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Contents
Main Chapters
Marine High Voltage Regulations
- Introduction
- Competency Requirements for Personnel Working on High Voltage Systems
- Advantages and Disadvantages of High Voltage (HV) Onboard
- A Typical High Voltage Installation
- Marine / Offshore Statutory Requirements
- International Association of Classification Societies Requirements for High Voltage The following requirements apply to alternating current three-phase systems with the
- Auxiliary Systems
- Number of External Supply Sources
Lower voltage systems fed through transformers from high voltage systems must be protected against overvoltage. In residential areas, high-voltage cables must be laid in closed cable transit systems.
High Voltage Hazards and Protective Equipment
The Risk of Electricity
The effects of this risk depend on the strength of the current and the potential difference varies from panic to death.
Electrical Hazards Associated with High Voltage Systems
The amount of air in which the arc develops is superheated due to the release of energy. The temperature inside the switching equipment approaches that of the arc after the exhaust of the air.
Shock Protection When
It is very important to wear appropriate arc protection personal protective equipment to prevent a possible arc flash. Therefore, a 650-nm or 820-nm fiber optic receiver can be used to detect the arc.
High Voltage Safe Working Procedures
Identifying the need for Safe Working Procedures
After any incident, the first question is whether or not a risk assessment has been carried out. It is known to be alive, but those involved do not have the proper training or proper equipment to prevent any injury, or fail to take adequate safety precautions. Turning on a forgotten system that has an additional ground connection that has not been removed.
The Inherent Dangers and Avoidance of Disastrous Consequences What is risk?
The toolbox meeting should include all personnel likely to be engaged in the operation or whose work may be affected by it. Make sure a safety harness is worn, secured to a strong point, inspect and secure the scheme, a portable ladder will be used. Check all LV circuits and prove that the circuit is dead before starting work.
Important Terminology Associated with High Voltage Systems
Demonstrate proper use of precautionary techniques and use of PPE, including arc and shock protection and use of insulated tools. A form of declaration signed and given by an authorized person to a competent person responsible for the work to be carried out on or near a high-voltage apparatus, which acquaints him with the scope (in time and space) of the work, exactly what the appliance is dead, is isolated from all live conductors, has been discharged and grounded, and in terms of electrical hazards that it is safe to work on. Note: Low voltage system work permits are not appropriate for work on high voltage systems.
Permit to Work Procedure
Read the permit to the person who will be working on the equipment and point out the scope and boundaries of the work. Please note: After signing the acknowledgment of receipt, this work permit must be retained by the responsible person at the location where the work is being carried out until the work is completed and the release section is signed. The work for which this work permit was issued has now been suspended*/completed* and all people under my supervision have been withdrawn and warned that it is no longer safe to work on the equipment described in this work permit.
Sanction for Test (SFT)
I accept responsibility for performing the work on the apparatus detailed in this work permit and no attempt will be made by me or by persons under my responsibility to work on any other apparatus or in any other area. I accept responsibility for Testing the Electrical Equipment detailed in the Test Sanction and for taking precautions to prevent danger. All persons under my responsibility have now withdrawn and been warned that it is no longer safe to test the electrical equipment detailed in this Test Sanction.
Limitation of Access Form (LOA)
I declare that the work for which this Access Restriction was issued is now suspended/completed that all people under my supervision have withdrawn and warned that this Access Restriction is no longer valid and warned that the work specified in this Access Restriction.
Caution and Danger Notices
Earthing Down
The earth stick can be used to earth the lead conductors of any supply conductor after the circuit has been de-energized to ensure that the stored energy in the HV conductor is discharged to the hull of the ship. Under these circumstances, it is acceptable to lock either the cubical door or the rack mechanism, whichever is appropriate, which should prevent further withdrawal of the circuit breaker, as long as the circuit breaker is withdrawn from its normal operating position. The safety shutter will be closed during the withdrawal of the circuit breaker so that the HV terminal of the bus bar is not exposed.
Safety Rules Related to the Code of Safe Working Practices in H V Systems
Once the permit to work or test sanction has been revoked, the authorized person must ensure that all insulators and grounds have been removed and that the system is safe to turn on.
Working on De-Energized High Voltage Power Systems
Safe Working Procedures
Compartments and other enclosures containing high-voltage equipment must be locked except when access or egress is necessary. Circuit main earths must be installed at the points of isolation of the high voltage supply. All cables will be assumed to be live high voltage cables until proven otherwise.
Trapped Key and Key Safe Systems
Insert both keys (GM31) and (GM32) into the ground switch door lock and turn to unlock the door. Now the switch is locked and the earthing switch door can be opened. When the earthing switch needs to be closed, turn the switch (BT12) to lock the earthing switch.
Procedure for Isolation in High Voltage Switch Gear Before commencing the job ensure that
After engaging the grounding switch, wait 30 minutes to allow residual voltage to ground. Keeping the ground switch active, remove all tools and equipment and close the rear door. Disconnect the earthing switch by inserting the operating handle and turning it clockwise.
High Voltage Generation and Distribution
Medium Voltage Alternator
When the rotor is excited with a direct current and rotates, the resultant field will also rotate so as to generate sinusoidal voltages in the 3 stator phases, shifted 1200 in time with a frequency directly related to the speed of the rotor. Damper windings on the rotor stabilize the AC generator speed to reduce hunting under variable loads. If the speed tends to decrease, the action of the induction motor occurs in the damper coil, tending to accelerate the car.
The Brushless Alternator (Rotary Excitation System)
Three-phase current is generated at a higher frequency of 150 Hz or even more in the windings of the excitation rotor and passes through a rectifier on the shaft and then to the main alternator poles. This higher frequency (depending on the number of poles) contributes to the stability of the rectified output, as there is typically no smoothing or filtering circuit between these diodes and the main rotating field. The silicon (rotary) rectifiers are mounted on plates and installed in the housing at the end of the shaft, as their rotation also contributes to cooling; these are accessible for replacement if necessary.
The rectified output is fed to the main field of the alternator, which also rotates on the same axis. This section of the generator is used to provide the AC power input to the rotary rectifier via coaxially mounted cables. To produce the enhanced three-phase output from the generator's main armature (necessary for the large power requirements of the distribution system), the main field must be supplied with a direct current source.
The Alternator with a Self-excited System
The reactor coils create an inductive effect so that the current in the shunt winding lags 900 behind the main output voltage. Diodes in the three-phase rectifier change the alternating current to direct current, which is then smoothed and fed to the rotor of the alternator through slip. call. The AVR may be of the static type already described with the error signal amplified and fed to coils in the three-phase transformer.
The Alternator with a Separately Excited System
If there is a fault in the generator winding, differential relay 87 is energized, energizing the on-delay timer 87 T. There will be no output signal from the AVR in the J and K lines (these are the +ve and -ve terminals of the local power supply) and so the alternator is de-energized. But when the generator load is increased more than 50%, a voltage drop will occur and the AVR cannot compensate further.
The Neutral Point of a Supply System
In an HV system, certain essential loads may be supplied by a transformer with its secondary insulation to ensure that earth fault current does not flow to the equipment. In any installation, the continuity of service in the presence of an insulation fault also depends on the earthing system. Thus, a voltage 1.73 times higher than the normal voltage is present at all insulation points in the system.
Resistance Earthed Systems
As an example, the value of the NER to limit the earth fault current to the full load rating for a 2 MVA, 0.8 PF, 6.5 kV 3-Phase alternator,. If the value of the earthing resistance R is very low, the earth fault current will be large and the system will become like the solid earthing system. It continuously monitors through its sensor, the continuity of the NER (or variation in the resistance value of the NER) as well as the continuity of neutral earth connections.
Basic features of a Marine HV Power Supply and Distribution System
The circuit breakers are normally operated by the power management system, but can also be operated manually (at the switchboard). The HV power distribution systems are arranged so that in the event of a fault in any of the HV main switchboard, Cargo switchboard 1 and 2 can be connected to bus tie breaker CB1 and CB 2. HCBTB1 and HCBTB2 are normally open HCCSB1, HCCSB2, HCBTB1 and HCBTB2. are mutually locked, only three of them can be closed.
High Voltage Switchgear
Basic Design of Marine High Voltage Switchgear and Control Gear
Insulators are mechanical switching devices that, in the open position, provide an insulating distance so that the circuit cannot be re-established in the event of an electric arc. The earthing switch cannot be turned on until the switch is pulled out to the isolated position. On withdrawable units, mechanical locks ensure that the breaker cannot be racked in the service position until the grounding switch is turned off.
HV Switchgear Panel
- The Bus Bar Compartment
The safety shutter will be closed during the withdrawal of the circuit breaker so that the HV terminal of the busbar is not exposed. The insulating spigots in the circuit breaker compartment hold the fixed contacts and facilitate the connection of the apparatus to the busbar compartment and the feeder compartment respectively. The cable compartment contains the branch system for connecting power cables to the lower contacts of the circuit breaker.
Medium Voltage Circuit Breakers
CuCr is the ideal material used for live contacts; plays an important role in the performance of the vacuum breaker. Due to its high electronegativity, it absorbs free electrons which are produced due to arcing between the contacts of the switch. Due to the presence of the fixed piston, the SF6 gas inside the cylinder is compressed.
When the circuit breaker closes, and while the control knob is not held in the C position, an auxiliary switch completes a circuit to energize the anti-pump relay. Thus, the breaker will open if tripped by an immediate fault condition, but no further closing operations can occur until control.
Failure of a Vacuum Interrupter
Suppose there is a power circuit breaker with a vacuum breaker on phase 3 that has lost vacuum, and if the load served by the faulty breaker is a delta-connected (ungrounded) load, a switching operation would not result in a fault. Before putting the circuit breaker into service or if you suspect a vacuum breaker is leaking due to mechanical damage, check the vacuum electrically using a high voltage IR test meter (Megger). To determine contact erosion, close the circuit breaker and check the moving stem of the vacuum breaker from the rear of the breaker.
High Voltage Protection Systems
Types of Faults and their Effects
These faults occur due to a sudden and complete breakdown of the insulation due to external damage, resulting in very high fault currents and an explosion. However, of the two parameters, duration is more critical, so that the fault energy is kept to a minimum level to limit damage to a plant and more importantly, to prevent injury to personnel. It can only minimize damage due to a bug, but not prevent damage to the affected plant.
Protection Relays
Thus, the role of the protection system is to detect a fault at the lowest possible level consistent with its ability to supply the full load of the installation. Sensitivity: The system must be able to detect the minimum value of the fault current, thereby reducing the resulting damage. These are being phased out due to the problem of less sensitivity and operation due to the mechanical movement due to electromagnetic force.
