Unlike the Conventional Generators That We Use on Land, a Ship's Generator Requires a Special Procedure for Starting and Stopp
Total Page：16
File Type：pdf, Size：1020Kb
Unlike the conventional generators that we use on land, a ship’s generator requires a special procedure for starting and stopping it. Though not a very complex one, the process demands a step-by-step system to be followed. Missing even a single step might lead to failure in starting or stopping the generator and can even lead to “black-out”, a situation which everyone on ship tries their best to stay away from. In this article, we bring to you an accurate, step by step procedure for starting and stopping a generator on a ship. Generator starting procedure Automatic Start 1. Ÿ This method is only possible if sufficient amount of starting air is available. The air valves and interlocks are operated like in the turning gear operation. 2. Ÿ In this method the operator has nothing to do, for the generator starts itself depending on the load requirement. 3. Ÿ However during the Maneuvering process and in restricted areas, the operator has to start by going into the computer based Power Management System (pms). Once inside the system, the operator needs to go to the generator page and click start. 4. Ÿ In PMS system, the automation follows sequence of starting, matching voltage and frequency of the incoming generator and the generator comes on load automatically. 5. Ÿ In case of a blackout condition or a dead ship condition, the operator might have to start the generator manually. Manual start The manual process is totally different from the automatic start system. The following steps need to be followed: 1. Ÿ Check that all the necessary valves and lines are open and no interlock is active on the generator before operating. 2. Ÿ Generally before starting the generator the indicator cocks are opened and small air kick is given with the help of the starting lever. After this, the lever is brought back to the zero position, which ensures there is no water leakage in the generator. The leakage can be from cylinder head, liner or from the turbocharger . 3. Ÿ The step is performed by putting the control to local position and then the generator is started locally. 4. Ÿ In case any water leakage is found, it is to be reported to a senior officer or chief engineer and further actions are to be taken. 5. Ÿ It is to note that this manual starting procedure is not followed generally on Ums ships, but it is a common procedure on manned engine room. 6. Ÿ In engine rooms, which have water mist fire fighting system installed, this procedure is not followed because when the engine is given a manual kick with open indicator cocks, small amount of smoke comes out of the heads which can lead to false fire alarm, resulting in release of water mist in the specified area. 7. Ÿ After checking the leakage, in case of any, the indicator cocks are closed and generator is started again from the local panel. 8. Ÿ The generator is then allowed to run on zero or no load condition for some time for about 5 minutes. 9. Ÿ After this the generator control is put to the remote mode. 10. Ÿ If the automation of the ship is in working after putting in remote mode the generator will come on load automatically after checking voltage and frequency parameters. 11. Ÿ If this doesn’t happen automatically, then one has to go to the generator panel in Engine control room and check the parameters. 12. Ÿ The parameters checked are voltage and the frequency of the incoming generator. 13. Ÿ The frequency can be increased or decreased by the frequency controller or governor control on the panel. 14. Ÿ The incoming generator is checked in synchroscope to see if it’s running fast or slow, which means if frequency is high or low. 15. Ÿ In synchroscope, it is checked that the needle moves in clockwise and anticlockwise direction. 16. Ÿ Clockwise direction means it is running fast and anti-clockwise means it is running slow. 17. Ÿ Generally the breaker is pressed when the needle moves in clockwise direction very slowly and when it comes in 11’o clock position. 18. Ÿ This process is to be done in supervision of experienced officer if someone is doing for the first time, for if this is done incorrectly the blackout can happen which can lead to accidents, if the ship is operating in restricted areas. 19. Ÿ Once this is done, the generator load will be shared almost equally by the number of generators running. 20. After this the parameters of the generator are checked for any abnormalities. Stopping procedure Automatic Procedure Ÿ In this procedure the generator is stopped by going into the PMS system in the computer and pressing the stop button to bring stop the generator. 1. Ÿ This is to be followed only when two or more generators are running. 2. Ÿ Even if you trying to stop the only running generator it will not stop due to inbuilt safety. The safety system thus prevents a blackout. 3. Ÿ When the stop button is pressed the load is gradually reduced by the PMS and after following the procedure the generator is stopped. Manual Procedure 1. Ÿ In this procedure the generator to be stopped, is put off load from the generator panel in the Engine control room. 2. Ÿ The load is reduced slowly by the governor control on the panel. 3. Ÿ The load is reduced until the load comes on the panel below 100 kw. 4. Ÿ When the load is below 100kw the breaker is pressed and the generator is taken off- load. 5. Ÿ The generator is allowed to run for 5 minutes in idle condition and the stop button is pressed on the panel. 6. Ÿ The generator is then stopped Generator Set Motor Starting Motor starting is an important issue which must be considered when applying a generator set. The high current that motors draw when starting causes voltage dips in the system. This may require oversizing the generator or applying motor starting techniques maintain this voltage dip at acceptable levels for your system and its attached components. Motors, either loaded or unloaded, draw several times rated full load current when starting. This is termed locked rotor current or starting kVA (SkVA). SkVA is calculated from locked rotor current like this: SkVA = V x A x 1.732 / 1000 In-rush current to the motor causes a rapid drop of generator output voltage. In most cases, a 30 percent voltage dip is acceptable, depending on the equipment you already have on line. The degree of dip must be identified by an oscilloscope, since mechanical recorders are too slow. Motor Starting Options If you have an application where motor starting is a concern, consider the following: Change the starting sequence, with largest motors first. More SkVA is available, although it does not provide better voltage recovery time. Use reduced voltage starters. This reduces kVA required to start a giver motor. If you’re starting under load, remember this starting method also reduces starting torque. Specify oversized generators. Use wound rotor motors, since they require lower starting current. Wound motors typical cost more, however. Provide clutches so motors start before loads are applied. While SkVA demand is not reduced, the time interval of high kVA demand is shortened. Improve the system power factor. This reduces the generator set requirement to produce reactive kVA, making more kVA available for starting. Use a motor generator set. A motor drives the generator which, in turn, supplies power to the motor to be started. This system runs continuously and current surge, caused by the starting of the equipment motor, is isolated from the remainder of the load. Watch Voltage Dip Motor starting is affected by motor and generator design, and load on the motor. Initial voltage dip depends mostly on motor and generator windings. Addition of series boost to the regulator or use of a permanent magnet exciter will not significantly decrease this dip. The magnitude of voltage dip tolerable depends on the type of equipment on line. Motor starting contactors may open if voltage drops below 65 percent of rated. Motors draw starting currents to eight times normal running current. Preloads on motors do not vary maximum starting currents but do determine time required from motors to achieve rated speed and current to drop back to normal running value. If motors are excessively loaded, they may not start or may run at reduced speed. Motors connected directly to high inertia centrifugal devices or loaded reciprocating compressors will cause severe frequency excursions and lengthy motor run up. Comparing starting current between loaded and unloaded motors shows the extended time loaded motors demand high current. When specifying motor loads, skVA and acceptable system voltage dip to a gen set specifier, it is important to ensure that you are evaluating the instantaneous voltage dip of the generator’s voltage on the system. Instantaneous voltage dip is the actual maximum voltage dip experienced when a motor load is applied. Some gen set manufacturers state voltage dip in terms of “sustained” voltage dip. Sustained voltage dip is calculated by ignoring the actual voltage dip for the first few cycles of motor starting, where the voltage dip is highest, and then averaging the voltage dip during part of the recovery period. This significantly understands the actual voltage dip any equipment attached to the system experiences and may cause system and equipment problems due to higher instantaneous voltage dip. If you have motor starting questions, please contact us.