Direct measurement of high current at high
voltage system is not possible because of
limitation and insulation problem of measuring
instruments. It is also not possible to use
current flowing through the system directly for
protection purpose due to its high value and
high insulation problem.
Basic Functions of Current Transformers
are :-
To transform the line current with a
specified accuracy to a value which is
suitable for
standard measuring instruments, relays
etc.
To isolate the measuring instruments,
meters, relays etc. from high voltage
side of
To protect measuring instruments against
short circuit currents.
To sense abnormalities in current and
give current signals to protective
relays to isolate the
defective system.
Technical information required for tendering :-
RATIO
NUMBER OF CORES
VA BURDEN OF EACH CORE
ACCURACY CLASS
ACCURACY LIMIT FACTOR FOR PROTECTION
CORE
FOR CLASS PS - MIN. KNEE VOLTAGE,
EXCITATION CURRENT & RCT AT 75 DEG.C.
