MEOclassIIexamnotes

 50 Hz will make motors run slower. 50/60=83% that will have the effect on the efficiency and the connected load .  If we supply a reduced frequency then we also need to reduce the voltage accordingly to prevent the motor to draw more current.  Voltage/frequency of ship equals to Voltage/frequency shore. That’s gives us a calculated voltage of 366 volts, which closer to the standard 380 volts 50 Hz, that can be accepted.  By doing so the through put of the pumps will be reduced, and we definitely have to keep an eye on the temperatures of the motor windings.

A turning propeller is electrically insulated from the hull by lubricating oil film in bearings Electrical potential is generated between the shaft and the hull  As a result the cathodic protection of the ship will not protect the propeller Electrical potential can cause currents in the bearigngs resulting in pitting of the bearing surfaces Problems can be avoide if the shaft is earthed with a propeller shaft slip ring This shaft earthing assembly comprises a pair of high silver content\graphite compound brushes mounted in a balanced brush holder, running on a copper slip ring with solid silver track

 200 % load carrying capacity Phase failure alarm Short circuit trip Overload alarm ( no trip ) One motor connected to ESB Zero time delay after power recovery with auto start. Power failure alarm

NERs, sometimes called  Neutral Grounding Resistors , are used in an AC distribution networks to limit transient overvoltage that flow through the neutral point of a transformer or generator to a safe value during a fault event. In case of high voltage NER is used to reduce fault current. It is connected in between neutral to earth. If a generator is high voltage then it's neutral will be connected to earth via NER

Neutral Neutral is return path for an AC circuit which is supposed to carry current in normal condition. This current may be because of many reasons, primarily because of phase current imbalance and some time because 3rd and 5th harmonics also.  There may be others reasons too but the magnitude of this current is in fraction of phase current and in few case it can be even double of phase current. So Neutral wire is always assumed to be charged (in active circuit). This neutral wire is given to ground (by grounding) to make the second terminal of neutral wire at zero potential. Earth or Ground Earth or Ground is for safety concerns against leakage or residual currents on the system via least resistance path. While phase and neutral is connected to main power wiring, earth may be connected to body of equipment or to any system which in normal condition doesn’t carry current but in case of some insulation failure, is supposed to carry some minor current. This current is not direc...

Single phase or 3 phase transformer. System current requirement to be mentioned. (10 A – 200 A) Cable size and insulation requirements. Holder size (3.5 mm to 18 mm) Physical size of transformer Only for welding transformer rating in KW, (5 to 40 KW)

With a megger,a voltage of not less than 500 volts DC is used for testing the insulation resistance of windings.  With a multi-meter, the voltage used is not more than 3-volts DC.  Megger uses high impedance testing and is therefore more accurate than a multi-meter