Bus Protection
Bus Protection Applications
1
198
Bus protection reliability issues and how GE Multilin products provide enhanced reliability through special
techniques and methods are described in this section. Different bus protection applications and how GE Multilin
products fit into each are provided at the end of the section.
ZONE 1
2
Selector Guide
Complete bus protection comparison
A reference table highlighting the feature set for each protection system
204
B90
Low impedance numerical bus differential system
The B90, a member of the UR Family, features integrated protection and breaker failure for re-configurable LV,
HV, EHV multi-section busbars with up to 24 feeders. Use one or more B90s together to build a sophisticated
protection system that can be engineered to meet specific application requirements. The B90 performs fast and
secure low impedance bus protection with a sub-cycle tripping time of 0.75 cycles.
205
B30
Cost effective bus protection and metering for up to six feeders
The B30, a member of the UR Family, features integrated protection, control and metering for HV and EHV
busbars, providing cost effective, feature-focused busbar protection. Use the B30 to protect busbars with up to
6 feeders in a single three phase zone. The B30 is a cost effective alternative to high impedance schemes, ideal
for breaker-and-half bus schemes, with integrated feeder backup protection and metering. The B30 performs
fast and secure low impedance bus protection with a sub-cycle tripping time of 0.75 cycles.
213
High impedance numerical differential protection system
221
MIB
The MIB is a high impedance numerical bus protection relay designed for fast and selective differential protection
based on the high-impedance circulating current principle. The MIB is used for the protection of busbars,
generators, transformers, reactor against phase-to-phase and phase-to-earth faults. It can be applied for
protection of bus bars of different voltage levels.
HID
High impedance differential module
227
Auxiliary resistors and varistors for high impedance differential schemes. The HID module provides resistors together with voltage limiters (MOVs) normally used in conjunction with a high-speed overcurrent relay to achieve
high impedance differential protection. Use the HID in applications that include high impedance differential protection for busbars and electrical machines, such as transformers, generators or motors, as well as restricted
earth fault protection
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Multilin
197
BUS Protection Applications
Introduction
Incoming Source
Busbars in power systems are the location where transmission lines,
generation sources, and distribution loads converge. Because of
this convergence, short circuits located on or near the busbar tend
to have very high magnitude currents. The high magnitude fault
currents require high-speed operation of the busbar protection to
limit equipment damage. However, this high-speed clearing must
be balanced against the need for security. Tripping incorrectly for
an external fault may cause large outages, and jeopardize power
system stability. The high fault magnitudes increase the possibility
of CT saturation during external faults close to the busbar, and CT
saturation increases the possibility of an incorrect operation of the
busbar protection.
Protection of the busbar may be complicated and varies with
the topology of the bus. Many busbars connect all circuits to one
common segment of busbar. The complication for these buses is
simply the number of connected circuits. However, a specific busbar
may have multiple bus segments, with individual circuits that
connect to different bus segments depending on operating needs.
For such complex buses, busbar protection must be able to protect
each bus segment individually, and dynamically keep track of the
circuits connected to a specific bus segment.
Busbar Protection Techniques
The choice of protection technique used for a specific busbar
depends on the protection requirements for speed and security,
balanced against the cost of implementing a specific solution,
and the operating requirements for a specific bus. Common
methods of protecting busbars include overcurrent-based
interlocking schemes, overcurrent-based differential protection,
high-impedance differential protection, and percentage differential
protection. Interlocking and overcurrent differential protection can
be implemented with any suitable overcurrent relay from GE Multilin,
and performance has to be balanced in terms of speed and security
against the reduced cost of protection. These types of protection
are typically applied on distribution busbars, where fault current
magnitudes are lower and speed is generally less critical than with
transmission busbars.
Differential protection provides high speed fault-clearing necessary
for critical busbars such as transmission busbars, or distribution
busbars where arc flash hazards are a concern. High-impedance
differential protection or percentage differential protection may be
the correct choice depending on the bus configuration and specifics
of application. Both methods address loss of security for external
faults due to CT saturation.
Distribution Busbar Protection
Distribution busbars typically have a single incoming source
supplying multiple radial distribution feeders. For these applications,
the chief concerns for protecting the bus are normally meeting
operating requirements and cost of protection. High speed clearing
to maintain system stability is not normally necessary. Security
198
51
51N
50
50N
Inverse Time Overcurrent
or Reverse Interlocked
Overcurrent
52
51
51
51
51
51N
51N
51N
51N
52
52
52
52
Radial Feeders
Overcurrent based interlocking schemes for simple Bus protection
is maintained by simple time coordination, or via hardwired
communications in reverse interlocking protection schemes.
The most significant factor in terms of operating speed is arcflash hazards. The slow operating time of overcurrent-based bus
protection can result in a larger arc-flash zone or in more restrictive
hazard protection requirements. In these instances, high speed
differential protection is appropriate.
Transmission Busbar Protection
The predominant requirements for protecting transmission
busbars is the speed and security of the protection scheme. These
requirements are built around the need to minimize equipment
damage and maintain system stability during fault events. If these
are the only two considerations for transmission busbar protection,
then high-impedance differential protection may be appropriate.
High-impedance voltage differential protection is a solution to
the challenge of CT saturation during external faults, as the high
impedance of the relay forces the error current due to the saturated
CT back through the CTs instead of the relay operating coil. The relay
uses a setpoint to differentiate between the maximum error voltage
due to CT saturation, and the full voltage of an internal fault.
When also considering the requirements for operating a specific bus,
and the cost of installation, high-impedance differential protection
schemes have some limitations. The major limitation is the strict
requirements on the CT circuits necessary for the high-impedance
scheme. All CTs used in the scheme must have the identical
performance class and turns ratio, must be tapped at full ratio, and
must be dedicated to the bus protection scheme. Additionally, the
secondary lead burden from the each CT to the relay should also
be identical. These requirements are necessary to keep the level of
error voltage as low as possible to prevent maloperation of the relay.
Making modifications to an existing bus protection scheme, such as
adding an additional circuit, may be very challenging in engineering
and installation.
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BUS Protection Applications
In addition, high-impedance differential relays also have some
limitations in terms of normal operations and maintenance. The
relay sees only the voltage from the differential junction point, and
therefore cannot provide any auxiliary protection functions such
as breaker failure, or record the individual currents from each CT
connected to the relay. Data to analyze fault events must therefore
come from additional sources. Another operating limitation of highimpedance differential is the ability to handle routine bus switching,
such as removing a circuit breaker for maintenance. Typical, the
differential relay must be blocked during such switching operations.
While this type of switching is uncommon with the typical single
segment busbar, it is a routine occurrence with multiple segment
busbars, making high-impedance differential schemes difficult to
apply on such multiple segment busbars.
Percentage differential relays, also known as low-impedance
differential relays, provide similar operating speed, and can provide
a similar level of security, as high-impedance differential relays. In
addition, low-impedance relays are simple to apply, as there are
no special requirements for CT performance class, turns ratio, or
secondary lead burden other than good performance practice. A
microprocessor-based low-impedance differential relay measures
input currents from each set of CT, and therefore can provide
auxiliary functions such as breaker failure for every circuit, and
measure and record all currents during a fault event. In addition,
switching events can be routinely handled in the relay, and lowimpedance differential relays can be specifically designed for
multiple segment busbars.
GE Multilin Busbar Protection
GE Multilin provides protective relays that support all busbar
protection techniques, including overcurrent , high-impedance
differential, and percentage (low-impedance) differential. The
protection techniques for overcurrent and high-impedance
differential protection are well known. GE Multilin low-impedance
differential relays are designed to provide specific performance
advantages on applications for all busbars, from single segment
busbars with up to 24 connected circuits, or large multiple segment
busbar configurations. These include the correct restraint while
facing CT saturation during a fault event, detecting the failure of a
CT secondary circuit connected to the relay, protection of multiple
segment busbars, and providing enough digital inputs and outputs
for proper bus protection.
CT Saturation
Saturation of a CT connected to a low-impedance differential relay
during an external fault produces an incorrect differential current
that may cause the relay to operate. GE Multilin relays use adaptive
trip logic to prevent an operation due to CT saturation during
external faults.
The adaptive trip logic is designed around the differential
characteristic. The restraint current of the differential element
is based on the maximum measured current, as opposed to the
traditional magnitude sum of the currents. This ensures ideal
restraint for the actual fault condition, balancing sensitivity
Differential characteristic region
Adaptive Trip logic
and security. The differential element uses a dual slope-dual
breakpoint characteristic matching the differential characteristic
to the saturation performance of the CT ensuring security, while
maintaining sensitivity.
The differential characteristic can correctly restrain for many
external faults when CT saturation occurs. However, the differential
element itself is not enough to ensure correct restraint to external
faults when severe CT saturation occurs. The differential protection
is always supervised by a directional element. The directional
element compares the angle of the measured fault currents. If at
least one current is away from the sum of the remaining currents
by an angle greater than 900, the fault is considered an external
fault. If all fault currents are within 90° of each other, the fault is
considered internal.
During low magnitude fault events, the differential element must
assert and the directional element must declare an internal fault
for the relay to trip. A low magnitude fault event occurs when the
differential current is less than the breakpoint for the second slope
of the element characteristic. During high magnitude faults a CT
saturation detector additionally supervises the differential protection.
During such a fault, the differential protection may operate only if
the differential element asserts while no CT saturation is present,
or when the directional element declares an internal fault when CT
saturation is present. The CT saturation detector simply sets a logic
flag when the restraint current exceeds the setting for the second
breakpoint of the differential characteristic, and the differential
current remains below the first slope of the characteristic.
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199
BUS Protection Applications
CT Trouble
Any differential protection scheme depends on the correctness
of the CT secondary circuits connected to the relay. In addition to
CT saturation and linear CT measurement error, broken or shorted
CT connections cause the relay to see a false differential current.
During normal operations, the false differential current due to an
broken or shorted CT secondary circuit is typically too small to
cause a relay operation. However, during external faults or high load
periods, this false differential current can result in an incorrect relay
operation. The CT Trouble function in the B30 and B90 relays detects
this condition by using a low-set differential element, typically set
around 10% of the least heavily loaded circuit connected to the bus,
that asserts after a settable time delay. The CT Trouble alarm can be
sent via SCADA to operating personnel, or it may be used to block
the differential element.
Multiple segment busbar protection
Multiple segment busbars, such as double busbar and triple
busbar arrangements, are used to balance loads between various
transmission circuits, minimize the physical space required for
a substation, and provide simpler operating procedures when
performing breaker maintenance. The protection challenge for
these busbar configurations actually lies in operations. The busbar
protection must recognize which segment is faulted, and clear only
that segment. Additionally, the busbar protection must not operate
when breakers are transferred between busbar segments.
The figure shows a typical double busbar configuration. For an
internal fault, the busbar protection must identify the faulted bus
segment, and trip the circuit breakers attached to that bus segment.
This requires the busbar protection to use a dynamic bus replica to
track which circuit breakers are connected to the bus segment.
The B90 Bus Differential Relay provides protection of multiple
segment busbars, using a phase-segregated, centralized protection
scheme. The B90 is phase-segregated to simplify the design of the
system. One B90 is used for each phase, and processes only the
AC signals for that phase, eliminating the need for data transfer
and synchronized sampling between the devices. The B90 uses a
centralized protection scheme to also simplify the design of the
system. The relays are in the substation control house, and all
current circuits and control wiring are brought to the control house
as per typical relay installations. No special equipment needs to be
mounted in the substation yard or circuit breaker control cabinets.
Dynamic bus replica
The objective for protecting complex busbar arrangements is
to provide for optimum protection by avoiding blind spots or
unnecessary bus outages. As a rule, this task calls for dynamic
adjustments of boundaries of differential zones of protection, and
can be safely accomplished when using numerical relays. Dynamic
bus replica and CT switching were initially done outside the relay and
as such complicated the bus protection schemes. The B90 and B30
relays provide user programmable logic to create a dynamic bus
replica inside the system, catering for dynamic switching schemes
necessary to make the bus protection scheme secure and reliable.
End-zone fault protection
End fault protection is one use of a dynamic bus replica. When
using line-side CTs, the circuit breaker is included in the bus zone
of protection. When the relay determines the circuit breaker is open
through the use of breaker status contacts, the circuit breaker is
removed from the bus zone. In this case, a fault between the CT
location and the circuit breaker is in a protection blind spot. Since
ZONE 1
Dynamic bus
replica knows
breaker status,
isolator status
ZONE 2
Bus side CT:
bus protection
must detect this
fault when CB is
open
T
1
2
3
Zone 2 trips CB-3,
CB-4, and T for
this fault, based
on dynamic bus
replica
End-zone fault:
bus protection
must detect this
fault when CB is
open
Re-configurable busbar with zone boundaries
200
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4
5
BUS Protection Applications
End Zone Fault - Bus side CTs
Flexible input and output options
End Zone Fault - Line side CTs
the B90 is still measuring the current, a simple overcurrent function,
can be used to determine the fault exists, and send a direct transfer
trip signal to the circuit breaker on the other end of the transmission
line. Without the use of a dynamic bus replica, this fault would
cause an operation of the bus protection for what is essentially an
external fault.
Bus side CTS
Bus side CTs provide another illustration of the use of a dynamic
bus replica. Similar situation occurs for bus-side CTs. A fault
between the circuit breaker and the CT is in a blind spot of the
bus protection. To clear the fault the busbar must be tripped, but
the differential zone will not see this fault. Similar to the end-zone
fault, this situation requires using breaker position as a connection
status for the associated current. The fault is cleared sequentially.
First, protection of the circuit, fed from the CT, responds to the fault
and opens the breaker. When the breaker opens, the CT current
is removed from the differential zone by the dynamic bus replica.
As a result, the zone expands to the bus-side pole of the opened
breaker, the fault becomes internal, and the bus protection clears
the busbar.
Traditional busbar protection and control schemes typically use a
lockout relay to open the connected circuit breakers when a bus
fault is detected. For simple busbars, this is the most effective
way to open the circuit breakers. GE Multilin relays can replace the
separate lockout relay with mechanically latched output contacts.
Once asserted, these contacts latch closed until manually reset via
contact input, pushbutton control from the relay HMI, or SCADA
command.
For applications where the bus protection relay will be used for
control and status information, or the relay is protecting a complex
busbar where the status of circuit breakers and isolator switches
is vital, the number of inputs and outputs is quite large. Taking a
double busbar example with 5 feeders and a tie breaker, the relay
requires 12 output contacts (trip and close for each circuit breaker),
and 16 to 32 contact inputs (1 or 2 status inputs for each circuit
breaker and isolator switch). This many inputs and outputs may be
beyond the physical limits of an individual relay. For this reason, GE
Multilin provides an additional B90 to add a combination of up to
96 additional inputs and 84 additional outputs for a bus protection
system. The relays can communicate via Direct I/O communications
to pass digital input status and control output contacts. Direct I/O
is a robust communications protocol that uses copper or fiber optic
communications. The protocol is very reliable, and includes 32-bit
CRC error checking, and may integrate up to 16 different relays on
one communications circuit.
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201
BUS Protection Applications
Typical Applications
This section highlights some typical GE Multilin numerical bus relay applications for different bus configurations. GE Multilin also provides
engineered solutions using B90 bus protection relays and supports a variety of bus topologies. In some cases more details can be requested
by contacting GE Multilin. This section is not intended as a comprehensive list of possible applications. For questions about the correct relay
for a specific application, please contact GE Multilin.
Typical Functions
Single Bus Bar, 8 feeders or less, 1 Zone
ZONE 1
1
2
3
Double Busbar, 24 feeders or less, Multiple Zone
87B
Bus Differential
86
Lockout auxiliary
50/51
TOC and IOC (Phase, ground, neutral)
Functions
Typical Product Order Code
Typical Functions (Phase
segregated bus differential)
+ check zone
Alternative
+ check zone
Alternative (high Impedance
bus differential)
+ Harsh Environment
Conformal Coating
Alternative
Auxiliary lockout relay
B90-N00-HPH-F8H-H6C-L8H-N6C-S8H-U6D-WXX
B90-N00-HPH-F8H-H6C-L8H-N6C-S8H-U6D-WXX
B30-N03-HPH-F8N-H6C-L8N-N6C-S8N-U6C-WXX
B30-N03-HPH-F8N-H6C-L8N-N6C-S8N-U6C-WXX
MIB-3-0-HI-C-E-000-00
B90-N00-APH-F8H-H6C-L8H-N6C-S8H-U6D-WXX
B30-N03-APH-F8N-H6C-L8N-N6C-S8N-U6C-WXX
HEA61-A-RU-220-X2
Typical Functions
ZONE 1
87B
Bus Differential
87B
Check Zone
ZONE 2
86
Lockout auxiliary
50/51
TOC and IOC (Phase, ground, neutral)
50BF
Breaker Failure
End Zone Fault
23
1
2
24
3
21
22
Breaker-and-Half Busbar, 24 feeders or less, Multiple Zone
ZONE 1
1
1
3
21
3
21
22
22
Functions
Typical Product Order Code
Typical Functions (Phase
segregated bus differential)
Alternative (high Impedance bus
differential)
+ Harsh Environment Conformal
Coating
Auxiliary lockout relay
B90-N03-HPH-F8H-H6C-L8H-N6C-S8H-U6C-WXX
(3 B90s required)
MIB-3-0-HI-C-E-000-00
Typical Functions
87B
Bus Differential
87B
Check Zone
86
Lockout auxiliary
50/51
TOC and IOC (Phase, ground, neutral)
Functions
Typical Product Order Code
Typical Functions (Phase
segregated bus differential)
B90-N03-HPH-F8H-H6C-L8H-N6C-S8H-U6C-WXX
(3 B90s required)
Alternative (high Impedance bus
differential)
MIB-3-0-HI-C-E-000-00
+ Harsh Environment Conformal
Coating
B90-N03-APH-F8H-H6C-L8H-N6C-S8H-U6C-WXX
(3 B90s required)
Auxiliary lockout relay
HEA61-A-RU-220-X2
ZONE 2
202
B90-N03-APH-F8H-H6C-L8H-N6C-S8H-U6C-WXX
(3 B90s required)
HEA61-A-RU-220-X2
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BUS Protection Applications
Two Section Busbar with a Bus Tie, 24 feeders, Multiple zones
23
ZONE 1
1
2
24
3
ZONE 2
12
13
22
Double Busbar with Transfer Bus and Tie-Breaker
87B
Bus Differential
87B
Check Zone
86
Lockout auxiliary
50/51
TOC and IOC (Phase, ground, neutral)
Functions
Typical Product Order Code
Typical Functions (Phase
segregated bus differential)
B90-N03-HPH-F8H-H6C-L8H-N6C-S8H-U6C-WXX
(3 B90s required)
Alternative (high Impedance bus
differential)
MIB-3-0-HI-C-E-000-00
+ Harsh Environment Conformal
Coating
B90-N03-APH-F8H-H6C-L8H-N6C-S8H-U6C-WXX
(3 B90s required)
Auxiliary lockout relay
HEA61-A-RU-220-X2
Typical Functions
ZONE 1
ZONE 2
23
Typical Functions
24
22
87B
Bus Differential
87B
Check Zone
86
Lockout auxiliary
50/51
TOC and IOC (Phase, ground, neutral)
Functions
Typical Product Order Code
Typical Functions (Phase
segregated bus differential)
B90-N03-HPH-F8H-H6C-L8H-N6C-S8H-U6C-WXX
(3 B90s required)
Alternative (high Impedance bus
differential)
MIB-3-0-HI-C-E-000-00
+ Harsh Environment Conformal
Coating
B90-N03-APH-F8H-H6C-L8H-N6C-S8H-U6C-WXX
(3 B90s required)
Auxiliary lockout relay
HEA61-A-RU-220-X2
ZONE 3
1
2
Triple Busbar
21
23
Typical Functions
24
ZONE 1
ZONE 2
ZONE 3
21
1
2
22
19
87B
Bus Differential
87B
Check Zone
86
Lockout auxiliary
50/51
TOC and IOC (Phase, ground, neutral)
Functions
Typical Product Order Code
Typical Functions (Phase
segregated bus differential)
B90-N03-HPH-F8H-H6C-L8H-N6C-S8H-U6C-WXX
(3 B90s required)
Alternative (high Impedance bus
differential)
MIB-3-0-HI-C-E-000-00
+ Harsh Environment Conformal
Coating
B90-N03-APH-F8H-H6C-L8H-N6C-S8H-U6C-WXX
(3 B90s required)
20
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203
BUS Protection Applications
Bus Protection Selector Guide
PROTOCOLS
COMMS
MONITORING &
METERING
AUTOMATION
PROTECTION & CONTROL
APPS
FEATURES
ANSI
Low impedance Bus differential
High impedance Bus differential
High impedance Restricted Ground Fault
Typical Operating Time (cycles)
Bus differential
IOC, Ground/Neutral/Phase
TOC, Ground/Neutral/Phase
Overvoltage Auxiliary/Neutral
Phase Undervoltage
Current Transformer Supervision
Breaker Failure
Breaker Flashover
Lockout Functionality
Dynamic Bus Replica
Programmable Logic
FlexElements™
Settings Groups
Non-volatile latches (up to)
Contact Inputs Programmable - (up to)
Contact Outputs Programmable - (up to)
Virtual Inputs - (up to)
Virtual Outputs - (up to)
Direct Inputs/Outputs
User-Programmable LEDs (up to)
User-Programmable Push Buttons (up to)
User-Programmable Self Test
User Definable Displays
User Programmable Self-Test Contact
Timers
Selector Switch
Digital Counters
Digital Elements
IRIG-B Input
Current
Voltage
Symmetrical Components
Power - Apparent, Real, Reactive
Energy
Power Factor
Frequency
Event Recorder - Number of Events
Oscillography
Trip/Close Coil Supervision
RS232 Port
RS485 Port
Ethernet Port (Fiber and Copper, up to)
Direct Fiber Communications (800nm, 1330nm, 1550nm)
ModBus (RTU and TCP/IP)
DNP 3.0
IEC60870-5-104
UCA2/MMS
IEC 61850
Simple Network Time Protocol (SNTP)
HTTP
TFTP
87B
87B
87RGF
87B
50G/N/P
51G/N/P
59X/N
27P
50BF
MIB
•
•
<2
•
•
86
•
2
4
4
4
•
•
24
•
•
•
•
•
B30
B90
•
•
<1
•
G/N/P
G/N/P
X/N
•
•
•
•
•
•
•
•
6
16
80
64
32
64
•
48
12
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
1024
•
•
•
•
1
•
•
•
•
•
•
•
•
•
<1
•
G/N/P
G/N/P
•
•
•
•
•
•
•
•
6
16/box
96/box
64/box
32
64
•
48/box
12/box
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
1024
•
•
•
•
1
•
•
•
•
•
•
•
•
•
For the most current comparison list see: www.GEMultilin.com/selector/bus.pdf
204
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0216-v4