Design And Construction Of Automatic Change-over For Three Phases

Voltmeter
    Voltmeter is used to indicate the voltage of the generator and that of the utility supply
Casing
    This is the structure which enclose the main construction of the automatic change-over panel. It is constructed using metal sheet of thickness 2mm. the shape of the change-over panel is first drawn on a plane paper with dimension that will adequately accommodate the change-over panel.
    The required dimension is then traced out on the iron sheet chisel and hammers where used to cut the traced end.
    After this, each part are joined together by the use of welding machine and the necessary holes for both and screw where drilled on the change-over house required.
    After the construction, this change-over panel is then painted. The tools used for the construction are:-
    Chisel
    Hammer
    File
    Welding machine
4.5.1     Testing, maintenance and discussion
     Testing is an important process in the engineering field especially in both electrical and electronics engineering.
    Therefore, testing can be define as the process by which any faulty condition is detected before a dangerous situation arose.
    Having designed and construction or installed s system with an appropriate selected materials component and equipment what now remain is to put the system into use.
However, before the system is put use, it must be tasted and inspected to ensure that is complies with regulation of installation.
Below is the test carried out.
    Polarity test
    Insulation resistance test between the alive and neutral conductors
    Insulation resistance test between earth and non-earthling conductors
    Earthling test
4.5.2     POLARITY TEST
    This test is carried out on the construction of automatic change-over panel to ensure that only live conductor is taken through the beaker on the load contactor.
4.5.3     INSULATION RESISTANCE TEST BETWEEN THE LIVE AND NEUTRAL CONDUCTORS
An insulation resistance test was made between live and neutral conductor to ensure that there are no short-circuit in the wiring
One lead from the insulation tester was connected to the outgoing live terminal and the other to the neutral of the main switch. The instrument is operated and accurate reading was reading out.
4.5.4     EARTLING TEST
This test carried out to ensure that there is no leakage to the body of appliance.
    On led of ohm meter is placed on conductor and the other lead to the body of appliance. Zero resistance indicates that there is no leakage to the body.
4.6     MAINTENANCE OF CONTACTOR AND IINSTALLATION
    Generally the contact and wiring of the contactor should be properly maintained for adequate functioning of the contactors. In addition, the following should be a also be put into consideration. To replace an operating coil, the contactor must be removed from enclosure and the following procedure must be under taken.
(i)    Remove the spring-clip on either side of the contactor, carefully live the auxiliary contact compress coil magnet slight and take whole magnet system and moving contact carries from auxiliary contact button
(ii)    Invert the assembly and lift out the lift magnet and coil vertically, taken care that the magnet spring remain in place. Note the position of the coil terminations.
(iii)    Change the coil and re-assemble the unity by reversing the above procedure, remembering to compress slightly the magnet when replacing the auxiliary contact.