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Main Electrical Survey Items, Generators and Governors, , Circuit Breakers, Switchboards and Fittings. (Adapted from:D.T. Hall:Practical Marine Electrical Knowledge). Main Electrical Survey Items. The following survey items apply in general to all ships: Generators and Governors
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(Adapted from:D.T. Hall:Practical Marine Electrical Knowledge)
The following survey items apply in general to all ships:
For UMS operation, a survey of the associated alarms, controls and fire detection is required.
Generator windings on stator and rotor must be free of dust, oil and moisture.
An insulation test to earth and between stator phase windings (if the neutral point can be disconnected at the terminal box) should be carried out while the machine is still hot after running on load.
Arc chutes must be clean, free of arc debris and correctly aligned. All internal wiring should be in good condition and its end connections must be tight. All mechanical linkages will be checked for any signs of wear or stress.
Tests on a circuit-breaker will include close and trip operations while in its isolated position (i.e. not connected in circuit). The racking mechanism formoving the breaker from the service to the isolated position must be demonstrated to be free moving and the fixed main terminals must be seen to be shuttered off when the breaker is withdrawn. Emergency hand charging (if fitted) of the closing spring will be tested. Correct operation of the mechanical indicators to show whether the breaker is open, closed or isolated, is required.
Theundervoltage release mechanism andovercurrent trip settings for level and time delay may have to be demonstrated to the surveyor\'s satisfaction. An overcurrent trip for a generator breaker is typically set for 130% of full load current (FLC) with a typical time delay of 3 s, but this has to suit the thermal capacity of the generator and be co-ordinated with the overall protection scheme for the power system.
Although the overcurrent and time delay settings on the breaker can be seen to be correctly adjusted to the desired values, only a proper current injection test will prove these settings against the manufacturer\'s I/t characteristics. In this test the circuit-breaker is isolated from the busbarand a set of calibrated currents from a current injection set are fed directly through the closed circuit-breaker (primary injection) or (more usually) through the overcurrent relay (secondary injection). This is generally a specialist task for an outside contractor
Circuit-breaker time delay mechanisms with oil dash1 pots must have the pots filled to Site correct level with clean oil of a type recommended by the manufacturer.
All the main bus-bar and auxiliary connections throughout the boards should be checked for tightness during the dead period of a major internal clean up. Overheating signs at a connection junction are probably due to a loose joint. Direct heat testing on load with an infra-red thermal camera is now a very useful technique for locating hot-spots.
Bus-bar supports will be examined for surface tracking and damage to the insulation material. All internal wiring within the switchboard panels must be securely fixed. Cable entries at the bottom of the switchboard should be sealed with a non-flammable material to exclude dirt and act as a fire stop.
The main switchboard earth bar must be securely bonded to both the frame of the board and, of course, to the ship\'s hull. One secondary terminal of each current transformer (CT) and the metal cases of instruments and relays should be wired to the main earth bar. Hinged panel doors should be bonded with an earth strap to the main switchboard frame.