Schweitzer Engineering Laboratories SEL-587Z - Table 4.4 Local Bit LB3 Used as Bus Zone ON;OFF Switch; Example 4.6 Local Bit Controls Bus Protection

4.7
Date Code 20020903 SEL-587Z Instruction Manual
Control Logic
Local Control Switches (NLBn, SLBn, CLBn, PLBn)
EXAMPLE 4.6 Local Bit Controls Bus Protection
Use Local Bit 3 to enable/disable the bus protection. Assume the
scheme trip equations are as follows:
Equation 4.2
L
Consider two possible trip equation modifications to AND the
differential elements and the switch position.
Equation 4.3
or
Equation 4.4
In Equation 4.3, the trip logic cannot assert when the bus zone switch
is OFF, preventing incorrect protection operation. However, because
TRIP1 cannot assert with the switch OFF, the associated LED cannot
assert either. This means if a bus fault occurred during the period
when the bus zone was switched OFF, no indication would be
available. In the second option, Equation 4.4, provides the same
security but also makes the indication available.
Local Bit
States Retained
Power Loss
The states of the local bits (Relay Word bits LB1 through LB8) are retained if
power to the relay is lost and then restored. If a local control switch is in the
ON position (corresponding local bit is asserted to logical 1) when power is
lost, it will come back in the ON position (corresponding local bit is still
asserted to logical 1) when power is restored. If a local control switch is in the
OFF position (corresponding local bit is deasserted to logical 0) when power
is lost, it will come back in the OFF position (corresponding local bit is still
deasserted to logical 0) when power is restored. This is like a traditional
installation with front-panel control switches. If power is lost to the panel, the
front-panel control switches remain in position.
Table 4.4 Local Bit LB3 Used as Bus Zone ON/OFF Switch
Local Bit Label Settings Function
LB3 NLB1 = Bus Zone Switch Enable the switch and
identify functions
SLB1 = Turn ON ON position, i.e., close switch
CLB1 = Turn OFF OFF position, i.e., open switch
PLB1 = MOMENTARY position–not used
TR1 87A1 + 87B1 + 87C1=
OUT1 TRIP1=
TR1 87A1 + 87B1 + 87C1
() * LB3=
OUT1 TRIP1=
TR1 87A1 + 87B1 + 87C1=
OUT1 TRIP * LB3=