MAIN ELECTRICAL SURVEY ITEMS,
GENERATORS AND GOVERNORS, ,
CIRCUIT BREAKERS,
SWITCHBOARDS AND FITTINGS
(Adapted from:D.T. Hall:Practical Marine Electrical Knowledge)
Main Electrical Survey Items
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The following survey items apply in general to all ships:
Generators and Governors
Circuit-Breakers
Switchboards and Fittings
Cables
Insulation Resistance
Motors and Starters
Emergency Power Equipment
Parts of Steering Gear
Navigation Light Indicators
UMS
TANKERS
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For UMS operation, a survey of the associated
alarms, controls and fire detection is required.
Generators and Governors 169
For tankers/gas carriers and other ships transporting
flammable cargo, an additional survey of all
electrical equipment in hazardous areas is carried
out during each docking survey and annual survey.
This means that hazardous area electrical equipment
is surveyed every year.
Generators and Governors
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The surveyor will require that main and emergency
generators are clean, respond correctly to controls
and load changes, and show stable operation when
required to run in parallel with other generators.
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Generator windings on stator and rotor must be
free of dust, oil and moisture.
A visual check will be made for any obvious
deterioration, abrasion or cracking of the insulation
around the end winding coils on the stator.
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An insulation test to earth and between stator phase
windings (if the neutral point can be disconnected at
the terminal box) should be carried out while the
machine is still hot after running on load.
Circuit Breakers
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A visual examination of circuit-breakers in main,
emergency and section boards will usually precede
operational tests.
The surveyor will particularly check the condition of
main, arcing and auxiliary contacts for signs of
wear, misalignment and overheating. A similar
inspection of fixed and moving isolator contacts at
the rear of a circuit-breaker will be made.
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Arc chutes must be clean, free of arc debris and
correctly aligned. All internal wiring should be in
good condition and its end connections must be tight.
All mechanical linkages will be checked for any
signs of wear or stress.
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Tests on a circuit-breaker will include close and trip
operations while in its isolated position (i.e. not
connected in circuit). The racking mechanism for
moving the breaker from the service to the isolated
position must be demonstrated to be free moving
and the fixed main terminals must be seen to be
shuttered off when the breaker is withdrawn.
Emergency hand charging (if fitted) of the closing
spring will be tested. Correct operation of the
mechanical indicators to show whether the breaker is
open, closed or isolated, is required.
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The undervoltage release mechanism and overcurrent
trip settings for level and time delay may have to
be demonstrated to the surveyor's satisfaction. An
overcurrent trip for a generator breaker is typically
set for 130% of full load current (FLC) with a typical
time delay of 3 s, but this has to suit the thermal
capacity of the generator and be co-ordinated with
the overall protection scheme for the power system.
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Although the overcurrent and time delay settings on
the breaker can be seen to be correctly adjusted to
the desired values, only a proper current injection
test will prove these settings against the
manufacturer's I/t characteristics. In this test the
circuit-breaker is isolated from the busbar and a set
of calibrated currents from a current injection set are
fed directly through the closed circuit-breaker
(primary injection) or (more usually) through the
overcurrent relay (secondary injection). This is
generally a specialist task for an outside contractor
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Circuit-breaker time delay mechanisms with oil dash1
pots must have the pots filled to Site correct level
with clean oil of a type recommended by the
manufacturer.
Switchboards and Fittings
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An obvious survey requirement for any switchboard,
section board or distribution board is that they are
clean. This includes all internal surfaces as well as
the external panel surfaces, instrument faces and
control switches. A thorough cleaning job on the
inside of the main switchboard can only be safely
carried out when the board is completely dead (all
generators stopped and prime movers locked-off).
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All the main bus-bar and auxiliary connections
throughout the boards should be checked for
tightness during the dead period of a major internal
clean up. Overheating signs at a connection junction
are probably due to a loose joint. Direct heat
testing on load with an infra-red thermal camera is
now a very useful technique for locating hot-spots.
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Bus-bar supports will be examined for surface
tracking and damage to the insulation material. All
internal wiring within the switchboard panels must
be securely fixed. Cable entries at the bottom of the
switchboard should be sealed with a non-flammable
material to exclude dirt and act as a fire stop.
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The main switchboard earth bar must be securely
bonded to both the frame of the board and, of
course, to the ship's hull. One secondary terminal of
each current transformer (CT) and the metal cases of
instruments and relays should be wired to the main
earth bar. Hinged panel doors should be bonded
with an earth strap to the main switchboard frame.