1. POWER CIRCUIT BREAKERS
AND
SUBSTATIONS
BY
“Prof Dr. Suhail Aftab Qureshi”
"Prof Dr. Suhail Aftab Qureshi"
1

2. Power Circuit Breakers and Substations
Classification
of
circuit
Breaker
and
isolators,
Terminology’ Circuit Breakers, Arcs, SF6 Switchgear & Circuit
Breakers, Air Blast Circuit Breakers, oil Circuit Breaker, Special
Purpose Circuit Breakers & Isolators, D.C Circuit Breakers,
Breakers requirement, Testing, Switchgear Testing, Synthetic Testing,
Substation Layout and Design,
"Prof Dr. Suhail Aftab Qureshi"
2

3. Power Circuit Breakers and Substations
BOOKS
1.
"Advances in H.V insulation and Arc
interruption'in SF6 and Vacuum",
By V.N. Maller & M.S Naidu.
2.
"Power Circuit Breakers Theory and Design",
By C.H. Flurscheim.
3.
"ELECTRICAL SUBSTATION", ENGINEERING
AND PRACTICE,
BY S RAO.
"Prof Dr. Suhail Aftab Qureshi"
3

4. Contents
1.
Classification of Circuit Breakers and
Isolators
a.
b.
Introduction
Circuit Breakers, Switching Isolators,
Isolator or Disconnectors
"Prof Dr. Suhail Aftab Qureshi"
4

5. 2. Terminology:
a.
b.
c.
d.
e.
f.
g.
h.
i.
j.
k.
l.
m.
Contents
Service Voltage
Recovery Voltage
Restriking Voltage (TRV)
Interruption with Restrikes
Prospective Current
Prospective Breaking Current
Breaking Capacity
Symmetrical Breaking Capacity
Asymmetrical Breaking Capacity
Making Current
Arcing Duration
Make Time
Operating Duty
"Prof Dr. Suhail Aftab Qureshi"
5

6. Contents
2.
Terminology:
n.
Load Current Interruption
Interruption of Induction Current (Fault
Currents, small, inductive current)
Interruption of capacitive Currents
Asynchronous switching
Auto Reclosure
Delayed Current Zero
Fault Making
Evolving faults.
o.
p.
q.
r.
s.
t.
u.
"Prof Dr. Suhail Aftab Qureshi"
6

7. 3.
a.
b.
c.
d.
e.
f.
g.
h.
i.
j.
k.
l.
Contents
Circuit Breaker Arcs
Plasma and Thermal Ionisation (Substance i.e.
solid liquid, Gas, Plasma)
Ionisation Due to collision of Electrons
Deionization
Properties of the Arc
Striking the Arc
External Characteristics of the Arc
Arc stability.
Dynamic Arc characteristics
The A.C Arc
General Mathematical Arc Model
The Mayr Arc equation
The Cassie Arc equation
"Prof Dr. Suhail Aftab Qureshi"
7

8. Contents
3.
Circuit Breaker Arcs
m. Application of Arc Models.
m1. Pre-zero current (low Arc Resistance)
m2. Post-zero current (High Arc Resistance)
"Prof Dr. Suhail Aftab Qureshi"
8

9. Contents
4. SF6 Switchgear
a. Arc Interruption is SF6
al .
Physical & Chemical Properties
a2.
Arc Extinction is SF6
a3.
a4.
a5.
Nozzle Design
Arc Extinction Parameters.
Throat Blocking)
"Prof Dr. Suhail Aftab Qureshi"
9

10. Contents
4.
SF6 Switchgear
b.
SF6 Circuit Breaker
bl.
b2.
b3.
c.
Arc chamber; General
Double pressure Arc chamber
Circuit Breaker Type. (Live Tank &
Dead)
SF6 switching Isolators & other equipment.
cl.
c2.
Switching Isolators.
Current Transformers
"Prof Dr. Suhail Aftab Qureshi"
10

11. Contents
5. Air Blast Circuit Breakers.
a.
b.
Arc extension
Pressurised Head- Atmospheric Head, Air
Blast C.B
b1. Constructions.
b11.
b12.
b13.
Auxiliary Chambers.
Tripping/Closing resistors.
Auxiliary Equipment.
"Prof Dr. Suhail Aftab Qureshi"
11

12. Contents
6. Oil Circuit Breaker
a.
b.
c.
General
Bulk-Oil circuit Breakers.
Minimum Oil Circuit Breaker.
7. Special Purpose Circuit Breakers &
Isolators.
a.
b.
c.
Air Blast Breakers with transverse air Jet
Water circuit Breakers
Pantograph Isolator
"Prof Dr. Suhail Aftab Qureshi"
12

13. Contents
8. D.C Circuit Breakers.
a.
Producing of current zero (Four different methods)
9. Circuit Breakers requirement.
a.
b.
c.
d.
Current Interruption
Recovery voltage withstand.
Recovery voltages calculation by current Injection
Techniques
c1.
Current injection sequence.
c2.
Examples of current Injection
Arc theory in short-line fault calculations
"Prof Dr. Suhail Aftab Qureshi"
13

14. Contents
10. Switchqear Testinq
a.
b.
High voltage TYPE TESTS (IEC-56-4)
al. Lightning Impulse Tests
a2. Switching Impulse test.
a3. Power-Frequency voltage tests
Short circuit current TYPE TESTS.
b1.
Short-time current
b2.
Breaking current
b3.
Transient Restriking
b4.
Load switching
b5.
Earthing Condition
b6
Latching
b7.
Contact Condition
b8.
Critical current
"Prof Dr. Suhail Aftab Qureshi"
14

15. Contents
c. Type tests related to service conditions
c1.
Short line fault
c2.
c3.
c4.
Asynchronous switching
Close loop switching
Transformer magnetisting current
switching
c5.
Capacitance current switching
"Prof Dr. Suhail Aftab Qureshi"
15

16. Contents
d. Miscellaneous TYPE tests.
d1.
Mechanical
d2.
d3.
d4.
Climatic Conditions
Geographical Conditions
Thermal
"Prof Dr. Suhail Aftab Qureshi"
16

17. Contents
e. Testing Equipment
e1.
Generators and Transformers
e2.
Part testing
e2.1
e2.2
Single phase testing
Unit testing
"Prof Dr. Suhail Aftab Qureshi"
17

18. Contents
11. Synthetic Testing
f1.
Principles of synthetic testing
f2.
f3.
f4.
Skeats Circuit
Parallel Injection test circuit
Series Injection test circuit
"Prof Dr. Suhail Aftab Qureshi"
18

19. Contents
12. Substation Layout and Design
Introduction
b. Basic Requirements
a.
b1.
b2.
b3.
b4.
b5.
b6.
System security
Flexibility of operation
Maintenance Facilities
Protection Facilities
Site-area & location
Cost
"Prof Dr. Suhail Aftab Qureshi"
19

20. Contents
12.
Substation Layout and Design
c. Busbar Configuration
c1. Single busbar
c2. Duplicate Busbar
c3. Duplicate Back to Back
c4. Transfer Busbar
c5. 1&1/2 Circuit Breaker Arrangement
c6. Mesh Arrangement
c7. By Pass Facilities.
c8. Location of current transformers
c9. Indoor or Outdoor substation
c10. Segregation
e11. Phase-segregated & Insulated phase Busbar.
"Prof Dr. Suhail Aftab Qureshi"
20

21. Contents
12.
Substation Layout and Design
d. Substation Earthing.
d1. Earth Resistivity
d2. Design of earth meshes.
"Prof Dr. Suhail Aftab Qureshi"
21