D
Journal of Energy and Power Engineering 6 (2012) 315-320
DAVID
PUBLISHING
New Generation of Outdoor Vacuum Circuit Breakers
with Rated Voltage up to 40.5 kV
Alexey Chaly and Sergey Benzoruk
Industrial Group Tavrida Electric Ltd., Moscow 123298, Russia
Received: December 28, 2010 / Accepted: June 09, 2011 / Published: February 29, 2012.
Abstract: The article describes design peculiarities of the novel compact vacuum circuit breaker with rated voltage 40.5 kV. The
design incorporates several novel technical solutions: polycarbonate support insulation, mono-stable magnetic actuator, labyrinth
pulling insulator, core-type flexible contact and new compact vacuum interrupter (VI). Phases are encapsulated into silicone rubber
providing required creepage distance and excellent tracking resistance. These novelties along with extensive modeling of the
mechanical and electrical fields followed by design optimization resulted in weight reduction of more than 50% compared with
alternatives available in the market. And this is in spite of built in sensors measuring: phase currents, zero-sequence current, phase
voltages.
Key words: Outdoor vacuum circuit breaker, magnetic actuator, combined voltage and current sensor, silicon rubber.
1. Introduction
33-40.5 kV outdoor substations are widely used
throughout the world. With the development of the
vacuum interrupting technology these substations are
more often equipped with the outdoor vacuum circuit
breakers (OVCB).
OVCB with respect to their design can be divided
into two groups: dead-tank and live-tank.
In a dead-tank OVCB the vacuum interrupter is
arranged in a weather-proof manner inside a metal
enclosure [1-3]. In comparison with live-tank, the
dead-design allows implementation of voltage
measurement from both side (demands in ring
overhead lines) and provides reliable protection and
internal insulation against weather exposure and
contamination. On the other hand dead-tank modules
exhibit larger weight, dimension and cost. As a result
the live-tank design looks more attractive for radial
line configurations (where it is required to measure
Corresponding author: Alexey Chaly, Ph.D., research
fields: vacuum interrupters, circuit breakers, reclosers and
switchgear. E-mail: cam@tavrida.com.
voltage from the load side).
In live-tank circuit-breakers, the vacuum interrupter
is arranged in a weather-proof way inside an
insulating enclosure (the vacuum interrupter is at
electrical potential, which means “live”) [4-8]. Epoxy
and porcelain insulation are usually used for the
enclosure.
Overhead lines 34.5-40.5 kV commonly have a
radial structure, therefore live-tank outdoor vacuum
circuit breakers are generally presented in the market
for these voltages.
The live-tank OVCB 34.5-40.5 kV can be divided
into two subgroups:
 Assembled design [4, 5];
 Solid insulated design [6-8].
The assembled design is shown in Fig. 1. A phase
consists of two support insulators joined through a
lower terminal.
This design may be considered as obsolete due to
excessive dimensions and weight.
Current and voltage sensors may be installed as
separate devices but this leads to higher transport,
316
New Generation of Outdoor Vacuum Circuit Breakers with Rated Voltage up to 40.5 kV
Fig. 2
Fig. 1
Assembled design.
installation and service costs. Moreover, epoxy and
porcelain lose hydrophobicity under the influence of
contamination (epoxy loses its irreversibility within
the first years of service under solar radiation) thus
leading to the development of a completely wetted,
resistive conductive surface on outdoor insulation. As
a result, leakage currents are increased which enlarges
arcing and risk of insulator flashover.
The solidly insulated design was developed during
the 1990s. These OVCB are based on the application
of epoxy material, serving simultaneously as
mechanical support structure and external insulation
(see Fig. 2). The vacuum interrupter (VI) along with
terminals and sensor are encapsulated in epoxy resin.
Solid insulated OVCB have lower dimensions and
weight in comparison to assembled ones. Integrated
voltage and current sensors are also significant
advantage of these circuit breakers.
However, the solid dielectric design could not
overcome the disadvantage of the assembly design.
For outdoor insulation epoxy resins are used.
Despite the increase of hydrophobicity and
tracking-erosion features, the usage of an epoxy
polymer OVCB still seems undesirable in regions with
a severely contaminated environment.
Solid dielectric design.
Moreover, solidly dielectric circuit breakers were
designed for IEC and IEEE markets and 38 kV
versions have rated power frequency withstand
voltage up to Ud =70 kV [9, 10] and rated lightning
impulse withstand voltage not more than Up = 170 kV
[9, 10]. The Russian market requires Ud/Up = 95/190
kV [11], the Chinese market requires Ud/Up = 95/185
kV [12], the IEEE market of outdoor circuit breakers
demands, Ud/Up = 80/200 kV [13]. Currently
available in the market solid dielectric OVCB do not
satisfy requirements of the said markets.
As it follows from the presented review there is no
universal OVCB design that would fit technical
requirements of the different markets:
 applicability to severe environmental conditions;
 BIL level up to 200 kV;
 extended metering capabilities;
 low dimensions and lightweight;
 cost effectiveness.
The goal of the present research is to develop such a
design.
2. Advantages of the Silicone Rubber for
Outdoor Insulation
Silicone rubber possesses excellent hydrophobicity
and high tracking resistance. A further feature makes
this material attractive for outdoor applications.
New Generation of Outdoor Vacuum Circuit Breakers with Rated Voltage up to 40.5 kV
Silicone rubber can transfer hydrophobicity onto a
polluted layer (hydrophobicity transfer material) and
this process occurs during the lifetime of an insulator
[14]. If the creepage distance is more than 31 mm/kV
the hydrophobicity transfer velocity is sufficient to
prevent flashover in severely contaminated
environments.
The
outdoor
circuit
breaker
OSM\TEL-27-12.5/630-205 with silicone outdoor
insulation and creepage distance of 860 mm [15]
successfully passed the environmental test in KIPTS
without any incident of insulation leakage current
exceeding 750 mA [16]. Solid dielectric OVCB
OVR-3 (ABB) with the last modification of the
Cycloaliphatic Epoxy (so call Hydrophobic
Cycloaliphatic Epoxy) and creepage distance of 960
mm [7] passed the test with one incident [17]. This is
one of the numerous evidences of the superiority of
silicone rubber for outdoor insulators.
In spite of above mentioned advantages, outdoor
vacuum circuit breakers 34.5-40.5 kV with fully
encapsulated phases with silicone rubber are not
available in the market. The novel outdoor circuit
breakers from IG Tavrida Electric will change this
situation.
3. The OSM35_Smart Design
The OSM35_Smart design is a symbiosis of the two
above mentioned designs: solid dielectric and
assembled. Support insulation consists of two
insulators (1, 2, Fig. 3) which are jointed through a
lower terminal (3). The lower terminal performs three
functions: current carrying, screening sharp edges of
the VI bellow and flexible contact, and heat
dissipation. The compact VI (4) is fixed between the
upper (5) and lower terminal (3). The terminals
configuration is designed in order to decrease induced
potential shift of the screen of the VI in open position.
А sensor block (6, Fig. 3) is installed near the lower
terminal.
The block includes:
 phase current sensor (Rogowsky coil);
Fig. 3
317
OSM35_Smart cross section.
 special transformer for zero-sequence current
sensor;
 capacitor-type phase voltage sensor.
The assembled phase together with the sensor block
is encapsulated in RTV silicone rubber (7, Fig. 3).
Silicone rubber forms:
 insulation of terminals and sensors;
 protective layer of support insulator;
 ribs in order to provide creepage distance 1050
mm (the ribs shape meets the requirement of
IEC/TS60815-3 [18]).
The OSM35_Smart provides Ud/Up = 70/150 kV.
The creepage distance of 1050 mm and the utilization
of hydrophobicity transfer material (silicone rubber)
definitely allow to use this module in regions with
medium pollution (c class of pollution level [18]).
In markets with higher Ud and Up requirements
(Russia, China, America, etc.) and in regions with
heavy or very heavily polluted atmosphere (d and e
class of pollution level [18]) the OSM35_Smart will
be supplied with extensions (Fig. 4). The extensions
allow for an increased creepage distance of up to 1750
mm and BIL level up to 200 kV.
The circuit breaker has a phase to phase distance of
280 mm. Arrangement of the extensions provides
minimum strike distance 400 mm (Table 1).
Basic parameters of the OSM35_Smart are shown
in Table 1. Dimensions are presented in Fig. 5.
These parameters were achieved as follows:
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New Generation of Outdoor Vacuum Circuit Breakers with Rated Voltage up to 40.5 kV
Table 1
No.
1
2
The OSM35_Smart parameters.
6
7
8
9
10
Parameter
Rated voltage (kV)
Rated current (A)
Rated symmetrical interrupting
current (kA)
Rated impulse voltage Up (kV)
Rated power frequency test voltage
Ud (kV)
Creepage distance (mm)
Min external strike distance (mm)
Mechanical life, CO cycles
Ambient temperature (C)
Weight (kg)
11
Dimensions (W × H × D) (mm)
3
4
5
Value
40.5
1250
1250
20
25
150 (200*) 150
70 (95*)
1050 (1710*)
240 (400*)
20 000
-60 + 55
72 (82*)
770/600/440
(900*/770*/600*)
arc and the use of finite element analysis.
The miniaturization of vacuum interrupter is
achieved by:
 decreasing the contact gap and height of the
ceramic envelope;
 reducing the flexible contact mass and bellow
rigidity;
 minimizing the holding force and providing
minimum VI resistance thus simplifying the magnetic
actuator design, reducing the energy of the control
module and thus simplifying temperature-rise tests
requirements.
*- with extensions (see Fig. 5)
3.2 Core-Type Flexible Contact
Fig. 4
The application of core-type flexible contact (8,
Fig. 3) results in a decrease of phase height and
reduction of actuator energy consumption.
The flexible contact increases the height of the
phase by only 16 mm. Due to a resistance of around 4
Ohm the opposing force is negligible.
The Core-type contact required meticulous
technological development in order to achieve a cheap
design with stable resistance under series
manufacture.
OSM35_Smart with extensions.
3.3 Pulling Insulator
The pulling insulator length substantially defines a
phase height. The application of the labyrinth pulling
insulator in the OSM35_Smart (9, Fig. 3) resulted in a
decrease of terminal to frame distance to 200 mm.
Moreover, the pulling insulator provides Ud/Up =
95/200 kV.
The concept of labyrinth pulling insulators is
described in a Tavrida Electric patent [21].
Fig. 5
OSM35_Smart dimensions.
3.4 Polycarbonate Support Insulation
3.1 Compact VI
The essential advantage of Tavrida’s 40.5 kV
vacuum interrupter design (Fig. 3) is its very compact
design. The vacuum interrupters have a height of 153
mm. Such miniaturization has been achieved with
long-term research in the field of high current vacuum
Tavrida Electric has utilized polycarbonate polymer
for support insulation of vacuum circuit breaker for
more than 10 years. Field experience supports the
claim that polycarbonate is one of the most advanced
polymers for medium voltage switchgear:
Mechanical properties, impact strength, thermal
New Generation of Outdoor Vacuum Circuit Breakers with Rated Voltage up to 40.5 kV
properties are sufficient to design support insulation
with wall thickness not exceeding 6 mm (technology
requirement);
Injection molding provides insulation manufacture
without minor pores;
Low polymer cost (7$/kg) together with cheap
processing enables the manufacture of low cost
insulators.
Using polymers such as polycarbonate resulted in
the development of new criteria for static and dynamic
structural analysis. Positive field experience of
Tavrida Electric indoor circuit breakers has made it
possible to develop essential criteria for the design of
a support insulator without huge strength margins.
3.5 Silicone Rubber Encapsulation
319
Novel magnetic actuator design has been used for
the OSM35_Smart [20, 21] (10, Fig. 3). Phase to
phase distance of 280 mm allowed an increase of
outer diameter of the actuator of up to 150 mm. This
resulted in an opportunity to decrease the height of the
magnetic actuator up to 100 mm and a frame height of
120 mm.
A distinct feature of actuator’s block of the
OSM35_Smart is the lack of a synchronizing shaft.
Each magnetic actuator is operated by a separate driver
to allow single-phase tripping and eliminate
complicated linkage (in comparison to shafted
variants).
Compact and lightweight design of the mono-stable
magnetic actuator has been achieved with the aid of
finite-element analysis optimization.
Except for advantages mentioned above, phase
encapsulation by silicone rubber enables a decrease of
dimensions to values which are influenced by the
internal part of the vacuum circuit breaker. For
example, lower terminal to frame distance is defined
only by the dimension of labyrinth pulling insulation.
RTV silicone rubber is used for the encapsulation. The
rubber is injected in a mould form under low pressure
(several bars). The shapes of support insulators,
terminals and sensor have been optimized in order to
prevent trapping of air inside the encapsulation.
Moreover,
substantial
experimental
and
computational efforts have been undertaken in order
to guarantee stable adhesion of RTV rubber to
substrates (support insulators, terminals, sensors) in
temperature range -60-+90 С.
3.6 Mono-stabile Magnetic Actuator
All Tavrida Electric circuit breakers are equipped
with mono-stabile magnetic actuators. Each phase has
a separate actuator. All movable parts travel linearly
along the phase axis. Lack of transmission knots and
friction surfaces provide reliable operation during the
life cycle of the TEL-type circuit breaker without any
maintenance.
Fig. 6 OSM35_Smart and conventional outdoor vacuum
circuit breaker (assembled design) with the same
parameters.
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New Generation of Outdoor Vacuum Circuit Breakers with Rated Voltage up to 40.5 kV
4. Conclusions
As you can see in Fig. 6 long-term research efforts,
skills in finite-element methods analysis, application
of advanced materials and technologies have made it
possible to create compact and lightweight outdoor
vacuum circuit breakers up to 40.5 kV with integrated
metering capabilities
On the basis of these current parameters the
OSM35_Smart can be seen as a new milestone in the
development of medium voltage outdoor vacuum
circuit breakers.
Acknowledgments
The authors wish to express their sincere thanks to
all engineers of Tavrida Electric who participated and
supported this development project.
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