The document discusses protection coordination at an electrical substation. It provides an overview of protection coordination and selective coordination. It also details the data required for a coordination study including single line diagrams, system voltages, impedances, and fault current data. The document analyzes several fault scenarios and observations regarding protection coordination and makes recommendations for further audit and testing to improve coordination.
2. CONTENTS
Introduction to Protection Coordination
Selective Coordination
Data Required for Coordination Study
Protection Coordination at FFC-MM
Anomalies in Protection Coordination Scheme
Recommendations
3. PROTECTION COORDINATION
Protective device coordination is the process of
determining the "best fit" timing of current interruption
when abnormal electrical conditions occur.
The goal is to minimize an outage to the smallest extent
possible.
Successful system design hinges on coordination of each
relaying scheme.
4. SELECTIVE COORDINATION
ISOLATION of a faulted circuit from the remainder of
the installation is MANDATORY in today's modern
electrical systems.
Power BLACKOUTS CANNOT be tolerated.
A properly engineered system will allow ONLY the
protective device nearest the fault to open, leaving the
remainder of the system undisturbed and preserving
continuity of service.
5. SELECTIVE COORDINATION
“Localization of an overcurrent condition to restrict
outages to the circuit or equipment affected,
accomplished by the choice of overcurrent protective
devices and their ratings or settings.”[1]
The faulted circuit is isolated by the selective operation of
only that overcurrent protective device closest to the
overcurrent condition.
[1] The National Electrical Code, NFPA 70, The National Fire Protection
Association, Inc., 2005 Edition.
6. Not Affected Not Affected
De-Energized
A Portion of System A
Also Opens Not Affected
B B
Also Opens Not
Affected
C
C
Opens Opens
D D
Branch De-Energized
Circuit Portion of System Fault
Fault
7. DATA REQUIRED
Single-line System voltage
diagram levels
Data required for
coordination
study
Short-circuit and
Impedances
load current data
8. G TG-701A
6.3 KV
G TG-701B G MG-702
6.3 KV 6.3 KV
10000 KVA, 14% 10000 KVA, 14% 1900 KVA
42-G1A 42-G1B 42G2
124 AC 124 BC 124 DE
152 CD 152 C1D1
TR1A-4 TR1B-4
M 6.3/0.38kV 6.3/0.38kV M
2000 kVA, 6.25% 2000 kVA, 6.25%
MP 601C MP 604
52B
52A
24
9. FOR LINE TO LINE FAULT OF 6000 AMPS ON LV BUSBAR:
TG-701A
6.3 KV
G 10000 KVA, 14%
O/C Relay of 42-G1A will NOT
pick up as per IDMT curves
1000/1 51
42-G1A 124 AC
O/C Relay of MV CB will pick
up & trip the CB in 18 seconds.
50
200/1 51 Inst O/C Relay of 52A will
NOT pick up as per IDMT
TR1A-4 curves
2000 KVA, 6.25%
50
3000/1 51
O/C Relay of 52A will pick up &
52A
trip the CB in 5 seconds.
10. FOR LINE TO LINE FAULT OF 18000 AMPS (Pickup Current of Inst.
O/C Relay 50 of 52A) ON LV BUSBAR:
TG-701A
6.3 KV
G 10000 KVA, 14%
O/C Relay of 42-G1A will pick up
& trip the CB in 90 seconds.
1000/1 51
42-G1A 124 AC
O/C Relay of MV CB will pick
up & trip the CB in 1.3
seconds.
50
200/1 51 Inst. O/C Relay of 52A will also pick up
TR1A-4 in 0.1 seconds and block the automatic
2000 KVA, 6.25% changeover
50
3000/1 51
O/C Relay of 52A will pick up &
52A
trip the CB in 0.42 seconds.
11. FOR LINE TO LINE FAULT OF 43350 AMPS ON LV BUSBAR:
TG-701A
6.3 KV
G 10000 KVA, 14%
O/C Relay of 42-G1A will pick up
& trip the CB in 3.8 seconds.
1000/1 51
42-G1A 124 AC
O/C Relay of MV CB will pick
up & trip the CB in 0.42
seconds.
50
200/1 51 Inst. O/C Relay of 52A will also pick up
TR1A-4 in 0.1 seconds and block the automatic
2000 KVA, 6.25% changeover
50
3000/1 51
O/C Relay of 52A will pick up &
52A
trip the CB in 0.42 seconds.
12. FOR LINE TO LINE FAULT OF 48000 AMPS (TR1A-4 Short Circuit
Level) ON LV BUSBAR:
TG-701A
6.3 KV
O/C Relay of 42-G1A will pick up &
G 10000 KVA, 14% trip the CB in 2.7 seconds.
1000/1 51
Inst O/C Relay of MV CB will
42-G1A
NOT pick up as per IDMT curves
124 AC
O/C Relay of MV CB will pick
50 up & trip the CB in 0.36
seconds.
200/1 51
TR1A-4 Inst. O/C Relay of 52A will also pick up
2000 KVA, 6.25%
50 in 0.1 seconds and block the automatic
changeover
3000/1 51
O/C Relay of 52A will pick up &
52A
trip the CB in 0.42 seconds.
14. FOR LINE TO LINE FAULT OF 4000 AMPS (Pickup Current of Inst. O/C
Relay6.3KV MV CB) ONSHORT CIRCUIT ON MV SIDE OF (22000 AMPS):
50 of MAXIMUM MV SIDE OF T/F:
FOR LINE TO LINE FAULT OF 275 AMPSLEVEL CURRENTT/F:
G TG-701A
6.3 KV
10000 KVA, 14%
O/C Relay of 42-G1A will pick up &
O/C Relay of 42-G1A will NOT
&pick up as per 0.42seconds.
trip the CB in IDMT curves
trip the CB in 1.6 seconds.
1000/1
51
67A
42-G1A
124 AC Directional O/C Relay of 124 AC
Directional O/C Relay of 124 AC
1000/1 Directionalsense the fault current
will NOT O/C Relay of 124 AC
will NOT pick up as per IDMT
will NOT sense the fault current.
curves
Inst. O/C Relay of MV CB will
50 Inst. O/C Relay of MV CB will
also pick up and trip the CB in
NOT pick up as per IDMT curves
0.03 seconds.
200/1
51
TR1A-4 O/C Relay of MV CB will pick up &
6.3/0.38kV
2000 kVA, 6.25% trip the CB in 0.28seconds.
trip the CB in 50 seconds.
15. FOR LINE TO LINE FAULT OF 1467 AMPS ON BUSBAR ‘A’:
O/C Relay of 42-G1A & 42G1-B will
Directional O/C Relays on Busbar
pick up & trip the respective CB’s in 20
‘A ‘ & Busbar ‘B’ will not sense the
seconds.
fault current.
TG-701A TG-701B MG-702
6.3 KV
G 6.3 KV
10000 KVA, 14% G 10000 KVA, 14% G 6.3 KV
1900 KVA
1000/1 51 1000/1 51
42-G1A 67A 67B 42-G1B 42-G2
1000/1 1000/1
124 AC 124 BC 124 DE
152 CD 152 C1D1
500/1
51
17. FOR LINE TO LINE FAULT OF 1467 AMPS ON BUSBAR ‘B’:
Directional O/C Relay on Busbar ‘A’ will Directional O/C Relay on Busbar ‘B’ will
pick up & trip 124AC in 8 seconds. pick up & trip 124BC in 8 seconds.
TG-701A TG-701B MG-702
6.3 KV
G 6.3 KV
10000 KVA, 14% G 10000 KVA, 14% G 6.3 KV
1900 KVA
1000/1 51 1000/1 51
42-G1A 67A 67B 42-G1B 42-G2
1000/1 1000/1
124 AC 124 BC 124 DE
152 C1D1
152 CD
O/C Relay of 42-G1B will pick up
500/1 & trip the CB in 20 seconds.
51
18. FOR LINE TO LINE FAULT OF 1467 AMPS ON BUSBAR ‘C’:
Directional O/C Relay on Busbar ‘A’ will Directional O/C Relays on Busbar
pick up & trip 124AC in 8 seconds. ‘B’ will not sense the fault current.
TG-701A TG-701B MG-702
6.3 KV
G 6.3 KV
10000 KVA, 14% G 10000 KVA, 14% G 6.3 KV
1900 KVA
1000/1 51 1000/1 51
42-G1A 67A 67B 42-G1B 42-G2
1000/1 1000/1
124 AC 124 BC 124 DE
152 C1D1
152 CD
O/C Relay of 42-G1B will pick up
500/1 & trip the CB in 20 seconds.
51
19. FOR LINE TO LINE FAULT OF 1467 AMPS ON CABLE LINK:
Directional O/C Relay on Busbar ‘A’ will Directional O/C Relays on Busbar
pick up & trip 124AC in 8 seconds. ‘B’ will not sense the fault current.
TG-701A TG-701B MG-702
6.3 KV
G 6.3 KV
10000 KVA, 14% G 10000 KVA, 14% G 6.3 KV
1900 KVA
1000/1 51 1000/1 51
42-G1A 67A 67B 42-G1B 42-G2
1000/1 1000/1
124 AC 124 BC 124 DE
152 C1D1
152 CD
U/V Relay of 124DE will
500/1 pick up & open the CB.
51
O/C Relay of 152CD will pick up O/C Relay of 42-G1B will pick up
& trip the CB in 5 seconds.` & trip the CB in 20 seconds.
20. RECOMMENDATIONS
An extensive audit is needed to be carried out to
check the Dot Notation of Current Transformers.
Secondary Current Injection Test should be planned
in order to determine the correct behavior of
Directional Relays in case of occurrence of fault on
MV Busbars .
The objective of a protection scheme is to keep the power system stable by isolating only the components that are under fault, whilst leaving as much of thenetwork as possible still in operation
Today, more than ever, one of the most important parts of any installation - whether it is an office building or an industrial plant is the electrical distribution system.Nothing will stop all activity, paralyze production and possibly cause a panic more effectively than a major power failure.
The term “selective coordination” refers to the selection and setting of protective devices in an electric power system in such a manner as to cause the smallest possible portion of the system to be de-energized due to an abnormal condition.The most commonly encountered abnormal condition is an overcurrent condition, so we may use a more restricted definition of selective coordination as follows:
Non-Selective Coordination Resulting in a BlackoutA fault on a branch circuit opens protective devices "D", "C" and "B". The entire power supply to the building is completely shut down.Selective CoordinationA fault on a branch circuit opens protective device " D“ only. Since A, B and C are not disturbed, the remainder of the electrical system is still energized.
