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Tuesday, 9 October 2012

Electrical Testing and Commissioning Of Switch Board

Electrical Testing and Commissioning Of Switch Board
Testing and start-up / commissioning procedures for all the components of medium voltage switchgear like circuit breaker, busbar, instrument transformers (current/voltage), disconnect   and grounding switches etc regardless of its size, type or industry.
Objective   
To verify the physical condition and proper connections of bus bar.
Frequency
Before commissioning of the equipment
Periodic maintenance test once in a year/planned schedule
After general overhaul
Test Equipment Required:
• Insulation test (Megger)
• Micro ohmmeter
• High voltage tester
• Torque wrench
 Test Procedure:
 Mechanical Checks and Visual Inspection:
• Inspect switchgear and all components for any physical damage / defects.
• Check nameplate information for correctness.
• Inspect enclosures for proper alignment, foundation fixing, and grounding and vermin entry.
• Inspect all covers, panels’ section and doors for paintwork and proper fit.
• Check all the transport locks are removed.
• Check for smooth and proper movement of racking mechanisms, shutter, rollers, rails and guides.
• Check proper alignment of the primary and secondary contacts.
• Check operation of all mechanical interlocks.
• Check tightness of all bolted connections.
• Check for correct phasing connection of bus bar.
• Perform mechanical check and visual inspection for breaker / Contactor as per section.
• Perform mechanical check and visual inspection for instrument transformers as per section
• Perform mechanical check and visual inspection on all disconnect / grounding switches as per section.
 Insulation Resistance Test:
It includes panel enclosure, bus bar, CT and circuit breaker. The following precautions should be taken care, before starting the testing.
A visual inspection will be made to ensure the surface dust and moisture has been removed from the component under test. Ensure the component is isolated from other connected system, which may feed back to other components or circuits not under test.
On testing, voltage shall be applied between one phase and other phases connected with ground, testing shall be repeated for other phases as mentioned above. Test voltage limits mentioned in table below:
Rated voltage
Test voltage
100-700V AC/DC
500V DC
>700 to <33000V AC
Min 2500V DC
> 33000V AC
Min 5000V DC

Ref: IS7118-3
 Contact Resistance Test:
This test is to confirm the busbar joints are connected properly and verify the tightness.
The test connection diagram is as shown in Figure below.
The test shall be done with CBs inserted and closed. Measure the contact dc resistance between panels by injecting 100A DC. This will include busbar joint, CB contact resistance, CB cluster resistance, and CT primary resistance (if applicable).
Limits:
The obtained results should be similar for all phases for each set of measurement. Other influencing factors to be considered, like length of the measured path, rating of the busbar, rating of CB, rating of CT and temperature.

Contact resistance test

  
 High Voltage Test
To determine the equipment is in proper condition to put in service, after installation for which it was designed and to give some basis for predicting whether or not that a healthy condition will remain or if deterioration is underway which can result in abnormally short life.
Test Instruments Required:
• Calibrated AC Hi-pot test set for switchgear with leakage current indicator and overload protection.
• Calibrated DC Hi-pot test set for cables with leakage current indicator and overload protection.

Check List for Switch Board Maintenance
Date:                             
Substation No:                                 
SWB No:                                                         Rating:                     

Slno
Activities
Checks carried
Remarks
1
Obtain LC from Sub-station Operation


2
Ensure isolation of the Incomer and Bus coupler breaker and control supply and Heater supply of the section


3
Ensure all back feeding sources are isolated


4
Remove all breakers/modules and PT Cubicles (If it is draw able type)


5
Open the top and side covers of the busbar chamber.


6
Clean the busbar chamber, breaker rear and front compartment with air blower, vacuum cleaner and dry cloth.


7
Clean all insulators by soft dry cloth & contact Cleaner.
Check for cracks, damages & replace the defective one.


8
Check and tighten the exposed joints of the busbar. Check for any signs of heating.


9
Check and tighten the power connections of CT/ PT  and out going cables.


10
Check for any unplugged opening, missing bolts


11
Box up busbar chamber & rear compartments of breaker.


12
Check earthing system is proper & intact


13
Check IR value
a) R-E       b) Y-E    c)  B-E


14
Any other abnormality




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