Stub Bus - GE UR Series Instruction Manual

5 SETTINGS
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PATH: SETTINGS GROUPED ELEMENTS
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STUB BUS

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The Stub Bus protects for faults between 2 breakers in a breaker-and-a-half or ring bus configuration when the line discon-
nect switch is open. At the same time, if the line is still energized through the remote terminal(s), differential protection 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.
There are three requirements for Stub Bus operation: the element be enabled, an indication that the line disconnect is
open, and the
STUB BUS TRIGGER
thus setting up Stub Bus operation:
1. If is set to "On", the STUB BUS OPERATE operand picks up as soon as the disconnect switch
STUB BUS TRIGGER
opens, causing zero currents to be transmitted to remote end(s) and DTT receipt from remote end(s) to be perma-
nently blocked. An overcurrent element, blocked by disconnect switch closed, provides protection for the local bus.
2. An alternate method is to set
The IOC element must operate quickly enough to pick up the "STUB BUS OPERATE" operand, disable the local differ-
ential, and send zero currents to the other terminal(s). If the bus minimum fault current is above 5 times the IOC pickup
setting, tests have confirmed that the "STUB BUS OPERATE" operand will always pick up correctly for a stub bus fault
and prevent 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 con-
tact(s) to trip the stub bus breakers. It should be blocked unless disconnect is open.
STUB BUS DISCONNECT:
This setting selects a FlexLogic™ operand to represent the open state of auxiliary contact of line disconnect switch (logic
"1" when line disconnect switch is open). If necessary, simple logic representing not only line disconnect 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 "STUB BUS OPERATE" operand to pick up if the line disconnect is open.
As described above, it can be set either to "On" or to an IOC element. If the IOC to be used for the stub bus protection is set
with a time delay, then
STUB BUS TRIGGER
of this element must cover the stub between current transformers of the associated breakers and disconnect switch.
GE Power Management
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SETTING GROUP 1(8)
STUB BUS FUNCTION:
Disabled
STUB BUS DISCONNECT:
Off
STUB BUS TRIGGER:
Off
STUB BUS TARGET:
Self-reset
STUB BUS EVENTS:
Disabled
setting is set as indicated below. There are two ways of setting the stub bus trigger and
to be the pickup of an assigned instantaneous overcurrent element.
STUB BUS TRIGGER
should use the IOC PKP (pickup) operand. The source assigned for the current
L90 Line Differential Relay
5.5 GROUPED ELEMENTS
LINE DIFFERENTIAL ELEMENTS
Range: Disabled, Enabled
Range: FlexLogic™ operand
Range: FlexLogic™ operand
Range: Self-reset, Latched, Disabled
Range: Disabled, Enabled
5.5.5 STUB BUS
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STUB BUS
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