insulated and neutral earthing system
Annex II
This document is to consider as a supplement to the IEC 60092-serie (NEK 410:2000 in Norwegian), and may be used to meet the requirements in the Regulations Relating to Maritime Electrical Installations. The text of this annex is a guide and thus not legally binding. There may be ways of meeting the legal functional requirements of the Regulations other than those stated i standards and guides. However, if the guide and the standards are used, the legal requirements of the Regulations will be presumed met.
DEFINITIONS AND GENERAL REQUIREMENTS
Combinations of materials. Corrosion
During both the construction and installation of electrical equipment special considerations is to be given when choosing materials to avoid corrosion due to different electrolytic potential. (NEK 410/IEC 60092.101.2.10)
SYSTEM DESIGN - GENERAL
Starting arrangement for propulsion engines
Starting arrangements for propulsion engine(s) are to have at least two batteries installed in separate boxes or lockers, or in a battery room. If the batteries are installed in a common battery room they must not be installed above each other, or on common shelves. The batteries are to have separate circuits installed as far apart as practical.
The starting arrangements for a single propulsion engine must have a changeover switch for alternative connection of the starting motor to either of the two batteries.
The starting arrangement for two or more propulsion engines must be divided between the two batteries and connected by separate circuits.
Alternative connection of one battery to both (or all) propulsion engines may be accepted.
Starting arrangements for emergency generator, essential services etc.
Starting arrangements for each prime mover of an emergency generator, emergency fire pump or other prime movers of important services are to have a separate battery, which is not used for other purposes.
See amendment to SOLAS 1974, Chapter II-1 regulation 44 concerning requirements apply to the starting arrangements for emergency generating sets.
NEK/IEC 60092.201.6.2.4 makes the same demands on starting arrangements for prime movers of important services as for emergency generators.
Starting arrangements for a prime mover which is not for emergency use
Starting arrangements for a prime mover, which is not for emergency use, is to be by a separate battery or to be connected by a separate circuit to batteries for propulsion engines.
Starting arrangements for more than one prime mover
Starting arrangements for more than one prime mover are to be from at least two batteries as for propulsion engines. Batteries for propulsion engines may be used.
Capacity of batteries
Each battery is to be of sufficient capacity for at least the following number of start attempts of the prime mover which it normally supplies, each attempt of minimum 10 seconds duration:
· 12 starts for each reversible propulsion engine.
· 6 starts for each nonreversible propulsion engine connected to a variable pitch propeller or other device enabling the engine to be started with no load.
· 3 starts for each prime mover for generators, except emergency generators.
If starter batteries are used also for supplying other services, the capacity is to be increased accordingly.
When determining the battery capacity the following must also be taken into consideration:
· The battery is normally not fully charged
· Reduction of capacity due to ageing
· Reduction of capacity due to high or low temperatures
· Reduction of capacity due to rapid discharge
Number and capacity of power units
The requirements in NEK 410/IEC 60092.201.6.2.2 means that there shall be equipment for automatic disconnection (tripping) of nonessential services to prevent disconnection of the generator in the event of overload. See also NEK 410/IEC 60092.202.8.3
Distribution systems with neutral earthed (TN-systems)
Concerning the description of the systems and the current rating of the neutral conductor (N-conductor), reference is made to relevant regulations in NEK 400. (NEK 410/IEC 60092.201.7.1).
Parallel operation in installations with earthed neutral
When generators are run in parallel in installations with the neutral earthed, it is to be ensured that the equalising current caused by harmonics does not exceed harmful values. Reference is made to guidance from the generator manufacturer.
Duplicated essential services
Two or more essential services for the same purpose are to be supplied from at least two distribution switchboards. Each of these is to be supplied by a separate supply circuit from the main switchboard or from the emergency switchboard.
The cables to such services are to be separated along their whole length as far as practicable. Wherever possible, however, the cables are not to be installed in a collision zone.
The collision zone is a zone distanced from the ship’s side of width 1/5 that of the ship at any place.
Shore connection
In the shore connection switchboard the circuit is to have at least an interlocked switch or a changeover arrangement to disconnect the generator from the shore connection circuit.
Three-phase AC installations are to be provided with a phase-sequence indicator and a phase-sequence changeover switch on the shore connection cabinet or on the switchboard. A phase-sequence changeover switch may be omitted on ships having an electrician, when the flexible cable from shore is not permanently connected or cannot be connected by means of an appliance connector on board. (NECK 410/IEC 60092.201.14).
Degree of protection
Stoves, ovens and similar equipment in galleys, laundries etc may be accepted with IP 22 when additionally protected against water splashing off the floor during hose washing.
(NECK 410/IEC 60092.201.26 and 307.3.1)
SYSTEM DESIGN - PROTECTION
Protection of generators - reconnection
Short-circuit, overcurrent and reversepower relays are to be such that it is possible to reconnect the circuit breaker within 30 seconds, provided that the voltage is within the range 85 110 % of the rate voltage. (NECK 410/IEC 60092.202.8.2.1)
Protection of generators – additional requirements for circuit-breakers
Miniature circuit breakers may be used as generator protection or protection in outgoing main circuits in installations with generator capacity less than 35 kVA. (NEK 410/IEC 60092.202.8.2.1)
Reverse-power protection
The time delay is “normally” to be 3 10 seconds. (NEK 410/IEC 60092.202.9.1)
EQUIPMENT – GENERATORS AND MOTORS
Voltage regulation
The requirements for voltage regulators must as far as possible apply to generators with capacity less than 50 kVA. (NEK 410/IEC 60092.301.4)
LOW- VOLTAGE SWITCHGEAR AND CONTROLGEAR ASSEMBLIES
Instruments - location
Instruments, equipment etc. on a switchboard required to be operated during normal use are to be installed on the front of the switchboard or easily accessible behind hinged front doors.
When such items are installed behind front doors, bare live parts are to be protected against inadvertent touching by means of fixed covers of at east flame-retardant material. These covers are to comply with the requirements for enclosure IP 20. (NEK 410/IEC 60092.302.7.6.101)
Instrumentation -secondary distribution system
Each secondary distribution system is to have one voltmeter. (NEK 410/IEC 60092.7.6.101)
Instruments - construction
Scales for ammeters, wattmeter’s and voltmeters, which are required in these regulations, are to have a red marking line at the rated value. (NEK 410/IEC 60092.302.7.6.101.4)
Separation of generator cubicles and other cubicles
Each generator is to have a separate control cubicle. Partitions between the generator cubicles themselves and between the generator cubicles and other cubicles are at least to be of flameretardant material. The partitions are to be designed to prevent the spread of arcing.
Reference to IEC 60439.7.7 and IEC 60439 appendix D. (NEK 410/IEC 60092.302.7.7.101)
EQUIPMENT – TRANSFORMERS FOR EFFECT AND LIGHTING
Transformers – type of connection
Y/Yconnected transformers have relatively high values of the zerosequence reactances and should therefore be avoided in installations having directly earthed neutral if the requirement concerning disconnection may be difficult to fulfil. (NEK 410/IEC 60092.303.3)
Equipment containing PCB
Electrical equipment such as transformers, converters, condensatores etc. with liquids containing polychlorinated biphenyl's (PCB) are not permitted.
Ministry of the Environment has established regulations for the use of PCB and products containing PCB. The Norwegian Directorate for Product and Electrical Safety is directed to survey that some of these requirements are complied with. (NEK/IEC 60092.303.3 and 401.15.2)
EQUIPMENT – ACCUMULATOR BATTERIES
Charging devices for accumulator batteries
Batteries are to have suitable automatic charging devices. For batteries whose capacity is taken into consideration when determining the capacity and number of the power supply units, two mutually independent-charging devices with separate supply circuits from the main switchboard may be required.
By suitable charging device it is meant that the charging device is to be capable of keeping the battery fully charged as far as possible at all times. (NEK 410/IEC 60092.305.6)
EQUIPMENT – APPARATURES FOR HEATING AND COOKING
Space Heaters
Space heaters may be one of the following types
· convector heaters
· panel heaters
· heaters with ribs
Portable fan heaters are not permitted.
Other types may, however, be allowed after consideration in each case. Reference to relevant regulations in NEK 400. (NEK 410/IEC 60092.307)
Hot air equipment
Hot air equipment is, in addition to excess temperature protection, also to have thermostats. The excesstemperature protection is to be located at that place where the highest temperature occurs.
Reference to relevant regulations in NEK 400. (NEK 410/IEC 60092.307)
Heating cable installations
Heating cable installations are normally to have earth leakage circuit breakers or earth leakage relays with tripping not above 30 mA. Where this is necessary for operational reasons tripping currents up to 300 mA may be permitted if special measures are taken to avoid dangerous exposure to live parts. Reference to relevant regulations in NEK 400. (NEK 410/IEC 60092.307)
INSTALLATION AND TEST OF COMPLETED INSTALLATION
Switchboards – passage way
In front of main switchboards there is to be a passageway with a free height of at least 2 m.
Switchboard doors, when in the open position, must not obstruct passage way. (NEK 410/IEC 60092.401.11)
Charging stations
Batteries for trucks are to be charged in charging stations. Such a charging station is understood to be a separate room or a special part of a larger room, e.g. a cargo hold.
This special part of the room is to have a base of at least the area occupied by the trucks plus 1 meter in all directions.
Installations in charging stations are normally to have explosion protected enclosures. However, this does not apply if the batteries are hermetically sealed.
Socketoutlets interlocked with switchgear, for connection of the charging cables can be installed. They are to have enclosures at least IP 56 or IP 44, depending on the location. (NEK 410/IEC 60092.401.17)
Accumulator batteries - Location
Rooms, lockers and boxes for batteries are to be used for this purpose only. (NEK 410/IEC 60092.401.17)
Cable bridges
Cables, which have temperature classes above 85 °C, are not permitted to be installed on combustible supports. Cables are not, under any circumstances, to cause the temperature of any support or adjacent combustible materials to rise above 80 °C.
Cablebridges, ladders, cable conduits and ducts are not to be used for other purposes, e.g. carrying water pipes, oil pipes or other pipes.
Such pipes, rails and similar are not normally permitted as supports for cables. (NEK 410/IEC 60092.401.31)
Cable bridges – protection against corrosion. Mechanical strength.
Cable bridges and ladders are to be made of steel, and are to be protected against corrosion. On open decks and in cargo holds the corrosion protection is normally to be hotdip galvanizing.
In areas where equipment may be exposed to heavy corrosive ambient conditions, special requirements may be laid down.
Cable bridges and ladders must be able to withstand any mechanical and electrodynamic stresses, which may occur. When deciding the dimensions of cable bridges and ladders intended for singlecore cables, special attention should be paid to electrodynamic stresses in case of a shortcircuit. (NEK 410/IEC 60092.401.31)
Cable bridges – expansion and contraction
Cable bridges and ladders are to be constructed and installed in such a manner that they do not absorb forces or transfer stresses caused by the ship’s movements, changing load conditions, temperature variations etc. (NEK 410/IEC 60092.401.31)
Cable bridges – division into sections
Cable bridges, pipes and ducts along the main deck are to be divided into sections. They are to be rigidly fixed to the deck at one point only. At other points they are to have sliding supports. (NEK 410/IEC 60092.401.31)
Protection against mechanical stresses. Insulating sleeving.
Cable cores are to have a special insulation of at least flameretardant material if they are likely to be subject to mechanical stresses once the core insulation has been stripped back. Cores, which have flammable conductor insulation, are also to have flame retardant insulating sleeving if the length of the tail exceeds 20 cm. This also applies to cables at conduit outlets and similar in connection boxes, terminal boards etc.
Insulating sleeving must have temperature durability corresponding at least to the temperature class of the cable. (NEK 410/IEC 60092.401.35)
Mechanical protection of cables
The thickness of the protection covers is to be at least 4 mm. The wall thickness of the protection pipes is to be at least 2,5 mm.
Cables laid on aluminium supports may have a corresponding protection of aluminium. The thickness is to be at least 4 mm. (NEK 410/IEC 60092.401.35.2)
Fixing of cables
The requirement concerning fixing can normally be fulfilled when the cables are clamped as follows:
• For cables entering enclosures and conduits, the nearest clamp is to be placed at a maximum distance of 10 times the diameter of the cable concerned from the entry.
• At other points the distance between the clamps must not exceed
the values in the following table:
(NEK 410/IEC 60092.401.38)
Cable conduits and ducts - Protection against corrosion. Mechanical strength
Cable conduits and ducts are to be made of steel, and are to be protected against corrosion. On open decks and in cargo holds, the corrosion protection is to be hotdip galvanizing or equivalent.
When the conduits and ducts have aluminium supports, these may be made of aluminium.
Conduits are to have the following minimum average wall thickness:
External diameter of the pipe in mm
Minimum wall thickness in
mm
External diameter of the pipe in inches
Minimum
Conduits of larger diameter are to have a minimum average wall thickness of at least 4 mm.
Ducts are to have similar minimum average wall thickness corresponding to the external crosssection of the duct.
Conduits with internal diameter exceeding 304,8 mm (12 inches) are not permitted. This also applies to ducts, which have a similar cross-section.
Ducts are to have similar wall thickness corresponding to the equivalent internal crosssection of the duct.
Two concentric pipes should be used through tanks containing combustible liquids and in cargo holds containing combustible loads. (NEK 410/IEC 60092.401.40)
Cables behind panels or deckplatings
When cables are laid behind panels or deckplatings, these are to be easily removable. The cables are to be directly available when the panel or deckplating is removed. However, single cables for lamps, socketoutlets and switches in dry areas may be installed behind wall panels, which are not easy to remove.
The requirements that panels or deck platings, are to be “easily removable” means that the panels or deck platings have to be hinged or fixed by screws in such a way that they can be dismantled without difficulty. Such panels or deckplatings should be able to be dismantled without damaging the interior. (NEK 410/IEC 60092.401.41)
Installation in thermal insulation
Cables are not to be installed in or covered over by thermal insulation, but they may be run the shortest way through such insulation. However cables in lighting final subcircuits e.g. in cabins, may be installed in such insulation provided that documentation shows adequate heat dispersion. Cables laid along outerdecks, bulkheads or the hull, are to lie on the inside of the thermal insulation. (NEK 410/IEC 60092.401.41
Reference to relevant regulations in NEK 400.
Plastic conduit installation
Plastic conduits are only permitted in dry areas in accommodation quarters. For this installation special precautions are to be taken concerning expansion, contraction, fastening and jointing. (NEK 410/IEC 60092.401.41) Reference also to relevant regulations in NEK 400.
Terminations for conductors – Stripping and termination
Conductor insulation and sheaths are not to be stripped back more than is absolutely necessary.
Cables are to be terminated in a box or a board, etc. suitable for the purpose. (NEK 410/IEC 60092.401.46)
Branching off and splicing of cables – connection boxes
In dry areas in accommodation quarter’s boxes may be concealed behind wall and ceiling panels. Such boxes shall normally have a degree of protection IP44. The location is then to be plainly indicated on the panel. The panels are to have adjustable openings giving easy access to the boxes. The covers of the openings are to be fixed in such a way that they can be easily removed without dismounting other equipment.
The inspection body may accept a lower degree of protection, if the risk of leakage from pipes etc. is low and the wall etc. are of incombustible material. (NEK 410/IEC 60092.401.48)
Testing – insulation resistance
Machines, transformers, appliances and other apparatus are to have, at both ambient and operating temperatures, an insulation resistance of at least:
3 x rated voltage in V [MW]
output in kVA + 1000
Heating appliances may, however, at normal operating temperature, have a lower insulation resistance, but not below the following values:
· Appliances without earth connection: 50 000 ohms
· Appliances with earth connection: up to 5 kW 50 000 “
5 10 “ 40 000 “
10 20 “ 30 000 “
20 50 “ 20 000 “
above 50 “ 10 000 “
In battery circuits the insulation resistance between each batterypole and earth is to be at least 250 ohms per V of the nominal voltage.
Measurement of insulation resistance
Insulation resistance measurements are to be carried out by using direct current at a voltage of at least twice the nominal voltage of the installation, but not less than 250 V. However, a higher measuring voltage than 500 V is not required for installations with an operating voltage up to 1000 V
During insulation measurement care must be taken to ensure that equipment which cannot withstand the measuring voltage is not damaged. It might be necessary to short circuit electronic equipment, such as thyristors and diodes while measuring. (NEK 410/IEC 60092.401.55)
Special features-A.C. supply systems with voltages in range above 1 kv up to and including 11 kv
1. Scope
The requirements in this section apply to high voltage AC installations with a system voltage above 1 kV up to and including 11 kV in addition to the general requirements for installations on board ships, mobile drilling platforms, dredgers, floating cranes etc.
These additional requirements for high voltage installations is based upon IECPublication 92503(1975) «AC Supply system, with voltages above 1 kV up to and including ll kV with the additional requirements laid down in this section. The inspection body may consider the use of higher voltage.
2. General requirements
2.l Design
All equipment is normally to be designed and tested according to relevant IECstandards or to equivalent and recognised national standards. The design must be for the special environmental conditions found onboard.
2.2 Protection against live parts
2.2.1 Parts of the installation, which are not made safe to touch, are to be located so that they are not accessible to unauthorized persons.
A part of an installation, which is made safe to touch, is a part of an installation, which has an earthed screen, earthed enclosure or approved insulation.
2.2.2 Live parts, which are to be operated, or examined, are to be located and protected in such a way that they may be operated or examined easily and without danger.
2.2.3 An approved warning notice is to be fixed in a visible position at the highvoltage equipment and at places where the high voltage cables are accessible. Approved warning signboards are to be placed at suitable locations both inside highvoltage rooms and at the entrance.
2.3 Insulation resistance
2.3.1 On systems designed with an insulated neutral or with a high resistance-earthed neutral, control of the insulation level must be possible. In addition the following must be established:
a fixed monitoring device giving an alarm in the event of an
insulation fault or earth fault in the installation, or
a device for automatic disconnection of the circuit when an earth fault occurs.
2.3.2 On systems designed with directly earthed neutral or low resistance earthed neutral, automatic disconnection of circuits in the event of an insulation fault is to be arranged. This earth fault protection is to operate at 1/3 of the maximum stipulated earth fault current. For lower earth fault current alarm must be given.
2.4 Clearance and creepage distances
2.4.1Uninsulated conductors which are not earthed shall be installed with a clearance from one another and from other conductive objects and from walls, ceilings or their own protective covers of at least 5 cm + 0.5 cm for each 1 kV of operating voltage unless voltage tests carried out according to Norwegian or other similar standards shows that the insulation is adequate with less clearance. The Norwegian Directorate for Product and Electrical Safety may after consideration of each case base the approval on other minimum clearances.
Other minimum clearances upon which approval may be based are as follows:
Nominal Voltage (V)
Minimum clearance, distance (mm) for
Main switchboards
Other equipment and generators
80
*) 25 mm is required for busbars and other bare conductors in main switchboards
2.4.2 All equipment is to have satisfactory creepage distances.
Satisfactory creepage distances are given in the following tables:
Main switchboards and generators:
Nominal
Voltage (V)
Minimum creepage distance (mm) for proof tracking index
*) 35-mm minimum is required for bus bars and other bare conductors in main switchboards.
Other equipment:
Nominal
Voltage (V)
Minimum creepage distance (mm) for proof tracking index
2.5. Earthing
2.5.1 Earthing conductors are normally to be of copper and are to have a cross section area of at least 30 mm2. The current density shall not exceed 150 A/mm2 for copper earthing conductors at the maximum earth fault, which may occur
2.5.2 Arrangements for earthing when working on an installation are to be established in accordance with the requirements laid down in the Safety regulations for highvoltage installation. At busbars and on all incoming and outgoing circuits on switchboards or similar, where reliable interlocking is not arranged, earthing and short-circuiting devices are to be provided, using fixed earthing switches which have adequate making capacity for operation on system voltage.
In other locations earthing and shortcircuiting may be executed by means of fixed earthing switches, portable earthing equipment or other suitable earthing equipment.
2.5.3 The secondary winding of current and voltage transformers is to be earthed. The earthing conductor is to be of copper and with a minimum crosssection area of 4 mm2. The earthing conductor may be connected directly to the earthed enclosure of the transformer or to an earthed support.
Earthing switches will be approved according to IECPublication 129 (1984).
2.6 Enclosures.
2.6.1 Enclosures are to comply at least with the requirements in NEK 410/IEC 60092.201.26 unless a higher degree of protection is required in item 2.6.2- 2.6.4
2.6.2 Rotating machines and neutral resistors are to have degree of protection of at least IP 43. However, in rooms, which are accessible for qualified persons only, a degree of IP23 may be accepted. Connection boxes are to have a degree of protection of at least IP 44.
Machinery spaces will generally be considered as being accessible only to qualified personnel. The same applies to other compartments which normally are kept locked, under the responsibility of the ship’s officers.
2.6.3 Power transformers are to have a degree of protection of at least IP23 when located in rooms accessible to qualified personnel only and at least IP54 when located elsewhere. Alternatively power transformers with a lower degree of protection may be located in a separate room which is locked.
2.6.4 Switchgear and controlgear assemblies are to have a degree of protection of at least IP32.
2.7 Overvoltage protection
Overvoltage protection is to be arranged for lower voltage systems supplied through transformers from high voltage systems. The protection device e.g. a neutral voltage limiter or direct earthing of the lower voltage system, is to be fitted at the secondary winding of the transformer. Alternative protection may be considered in each case.
2.8 Anticondensation heating
Equipment which can be expected to be periodically out of service and which is not located in heated and ventilated rooms is to be provided with a heating element. The heating is to be automatically switched on when the equipment is at standstill.
3. Distribution systems and voltages
3.1 Distribution systems
The following distribution systems are permitted:
3.1.1 threephase threewire with highresistance earthed neutral,
3.1.2 threephase threewire with lowresistance earthed neutral,
3.1.3 threephase threewire with directly earthed neutral,
3.1.4 threephase threewire with the neutral earthed with equipment specially approved by the Directorate for Product and Electrical Safety, and
3.1.5 threephase threewire with insulated neutral.
For systems having insulated neutral, test voltages higher than that for the other systems are required
For rotating machines, power transformers, current and voltage transformers, cables, switch-gear and fuse-gear for use in systems with insulated neutral point, the test voltage for the one-minute powerfrequency test shall be not less than 7.5 times the normal voltage between phase and neutral of the system. The «inspection body» in each case may however, separately consider the test voltage.
A high resistance earthed neutral: is a system where the neutral is earthed through a resistance with numerical value equal to or somewhat less than 1/3 of the capacitive reactance between phase and earth.
A lowresistance earthed neutral: is a system where the neutral is earthed through a resistance which limits the earth fault current to a minimum value of 20 % and maximum 100 % of the rated current of the largest generator
Insulated neutral: the requirement in this clause of these regulations for higher testvoltages is because of the overvoltages, which may occur in the event of intermittent earth faults.
3.2 Maximum system voltages
The maximum nominal system voltage permitted is 11 kV. For control systems the maximum nominal system voltage permitted is 250 V.
The following nominal system voltages are standardized: 3, 3.3, 6, 6.6, 10 and 11 kV.
4. Power sources and power supply installations
4.1 Generators
4.1.1 If the cooling of generators is arranged by means of water/air heat exchangers these are to be of the double tube type. Leakage monitoring with alarm is to be provided.
4.1.2 When auxiliary power is used for the cooling system of a generator, e.g. water pump or separate fan, it is either to be interlocked so that the generator is stopped if the auxiliary power fails, or the generator is to have winding temperature detectors which actuate an alarm at the maximum rated winding temperature, and stop the generator at 10 % overtemperature.
4.1.3 All generators are to be provided with temperature detectors for monitoring and alarm.
Overvoltage protection may be required for temperature detector circuits.
4.2 Power transformers
Special measures may be required to avoid undesirable effects of current inrush, if necessary
4.3 Earthed neutral connections
Means for disconnection of each earthed neutral connection is to be provided. If a switch is used for this disconnection, an arrangement for locking must be provided.
5. Distribution systems, switchboards, controlgear
5.1 Distribution systems
5.1.1 The busbars of the main switchboard are to be divided into at least two independent sections, interconnected by circuit breakers or switches.
Connections from generators to important services are to be divided between the sections so that safe operation of the ship is ensured even with any one busbar section out of service.
5.1.2 When auxiliary power is needed for the operation of switches, an independent auxiliary power system is to be provided for each of the switchboard sections. The auxiliary power system is to have sufficient capacity for at least two operations of each circuit breaker on the system.
This requirement applies to switches being simultaneously disconnected, and without any abnormal voltage drop in the auxiliary power circuit or any abnormal drop of pressure in the hydraulic system used for the switch operation.
5.2 Generator circuits
Each generator output circuit is to be connected through a circuitbreaker.
In addition to the general requirements, a protection device is to be provided to include protection against shortcircuit or earth fault in the generator or in the cable connection from the generator to the switchboard, by disconnection of the generator circuit breaker and deexitation of the generator.
In systems with isolated neutral or highresistance earthed neutral an alarm may replace disconnection in case of earth fault in the generator or in the cable connection between generator and the switchboard.
5.3 Outgoing circuits
Outgoing circuits are normally to be provided with a circuit breaker.
A fused circuit breaker may be accepted provided that the arrangement is such that the fuses can be isolated and replaced without any danger of personnel coming inside the voltage distance.
Fuses are not to be used for overload protection.
Switchgear for outgoing circuits may be used as motor starters, only if the switchgear is designed for the current inrush and the stipulated number of switching operations.
Certain types of fuses have an insufficient breaking capacity at currents between fullload and short-circuit.
When using fused circuit breakers it is assumed that the overcurrent protection device operates within the current range.
The voltage distance is the shortest distance from unshielded, uninsulated live parts of installations parts, intended to give an adequate electrical insulation level through air. The minimum voltage distance is 50 cm.
5.4 Power transformer circuits
5.4.1 Supply circuits to the primary side of transformers are to comply with the requirements in item 5.3 above. The protection system is to include alarm for overcurrent or overtemperature if a load diversity factor has been used when deciding the current rating of the transformer.
5.4.2 If the power transformers are arranged for parallel operation the secondary side circuits are to be provided with switchgear. The switchgear on the secondary side is to be interlocked with the switchgear on the primary side.
5.5 Voltage transformers
Voltage transformers are to be provided with fuses on the secondary side. Fuses may, however, be omitted in circuits to voltage detectors in generator voltage regulators.
5.6 Shore connection circuits and circuits to other units
Shore connections and circuits to other units are permitted only with special approval by the Directorate for Product and Electrical Safety.
5.7 Switchboards. Design and construction
5.7.1 Switchboards are to be of metal clad construction in accordance with IECPublication No. 60298 “AC metal enclosed switchgear and controlgear for rated voltage above 1 kV and up to and including 52 kV”, with the deviations and supplementary requirements given in the following subclauses.
Internal partitions of materials other than metal may be accepted by the Directorate for Product and Electrical Safety after consideration of each case.
On outgoing circuits if reverse energising from the load side is not possible, enclosure between the cable terminals and the switchgear may be omitted.
Switchgear or controlgear is considered to be metal enclosed when it consists of an outer metal enclosure with components arranged in separate metal enclosed compartments. The metal enclosures are to be earthed.
5.7.2 Switchgear and control gear shall be able to withstand all stresses due to shortcircuiting. Documentation may be required.
5.7.3 The switchboard manufacturer shall issue a test report giving all the necessary information refered to in IEC 60298. For the impulse voltage test in this IEC publication “List 2” applies to systems without automatic disconnection in case of earth fault, “List 1” applies to other systems.
5.7.4 Means are to be provided for the disconnection of all circuit breakers and fused circuit breakers from the busbars. This can be effected by means of a disconnector having a visible isolating distance or gap or a reliable position indicating device for each movable contact system, or similar visible means e.g. a withdrawable multipole circuitbreaker in its isolating position.
5.7.5 Doors of switchboards are preferably to be equipped with locking devices. Alternatively the switchboard may be located in a special room or fenced in area with lockable entrance doors.
Other alternatives may be accepted.
5.7.6 Except for short connections to instrument transformers, relays, auxiliary switches etc. control and instrumentation circuits are to be installed separated from the main circuits by means of partitions of insulating and flame retardant material.
The requirement concerning partitions may be effected e.g. by using cable conduits.
Alternative cableconnections may be accepted.
Fuses in control and instrumentation circuits requiring attention while the equipment is in service shall be accessible without anyone coming inside the voltage distance.
5.8 Passageways
In front of each switchboard there is to be a passageway with a free width of at least 1 metre.
Switchboards doors, when in the open position, or withdrawable switchgear in their isolating position, must not obstruct the passageways.
Access from both the front and rear of the switchboard may be required after consideration of each case.
6. Cables
6.1 Approval
6.1.1 Cables are to be of a manufacture and type of approved standards.
6.1.2 Cables for permanent installations will normally be approved if they comply with the specifications in IEC Publication No. 60502 “Extruded solid dielectric insulated power cables for rated voltages from 1 kV up to 30 kV”, and with the special requirements laid down in the following:
· Crosslinked polyethylene (XLPE) or ethylene propylene rubber (EPR) only is to be used as core insulation. Butyl rubber, PVC and thermoplastic polyethylene (PE) are not accepted.
· Conductor screening is required for all cables with XLPE insulation, and for EPRinsulated cables with rated voltage Uo/U above 3.6/6 kV.
· Insulation screening is required for all cables.
· Only the types specified in IECPublication No. 60092359 are to be used for sheath materials i.e. PVC or chlorosulfphonated polyethylene.
· Other constructions and materials may be considered for approval, depending upon the application.
6.1.3 Flexible cables for portable equipment can only be used after special consideration of each case.
6.1.4 The rated value (U) of cables shall be at least that of the nominal system voltage.
In systems with highresistance earthed neutral without means of disconnection in the event of earth fault, and in systems with isolated neutral the voltage class U between phase and earth shall be the same as the nominal system voltage.
This requirement means for instance that in a 6 kV installation with isolated neutral, cables with a voltage class Uo/U = 3.6/6 kV will not be accepted. Cables with a voltage class 6/10 kV are to be used.
6.2 Installation
6.2.1 Cables for highvoltage are to be installed separately from cables for lower voltages, e.g. not grouped together or installed in the same conduit.
6.2.2 The Norwegian Directorate for Product and Electrical safety depending on the application only permit installation of high-voltage cables in accommodation areas after special consideration.
6.2.3 Cables for highvoltage are to be specially marked, see item 2.2.3 above.
6.2.4 For uninsulated conductors the clearance distances laid down in item 2.4.1 apply.
6.2.5 For terminations and joints not protected by earthed metal screens the clearance distances in item 2.4.1 apply.
If the terminations are made in accordance with the installation instructions given by the manufacturer, these installation instructions may be considered to be sufficient documentation. A relevant test report has, however, to be available. Cable terminations are not to be made in the same enclosures as equipment at lower voltages, see item 5.7.6 above.
6.3 Current rating
The requirements for cables with temperature class 85 °C given in NEK 410/ IEC 60092.201, table 6 and NEK 410/IEC 60092.352.6, table 1, are to be used with a derating factor of 10%.
6.4 Testing
Cables with terminations and joints are to be subjected to a voltage test after installation according to “clause 18» of IEC Publication No.60502. This means a D.C. voltage test at least 4 x Uo for 15 minutes. Uo is the rated phase to earth voltage of the cable.
Alternatively an AC voltage test may be accepted. This must, however, be agreed upon by the cable manufacturer.
7. Switch-gear, controlgear, fuses and socket-outlets
7.1 Switchgear, controlgear and fuses
Switchgear, controlgear and fuses are to be designed so as to comply with relevant IECstandards
With relevant IEC standards means:
· IEC Publication No. 60056.” Highvoltage alternating current circuit breakers”
· IEC Publication No. 60129. “ Alternating current disconnectors and earthing switches”
· IEC Publication No. 60282. “Highvoltage fuses”.
7.2 Socketoutlets
Socketoutlets may be used only with the special approval of the Norwegian Directorate for Product and Electrical Safety.
8. Motors
The requirements laid down for generators applies to motors as far as these requirements are relevant for the purpose.