Busbar protection

1. ©ABBGroup-1-
14-Nov-07
Busbar ProtectionProtection Application
Handbook

2. ©ABBGroup-2-
14-Nov-07
Busbar protection
Need for Bus bar protection
in its absence fault clearance takes place in Zone-II of distance
relay by remote end tripping
This means slow and unselective tripping and wide spread black
out
Greater damage at fault point
Indirect shock to connected equipments like shafts of
Generator and windings of transformer.
Effect of delayed clearance

3. ©ABBGroup-3-
14-Nov-07
Busbar protection
Types of Switchgear
Open-air switchgear
Metal enclosed switchgear
Air-insulated
SF6-insulated

4. ©ABBGroup-4-
14-Nov-07
Busbar protection
Requirements
Short tripping time
Detect internal faults
Stable at external faults
Disconnect only faulty part of bus
Secure against mal operation due to
Auxiliary contact failure
Human mistakes
Faults in secondary circuits

5. ©ABBGroup-5-
14-Nov-07
Busbar protection
Types of BB Protections
High impedance
Medium impedance
Low impedance
Block able O/C relay ( For radial systems in distribution
systems)

6. ©ABBGroup-6-
14-Nov-07
Busbar protection
High impedance bus differential relay
Basic features
SETTING VR > IF ( RCT + 2 RL)
VK > 2 VR
FOR VR TO BE ZERO FOR
EXTERNAL FAULT
nA = nB 1 + RA / ZA
1 + RB / ZB
n = TURNS RATIO
R = RCT + 2 RL
Z = MAGNETIZING IMPEDANCE
A B
RCT
RL
VR

7. ©ABBGroup-7-
14-Nov-07
Busbar protection
Limitations of High impedance differential
relay
Puts stringent requirements on CTs
Need for dedicated CTs
Identical CT ratios , magnetising impedances
Aux CTs not acceptable
Inability to cope with increasing fault levels

8. ©ABBGroup-8-
14-Nov-07
Busbar protection
T MD
n MD
D 1D 2
IR1
Ud3
US
RADSS medium
impedance relay
dR

9. ©ABBGroup-9-
14-Nov-07
Busbar protection
Distributed installation
ABB Network Partner AG REB 500
Bay Unit
C
E
ABB Network Partner AG REB 500
Bay Unit
C
E
ABB Network Partner AG REB 500
Bay Unit
C
E
ABB Network Partner AG REB 500
Bay Unit
C
E
Central Unit
ABB Network Partner AG REB 500
C
E
REB500 - Numerical Busbar
and Breaker Failure Protection

10. ©ABBGroup-10-
14-Nov-07
Busbar protection
Central installation
REB004aE
Cubicle
ABB NETWORK CONTROL & PROTECTION
Cubicle
E
C
SCS/SMS
REB500 - Numerical Busbar and Breaker Failure Protection

11. ©ABBGroup-11-
14-Nov-07
Busbar protection
Advantages of medium/ Low impedance
relays
Free from any need for Identical CT ratios or matched CT s
Other relays can be included in the same CT core
Increasing fault levels have no impact

12. ©ABBGroup-12-
14-Nov-07
Busbar protection
Gas Density Detectors
Applicable only in GIS
Usually, gas density detectors give alarm
May require intertrip to remote substations

13. ©ABBGroup-13-
14-Nov-07
Busbar protection
Blockable O/C relays

14. ©ABBGroup-14-
14-Nov-07
Busbar protection
Back-up Protection
System protection
Duplication of local busbar protection

15. ©ABBGroup-15-
14-Nov-07
Busbar protection

16. ©ABBGroup-16-
14-Nov-07
Busbar protection
RADSS - Ultrahigh-speed percentage bias
Bus Differential Relay
• Protection for buses or short lines
• 1-3ms fault detection, 8-13ms to trip
• Fault sensitivity 20% of rated current
• No maximum fault current restrictions
• No practical limit to number of circuits to the bus
• No dedicated or matched CTs required and
CTs can be of different ratios and manufacture
• Long CT leads acceptable- up to 68 ohms
at 5A or 1705 ohms for 1A circuits
• Moderately High impedance (165-301 ohms)
in diff circuit.
• Selectable percentage restraint slope,
50 to 85%.
• Compact summation CT version available
• Adaptable to different bus configurations

17. ©ABBGroup-17-
14-Nov-07
Busbar protection
Busbar arrangements
Single bus single breaker
Single bus with bus sectionaliser
Main and transfer bus
Double bus single breaker with bus coupler
Double bus double breaker
Double bus one and a half breaker
Four breaker mesh
Ring busbar

18. ©ABBGroup-18-
14-Nov-07
Busbar protection
Diff. relay
1000/5 200/5 500/5
3.5 A 5 A5 A
500 A200 A700 A
0.7 A 0.2 A 0.5 A
5/1 5/0.2 5/0.5
RADSS IN SINGLE BUS

19. ©ABBGroup-19-
14-Nov-07
Busbar protection
# SINGLE ZONE DISCONNECTION UNIT
SINGLE BUSBAR SYSTEM WITH SECTIONALIZING ISOLATOR
RADSS
A
RADSS
B
BUS - BBUS - A
#

20. ©ABBGroup-20-
14-Nov-07
Busbar protection
# CT DISCONNECTION UNIT
SINGLE BUSBAR SYSTEM WITH SECTIONALIZING BREAKER
RADSS
B
RADSS
A
#
BUS - BBUS - A

21. ©ABBGroup-21-
14-Nov-07
Busbar protection
SINGLE BUSBAR SYSTEM WITH AUX. BUS & CT ON LINE SIDE
MAIN BUS
RADSS
AUX. BUS

22. ©ABBGroup-22-
14-Nov-07
Busbar protection
USE OF DIRECTIONAL RELAY IN BC CIRCUIT FOR AUX. BUS SELECTIVITY
MAIN BUS
AUX. BUS
DIR.
RELAY
RS/2
RS/2 Rd

23. ©ABBGroup-23-
14-Nov-07
Busbar protection
TYPE AB
DA
DB
L1 LX
L1 : 0 LX : 0
AB : 0
: 1: 1: 1
: 1 : 1
: 2 : 2
: 2 : 2
: 2
A
B
A
B
: 4
: 3 : 4 : 3

24. ©ABBGroup-24-
14-Nov-07
Busbar protection
REQUIREMENTS ON THE ISOLATOR AUXILIARY CONTACTS
Isolator Aux. Contact ‘a’ should
close before the primary contact
closes and
Aux contact’ b’ closes after the
primary contact opens.
Throw-over relay
100%0%
Main
contact
Aux.
Contact
a
Aux.
Contact
b
a b
O C

25. ©ABBGroup-25-
14-Nov-07
Busbar protection
DOUBLE BUSBAR SYSTEM WITH TRANSFER BUS
BUS - A
BUS - B
AUX. BUS

26. ©ABBGroup-26-
14-Nov-07
Busbar protection
APPLICATION OF RADSS TO ABC BUS CONFIGURATION
• AUX CTs FOR RATIO CORRECTION
• CHANGEOVER RELAYS FOR CT & TRIP CIRCUITS
• SINGLE ZONE RECONNECTION UNIT TO CONNECT TWO
ZONES TO SINGLE ZONE WHEN BOTH BUSES ARE
INTERCONNECTED THROUGH ISOLATORS.
• BUS COUPLER CT DISCONNECTION UNIT FOR FAULT
BETWEEN BUS COUPLER BREAKER AND CT
• DIRECTIONAL RELAYS FOR FAULTS ON TRANSFER BUS
• HIGH SPEED TRIP RELAYS

27. ©ABBGroup-27-
14-Nov-07
Busbar protection
1½- BREAKER SYSTEM
RADSS - A
B
RADSS - B
BUS - A
BUS -
L1 L3 L5
L4 L6L2

28. ©ABBGroup-28-
14-Nov-07
Bus bar protection
CBIP manual on Protection
of Generators, generator
transformers and 220kV
and 400 kV networks

29. ©ABBGroup-29-
14-Nov-07
Busbar protection
1.0 GENERAL1.0 GENERAL
• Bus bar protection is provided for high speed sensitive clearance
of bus bar faults by tripping all the circuit breakers connected to
faulty bus
• Recommendations for providing bus bar protection at different
voltage levels are as follows:
(i) Bus bar protection must be provided in all new 400kV and 220kV
substations as well as generating station switchyards.
(ii) For existing substations, provision of bus bar protection is
considered must at 400kV level and at 220kV level.
In case of radially fed 220kV substations, having more than one bus
it is desirable to have bus bar protection but is not a must.

30. ©ABBGroup-30-
14-Nov-07
Busbar protection
2.0 Special Comments2.0 Special Comments
2.12.1
• The D.C. supply for bus bar protection shall be from an independent
feeder
2.22.2
• Faults lying between C.B and C.T. shall be cleared from one side by
opening of C.B on bus bar protection operation
• However clearing of fault from other side shall be through breaker
failure protection/back up protection

31. ©ABBGroup-31-
14-Nov-07
Busbar protection
2.32.3
• 3 Phase trip relays shall be provided for each circuit breaker which
shall also initiate B.F.P. of concerned breaker
2.42.4
• Length of secondary leads should be kept as minimum as possible.
• Where lead runs are excessive, an increase in wire size or use of
parallel conductors are meant to reduce lead resistance
2.52.5
• In case of existing substations where current transformers are of
different ratios, biased type differential protection is recommended
for use

32. ©ABBGroup-32-
14-Nov-07
Busbar protection
3.0 Setting Criteria3.0 Setting Criteria
3.13.1
• C.T wire supervision relays should be set with a sensitivity such that
they can detect C.T secondary open circuit even in case of least
loaded feeder
3.23.2
• Bus bar differential protection should have overall sensitivity above
heaviest loaded feeder current unless a separate check zone has
been provided
• In case where faults currents are expected to be low, the protection
should be sensitive enough to take care of such expected low fault
current

33. ©ABBGroup-33-
14-Nov-07
Busbar protection
3.33.3
• In case of voltage operated high impedance type protection, the
voltage setting should be above expected voltage developed across
the relay during maximum through fault current condition
• In case of current operated relays for stability under through fault
condition, external resistance is to be set such that voltage
developed across relay and resistance combination is below the
voltage required for forcing required relay operating current

34. ©ABBGroup-34-
14-Nov-07
Busbar Protection
CBIP manual on Reliable
fault Clearance and Back-
UP Protection for EHV
and UHV Transmission
Network

35. ©ABBGroup-35-
14-Nov-07
Busbar protection
Bus bars
In the above paragraphs some important application
aspects connected with bus bar protection and some
recommendations have been brought out, and these
should be considered. A few of these are brought out
below.
A dedicated bus bar protection shall be provided
where security of supply is of paramount importance,
fault current levels are high, and the non-
discriminative fault clearance and relatively slow
clearance times are unacceptable.

36. ©ABBGroup-36-
14-Nov-07
Busbar protection
Bus bars
Bus bar protections being of unit type, back-up
protection is provided either by duplicating the bus
bar protection, or by reverse zone of line distance
protection, or by time delayed distance relays in the
remote stations, or by directional back-up over
current relays.
Where the main bus bar protection is provided by the
second zone elements of distance relays (i.e., when
no bus bar protection is provided), back-up
protection can be considered as being provided by
the 3rd zone elements of distance relays in the more
remote stations.

37. ©ABBGroup-37-
14-Nov-07
Busbar protection
Bus bars
For substations of high strategic importance or
where the bus arrangements are complex, the
complete bus bar protection should be fully
duplicated.
In cases where the burn-through time of SF6
switchgear is considered to be shorter than the
tripping time from remote back-up protection, then
also the bus bar protection must be duplicated.
High impedance bus bar protection is not
recommended when CT ratios are different and for
complex bus bar arrangements.

38. ©ABBGroup-38-
14-Nov-07
Busbar protection
Bus bars
As per the current practice bus bar protection is
provided for all substations at 765kV, 400kV, 220 kV
and for generating station switchyards. No change is
proposed in this practice. Reference may be made to
CBIP Manual No 274 “Protection of Generators,
Transformers and 220kV and 400kV Networks”
which gives details of current practices followed.

39. ©ABBGroup-39-
14-Nov-07
Busbar protection
Bus bars
For 132 kV substations too, it is recommended that
bus bar protection be provided, since failure to clear
a bus fault in a short time may lead to wide spread
tripping. The type of bus bar protection scheme
recommended for 132 kV system will depend upon
the quantum of power handled and the attendant
risks for loss of power supply and consequential
revenue loss.

40. ©ABBGroup-40-
14-Nov-07
Busbar protection
Bus bars
Many a times, periodic testing of bus bar protection
to check the healthiness of the relay and associated
circuits is difficult since shutdowns of the substations
or bus bars are not easily available. Thus the
problems, if any, in the protection or in the
associated circuits, gets discovered only when a fault
takes place and either the relay fails to operate or
has operated inadvertently.

41. ©ABBGroup-41-
14-Nov-07
Busbar protection
Bus bars
With modern numerical relays where self supervision
and on line monitoring of the relay and associated
circuits are possible, the task of testing gets
simplified considerably and these may be preferred
for this reason. The application of Numerical Relays
for bus bar protection therefore assumes a special
status.
Duplication of bus bar protection is recommended in
all substations where failure to operate may cause
disturbances in the grid

42. ©ABBGroup-42-
14-Nov-07
Busbar protection
Bus bars
For the 400kV and 765 kV substations that fall in this
class of substations, duplication of bus bar protection
is strongly recommended. It may be noted that even
those 400 kV substations, which do not fall in this
category initially, may become critical in future as the
system grows. In view of constraints in adding a
second bus bar protection at a later date, duplication
may be considered desirable from the initial stage
itself.

43. ©ABBGroup-43-
14-Nov-07
Busbar protection
Bus bars
In view of continuing thrust on station automation
and SCADA application, the preference towards
Numerical Protection schemes for all the elements of
a substation becomes quite beneficial.

44. ©ABBGroup-44-
14-Nov-07
Busbar Protection
Settings
Protection Application
Handbook

45. ©ABBGroup-45-
14-Nov-07
Busbar protection
T MD
n MD
D 1D 2
IR1
Ud3
US
dR

46. ©ABBGroup-46-
14-Nov-07
Busbar protection
RADSS CHARACTERISTICS APPLYING TO EXTERNAL AND INTERNAL FAULTS RELAY SLOPE S = 0.8
Restraint characteristic on external fault
ZL = RLX linear resistance
Id1 = S IT3 stability line
Id1 = SIT3 + K operating line
Operating characteristic on internal fault
ZL = ZLM magnetising impedance

47. ©ABBGroup-47-
14-Nov-07
Busbar protection
RADSS Settings and approximate operating
values
SLOPE (S) 0.5 0.66 0.8 0.85
Id min (A) 0.2 0.3 0.46 0.61
RLX (OHMS) 301 602 1204 1705

48. ©ABBGroup-48-
14-Nov-07
Busbar protection
Slope setting
Id1 = SIt3
Slope S = RS / ndRd3 + RS / 2
Usually S is set at 0.8
Id1 (min) = 0.092/ ( 1 – S)
With S = 0.8 Id1 = 0.46 A

49. ©ABBGroup-49-
14-Nov-07
Busbar protection
Start relay setting
Start relay ( SR ) is set higher than maximum through load thus
providing stability for open CT circuits under load condition .
A setting of 0.9 A is usually provided.

50. ©ABBGroup-50-
14-Nov-07
Busbar protection
Overall CT ratio 1200/1A
Total maximum incoming current 4000A
∴Maximum circulating current in the relay (IT3n) = 3.3A
This is less than max. permissible circulating current of the relay viz 4A.
CALCULATIONS FOR A TYPICAL STATION
RADSS - A
400 / 1A
1 / 1A 1 / 0.675A 1 / 0.325A
1200 / 1A 800 / 1A

51. ©ABBGroup-51-
14-Nov-07
Busbar protection
WITH S = 0.8 Id1 (SR) = 0.88
RdT = 165 + Rd11 = 165 + 136 = 301 Ohms
Id1 min = 0.46 A
MAXIMUM PERMISSIBLE LOOP RESISTANCE ON CT SEC SIDE
= 1204 = 127 Ohms
(1/0.325)2

52. ©ABBGroup-52-
14-Nov-07
Busbar protection