what is difference between differential protection and
distance protection and how we calculate the sloop?
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Answer Posted / jacob
A differential protection compares the currents flowing
into and
out from the transformer. Auxiliary current
transformer “aux.ct:s”,
for adjusting the phase angle and ratio are necessary.
Ratio correction
is normally calculated for tap changer at middle position.
Distance protection relays are the most common relays on
transmission
lines. The reason for this is the simple measuring
principle,
the built-in back-up and the low requirement on
communication with remote end.
The Distance protection relay is a directional
underimpedance
relay. Normally two to four measuring zones are available.
Basically the Distance protection relays measures the
quotient
“U/I”, considering also the phase angle between the
voltage “U”
and the current “I”. The measured “U/I” is then compared
with the
set value. The relay will trip when the measured value is
less than
the value set
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