GE L90 Instruction Manual page 167

5 SETTINGS
c) STUB BUS
!
PATH: SETTINGS GROUPED ELEMENTS
# STUB BUS
#
MESSAGE
MESSAGE
MESSAGE
MESSAGE
The Stub Bus element protects for faults between 2 breakers in a breaker-and-a-half or ring bus configuration when the line
disconnect switch is open. At the same time, if the line is still energized through the remote terminal(s), differential protec-
tion is still required (the line may still need to be energized because there is a tapped load on a two terminal line or because
the line is a three terminal line with two of the terminals still connected). Correct operation for this condition is achieved by
the local relay sending zero current values to the remote end(s) so that a local bus fault does not result in tripping the line.
At the local end, the differential element is disabled and stub bus protection is provided by a user-selected overcurrent ele-
ment. If there is a line fault, the remote end(s) will trip on differential but local differential function and DTT signal (if
enabled) to the local end, will be blocked by the stub bus logic allowing the local breakers to remain closed.
• STUB BUS TRIGGER: There are three requirements for Stub Bus operation: the element must be enabled, an indica-
tion that the line disconnect is open, and the
ods of setting the stub bus trigger and thus setting up Stub Bus operation:
1. If
STUB BUS TRIGGER
causing zero currents to be transmitted to remote end(s) and DTT receipt from remote end(s) to be permanently
blocked. An overcurrent element, blocked by disconnect switch closed, provides protection for the local bus.
2. An alternate method is to set
ment. The IOC element must operate quickly enough to pick up the
local differential, and send zero currents to the other terminal(s). If the bus minimum fault current is above 5 times
the IOC pickup, tests have confirmed that the
bus fault and prevents tripping of the remote terminal. If minimum stub bus fault current is below this value, then
Method 1 should be used. Note also that correct testing of stub bus operation, when this method is used, requires
sudden injection of a fault currents above 5 times IOC pickup. The assigned current element should be mapped to
appropriate output contact(s) to trip the stub bus breakers. It should be blocked unless disconnect is open.
• STUB BUS DISCONNECT: Selects a FlexLogic™ operand to represent the open state of auxiliary contact of line dis-
connect switch (logic "1" when line disconnect switch is open). If necessary, simple logic representing not only line dis-
connect switch but also the closed state of the breakers can be created with FlexLogic™ and assigned to this setting.
• STUB BUS TRIGGER: Selects a FlexLogic™ operand that causes the
line disconnect is open. It can be set either to "On" or to an IOC element (see above). If the IOC used for the stub bus
protection is set with a time delay, then
the current of this element must cover the stub between CTs of the associated breakers and disconnect switch.
GE Multilin
!
SETTING GROUP 1(6)
STUB BUS FUNCTION:
Disabled
STUB BUS DISCONNECT:
Off
STUB BUS TRIGGER:
Off
STUB BUS TARGET:
Self-reset
STUB BUS EVENTS:
Disabled
STUB BUS TRIGGER
is "On", the
STUB BUS OPERATE
to be the pickup of an assigned instantaneous overcurrent ele-
STUB BUS TRIGGER
STUB BUS OPERATE
STUB BUS TRIGGER
SETTING
STUB BUS
FUNCTION:
Disabled=0
Enabled=1
SETTING
STUB BUS
DISCONNECT:
Off=0
SETTING
STUB BUS
TRIGGER:
Off=0
Figure 5–36: STUB BUS SCHEME LOGIC
L90 Line Differential Relay
!
LINE DIFFERENTIAL ELEMENTS
Range: Disabled, Enabled
Range: FlexLogic™ operand
Range: FlexLogic™ operand
Range: Self-reset, Latched, Disabled
Range: Disabled, Enabled
setting is set as indicated below. There are two meth-
operand picks up as soon as the disconnect switch opens,
STUB BUS OPERATE
operand always pick up correctly for a stub
STUB BUS OPERATE
should use the IOC PKP operand. The source assigned for
FLEXLOGIC OPERAND
AND STUB BUS OP
831012A3.CDR
5.5 GROUPED ELEMENTS
!"
STUB BUS
operand, disable the
operand to pick up if the
5-77
5