Question
It is proposed to operate a bow thrusters unit from a 3.3 KV
electrical supply outline suitable option for the design of installation under
each of the following heading.
Protection of main switch board
Overload of a bow thrusters motor
Cable protection.
MSB protection.
The HV side panel must be separate on or probably insulated
from adjacent IV panel.
It must have an independent earthing
system to hull
The HV bus bar should have harmonic filters connected to
avoid waveform distribution due to linear loads
MSB should be designed to withstand the rigours of sea life
i.e. it must withstand vibration, humidity, high temperature, sea water etc.
encountered in the ship.
The distribution system should have its neutral point earthed
via NER.
The circuit breaker [incoming and outgoing] usually are of
ACB type. This could be vacuum interrupter type or gas filled type.
Circuit breaker closing mechanism may be manual
[spring-loaded] or motor driven, stored charge spring type preferred.
Standard interlock and trips for manual trip, under voltage,
over current and short circuit trips must be incorporated.
Main monitoring instrument and lamps must be included e.g.
incoming voltage, frequency, current meter in/out power lamps, load status lamp
etc.
Additional safety features like anti condensation heaters.
Interlocks for main / emergency power, Interlocks for door closure are
preferred.
Motor overload protection.
Usually HV motor have combined motor protection relay which
has overcorrect [inverse time delay]. A differential current and earth fault
monitor
This is connected to lock out relay to trip motor power in
the event of overload.
Beside this thermistor protection
is recommended for single phasing and high temperature trip.
Cable protection
Cable rating should be proper
Conductor should be rated for short circuit and maximum fault
current
Insulation material should be of higher quality preferred
EPR- ethylene propylene rubber.
XLPE cross linked polyethylene type.
Sheet material should be rated for short circuit, heat, oil,
chemical resistance, flame retardant type.
Cable installation standard like glanding,
junctions and cable tray routing to termination must be followed.