Wednesday, July 21, 2021

HOW POWER MANAGEMENT SYSTEM WORKS ON SHIPS

 INTRODUCTION

A ship can equate to a floating community with all equipment and devices that are used ashore to support life installed onboard. As a result, a reliable and continuous power supply becomes a must. Automatic control of machinery has become commonplace to maintain power continuity and effective administration. Most of the time, the power management system is part of the integrated automation system (IAS), which controls the ship's generating sets, switchboards, and heavy consuming loads automatically.

The power management system's main goal is to control electricity in diverse loads aboard. If the vessel's load or power demand exceeds the generating set's carrying capacity, or if the generating set's safe operation is jeopardized, the overload relay and other protection systems may trip to protect the generator.The priority of connecting or removing a generator from the busbar changes from time to time, depending on the vessel's power requirements. More importantly, the priority of connecting or removing a load from power is determined by the importance of the load to the vessel's safe navigation and the safety of the crew members onboard. 

In the past, power management systems were relay-based, but programmable logic controllers (PLCs) are now more often utilized. The power management system is integrated into the ship distributed control system on large ships. The system performs a number of functions to guarantee that the ship's electrical system is always powered up. The power management system, working in tandem with the ship's distributed control system, ensures that the diesel generators, fuel consumption, and emissions are all automatically controlled. Most of the time, a PLC is utilized to allocate priority to a load in a specific sequence using relay logic or ladder logic that has been programmed into the PLC.



POWER GENERATION ONBOARD SHIP

A vessel's electrical demand varies depending on the type of ship and its day-to-day operational requirements, whether at sea or in port. More generators have been installed to suit the vessel's power requirements, which are backed up by an emergency generator and an emergency battery system.

A ship's main generator power ratings typically range from 100kW to 6.6 kV at 440V, 60 Hz, however cargo ships and cruise liners also employ 3.3 kV and 11 kV respectively. Diesel, steam turbine, gas turbine, and propulsion shaft-driven prime movers are the most common generators.

Three sets of coil windings are slotted in the stator and encircled by revolving magnetic poles in a conventional ship's generator. The phase difference between the induced voltage in each phase of the stator winding is 120 degrees. The three-phase windings are labeled U-V-W, with red, yellow, and blue color labeling utilized on terminals and bus-bars. The neutral point of a star connection is formed by joining one end of each of the three phase windings together.

The phase windings' other ends are connected.

The output voltage and frequency are determined by the generator's prime mover speed. The excitation voltage applied to the revolving rotor magnetic poles maintains a steady output voltage and frequency.

The exciter provides direct current (d.c.) to the rotor poles. The d.c. excitation current is delivered into the field windings through carbon brushes on a pair of shaft mounted slip-rings if the exciter is a standard d.c. generator or is static.  Slip rings are not always employed and are substituted with an a.c exciter whose output is rectified by a silicon controlled rectifier in some circumstances. The rotating speed (n) and magnetic flux of the rotor are critical for the generation of a produced voltage in an a.c. generator. When the rotor field windings are activated with direct current, a strong magnetic field is induced on the generator's stationary stator winding. The exciter is designed to deliver the needed a.c output voltage from the stator terminals by supplying the correct direct current to the rotor magnetic poles. As the load fluctuates, the excitation must be continuously regulated to maintain the generator output voltage.

HOW POWER IS  DISTRIBUTED TO DIFFERENT BRANCHES ONBOARD SHIP

The ship distribution system is the system that distributes electricity generated by the generating sets to the various load devices onboard the ship. Through the use of wires, the electrical power generated is supplied to the main switchboard (MSB). The power from the generators is routed through the main circuit breaker to the high voltage part of the main switchboard. Step down transformers route and distribute the high power present in the 440v part of the main switchboard via cables to sections and sub-distributed boards. Finally, power is delivered to the load equipment from the sub-distribution board.
 Fuse and relays protect the distribution system from the devastating effects of large fault currents. Circuit-breakers and switches halt the flow of electric current, while fuses and relays protect the distribution system from the damaging effects of large fault currents.

The electrical distribution arrangement on a ship is usually similar to that on land. This allows ordinary industrial equipment to be utilized on board ship after being tested to be seaworthy. This means the equipment must endure the vibration, humidity, high temperature, ozone, seawater, and other rigors encountered in various portions of the ship.

The ship's main electrical load is split into essential and non-essential loads.

The term "essential vessel services" refers to the services that are required for the safety of the crew as well as the ship's navigation and propulsion. Essential loads include, but are not limited to, navigational, communications, firefighting, control stations, and steering equipment. The power for vital services can come directly from the main switchboard, or through section boards or distribution boards.

For cargoes that must deal with a potentially harmful scenario, emergency supplies are required. The ship's emergency generator is the primary source of backup power, supplemented by the emergency battery.The ship's emergency power supply must at all time be ready and available. Weekly routine testing is required to ensure the emergency power source's reliability.  In the event of an emergency or potential blackout situation, only emergency generator can automatically supply power for essential services. But in a situation where the emergency generator fails to start, emergency battery can supply power for lighting and important services for at least 45 minutes or more.

The main switchboard is at the heart of the ship's power distribution system (MSB). Most ships' primary switchboards are divided into BUS A and BUS B. You can have up to BUS C on a large ship. The bustie acts as a link between BUS A and BUS B or BUS C, depending on the situation. The main switchboard (MSB) has the following sections in a conventional configuration:

1. Diesel Generator 1 (DG1) and Diesel Generator 2 (DG2) incoming on main switchboard BUS A 

2. Diesel Generator 3 (DG3) and Diesel Generator 4 (DG4) incoming on main switchboard BUS B

3. 440V feeder

4. 220V feeder

5. Motor control centre for both BUS A and BUS B

6. Bustie feeder which is usually at the centre linking the buses.

All interlocks on the ship distribution system are supplemented by protective devices for overcurrent, undervoltage, unbalanced load, reverse power, and so on. 



POWER SYSTEM RELIABILITY ONBOARD SHIP

Any power system's dependability is the bane of any electrical design and installation. This can be accomplished by separating the distribution system into multiple sources, providing an emergency power source, subdividing power circuits, selecting an appropriate earthing system, and selecting the appropriate protective devices.

To decrease the amount of potential fault current and electric shock, the power system architecture must allow for the usage of a step down transformer to reduce the high power coming from the busbars to the distributed subsections.


To avoid a blackout, emergency generators are deployed to give electricity to important equipment and illumination when the main power goes out. Both the main switchboard and the emergency switchboard provide power to essential devices. This configuration would help isolate a high-priority circuit from faults that might occur in the secondary circuit. The sectioning is necessary to offer at least two power sources (main and emergency) for all vital equipment required for the vessel's safe navigation.




FUNCTIONS OF POWER MANAGEMENT SYSTEM ON SHIP  

1. Load demand monitoring: The overall power consumption of a vessel is measured and compared to the available generating capacity at any given time. Because the power management system regulates the overall number of generators connected to the main switchboard based on actual power consumption. The generators are started and stopped by the power management system based on the load.


2. Generator management: The primary goal of a power management system is to automatically control generators in order to ensure that electric power is available at all times and to avoid blackouts. Load-dependent start/stop of generating units is normally performed by a sophisticated power management system.The PMS will send a closing command to the circuit breaker protecting a standby generator in response to varying loads, interlocking its contacts and initiating the starting procedure to bring it on-line to share the available load. When a generator is no longer needed, the PMS can send an open instruction to the circuit breaker to separate it from the busbar and turn it off.


3. Automatic line frequency adjustment: By automatically raising or decreasing the signal to each generator's governor, PMS guarantees that the busbar frequency is monitored and kept within a set range.

4. Load shedding; When the generating capacity is insufficient to drive heavy consumers, the power management system acts to prevent a sudden increase in load. The power management system and the preferential trip relay work together to trip chosen loads in a predetermined order.


5. Generator auto-synchronization: To commence an auto-synchronizing system, the power management system's output signals are used to raise/lower generator governor settings.

BENEFITS OF POWER MANAGEMENT SYSTEM

1. It ensures that the generators function as efficiently as possible.


2. It limits the number of times the generating set and load equipment start and stop.


3. It ensures that all generators have the same amount of running time.


4. It ensures that available load is distributed across all running generators in proportion to their capacity.


5. It ensures the distribution system's safe and reliable operation.


6. It aids in the prevention of electrical fires and shocks.


7. It aids in the prevention of unplanned blackouts.


It improves power maintenance.

DUTIES OF POWER MANAGEMENT OFFICER ONBOARD

1.Determine the operational and maintenance needs.

2.Coordinate the maintenance of all onboard electrical systems and generators.


3.Coordinate the maintenance of all onboard air conditioning systems.


4.Assuring that the ship's electrical system is free of earth faults as much as is reasonably possible.


5. Creating (or supporting the 2nd Engineer or Chief Engineer in creating) work routines that guarantee all statutory and regulatory requirements are met.

6.Using best practices, maintain and repair the ship's electrical equipment while adhering to MCA rules, IEE regulations, and the Code of Safe Working Practices.

7.Attendance in the ECR at ‘Standby' as needed by the Chief Engineer, unless the Chief Engineer releases you to do other tasks.

8.Ensure that illumination levels are maintained at a safe level throughout the vessel.

9.As required by legislation, regular maintenance and testing of the emergency lighting system.

10. Keeping the workshop and storage rooms as clean and tidy as possible.

11.Assisting the 2nd Engineer in the Technical Department's employee training in accordance with legislative and company requirements.

12. Ensuring that the fleet regulations that apply to ETOs are read, comprehended, and followed.

13.Assisting the Chief Engineer with duty roster preparation

14.Assisting the Senior Chief Engineer in the preparation of repair lists and refit specifications for the ship's electrical, electronic, and control systems, plant, and equipment in order to comply with survey requirements.


THANKS FOR VIEWING!



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