Sel 551 - Instantaneous Overcurrent Elements

3.8
SEL-551 Relay Instruction Manual Date Code 20110408
Relay Elements and Logic
Instantaneous Overcurrent Elements
The switch representation in this figure is derived from the standard: Graphics
Symbols for Electrical and Electronics Diagrams IEEE Std 315-1975, CSA Z99-1975,
ANSI Y32.2-1975, 4.11 Combination Locking and Nonlocking Switch, Item 4.11.1
Figure 3.3 Remote Control Switches Drive Remote Bits RB1–RB8
Remote Bit States
Not Retained When
Power Is Lost
The states of the remote bits (Relay Word bits RB1–RB8) are not retained if
power is lost to the relay and then it is restored. The remote control switches
come back in the OFF position (corresponding remote bit is deasserted to
logical 0) when power is restored to the relay.
Remote Bit States
Retained When
Settings Changed
If relay settings are changed, the states of the remote bits (Relay Word bits
RB1–RB8) are retained. If a remote control switch is in the ON position
(corresponding remote bit is asserted to logical 1) before a settings change, it
will come back in the ON position (corresponding remote bit is still asserted to
logical 1) after the settings change. If a remote control switch is in the OFF
position (corresponding remote bit is deasserted to logical 0) before a settings
change, it will come back in the OFF position (corresponding remote bit is still
deasserted to logical 0) after the settings change.
Instantaneous Overcurrent Elements
See the setting sheets in Section 4: Setting the Relay for instantaneous
overcurrent element setting range information.
See Trip Logic on page 3.17 for an example of tripping with a phase
instantaneous overcurrent element (setting TR).
See Reclosing Relay on page 3.22 for an example of using a phase
instantaneous overcurrent element to skip a reclosing shot (setting 79SKP).
See SEL
OGIC Control Equation Variables/Timers on page 3.38 to create
definite-time overcurrent elements with SEL
OGIC control equations
(combining instantaneous overcurrent elements with timers.)
Phase Instantaneous
Overcurrent Elements
Six phase instantaneous overcurrent elements (50P1–50P6) are available (see
Figure 3.4). Their pickup settings (50P1P–50P6P, respectively) are compared
to the magnitude of the maximum phase current (I
P
= maximum of I
A
, I
B
, or
I
C
). The phase current is normally the output of the cosine filter algorithm, but
during CT saturation the phase current can be the output of the adaptive
current algorithm if the pickup setting is greater than eight times nominal
phase current.
Logical 1
LBn
(n = 1 through 16)
ON Position
(Maintained Logical 1
Position)
OFF Position
(Maintained Logical 0 Position)
MOMENTARY Position
(Logical 1 for One Processing Interval)
Relay
Word
Bit