Every day the owners and designers will show for greater profitability to larger ships. As the vessel size increases, it is necessary to install more powerful engines and other machines.
This increase in the size of the machines and other equipment requires more power and therefore higher voltage power system on board a ship must be used.
What is the high voltage?
In the maritime practice, most merchant ships have a neutral 3-phase 440 V Supply. This energy system belongs to the category of low voltage, used where Engine power requires an average power of 200 kW. In Straight terms Voltages up to 1000 V are known as low voltage system and if Greater than 1000 V voltages it is designated as high voltage system.
Advantages / disadvantages of HVS (high voltage system):
Advantage:
- Reduction of the size of generators, motors, cables etc.
- Weight and space saving
- easy construction
- Reduced installation costs
- The reduction of losses - a more efficient use of energy
- The reduced amounts of short circuit in the system, which decides the design and the implementation of Electrical equipment used in the energy system.
Disadvantage:
1. higher insulation requirements for cables and equipment used in the system.2. Increasing the risk factor and the need for strict compliance with the strict safety precautions.
A work permit for H.V SYSTEM:
1. Before a work permit is issued, the authorized person or electrician must identify the equipment you are working or test to be performed.
2. If the order includes or may involve access to equipment where the confusion could occur, the authorized person (HT) / electrical engineer must identify the elements to the appropriate person (HV) and apply the parking meter.
3. Before a work permit , the authorized person (HV) / electrical engineer must demonstrate the isolation of the knowledgeable diagram (HV) and ground and show areas of safety precautions, isolation and the working point or test.
4.Authorized person (HV) / electrical engineer must ensure that the appropriate person (HV) cover all procedures and safety precautions.
5. If the competent person (HV) then accepts the approval or sanction, this person is responsible for the work or final proof until the license becomes invalid or punishment.
6. Select the point of work.
7. Grant of work permit, the isolation of the diagram and grounding, and the key for the security key field of the expert person (HV).
8. Persons who perform (HV) / Electrical Engineer tasks requiring a work permit or sanctions for the test must issue the documents themselves.
9. Set the block diagram and fill the logbook of the site.
10. All these documents must be signed by an authorized person (HV) / electrical engineer before starting work or test.
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| A typical high voltage system line diagram |
High voltage safety measures
For additional safety, high-voltage systems incorporate the advanced circuit breaker system into the system, as part of the HV devices in general. Since ship uses high voltage generators, the network provides the high voltage motor (for the drive, the side rams and Air compressor) and the branches of the main transformers to the control unit 440 V. Additional power connections are used to interface with the emergency switchboard.
HV circuit breakers and contactors
Probably the main difference between HV and LV system system occurs in the main area of the HV. For HV, types of switches can be air breakage, break oil, gas from SF6 (sulfur hexafluoride) or loss of vacuum. Among these types, the most popular and reliable are the vacuum circuit breakers, which can also be used as motor starters, HV contactors.
Each phase of a circuit breaker or vacuum contactor comprises a fixed and movable contact in a sealed glass sleeve borosilicate and evacuated. The movable contact is actuated by flexible metal bellows by a loading motor / spring or a magnetic drive mechanism. The high electrical resistance of a vacuum allows a very short contact switch separation and rapid arc without sealing is achieved.
When an alternating current is interrupted by the disconnection of the contacts, an arc is formed by a metal vapor from the material on the contact surfaces, and further circulates alternating current to a zero current approaches. Wave form at this time, the arc is replaced by a high voltage strength region, which can withstand high voltage recovery. Most metal vapor condenses again to contacts and is available for the following arc. A small amount is placed in the shield around the contacts protecting the insulation sheath. Since the arc time is very short (usually in the order of 15 ms), the arc energy is much lower than that of the circuit breaker, so that the vacuum contacts suffer much less wear.
HV circuit breakers and contactors
Probably the main difference between HV and LV system system occurs in the main area of the HV. For HV, types of switches can be air breakage, break oil, gas from SF6 (sulfur hexafluoride) or loss of vacuum. Among these types, the most popular and reliable are the vacuum circuit breakers, which can also be used as motor starters, HV contactors.
Each phase of a circuit breaker or vacuum contactor comprises a fixed and movable contact in a sealed glass sleeve of borosilicate. The movable contact is actuated by flexible metal bellows by a loading motor / spring or a magnetic drive mechanism. The high electrical resistance of a vacuum allows a very short contact switch separation and no arc when connection is achieved.
When an alternating current is interrupted by the disconnection of the contacts, an arc is formed by a metal vapor from the material on the contact surfaces, and further circulates until alternating current to a zero current approaches. At this time, the arc is replaced by a high voltage strength region, which can withstand high voltage recovery. Most metal vapor condenses again to contacts and is available for the arc flow. A small amount is placed in the shield around the contacts protecting the insulation sheath. Since the arc time is very short (usually in the order of 15 ms), the arc energy is much lower than that of the circuit breaker, so that the vacuum contacts suffer much less wear.
Author Amit | Article Requested By: KV Gupta
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