High Voltage System on Ships
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High Voltage System on Ships
In ships, voltages upto and equal to 1000 volts is called as low voltage system and
voltages above 1000 volts is called high voltage system. Normally low voltage system
is common on board. But rising demand for power due to heavy consumers on new
ships require an efficient and surplus power supply. The answer is high voltage
system.
Why high voltage system used on ships ?
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As we mentioned, higher power demand for heavy consumers on ships is the first reason to
choose high voltage on ships. High power bow thruster electric motors, reefer containers in
container ships, cargo cooling machineries in gas carriers, etc. are examples of such heavy
power consumers.
High voltage machineries have much reduced size and weight compared to same power low
voltage counterpart.
Reduced weight and space for machinery means increased space for cargo and more profit.
Using electric propulsion further reduces engine room size, again more cargo space and
profit.
Ease of installation and reduced installation cost.
Conductor size is reduced due to low current flow in high voltage system, means reduced
copper requirement and low cost.
In high voltage system, copper loss or I²R losses are much reduced when compared to low
voltage system, as the current flow is less
Reduction in short circuit levels in the system which decides the design and application of
the electrical equipment used in the power system.
Disadvantages:
Handling high voltage means high class insulation to be used on conductors. (Generally ‘F’
class and above)
Higher voltages means greater risk and hence require stringent safety procedures.
Skilled labour required for handling high voltage system.
Danger of arcing, chances of arc flash and arc blast.
Special switch gears are required to preventing arcing.
Why copper loss and iron loss is less in high voltage system ?
From the above comparison on current flow between a high voltage system and low voltage
system, it is clear that current draw with high voltage is much lesser. Hence copper loss or
I²R losses and iron loss are considerably lesser. For study material and latest questions
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What is meant by arcing, arc flash and arc blast in high voltage system ?
Arcing is the production of unintentional electric arc during opening circuit breaker, isolator
or contactor due to the discharge of electricity through the medium between the two
contacts. (In fact arcing occurs during closing the breaker also).
Arcing also occurs when heavy current flow to earth during an earth fault or short circuit
fault due to insulation failure.
During arcing temperatures at the arc terminals can go upto 20000 ºC or more, which is
around 4 times the temperature of sun’s surface.
The intense light formed at the point of arc is called as arc flash.
Instant heating of air surrounding the arc occurs and conductors vaporises, resulting in
formation of a high pressure wave. If the pressure wave is not released, it results in an
explosion called arc blast.
What are the hazards of arc flash and arc blast ?
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Permanent damages to the electrical equipment. Join us on Telegram @mmdmeoclass4
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Irreversible damage to the human tissue and incurable burns due to very high
temperatures.
Arc flash produces intense UV light, resulting permanent or severe damages to the eye
vision.
Pressure wave from the arc blast compresses the eyes, resulting permanent or severe
damages to the eye vision.
Heavy noise (above 140 dB) may damage hearing ability, sudden pressure changes may
rupture ear drums also.
Arc blast explodes the equipment, ejecting parts with tremendous force and velocity. This
may result in damages to personnel and property.
Flammable materials present in the vicinity of arc may ignite, causing secondary fires.
What is the difference between short circuit and short circuit level ?
A short circuit is a fault which occurs when the current in a system deviates its normal path
and start flowing through an alternate path. Since the alternate path offers very low
resistance, the current increases very much above the normal value.
Short circuit level (SCL) is the maximum possible current that flows through a circuit during a
short circuit fault.
What is the effect of short circuit fault in high voltage system ?
High current flow during a short circuit fault result in increased temperatures, which
damages insulation, produces high thermal and mechanical stresses in the system, may
cause arcing, arc flash and arc blast.
What are the methods adopted to prevent ill effects of short circuit
fault ?
Protective relay installed in the system immediately trips and isolates the equipment during
a short circuit fault within a short time. This prevents the effects of high current flow
through the circuit.
The generators, cables, equipment, switch gears, etc. associated with the system are
designed to withstand the heavy current during short circuit fault for this short duration of
time.
SAFETIES USED ON HV SYSTEM
-Special breakers are used i.e. Gas or Vaccum Breakers
-Minimize size of earth fault current EARTHED NEUTRAL SYSTEM is used
-Special Realys are used for overall circuit protection
-Grounding stick is used to de-energize the system
-Better insulating material like micalastic is used
-Special tools, gloves are used. For study material and latest questions
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-Danger sign is marked for HV System
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-Insulation is checked time to time.
-Rubber mat is used
-For safety purpose never ever single person should work on HV system.
MEGGER USED ON HV SYSTEMS
-Voltage for testing produced by hand operated megger by rotation of crank in case
of hand operated type, a battery is used for electronic tester.
-FOR LOW VOLTAGE 500 Volt DC is sufficient for performing test on equipment
range up to 440 Volts.
-FOR HIGH VOLTAGE 1000 V to 5000 V DC is used for testing for high voltage
electrical systems.
