Commissioning of Electrical systems

By R . N .KAMARAJ , DEPUTY CHIEF ENGINEER SWITCHYARD MAINTENANCE / TPSII

Significance of Commissioning testsType Tests: To ensure compliance with the relevant National and International specifications & standardsTo ensure that the manufacturers performance claims are metTo ensure design validation

Routine Tests

To check quality of compounds used in manufacturingTo conform that individual protection equipments have been correctly manufactured and set up

Commissioning Tests:To demonstrate that equipment has not been damaged in transit and that it can be safely and confidently connected to the system .To prove that the specified equipment has been correctly installedTo show that the characteristics of the protections which are based on calculations are correctTo provide a set of test figures for future reference when required

CURRENT TRANSFORMERS

COMMISSIONING CHECK LIISTSYSTEM : ----------- LOCATION---------MAKE OF CT & Serial NO:1.0 CT Particulars: Protection / Metering : Ratio : Accuracy & Burden : Type : Oil filled / bar /wound / cast Core balance / Current balance: Any other details :

2.0 Visual Inspection:3.0 Continuity:------ CT Resistance:----4.0 Megger Test :---- volts -----M.ohms5.0 High Voltage Tests6.0 Polarity Check :7.0 Ratio Test :8.0 Magnetising Curve:9.0 Oil Test results for BDV and Tan Delta tests

VOLTAGE TRANSFORMERSYSTEM:------- LOCATION:---Make and Serial No:1.0 PT Data: Protection / Metering : Ratio :--- Accuracy:---- Burden:---- Any other specific details:2.0 Winding Continuity and Resistance: 3.0 Megger Test :4.0 High voltage test:

5.0 Polarity Check:6.0 Ratio Test :7.0 Oil test results

HT / LT BREAKERSSYSTEM: ---- LOCATION:---Make and Serial No:1.0 Breaker Details: Breaker type: Rated Voltage:-- Current:--- Breaking Capacity:

Checks on Breakers: Whether breaker rack in and out is smooth Breaker primary contacts are firm and tight on bus bar Check automatic operation of the shutter closing mechanism and ensure its effectiveness for safe shielding Check that all the fuse holders,mechanical position indicators are properly fitted Check that all indication meters,lamp holders are fixed properly

Check that shrouds are provided to prevent entry of vermin when the breaker is withdrawn outside Check that the breaker is tested for high potential. Check limit switches are positioned and proper in multiple operationsCheck breaker Main /Arcing contact alignments are properCheck oil level in all three polesCheck auxiliary contacts for positive and proper operationCheck spring charge mechanism Motor

Check spring charging mechanism operation is proper(Both manually and electrically)Check closing spring mechanism is in good conditionCheck breaker close/open indicators are firmly mounted and they indicate properlyCheck proper functioning of breaker interlocks for Test / Service positionCheck breaker locking arrangement is adequate

Check breaker body contacts ,insulators and all accessories mounted on breaker are thoroughly observed for any physical damageCheck interlock between link and breakersCheck closing and opening operation manually and mechanicallyCheck the operation of the following interlock mechanisms: # Breaker cannot be withdrawn or racked in to service position unless it is in OFF condition # Panel door can not be opened unless the breaker is in OFF condition

# Panel door cannot be closed with the breaker in ON condition # Access flaps for operating the CB and withdrawing CB can be independently locked to prevent unauthorized operation.Check that panel door can be locked securelyCheck and record the following Values: Closing Coil Megger value Trip Coil Megger value Pick up and drop out values of closing and opening coils for closing and opening operation

Spring Charging Time: Insulation resistance between the following values: Breaker poles (Breaker open condition) Breaker pole to earth Br. Closed condition) Breaker Closing Time:Breaker Opening Time:Resistance in Closing coil circuit and opening coil circuit:

HT / LT SWITCHGEAR Checks on BUS BARs: All bolted connections on the bus bar are checked for tightnessPhase to phase and phase to earth clearances are adequate at all pointsBus bars are adequately supported and clampedBus bars are not mechanically stressedMegger values are bus barHigh voltage test

Checks on Cubicles: All cubicles are properly bolted to each other and to floorAll extra opening are closedDoors operate freely,with out jerks and close properlyAll gaskets for enclosures / doors etc are proper and adequateAll ventilation covers are unobstructed and cleanCheck tightness of all panel cover bolts and mounting screws / bolts of PTs / CTs/Relays and other apparatus

Check TWO distinct earth connections from the panel to earth mat.Checks on Control and Protections: (Relevant drawings are to be made available)Check control wires are connected firmly and no damage done to TBsCheck the control wiring is neatly dressed,grouped, glanded, placed in cable channels with ferrules and easily identifiable without disconnectionCheck relay connections and CT secondary connections are firm and proper.

Check control fuse ratings are of proper type as per drawings.All blockings provided on relays are removedControl cables insulation testedRelays and settings with ranges availableChecks on Cables:The cables are properly sealed /grounded/connected and extra openings are closedNon magnetic gland plates are provided for single core cable entriesNo damage done to cable insulation while removing the sheath

Cable lug crimping is done properly and ensure that no oxide paste is applied on cable core at the time of crimpingCable are properly clamped to avoid strain on the connecting bus / insulatorBolting holes in their lug suits the boltCable connection on the bus bars are tight and corrosion inhibiting compound is applied at dissimilar metal functionsCheck for single core core cable,the glands and metal washers used are non magneticHV test & Megger valueCheck for armour earthing

Checks on Relays: Protection:---- Location:---- Relay designation:-----Relay Data: operating voltage / current:Make & Sl.No: Type : Time delay range: _-----(PU); ----- (DO)Settings:Range availablePhysical damage if any:Whether all blockings are removedWirings are are checked

Operating coil resistance:----Resetting coil resistance:----Main coil PU: ----- V / A / AC / DC / %Main coil DO:---- - do-Reset coil PU:--- -do-Reset coil DO:--- -do-CT ratio tap used:PT ratio tap used:Max. feeder load:Circuit voltage:

ISOLATORSChecking of Motor Operated Mechanism boxChecking of Isolator and earth switch interlocksChecking of alignment of power contacts,fixed contact assembly and moving arm assembly.

Check the healthiness of motorCheck the operation of isolator for close and open commandCheck the action of limit cut off for open and closeMeasure the contact resistance of Main contactsCheck the isolator over traveling protection mechanism

QuestionnaireWrite two electrical tests to be conducted on equipment insulating oil?Which of the following equipment is called as Instrument Transformers?Identify the test which ids not common for CT & PT a. Megger b. Polarity Check c. Magnetizing curve d. Ratio

What is MOCB?What is SF6?What is the difference between Isolator and Breaker regarding usage?Write one of the most important electrical test on Isolator?If a particular core secondary is not used while taking into service,what precaution is to be taken? In any breaker,which operation time will be higher?

Mention some of the Operating Mechanisms of Breaker?Any electrical panel or equipment should have how many earthing provisions?For any electrical systems,healthiness of insulation is ensured by which test?Protection relays are operated on which of the following? a. Voltage b. Current c.Both14. Before taking up any work on reenergized bus/switchgear,what should be done first?

By R . N .KAMARAJ , DEPUTY CHIEF ENGINEER / SWITCHYARD MAINTENANCE / TPSIICurrent Transformers