Gulf jobs walk in Abroad sector.

                         Precommissioning Tests:

 1.      Visual inspection – to confirm that the equipment has not been damaged during transit
 2.      Installation, Cabling and Wiring
 -         Capacity of cable leads to be checked
 -         Proper laying of cable to be confirmed
 -         Cable tags to be provided as per cable schedule
 -         Spare holes for future cable should be provided in panel plates.
 -         Care to be taken in glanding the cables the sheath wires should not end within the gland. Atleast          5 mm should protrude out and they should be bent towards outside so that they will not prick              the inner jacket and cause/insulation failure.
 -         The cable jacket should be removed only by skilled people without damaging the lead insulation. This is a common mistake done by unskilled persons without knowing the implications.
 -         The jacket over the inner leads should protrude out from the gland finishing atleast by 2 Cms.      Gland mouths should not be covered with insulation tapes to conceal unskilled finishing.
 -         Cable cores shall be identified at both ends and ferruled properly. In cables with same colour leads, clockwise – anti-clockwise method shall be used for easier identifying.
 -         Lead to lead meggering  between all leads individually should be done at this stage itself without fail.
 -         Any joints to make up short length of one or two cable leads should be prohibited altogether.
-         If lead connections are done without lugs, the end loop should be made clockwise only so that the round loop will not open while tightening screw or stud.
 -         Only proper lugs should be used. Dispensing with one or two strands of the cores to accommodate in the undersize lug should be avoided. Likewise the eye of the lug should not be developed to accommodate the screw or stud.
 -         Use snugly fitting ferrules
-         Each lead should be lugged separately. More than one lead should not be clubbed, in one lug.
 -         Lugs should not be taped or covered with anything.
 -         When two lugs are put in one TB, they should face back to back so that there is good meshing.
 -         Lugs should be crimped only with correct size crimpers.
 -         Use correct size screw drivers; use only star screw drivers where star screws are provided
 -         use washers always
 -         Another person should make 100% check of the connection with the drawing and also the tightness of the lug and screw.
 -         Bunch spare cores separately and leave their full length; put the cable number as ferrules; unconnected individual wire should not be left strayed
 -         Dress everything neatly.
 -         Plug out the spare cable holes for vermin proof.
 -         Clear the loose screws, washers, iron filings dust etc. from the panels.
 Testing individually: 

    a)      Breakers
-         Closing and opening time of main and auxiliary contacts.
 -         Meggering of H.V. terminals, (a) To earth individually (b) Between poles with breakers open.
 -         Meggering of A.C D.C. P.T. and C.T. circuits individually and in between each of them.
 -         Measuring the contract resistance.
 -         Checking the interlocks.
 -         Checking the minimum operating voltage level of closing (80%) and trip coils (70%)

b)   Isolators-         Control circuits -         Checking of simultaneous closing of main contacts
 -         Checking auxiliary contact
 -         Meggering of limbs
(Isolators should not be used to break currents in load circuits like PARALLEL TRANSFOMERS AND UNLOADED LINES.)       

      c)      P.Ts
-         Meggering of  HV windings, secondary windings between H.V. and each secondary winding
 -         Measuring the resistance of secondary winding with multimeters.
 -         Polarity tests.
 -         Ratio test.
 -         Checking the earthing.
 -         After wiring is finished, do the secondary injection in each phase at rated secondary voltage ensuring that the test voltage does not reach the P.T. secondary.
 -         Checking the transfer schemes if more than one P.T. are available.

       d)      C.Ts:
 -         Meggering between each windings in secondary
-         Meggering of H.V.Points
-         Meggering between H.V. and Secondary
-         Measuring the D.C. resistance of secondary cores
-         Polarity test
-         Magnetising test upto knee point is a must. It should be ensured that the applied voltage is slowly reduced to Zero after reaching the knee point. This is to avoid high rate of change of flux causing high induced voltage damaging secondary insulation.
-         Ratio test at rated primary current for all the taps in secondary. This test shall be done after magnetising test.
-         Unused cores shall be shorted
-         Unused portion of a core shall never be shorted
-         All the C.T. secondary circuits shall be earthed at only one point, preferably nearer to C.T. end.
-         After making the connections to load point, megger the entire secondary circuit and then do the secondary injection from the terminals at the C.T. end. The secondary injection shall first be done without the grounding and it shall be repeated with the grounding done. Now, the voltage burden at each terminals from the CT terminal upto the load shall be measured and promptly recorded for the rated secondary current of the C.T. When current is injected in one phase, it should be ensured that there  is  no current in other phase  at any point. Secondary injection is a very very important one. In multi secondary CTs, there is frequent possibility of protection wiring done to a metering secondary. ONLY secondary injection can reveal this fault. Primary injection will not reveal.

     e) Metering instruments  

      After making the connections Calibrration

      Checking the readings during secondary injection on PT and CTs and checking the burdens in current coils 

      checking the selector switches.  

     f)       Control Circuits – Check points:
-         Meggering
-         Energising the panels with auxiliary supply
-         Voltage across fuses should be clear zero
-         Indication circuits
-         Annunciator points
-         Semaphores
-         D.C. auxiliary relays to be checked for 60% voltage pick up
-         Interlocks
-         Inter trip
-         Functional tests
-         Closing circuits and trip circuits
-         Trip supervision cicuits to be checked
-         Trip healthy lamps – the lamps should be shorted several times and to be ensured that the trip Plunger does not move
-         Auto reclose
-         Protection trip circuits – it should operate even when the breaker control is in local or remote
  g)      Relays
 -         Megger wherever allowed
-         Test the relays for all P.U. settings
-         Adopt the final settings and test
-         See the operation during secondary injection wherever possible

h)      Power equipments like Generators: Transformers  Generators:      

      -         Winding D.C. resistance of stator and rotor-         Meggering of stator and rotor
-         H.V. test on stator and rotor
-         Pole drop test on rotor
-         Tan d test

AC MOTOR TEST

INSULATION TESTS

The earthing of the frame pedestals and any contactor cubicle or swithch box shall be checked with appropriate ohm meter.

An insulation resistance test shall always be made before connecting the supply, prefferly a few days before the motor is required for service to allow time for drying-out necessary.

Megger test for Insulation measurement

All accessories such as surge capacitors surge arrestors current transformers etc,. that have leads located at machine terminals shall be disconnected during this test with leads connected together and to the frame or core.

Voltage test

Insulation resistance test are usually coducted at constant direct voltage of 500-10000 v having negative polarity.Guidelines for test voltage are presented in table

Guide lines for dc voltages to be applied during insulation resistance test

• winding rated voltage (V) <1000

          Insulation Resistance test direct voltage (V) 500

• winding rated voltage (V) 1000- 2500
          

Insulation Resistance test direct voltage (V) 500-1000

• winding rated voltage (V) 1000- 2500 

          Insulation Resistance test direct voltage (V) 500-1000