Standards of Training, Certification

and Watchkeeping for Seafarers (STCW) introduced revised competence standards for the engine

department, including a new additional requirement for engine personnel to have undergone training

and education in HV systems.

The Manila Amendments entered into force on 1 January 2012. Seafarers who started their training

before 1 July 2013 may continue to meet the previous training requirements until 1 January 2017.However, from 1 January 2017, engineering personnel will have to be able to demonstrate that they

meet the new HV requirements. Companies should confirm individual flag state requirements, but it is

likely that, when it comes to revalidating their certificate, engineering officers who are unable toprovide documentary evidence of previous sea service on ships fitted with HV systems or of having

completed an appropriate HV course will have an HV limitation placed on their Certificate of

Competency.

Companies will also need to confirm any national requirements for the approval of HV courses, but

for engineering personnel at the management level, an appropriate course is likely to have to cover as

a minimum:

♦ The functional, operational and safety requirements for a marine HV system;

♦ Assignment of suitably qualified personnel to carry out maintenance and report of HV switchgear

of various types;

♦ Taking remedial action necessary during faults in a HV system;

♦ Producing a switching strategy for isolating components of a HV system;

♦ Selecting suitable apparatus for isolation and testing of HV equipment;

♦ Carrying out a switching and isolation procedure on a marine high-voltage system, complete with

safety documentation; and

♦

Performing tests of insulation resistance and polarization index on high-voltage equipment.

As an example, the UK Maritime Coastguard Agency (MCA) has provided guidance on the

implementation of these changes for UK registered ships (Manila Amendments 2010 – Revalidation),

but companies should confirm individual flag state requirements.

Additional guidance on HV training is also provided in IMCA C 010 – High voltage training: A syllabus

for training offshore workers involved with high voltage equipment – and IMCA R 005 – High voltageequipment – Safety procedures for working on ROVs.

7.2

Risk Assessment

The access procedure to HV switchboards and equipment must be strictly controlled by using a risk

assessment and a permit to work (PTW) system; isolation procedures must involve a safety key

system and earthing down procedures.

A useful acronym is:

– Locate – all points of isolation;

– Isolate – to prevent accidental re-energising;

– Verify – power is disconnected and that there are no secondary power sources;

– Earth – using appropriate approved equipment.

To help identify the precautions necessary for carrying out HV electrical work safely, there should be

a comprehensive assessment of the risk of injury posed by the work being done. Hazards, who or

what may be harmed and how, and the effectiveness of existing precautions should be taken intoaccount when assessing the risk. The examples of factors given in this information note which might

increase the risk of injury should be borne in mind.

http://www.imca-int.com/documents/core/ct/docs/IMCAC010.pdf



http://www.imca-int.com/documents/divisions/rov/docs/IMCAR005.pdf







When carrying out a risk assessment for HV electrical work, the following questions should be

considered:

♦ Can the work be done with the equipment dead?

♦ Is it absolutely necessary for someone to be working on or near equipment that is live at

dangerous voltages?

♦ Have suitable precautions been taken to avoid danger and prevent injury?

♦

Is the person(s) carrying out the work competent for that type of work, or if not, adequately

supervised?




8 Permit to Work System for HV Work

The company safety management system should already incorporate a permit to work system for electrical

equipment under 1kV but perhaps not for HV equipment. Samples of electrical permits to work for LV and HVinstallations are found in the Code of Safe Working Practices for Merchant Seamen (COSWP) 2010 edition at:

www.dft.gov.uk/mca/coswp2010.pdf

http://www.dft.gov.uk/mca/coswp2010.pdf






9 Additional Procedures to be Implemented for HV Systems

For HV systems, additional procedures and precautions should be taken. These are as follows:

9.1

Sanction-to-Test System

Following work on an HV system it is often necessary to perform tests. Usually testing may only be

carried out after the circuit main earth (CME) has been removed. An example of this is insulationtesting as it involves the system being checked for insulation to earth.

A sanction-to-test should be issued in a similar manner to a permit-to-work. A sanction-to-test

should not be issued on any apparatus on which a permit-to-work is still in force, or on which another

sanction-to-test is in force.

Note: Maintenance and repair cannot be carried out under a sanction-to-test.

An example of a sanction-to-test for testing work carried out on HV systems is shown in the Code of

Safe Working Practices (COSWP 2010 edition Annex 16.2.1). The example shows the headings for

each section and each section’s requirements. These should be adapted to the circumstances of the

individual vessel or vessel’s electrical HV system or the particular job to be carried out, in light of the

risk assessment.

9.2

Limitation of Access Form

When carrying out HV maintenance, it may be dangerous to allow unrestricted work to be carried

out nearby. Workers carrying out maintenance nearby may not have HV training and may not be

familiar with the risks involved when working on or near HV equipment. Due to these risks the

Limitation of Access form should be used. This form states the type of work that is allowed to be

carried out nearby the HV work, the limitations imposed and the safety precautions taken. The form

is to be issued and signed by the AP and a confirmation of receipt signature by the person carrying outthe work. The form should include sign off and a cancellation section.

9.3

Earthing Down

Earthing down is required to ensure that any stored electrical energy in the inherent capacitance of

the equipment insulation is safely discharged to earth after isolation. The higher levels of insulation

resistance required on HV cabling lead to higher values of insulation capacitance (C). When this iscoupled with the high voltage, it means that the energy stored (W) in HV equipment is far greater

than that in LV. This is clearly demonstrated by the electrical formula:

Energy stored (W) Joules = (Capacitance x Voltage²)/2

Earthing down also ensures that isolated equipment remains at a safe potential during work

procedures.

There are two types of earthing down at an HV switchboard:

♦ Circuit earthing – an incoming or outgoing feeder cable is connected by a heavy earth connection

from earth to all three conductors after the circuit breaker has been racked out. This is done atthe circuit breaker using a special key. This key is then locked in the key safe. The circuit

breaker cannot be racked in until the circuit earth has been removed;

♦ Busbar earthing – when it is necessary to work on a section of busbar it must be completelyisolated from all possible electrical sources. This will include generator incomers, section or bus

tie breakers and transformers on that busbar section. The busbars are connected together and

earthed down using portable leads which give visible confirmation of the earthing arrangement.




10 Safety Rules That Should be Implemented by Owners or Operators with HVEquipment Onboard Their Vessels

10.1

HV Enclosure Entry

♦ The HV enclosure should be kept locked;

♦ The access to the HV enclosure keys should be for authorised persons only;

♦ No one except the authorised person (AP) or the competent person under AP supervisionshould enter an HV enclosure if it is possible to touch HV conductors;

♦ Only the AP or person accompanied by the AP should be allowed inside an HV enclosure.

10.2

Work on HV Equipment

No personnel to carry out work unless the HV equipment is:

♦ Dead;

♦ Isolated;

♦

Verified dead;♦ Earthed at all HV disconnection points and caution notices posted;

♦ Screened off where necessary with caution and danger notices posted;

♦ Permit to work (PTW) or sanction for test (SFT) issued;

♦ Limitation of access form issued if required;

♦ Work personnel must be competent and must witness test to prove isolation.

10.3

Earthing

♦ CME is to be applied by the AP or the competent person in the presence of an AP;

♦

On isolated HV equipment, conductors to be earthed are to be proved dead using an approvedHV indicator tester;

♦ Additional earthing should be applied at the point of work;

♦ CME at the point of work can be removed or replaced one phase at a time to allow for work, butmust be carried out as documented in the PTW or SFT.

10.4 General

♦ Always double check that a system is isolated and is proven dead before earthing;

♦ Always trip the LV side of a transformer first;

♦

Re-close HV side of transformer first;♦ Do any HV switching on minimal load.

offshore vessel hv safety

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