Setting End X End Y End Z
Phase Is1 (Primary) 0.5*500 = 250A 0.5*800 = 400A 0.5*200 = 100A
Phase Is1 (Secondary) 0.5*5 = 2.5A 0.5*5 = 2.5A 0.5*1 = 0.5A
Phase Is2 [p.u.] 1000/200 = 5 1000/200 = 5 1000/200 = 5
Phase Is2 (Primary) 5*500 = 2500A 5*800 = 4000A 5*200 = 100A
Phase Is2 (Secondary) 5*5 = 25A 5*5 = 25A 5*1 = 5A
Id High Set [p.u.] 3000/200 = 15 3000/200 = 15 3000/200 = 15
Id High Set (Primary) 15*500 = 7500A 15*800 = 12000A 15*200 = 300A
Id High Set (Secondary) 15*5 = 75A 15*5 = 75A 15*1 = 15A
In Diff Is1 [p.u.] 50/200 = 0.25 50/200 = 0.25 50/200 = 0.25
In Diff Is1 (Primary) 0.25*500 = 125A 0.25*800 = 200A 0.25*200 = 50A
In Diff Is2 (Secondary) 0.25*5 = 0.75A 0.25*5 = 0.75A 0.25*1 = 0.25A
In Diff Is1 [p.u.] 1000/200 = 5 1000/200 = 5 1000/200 = 5
In Diff Is1 (Primary) 5*500 = 2500A 5*800 = 4000A 5*200 = 100A
In Diff Is2 (Secondary) 5*5 = 25A 5*5 = 25A 5*1 = 5A
13.5 FEEDERS WITH SMALL TAPPED LOADS
Where transformer loads are tapped off the protected line, it is not always necessary to install CTs at this location.
If the tee-off load is light, differential protection can be configured for the main line alone. The settings Phase
Char, Phase Time Delay and Phase TMS or Phase Time Dial allow the differential element to time grade with IDMT
overcurrent protection devices or fuses protecting the tap. This keeps stability of the differential protection for
external faults on the tee circuit.
13.6
SETTING A TWO-TERMINAL PHASE CURRENT DIFFERENTIAL ELEMENT
All four settings are user adjustable. This flexibility in settings allows the phase current differential characteristic to
be tailored to suit particular sensitivity and CT requirements. To simplify your task, we strongly recommend three of
the settings be fixed to:
Phase Is2 = 2.0 pu
Phase k1 = 30%
Phase k2 = 150%
These settings will give a characteristic suitable for most applications. It leaves only the Phase Is1 setting to be
decided by you. The value of this setting should be in excess of any mismatch between line ends. It should also
account for line charging current, where necessary.
By considering the circuit shown below, the settings for the phase current differential element can be established.
Chapter 6 - Current Differential Protection P543i/P545i
128 P54x1i-TM-EN-1
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