Post on 06-Mar-2018
IEEE C37.234 Guide for Protective
Relay Application to Power
System Buses
B.Kasztenny (Chairman), S.Conrad (Vice-Chairman),
P.Beaumont, K.Behrendt, O.Bolado, J.Boyle, G.Brunello,
J.Burger, F.Calero, S.Chano, G.Dalke, A.Darlington, H.DoCarmo,
D.Fontana, Z.Gajic, J.Holbach, L.Kojovic, F.Lopez, D.Lukach,
D.McGinn, J.Miller, P.Mysore, J.O'Brien, B.Pickett,
S.Sambasivan, G.Sessler, V.Skendzic, J.Smith, D.Tholomier,
M.Thompson, J.Uchiyama, D.Ware, D.Weers, R.Whittaker,
R.Young, S.Zocholl
Presentation to the Main Committee of PSRC, January 14, 2010, Orlando, FL
Table of Contents
• Definitions
• Bus configurations
• Introduction to bus protection
• Relay input sources
• Bus protection methods
• Application of bus protection schemes
• Annexes
Definitions
• 23 new terms defined
• Bus protection and primary equipment
breaker substitution – Temporary usage of a bus tie breaker in a
multiple bus configuration to substitute for one of the network
element’s circuit breakers, typically for the maintenance of the latter;
also known as breaker transfer
breaker substitution – Temporary usage of a bus tie breaker in a
multiple bus configuration to substitute for one of the network
element’s circuit breakers, typically for the maintenance of the latter;
also known as breaker transfer
check zone – Nonselective part of a multi-zone bus protection
system measuring current flows around the entire station and
supervising selective tripping from individual bus zones of protection
check zone – Nonselective part of a multi-zone bus protection
system measuring current flows around the entire station and
supervising selective tripping from individual bus zones of protection
stub bus – Area of a bus or line that becomes isolated from the
original zone of protection or an area that loses protection due to the
loss of sensing to zone protection relays
stub bus – Area of a bus or line that becomes isolated from the
original zone of protection or an area that loses protection due to the
loss of sensing to zone protection relays
Bus design considerations
• Continuity of service for the bus and essential network elements
• Equipment maintainability and network switching flexibility
• Economical and footprint constraints
• Sectionalizing requirements to avoid exceeding breaker fault duties
• Ease of future bus expansion
Bus arrangements
• Single bus
• Main and transfer bus
• Double-bus double-breaker
• Double-bus single-breaker
• Breaker-and-a-half
• Ring bus
Main and transfer bus
Bus zone
Transfer bus
TB
Main and transfer bus
Bus zone
Transfer bus
TB
Introduction to bus protection
• Zones of protection
• Bus protection methods
• Scheme selection guidelines
Zones of protection
Bus zone
Dynamic zones of protection
Dynamic zones of protection
Dynamic zones of protection
Zones of protection
Over-tripping spot for bus protection
Blind spot for network
element protection
Bus
Over-tripping spot for network element protection
Blind spot for bus protection
Bus
Bus protection methods
• Differential
– Differentially-connected overcurrent
• Instantaneous
• Time-delayed
– Percentage-restrained differential
• Restrained
• Advanced microprocessor based
– High-impedance differential
• Resistor-stabilized overcurrent
• High-impedance
– Partial differential overcurrent
– Fault bus
Bus protection methods
• Zone-interlocked schemes
– Simple blocking
– Directional blocking
• Time-coordinated relays overlapping the bus
• Protection (sensors) built into the gas isolated
switchgear*
* Not covered in the Guide
Scheme selection criteria
• Bus arrangement and flexibility
– Fixed vs. switchable buses
• Availability and characteristics of CTs
• For reconfigurable buses, availability of
auxiliary contacts of disconnect switches
• Performance requirements
– Security, Selectivity, Speed, Sensitivity
• Cost and complexity
Scheme
selection
Dif
fere
nti
ally
co
nn
ect
ed
ov
erc
urr
en
t
Pe
rce
nta
ge
-re
stra
ine
d
dif
fere
nti
al
Ad
van
ce
d p
erc
en
tage
-
rest
rain
ed
dif
fere
nti
al
Hig
h-i
mp
ed
an
ce d
iffe
ren
tia
l
Pa
rtia
l
dif
fere
nti
al
ov
erc
urr
en
t
Zon
e in
terl
ock
ed
sim
ple
blo
ckin
g
Zon
e i
nte
rlo
cke
d d
irec
tio
na
l
blo
ckin
g
Tim
e c
oo
rdin
ate
d r
ela
ys
tha
t
ov
erl
ap
th
e b
us
zon
e
Breaker/Bus Arrangements
Fixed bus arrangements R R R
Switchable bus arrangements R1 N
1
Bus Sectionalized with switches R R R
Buses with low short circuit levels R R R
Available CTs
Dedicated CTs available R R R
Shared CTs with other protection R R N R R
Unmonitored network elements N N N R R R R
CTs with unmatched ratios N R R N2 R R
CTs with low accuracy class N R3 R
4
Performance
Selectivity H H H H L H H L
Speed H5 M H H L
6 M M L
Sensitivity H5 M M H L M M M
Security L M H H L M M H7
Relay input sources
• Current transformers
– Types
– Accuracy classes
– Equivalent circuit & time to saturation
– No universal CT requirements
• Voltage Transformers
– Voltage trip supervision
– Directional blocking schemes
• Position of switches and breakers
Detailed scheme review
• Section 7 gives in-depth review of each
method following a consistent pattern
– Theory of operation
– Setting considerations
– CT requirements
–Application considerations
Example – High-impedance scheme
Voltage setting:
• Above the maximum voltage for an
external fault assuming that one CT
saturates completely
• High enough so that pickup current is
above the short circuit current on the
secondary of any PT or station service
transformer inside the bus zone
• Below the accuracy class voltage
rating of the lowest accuracy class CT
in the differential circuit
• Low enough so that pickup current is
below the minimum fault current for
the bus
ZSR50
59
MOV
86
87
Example – High-impedance scheme
CT requirements:
• CTs dedicated to bus protection
(cannot be shared)
• Equal CT ratios*
• The accuracy class voltage rating of
the CT with the lowest accuracy class
above the selected voltage setting,
with margin
ZSR50
59
MOV
86
87
* Ratio matching covered but discouraged
Application of bus protection
• Partial differential
– Loads
– Capacitor banks
– Application with overcurrent and distance relays
• Combined bus and transformer zone
• Buses with directly connected grounding
transformers
• Application of auxiliary transformers
– Generally discouraged
Application of bus protection
• Applications with paralleled CTs
– Generally discouraged
– Guidelines included
Application of bus protection
• Application of auxiliary tripping relays
– Lockout relays
– Non-lockout relays
– Ratings
• Automatic reclosing after bus faults
• Dynamic bus replica
• Check-zone
• Voltage trip supervision
Dynamic bus replica
Position of switches and breakers
89a 89b
Position
Filtering
Logic
Switch
Position
Discrepancy
Alarm
Bus Protection System
Binary Inputs
Auxiliary contacts Scheme output
89a 89b Declared position Discrepancy alarm
On Off Closed Normal
Off On Opened Normal
On On Closed Alarm
Off Off Closed Alarm
“If not opened, then closed” logic
In-service transfer
In-service transfer
In-service transfer
Check zoneCheck zone
Application of bus protection
• Application of CT trouble detection
– Detection methods
– Fallback strategies
• Reliable, selective tripping at the
differential zone boundary
– Line-side CT
– Bus-side CT
– Bus coupler considerations
– The role of Breaker Failure protection
Line-side CT
CB close command
Trip Network
Element
Instantaneous Overcurrent (50/CT-2)
Bus coupler considerations
Bus coupler considerations
Application of bus protection
• CT column ground fault protection
• In-zone grounds
– Surge arresters
– Safety grounds and circulating current while
testing
– In-zone grounding of out-of-service elements
• In-service transfer of network elements
and breaker substitution
Breaker substitution
C-1
CT-1
CB-1
BSw-1
CT-5
CB-4
CT-4
DSw-2DSw-1
C-2
CT-2
CB-2
BSw-2
DSw-4DSw-3
C-3
CT-3
CB-3
BSw-3
DSw-6DSw-5
BUS 1
BUS 2
Application of bus protection
• Stub bus considerations
• Breaker Failure considerations
• Backup protection
– Local backup
• Duplicated relays
• BF, batteries, wiring
• Reverse-looking distance relays
• Overcurrent relays
–Remote backup
Annexes
• Setting example for a high-impedance
scheme (Annex A)
• Logic example for double-bus single-
breaker configuration (Annex B)
– Bus and Breaker Failure protection
– Two zones, check zone and voltage supervision
– In-service transfers and breaker substitution
• Setting guidelines for differentially
connected OC schemes (Annex C)
C37.234 Highlights
• Complex bus arrangements and switching
• Advanced bus protection topics
(reconfigurable buses, µP relays)
• Balanced coverage of high- and low-
impedance schemes
• Protection scheme selection guidelines
• CT requirements given per scheme
• List of application considerations
• Detailed examples for most common schemes