Section 11 Electrical equipment cooling arrangements

11.1.1 Provision is to be made for an adequate supply of cooling to the electrical equipment used in Mobility and Ship Type engineering systems. The cooling arrangements may be worked from the engineering systems or be supplied by independent means.

11.1.2 The requirements of this Section are with the goal of providing sufficient cooling whereby normal operation of Mobility and Ship Type engineering systems can be sustained or restored even though any one of the sources of cooling becomes inoperative.

11.1.3 The temperature of cooling water supplied to coolers for electrical equipment is to take account of imposed loads when under normal design operating conditions and take into account the ambient temperatures likely to be experienced in the compartment where the equipment is located.

11.1.4 The possible formation of condensation due to low cooling temperatures where high humidity is likely to occur within electrical enclosures is also to be taken into account. The ambient temperatures and anticipated humidity levels are to be declared in the System Design Description required by Vol 2, Pt 7, Ch 3, 11.1 General 11.1.9.

11.1.5 Where chilled water systems are used for electrical equipment cooling, the arrangements are to comply with Vol 2, Pt 7, Ch 5 Ship Type Piping Systems as applicable.

11.1.6 Where fresh water systems are used for electrical equipment cooling, the arrangements are to comply with Vol 2, Pt 11, Ch 1 Made and Fresh Water Systems as applicable.

11.1.7 Heat exchangers used in cooling systems for electrical equipment are to comply with Vol 2, Pt 7, Ch 1, 18 Heat exchangers as applicable.

11.1.8 Where sea-water systems are used for electrical equipment cooling, the guidance in Vol 2, Pt 7, Ch 1, 17 Guidance notes on metal pipes for water service of Chapter 1 is to be complied with where applicable.

11.1.9 A System Design Description for cooling systems for electrical equipment used in Mobility and Ship Type category engineering systems is to be submitted for information purposes.

11.1.10 A Risk Assessment (RA) is to be carried out for the cooling arrangements for electrical equipment used in Mobility and Ship Type category systems. The analysis is to be in accordance with Vol 2, Pt 1, Ch 3, 18 Risk Assessment (RA) and is to address the effects of failure of cooling supplies related to the ability of equipment and systems to operate with short-term loss of cooling and to operate with any reduced standby cooling capability.

11.1.11 Reference is also to be made to the following Rules as applicable:

1. Location of pipes, joints and fittings - Vol 2, Pt 7, Ch 2, 2.8 Miscellaneous requirements 2.8.2.

2. Cooling of electrical rotating machine enclosures - Vol 2, Pt 9, Ch 2, 6.6 Machine enclosure 6.6.1.

3. Cooling of transformers - Vol 2, Pt 9, Ch 3, 7.1 Transformers 7.1.10 and Vol 2, Pt 9, Ch 3, 7.1 Transformers 7.1.12.

4. Cooling of semiconductor equipment - Vol 2, Pt 9, Ch 3, 7.2 Semiconductor converters 7.2.4.

11.2.1 Where the continuous operation of electrical equipment used in Mobility or Ship Type engineering systems is susceptible to interruptions in cooling arrangements (water or air), standby cooling arrangements are to be provided. In general, the standby cooling arrangements are to be automatically and immediately brought into effect on failure of the normal cooling supply. Such standby cooling arrangements may need to be supplied from an emergency source of power if the cooling is essential to the survivability of an item of equipment.

11.2.2 Where cooling arrangements are by cooling water system(s), provision is to be made for a separate supply of cooling water from a suitable independent pump of adequate capacity. The following arrangements are acceptable depending on the purpose for which the cooling water is intended:

1. Where only one electrically powered Mobility system is fitted, the standby cooling arrangements are to be connected ready for immediate use.

2. Where more than one electrically powered Mobility system is fitted, each with its own cooling pump, a complete spare pump of each type may be accepted. The complete spare pump is to be stored onboard such that can be readily installed if required.

3. Where a sea inlet scoop arrangement is fitted, and there is only one independent cooling pump, a further pump, or a connection to the largest available pump suitable for cooling duties, is to be fitted to provide the second means of cooling when the ship is manoeuvring. The pump is to be connected ready for immediate use.

4. Where fresh water cooling is employed for electrically powered Mobility systems, a standby fresh water pump need not be fitted if there are suitable emergency connections from a salt water system.

5. Where each auxiliary item of electrically powered mobility equipment is fitted with a cooling water pump, standby means of cooling need not be provided.

Where, however, a group of auxiliaries is supplied with cooling water from a common system, a standby cooling water pump is to be provided for this system. This pump is to be connected ready for immediate use and may be a suitable general service pump.

11.3.1 When selecting a pump for standby purposes, consideration is to be given to the maximum pressure which it can develop if the overboard discharge valve is partly or fully closed and, when necessary, end covers, water boxes, etc. are to be protected by an approved device against inadvertent over-pressure.

11.4.1 Where cooling water pumps can develop a pressure head greater than the design pressure of the system, they are to be provided with relief valves on the pump discharge to effectively limit the pump discharge pressure to the design pressure of the system. For location of relief valves, see Vol 2, Pt 7, Ch 2, 7.6 Location of fittings.

11.5.1 Not less than two sea inlets are to be provided for the pumps supplying a sea-water cooling system, one for the main pump and one for the standby pump. Alternatively, the sea inlets may be connected to a suction line available to main and standby pumps.

11.5.2 Where standby pumps are not connected ready for immediate use (see Vol 2, Pt 7, Ch 3, 11.2 Standby supply 11.2.2.(b)), the main pump is to be connected to both sea inlets.

11.5.3 Cooling water pump sea inlets are to be low inlets and one of them may be the ballast pump or general service pump sea inlet.

11.5.4 Auxiliary cooling water sea inlets are to be located one on each side of the ship.

11.5.5 Where sea inlets are connected to a common suction line serving main and standby cooling water pump units, the arrangements are to be such that a failure in the common suction line will not cause loss of sea-water supply to both pumps at the same time.

11.6.1 Where sea-water is used for the direct cooling of electrically powered Mobility and Ship Type systems, the cooling water suction pipes are to be provided with strainers that will prevent debris being introduced into the cooling systems. The strainer arrangements are to be such that a strainer can be cleaned without interruption to the cooling water supply whilst the electrically powered equipment is in operation at its rated capacity.

11.6.2 In general, the aperture openings in primary strainers should not exceed 10 mm diameter and for secondary strainers not less than 5 mm diameter. The open area through any strainer is to be not less than twice the area of the inlet valve to the strainer. Where it is proposed to use secondary strainers with apertures less than 5 mm diameter, the implications of using such are to be assessed by the manufacturer and included in the operating and maintenance manual.

11.7.1 Means are to be provided for the drainage and where necessary the storage of coolants, to enable maintenance and repair of the coolers and equipment.

11.7.2 All cooling systems are to be provided with means of venting air at high points and sufficient drain fittings to enable the system to be completely drained for maintenance.

11.8.1 Cooling water systems for electrical equipment in Mobility and Ship Type engineering systems are to be provided with high temperature and low flow alarms.