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   Current Transformers

• CT primary & secondary rated currents 

• Errors – reason and influencing factors

•  Metering CT:  Specification, application, ISF

• General protection class CT: Specification, ALF, voltage developed across CT secondary

• Special protection class: Specification, Saturation, concept of KPV and Exciting current limit, CT calculation for high impedance differential scheme

• CT calculation for numerical relay application

• CBCT – functioning and application in high resistance grounded / ungrounded systems

• Case studies: Saturation of CT; Selection of CT; Maintenance replacements; Applications; Over-specification and bulky CT; wrong applications in energy metering 

   Voltage Transformers 

• Connections     :     star – star & star – open delta connections

• Errors and accuracy

• Metering PT      :     Specification, application

• Protection PT   :     Specification, application, voltage factor and grounding

• Protection of PT and associated circuits : fuse on primary side and fuse on secondary side   

• Case studies    :     Reasons for PT failure; Fuse failure and prevention of protection
                                   scheme from initiating tripping

   Testing

   Current Transformer

    IR measurement; Polarity check; Ratio Check; Lead resistance measurement; Excitation characteristics 
    verification; Secondary and primary injection tests.

    Case studies    :     Detect faults in CT and CT circuits, Prevent protection failure by identifying defective 
                                     CTs, On line testing / checking of CTs and CT circuits .  

   Potential Transformer

    IR measurement; Polarity check; Ratio Check; Secondary and primary injection tests; Fuse failure scheme 
    checks

·    Case studies    :     Failure of PT due to ferro-resonance and preventive action; On line testing / checking 
                                     of PTs and PT circuits