ABB CWC, Instruction Leaflet

Page: 10 / 16

41-242.2F Type CWC and CWP Directional Ground Relay
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the value of Column 3 divided by the ratio of Column
4. The value is recorded in Column 7. The upper pole
relay current is the value of Column 5 divided by the
ratio of Column 6, and is recorded in Column 8. The
relay operating product is the values of Column 7
and 8 multiplied together and recorded in Column 9.
For the type CWC relays, the ratio of I
L
/I
U
is written in
Column 10. All of this data is fixed by the system
constants and characteristics, and is preliminary to
making the actual relay setting.
The choice of a tap recorded in Column 11 and of the
time lever in Column 14 is a matter of trial and error.
The breakers on this system have 8 cycle operating
time so that the coordinating time interval should be
about .4 second. The tap should be chosen so that
the relay times for the close-in fault and remote fault
product values will differ by about the coordinating
time interval or .4 second in this case. Practically this
can be accomplished by several taps with equal
results. Tap 36 was selected in this example. The
product value divided by the tap is recorded in Col-
umn 12. This value is the abscissa of the time prod-
uct relay curves. From these curves the lever
Column 14 and relay operating time Column 15 were
chosen so that the relay would operate at about .12
second for close-in faults and about .52 second for
the remote faults. These times for the type CWC
*
*