4.56
SEL-787 Relay Instruction Manual Date Code 20081022
Protection and Logic Functions
Voltage-Based Protection
➤ When 24CCS := DD the element operates with a dual-level
definite-time characteristic with pickup and delay of 24D2Pn
and 24D2Dn (n = 1 or 2).
➤ When 24CCS := ID the element operates with a composite
inverse-time and definite-time characteristic with pickup of
24IP (Inverse-time) and 24D2P2 (definite-time). The 24IC and
24ITD settings define the inverse-time curve shape (see
Table 4.32 through Ta ble 4 .34 ).
➤ When 24CCS := I the element operates with a simple inverse-
time characteristic, defined by the 24IP, 24IC and 24ITD
settings described above.
➤ When 24CCS := U the element operates with a user-defined
inverse-time characteristic with a pickup of 24IP. The user
curve should be set using SEL-5806 PC software. This program
handles individual mapping of points to make a curve that
matches any transformer characteristic. It also handles all relay
communication by either uploading the current curve or
programming a new curve.
The 24CR setting defines the composite element reset time. When the element
times out to trip, it will fully reset 24CR seconds after the applied volts/hertz
drops below the element pickup setting. The reset characteristic is linear, so if
the element times 60 percent toward a trip, it will fully reset (0.6 • 24CR)
seconds after the applied volts/hertz drops below the element pickup setting.
When the element is reset, the relay asserts the 24CR Relay Word bit.
Both volts/hertz elements are disabled when the 24TC
SELOGIC control
equation equals logical 0. The elements are allowed to operate when the 24TC
SELOGIC control equation equals logical 1, the default setting. You can add
other supervisory conditions if you need these for your application.
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