This is an attempt towards a comparative analysis of modern day Vacuum Switchgears used in MV Industrial Power Distribution.

1. HOW
MEDIUM VOLTAGE
METALCLAD
SWITCHGEAR HAS
EVOLVED
(VD4 & UNIGEAR)

2. UNIGEAR MODEL

3. INDOOR AIR INSULATED SWITCHGEAR
Vacuum Solution
• UniGear ZS1 with
VD4/Vmax upto
12KV application
• UniGear ZS2 with
VD4 36 for 36KV
application

4. UNIGEAR PANEL TYPE
• Single Busbar
 standard depth
 deeper version
 Floor rolling
version
• Double Busbar
version
• Unigear ZS2 for
36KV

5. UNIGEAR –SINGLE BUSBAR
Rated Voltage (kV) 12 12 12
Dry Power frequency High
Voltage (kV)
28 28 28
Impulse withstand
Voltage(kVpk)
75 75 75
Rated Frequency (Hz) 50 50 50
Rated Current of Main
Busbar (A)
630 to 1250 1250 to
2000
2500 to
3150/4000
Rated Short- Time
withstand current (kA)
26.3/3 sec 26.3/44/3
sec
44/3sec
Peak withstand Current
(kApk)
66 66/110 110
Rated current of circuit
breaker (A)
630 to 1250 630 to 2000 2500 to
3150

6. UNIGEAR ZS1- DOUBLE
BUSBAR
ZS2
Rated Voltage 12 36
Impulse withstand
Voltage(kVpk)
75/95 75/95
Rated Frequency (Hz) 50 50
Rated Current of Main Busbar
(A)
1250 to 3150 2000/2500
Rated Short- Time withstand
current (kA)
44/3Sec 31.5/3Sec
Peak withstand Current (kApk) 66 54
Rated current of circuit breaker
(A)
1250 to 3150 2000/2500

7. UNIGEAR PANEL COMPONENTS
1. Low Voltage Compartment
2. Gas exhaust duct
3. Busbar Compartment
4. Feeder Compartment
5. Circuit breaker
6. Circuit breaker
Compartment
7. Withdrawable voltage
transformer with fuses

8. UNIGEAR FEATURES
 Use of Alu-Zinc coating
instead of conventional
paint, making it more
environmental friendly.
 Internal arc proof with
1Sec. Test duration
 Self supported, Busbar
design without
conventional support
insulator.
 Specialized
design/construction of
cubicles CBs, Busbar, PTs

9. PANEL INTERNAL INTERLOCKING
 Circuit breaker can only be moved from the test position
when both the CB and Earthing switch are off.
 CB can only be switched ON when breaker is in the test
or service position.
 CB rack IN/OUT is possible only when there is supply to
control plug.
 Earth switch can be closed only if the circuit breaker is
in test position.
 Connecting & Disconnecting of the control plug is only
possible in the CB test position.
 If the Earthing switch is ON, the CB cannot be moved
from the test to service position.

10. THE ADVANTAGES BROUGHT BY UNIGEAR
• It is aimed at making AIS more compact and better
customization over a varied range of voltage & current.
• It uses tubular bus bars which requires less phase
clearance compared to rectangular bus bars.
• It has reduced the use of insulators thereby greatly
reducing the chance of insulator tracking.
• It is also emphasizing on the use of voltage detecting
insulators which can act as a direct replacement of PT.
• It has an improved external earthing truck, with more
refined interlock.

11. BRIEF HISTORY OF VACUUM
CIRCUIT BREAKER
1. Vacuum switching technology was developed originally
in the USA in the 1920’s but remained non-viable until
the late 1940’s and early 1950’s.
2. English Electric created an almost perfect material with
the invention of CLR Chrome copper contact material,
patented in 1970.
3. Slowly came the improvement in the interrupter
construction, its manufacturing and arc control
technique.
4. The market for vacuum circuit breakers finally came to
prominence from early 1970’s

12. ARC QUENCHING INSIDE VACUUM
INTERRUPTER
• At the instant of de-touching of contacts in a vacuum,
the increased current density make the metal on the
contact surface easily vaporize and create a conducting
media for arc path. The arc gets initiated and continues
until the next current zero.
• At current zero the arc is extinguished and the
conducting metal vapour is re-condensed on the contact
surface.
• At this point, the transient recovery voltage that
develops cannot create the electron avalanche necessary
to attain the breakdown voltage of the vacuum. Thus, the
arc cannot be re established again after current zero.

13. VD4 VACUUM CIRCUIT BREAKER

14. A LOOK AT THE PROS AND CONS OF
VACUUM SWITCHING
• Vacuum switching has the
most effective arc quenching
ability and a low life cycle cost
upto 52 KV.
• It is more environment friendly
and practically maintenance
free.
• It is effective in tackling the
problem of current chopping.
• VCB uses Butt type contact
with CuCr as the contact
material because of its good
electrical and mechanical
properties. CuCr is also
resistant to solid welding that
may otherwise occur at load
closing or short circuit
conditions.
• Vacuum medium has an
effective dielectric ceiling of
500 KV which roughly
corresponds to LIWL of 132
kV voltage medium.
• Beyond 132 KV chances of
X-Rays emission from the
vacuum interrupters cannot
be ruled out.
• High contact pressure upto
600 daN for fault level of 50
KA may be required to
prevent popping.
• It is to monitor the
condition of the vacuum. A
pressure of 10^-4 to 10^-8
mbar must be maintained.

15. VD4 INTERRUPTER
• In the circuit-breaker of type
VD4,
the complete pole and the
maintenance free
vacuum interrupter form a
positive unit.
• This is achieved by a specially
developed casting technique in
which the vacuum interrupter
is
directly embedded in epoxy
resin to form a complete pole.
• Disruptive external effects on
the switching element are
therefore
extensively precluded.
• For very high rated currents,
rated short-circuit breaking
currents and for rated voltages
upto 36 kV, they are used
• The contact gap of only 12
mm is sufficient to provide
high dielectric strength.

16. Arc Control technique
1. There can be two types of arc that can develop inside a
vacuum Interrupter the Diffused arc and the
Constricted arc.
2. The diffused arc is a natural outcome for fault current
upto 10 KA whereas constricted arc appears above 10
KA fault current.
3. In diffused arcing the arcs are uniformly distributed
over the entire contact surface whereas in constricted
arcing the arc tends to localize on a certain spot
causing damage to the interrupter contacts.
4. The objective of arc control technique is to prevent
formation of constricted arcing and keep diffused
arcing irrespective of the fault current vale.
5. This is achieved by developing either a Radial Magnetic
Field or Axial Magnetic Field around the arc using the
arc current.
6. VD4 uses Radial Magnetic Field as arc control
technique.

17. VD4 KEY ASPECTS AND STRENGTHS
• Application where space saving is a premium
• The panel contacts are mounted in the bushing and the metallic
shutters are provided hence, better compartmentalization is
achieved.
• Higher reliability and availability and longer life with fewer
fastening parts.
• It has moulded case design protecting the vacuum interrupters
from impact, dust, and condensation.
• High dielectric protection of the vacuum interrupters without
additional modifications.
• VD4 with manual mechanism is suitable for auto reclosing.
• It has only one type of operating mechanism (EL) for all the VD4
variants.

18. FIELD OF APPLICATIONS
Vacuum circuit-breaker of type VD4 is designed for
switching:
• Power Transmission and distribution substations
• Motor control and protection
• Capacitor bank control and protection
• Transformers and Generators under load and no-load
conditions
• Cables and overhead lines under load and no-load
conditions

19. FEATURES & OVERVIEW
• Vacuum interruption technique
• Contacts in vacuum protected against oxidation and
contamination
• Sealed for life vacuum interrupters
• In accordance with IEC 62271-100 STDs
• Operation sequence O - 0.3” - CO - 15” - CO
• Limited switching energy
• 10,000 mechanical operations
• Stored energy operating mechanism with built-in anti-pumping
device and closing spring charging lever
• Insulating monobloc
• Operating mechanism and monobloc fixed to a sturdy metal
frame
• Easy customization with a complete range of accessories
• Locks to prevent incorrect and hazardous operations

20. VD4 - OVERVIEW
Open/close aux. contacts (standard
set of ten aux.c.)
Additional opening release
Locking magnet in the actuator
Opening pushbutton
Closing pushbutton
Shunt tripping release
Built-in lever for closing spring
manual charging
Undervoltage release (missing in the
picture)
Shunt closing release
Signaling device for closing springs
charged/discharged
Mechanical operation counter
Geared motor for closing spring
charging

21. VD4 - STANDARD EQUIPMENT
•Mechanical signalling device for CB open/closed
•Mechanical signalling device for closing spring
charged/discharged
•Opening and closing pushbuttons
•Mechanical operation counter
•Built-in lever for manually charging of closing spring
•Anti-pumping mechanical built-in function
•5 + 5 auxiliary contacts
•Connection terminals and terminal board for auxiliary
circuits (for fixed CB)
•Isolating contacts, cord with connector (plug only), racking-
in/out lever (for withdrawable CB)

24. Brief view of Interrupter structure
1. The Vacuum Interrupter is housed inside a ceramic
porcelain cylinder having Alumina 94% and Silica 6%.
2. The Shield is made of oxygen free Copper and is
primarily used to capture the metal vapour produced
during arcing thereby maintaining the internal
insulation of the ceramic porcelain cylinder.
3. The shield also prevents direct exposure from the high
fault current/arc.
4. The bellows allow the motion of the movable contact
while maintaining vacuum tight seal where the speed of
the movable contact reaches from 0 to 2 m/s in less
than 100 micro second.
5. The impulse motion parted to the bellows are non
uniform and anti twist bushings are provided to improve
the mechanical strength of the bellows.

26. Vacuum Circvuit Breaker type VD-4
Rated Voltage KV 12 17.5 36 40.5
Rated Current A 1250 - 2500 3150 - 4000
1250-
2500
3150-
4000
1250-
3150
1250-
3150
Rated Short
Circuit
Symmetrical
current
breaking
capacity
KA 40 50 53 20-50 63 40 20-40 25-40 25-31.5
Rated Short
Circuit
Asymmetrical
current
breaking
capacity
KA 43.6 56.8 66.5
21.7-
56.8
65.6 43.6
21.7-
43.6
21.7-
43.6
27.3-
34.3
Rated Short
Circuit Making
current
capacity
KA 100 125 158 30-125 158 100 50-100 63-100 63-80
Rated Short
Circuit
Duration
SEC 3 3 3 3 3 3 3 3 3

27. ADVANTAGES OF VD4 WITH RESPECT TO HCA
• The reduced dimensions of the VCB enables to provide a very
compact air insulated switchgear panel that can rival a gas
insulated switchgear.
• The vacuum interrupters are enclosed inside epoxy resin
insulators making it more safe and versatile for indoor as well as
outdoor use.
• The breakers are customized to be floor mounted or cassette
mounted however mostly cassette mounted breakers are used
which eliminates the dependency on floor level.
• The cassette mounted VD4 breakers has electrical interlock
which ensures that rack in / rack out operations are not possible
without control supply.
• It forms the basis of Unigear in which the metering+ relay
module, breaker module and line PT can be clubbed into a single
compartmentalized cubicle.
• VD4 weighs around 125 to 150 kg and is lighter than HCA type
Breakers weighing approximately 190 kg.