Marine High Voltage Regulations
G.3 Auxiliary Systems
Chapter 1
G.2.2 Shutters
The fixed contacts of withdrawable circuit breakers and switches are to be so arranged that in the withdrawable position the live contacts are automatically covered. Shutters are to be clearly marked for incoming and outgoing circuits. This may be achieved with the use of colours or labels.
G.2.3 Earthing and Short-circuiting
For maintenance purposes, an adequate number of earthing and short-circuiting devices is to be provided to enable circuits to be worked upon with safety.
G.2.5 Internal Arc Classification (IAC)
Switchgear and control gear assemblies shall be internal arc classified (IAC) where switchgear and control gear are accessible by authorized personnel only. Type A accessibility is sufficient (IEC 62271-200; Annex AA; AA 2.2). Accessibility Type B is required if it is accessible by non-authorised personnel. Installation and location of the switchgear and control gear shall correspond with its internal arc classification & classified sides (F, L & R).
Marine High Voltage Regulations
H Installation
H.1 Electrical Equipment
Where equipment is not contained in an enclosure but a room forms the enclosure of the equipment, the access doors are to be so interlocked that they cannot be opened until the supply is isolated and the equipment is earthed down. At the entrance of the spaces where high-voltage electrical equipment is installed, a suitable marking is to be placed which indicates the danger of high-voltage. Regarding the high-voltage electrical equipment installed out-side the spaces, the similar marking is to be provided. An adequate, unobstructed working space is to be left near high voltage equipment to prevent severe injuries to personnel performing maintenance activities. In addition, the clearance between the switchboard and the ceiling / deck head above is to meet the requirements of the Internal Arc Classification according to IEC 62271-200.
H.2 Cables
H.2.1 Runs of Cables
In accommodation spaces, high voltage cables are to be run in enclosed cable transit systems.
H.2.2 Segregation
High voltage cables are to be segregated from cables operating at different voltage ratings;
they are not to be run in the same cable bunch, nor in the same ducts or pipes or in the same box.
High voltage cables are not to be installed on the same cable tray for the cables operating at the nominal system voltage of 1 kV and less.
H.2.3 Installation Arrangements
High voltage cables in general, are to be installed on cable trays when they are provided with a continuous metallic sheath or armour which is effectively bonded to the earth;
otherwise they are to be installed for their entire length in metallic castings effectively bonded to earth.
H.2.4 Terminations
Chapter 1
High voltage cables of the radial field type, i.e., having a conductive layer to control the electric field within the insulation, are to have terminations which provide electric stress control. Terminations are to be of a type compatible with the insulation and jacket material of the cable and are to be provided with means to ground all metallic shielding components.
H.2.5 Marking
High voltage cables are to be readily identifiable by suitable marking.
H.2.6 Testing After Installation
Before a new high voltage cable installation, or an addition to an existing installation, is put into service, a voltage withstand test is to be satisfactorily carried out on each completed cable and its accessories. The test is to be carried out after an insulation resistance test. For cables with a rated voltage (U0 / U) above 1.8 / 3 kV (Um = 3.6 kV) an AC voltage withstand test may be carried out upon advice from high voltage cable manufacturer. One of the following test methods must be used:
Test the cables for 5 min with the phase-to-phase voltage of the system applied between the conductor and the metallic screen / sheath.
Test the cables for 24 hours with the normal operating voltage of the system.
Alternatively, a DC test voltage equal to 4 Uo may be applied for 15 minutes.
After the completion of the test, the conductors are to be connected to the earth for a sufficient period to remove any trapped electric charge.
An insulation resistance test is then repeated.
J HV Insulation Requirements
The most dangerous hazards associated with high voltage are an arc flash and an arc blast explosion, which are due to a fault in the high voltage system. A fault is an abnormal or unintended connection of live elements of a system to each other or to the earth. The impedance of such connections is often very low, resulting in large currents flowing. The energy contained in fault currents can quickly heat components, create excessive forces and result in devastating explosions of equipment. Breakdown of insulation is one of the main reasons of a fault in a high voltage system. The winding arrangements for marine HV generators and motors are like those at low voltages (LV) except for the need for much better insulating materials such as Micalastic or similar materials.
The windings of HV transformers are usually insulated with an epoxy resin and quartz powder compound. This is a non-hazardous material which is maintenance free, humidity
Marine High Voltage Regulations
Insulation for the HV conductors requires a more complicated design than is necessary for LV cables. HV cables provide a significant saving in both weight and space, leading to easier installation and a more compact result. Where air is being used as the insulating medium between bare copper busbars and terminals, the creepage and clearance distances between live parts and the earth are greater for HV systems.
The insulation rating is the maximum allowable winding (hot spot) temperature of a transformer or electrical machine that is operating at an ambient temperature of 40°C.
Insulation systems are thus classified by the temperature rating. The following table summarizes the different insulation systems commonly available on-board ships.
40 40 40
10
10
15
125 105
80
Maximum Ambient Temperature
Permissible Temperature Rise Hotspot Temperature Margin 180
155
130
40
0
Insulation Class B F H
Maximum Winding Temperature 130 155 180
Figure 1.7 – Common Insulation Systems Onboard Ships
The main reasons for the failure of insulation are rise in temp above the insulation rating, high voltage surge, ingress of moisture and ageing. In general, a motor / generator / transformer should not operate at temperatures above the maximum limit. Each 10oC rise above the rating may reduce the motor lifetime by one half. It is important to be aware that insulation classes are directly related to a motor life. Allowable temperature rises are based upon a reference ambient temperature of 40oC. The operation temperature is the reference
Chapter 1
Example - a motor operating at 180O C will have an estimated life of:
Only 300 hours with a Class A insulation 1,800 hours with Class B insulation
8,500 hours with Class F insulation
Tens of thousands of hours with Class H insulation K Work Permit
Safe-to-work permits are to be used when work is carried on high voltage systems; it is mandatory that all personnel concerned are suitably qualified for the duties they are to perform. It is necessary that high voltage systems are operated and maintained in accordance with the laid down safety rules. These rules should lay down specific procedures that must be
followed a a
a a .
L Warning Notice
Permanent legible warning notices are to be attached to high voltage equipment and at the entrances to compartments where high voltage equipment is installed; such notices should carry the DANGER HIGH VOLTAGE a F 1.8 on the right.
Figure 1.8
A High Voltage Notice 1.7 Differences Between High Voltage Supply and Low Voltage Supply Onboard Ships The major differences are as follows:
1. Risk management must be carried out before commencing any kind of HV work.
2. Mandatory isolation procedures are to be adhered to at all times.
3. Isolated equipment must be earthed down (connected to the ground until the job is finished).
4. Strict and limited access to high voltage areas should be ensured at all times.
5. High voltage systems are more extensive with complex networks and connections.
6. Specific high voltage test probes and instruments must be used.
7. Diagnostic insulation resistance testing is necessary.