Retrofitting for
medium-voltage switchgear
Reducing maintenance costs
Reprint from ew, Volume 108 (2009), Issue 22 – 23
Author:
Dr.-Ing. Dieter Sämann, Siemens AG, Energy Sector, Erlangen
Answers for energy.
ew SUBJECT AREA
Switchgear
Reducing maintenance costs
Switchgear development over
the years
Retrofitting for medium-voltage
switchgear
Circuit-breakers are the core element of medium-voltage switchgear. They ensure that electric power is
made available to the consumer
and that the short-circuit current is
interrupted quickly and reliably in
the event of a fault. The technology,
properties, and behavior of circuitbreakers have evolved continuously
over the past 100 years, and today
provide largely maintenance-free
operation.
The following short review will describe the changes that have taken
place in switchgear; see Fig. 1.
Dead-tank oil circuit-breakers did
not yet have an arcing chamber, but
instead generated two partial arcs in
a large oil tank. The high arc energy
generated resulted in considerable
stressing, and so required considerable maintenance.
Expansion circuit-breakers used
water as the arc-extinguishing
medium. This first use of an arcing
chamber for interrupting the current enabled contact wear to be reduced compared with dead-tank oil
circuit-breakers. These circuitbreakers were manufactured from
1930 onward, and there are still a
few of them in operation today.
With the development of the minimum oil circuit-breaker – which
only needed a small amount of oil
compared with dead-tank oil circuit-breakers and a combined arcextinguishing medium flow – it was
possible to improve switching characteristics and reduce maintenance
Medium-voltage switchgear has a service
life of 30 to 40 years. As it ages and needs
more frequent servicing, maintenance
costs increase to the point where replacement of the entire switchgear becomes unavoidable. An alternative to exchanging the
whole switchgear is to replace the components that are subject to wear. This makes
it possible to continue using existing intact
switchgear with modern technology. By exchanging components, both the investment costs and the time spent on planning
and approval are lower than with a completely new system. The possibilities for exchanging components and the advantages
for the operator are explored in this paper.
I
n a medium-voltage system, electric power is generally distributed
in the voltage range between 6 kV
and 30 kV. Medium-voltage switching stations house the equip-ment
required for both switching and
protection, on which safe and reliable power distribution heavily depends. Formerly, air-insulated
switchgear was built with circuitbreakers on trucks or withdrawable
parts in order to facilitate inspection and maintenance work outside
the switch bay by pulling out the
breaker. Today, gas-insulated
switchgear is used as well as air-insulated switchgear. It is less dependent on the environment and,
thanks to maintenance-free circuitbreakers, hardly requires any maintenance. Modern circuit-breakers
based on the vacuum-switching
principle can also be integrated
with existing switchgear, resulting
in higher availability, reduced operating costs, and a smaller investment.
Vacuum Switchgear
Dr.-Ing. Dieter Sämann, Business
Development Management
medium-voltage components,
Siemens AG, Erlangen
2
(PDF 6330) published in
ew
No other switching principle can match these outstanding properties:
Constant dielectric
• Virtually no change in internal pressure even at the end of the service life
• No decomposition products
• No impact on the environment
Constant contact resistance
• No oxidation
• Low wear
High total current
• Very low arc power
• Special contact material from in-house production
• High degree of reliability
• Very low number of moving parts
• High-quality materials
vol.108 (2009), issue 22-23
Fig. 1: Dead-tank oil circuit-breaker, expansion circuit-breaker, and minimum oil circuit-breaker
intensity. These breakers are still in
operation in large numbers to the
present day. Assuming they were
regularly maintained after five
years, or after five to ten short-circuit-breaking operations, these devices will continue to function well
today.
The development of the vacuum
circuit-breaker marked a great leap
forward in technology. A totally new
arc-extinguishing principle meant
that the circuit-breaker could be
used universally and hardly required any maintenance. Vacuum
circuit-breakers were launched on
the German market by Siemens in
1977 and have now been in service
for more than 30 years. Over this period, operators at power supply
companies and in industry have
seen for themselves how reliable
and cost-efficient these modern devices are.
There has also been further development of the vacuum circuitbreaker. Thanks to new production
techniques, the contact material of
the vacuum circuit-breakers can be
matched more effectively with their
multiple applications. Detailed
knowledge of the switching process
in a vacuum acquired over this period and improved production methods have led to a reduction in the
size of the vacuum interrupters. The
result today is a modern vacuum
circuit-breaker with efficient vacuum interrupters of such small dimensions that they fit into any existing medium-voltage switchgear.
Properties of present-day vacuum switchgear
Vacuum circuit-breakers are now
available for the entire mediumvoltage range, and comprise the following spectrum of electrical data:
• Operating
voltages
from
7.2 kV to 40.5 kV
• Operating
currents
from
800 A to 6.300 A
• Short-circuit currents from
12.5 kA to 72 kA
Vacuum circuit-breakers from
Siemens are employed for all
switching tasks at medium voltage
levels. A special contact material for
the vacuum interrupters, produced
in a special in-house production
process, ensures that a very wide
range of different currents can be
switched reliably. The low chopping
current of 3 to 4 A prevents non-permissible overvoltages when switching small inductive currents. The
rapid dielectric recovery of the
breaker gap guarantees that all capacitive currents occurring in networks, as well as high short-circuit
currents up to 72 kA, are interrupted
reliably. This means that vacuum
circuit-breakers can be used to re(PDF 6330) published in
ew
place all old circuit-breakers of the
conventional type. The new SION
series is particularly suitable for replacing old circuit-breakers, since it
uses the highly compact vacuum interrupters and has minimal dimensions due to its special design.
What does retrofitting mean?
At the time when it was installed,
switchgear would have conformed
to the current state-of-the-art and
its design matched the technical
Fig. 2: SION vacuum circuit-breaker
vol.108 (2009), issue 22-23
3
Switchgear truck
38928.3
Fig. 3: Switchgear truck for switchgear 8BD with SION circuit-breaker
specifications of the networks.
However, over the course of years or
decades, conditions change and totally different factors can result in
the need to renew the entire
switchgear or parts of it:
• Availability
o Transmission performance of the
network has increased
o Supply reliability needs to be increased
o Individual devices are worn out
• Operating costs
o Costs for maintenance have increased
o Supply of spare parts becomes increasingly difficult
• Personnel protection
o Retrofitting for protection of personnel
• Legal situation
o Regulations or standards have
changed
The measure that is required depends significantly on the reason
for the modification or renewal, but
also on financial resources. If costs
do not have top priority and there
are no other constraints, the decision will go in favor of installing
completely new switchgear. However, there can be many reasons in
favor of replacing parts of the
equipment:
• The premises do not allow the entire switchgear to be exchanged
• The switchgear is in good condition
Fig. 4: SION circuit-breaker as retrofit solution on a switchgear truck
4
(PDF 6330) published in
ew
vol.108 (2009), issue 22-23
• The switching device requires intensive maintenance
• Spare parts can only be procured
at high cost or are no longer available
• There are no personnel left who
know how to maintain the old
equipment
There are also non-technical arguments in favor of retrofitting:
• Construction measures
• Interruption of the power supply
• Costs for a provisional solution
• Official certification procedures
• Investment and budget issues
In most cases of retrofitting, the
old circuit-breakers are replaced
with new ones. Depending on the
switchgear type, either the circuitbreaker only is replaced or the complete withdrawable part or
switchgear truck. Because of its
small dimensions, the SION vacuum circuit-breaker has proved to be
an excellent solution for retrofitting. Siemens offers switchgear
trucks or withdrawable parts for all
kinds of different switchgear.
A possible solution is described
here using the example of Siemens
8BD1 switchgear. These switchgear
were equipped with minimum oil
circuit-breakers, which may be over
40 years old now. The production of
low-oil-content circuit-breakers
and the switchgear were discontinued in 1998, and it is becoming
more and more difficult and expensive to obtain spare parts for these
products today. The switchgear as
such is in good condition, but the
costs for maintenance are no longer
acceptable. The electrical specifications of the network have not
changed since the time of initial installation. This is a simple and typical case for replacement of the minimum oil circuit-breaker with a
modern vacuum circuit-breaker.
Before the replacement is carried
out, the system is inspected and the
dimensions measured. The condition of the switchgear is assessed
and existing documents are reviewed in order to take into account
modifications that have been carried out over the course of time. A
check is made to see whether the
circuit diagrams correspond to the
current state so that the new solution can replace the old one directly.
The object is to directly replicate
the existing switchgear truck. This
means that the new truck will have
the same dimensions, the same
contact arm system, the same inter-
locking, the same secondary equipment and wiring, and the same lowvoltage connectors. The switchgear
truck is completed at the factory so
that replacement is a simple “plug
and play” operation at the customer’s location. Naturally, the
switchgear truck with SION is tested
in an 8BD switchgear, the circuitbreaker in accordance with IEC
62271-100, and the complete
switchgear truck in the bay according to the main criteria of IEC
62271-200. The circuit-breaker is
thus upgraded compared with the
old one and complies with the requirements of the latest standards.
The entire switchgear is upgraded
in the same way: even though it
cannot be brought completely up to
the current state-of-the-art, it will
be operational as long as some of
the built-in components still comply with old standards.
Siemens offers retrofit solutions
for a large number of different
switchgear. This is illustrated by a
few examples here.
Since SION circuit-breakers have
smaller dimensions than conventional switchgear, they can be installed on any switchgear truck.
They are adapted to the existing
switchgear via the contact arms.
What needs to be taken into
account for retrofitting?
Retrofitting means the partial renewal of existing switchgear. It
makes a big difference whether a
major modification is intended or
not, since this will involve a kind of
“status protection.” A major modification by definition is accompanied
by a change of function, e.g.:
• Change of the rated voltage by
more than 20 percent
• Increased power output
• Change in the supply
• Change in measures to protect
against electric shock
In a case such as this, the entire
switchgear has to be adapted to the
current electro-technical safety regulations, which may require additional measures as well as additional tests. In this instance, the
cost-effectiveness of retrofitting
compared with a new system
should be examined.
If there is no change of function,
for example, exchange or repair of
the switchgear, the regulations applicable at the time the switchgear
was installed remain valid. It is an
Fig. 5: SION circuit-breakers as replacement for an air-magnetic circuit-breaker
advantage if the new circuit-breaker
is type-tested in the particular
switchgear, since then only a few
tests will be required on site.
The “plug and play” solution causes
only a brief interruption of operation.
What are the benefits for the operator?
Opting for an entirely new
switchgear certainly has many advantages. However, the fact should
not be overlooked that in such a
case it may be necessary to perform
work in an existing building on the
floor openings and on the cables.
Old cables in particular must be
carefully adapted to the new cable
bushings and then subjected to a
test. Installation of a new
switchgear in a new building can involve lengthy approval procedures,
and so create costs that are not incurred through a retrofit.
By replacing the most important
equipment in a switchgear, namely
the circuit-breaker, the operator increases the reliability and availability of its switchgear quite substantially without incurring costs for
modifications to the building. The
maintenance-free breakers available today hardly incur any costs for
maintenance; see Fig. 6. Devices
still in operation that have a liquid
(PDF 6330) published in
ew
arc-extinguishing medium, particularly if they are more than 30 years
old, require intensive maintenance.
The contact systems have to be inspected at short intervals, and may
need to be exchanged. The costs for
replacing these worn parts increase
considerably once the manufacturers have discontinued production
of the devices, since the parts now
have to be manufactured on a onetime basis. This development is
shown in the maintenance cost progression in Fig. 6. A decision in favor
of a new maintenance-free breaker
is immediately reflected in reduced
maintenance costs.
Apart from the reduced maintenance costs, a retrofit also increases
the reliability of the operator’s
switchgear. The new circuit-breakers are tested according to the latest
standards, which have significantly
stricter requirements in terms of
verifying switching capacity than
conventional breakers. Moreover, a
circuit-breaker approaching the
end of their service life are more
likely to develop a fault than a new
breaker. And with modern vacuum
switching technology, the consequences of a fault are far less serious
than with conventional low-oilcontent and expansion circuitbreakers, since explosions do not
occur with vacuum circuit-breakers.
vol.108 (2009), issue 22-23
5
Costs
Maintenance costs
nce
ena
t
Main
rog
ost p
c
Commissioning
previously
Vacuum CB
Maintenance costs
Minimum oil and SF6 CB
Expansion CB
ion
ress
today
in the future
38928.6
Fig. 6: Maintenance costs of old and modern circuit-breakers
Summary
Modern vacuum circuit-breakers
have proved ideal for use in routine
operation, a fact that is confirmed
by the more than 600,000 vacuum
circuit-breakers from Siemens that
are in service worldwide today.
SION vacuum circuit-breakers are
an outstanding solution for retrofitting on medium-voltage
switchgear. The investment costs
are paid off quickly, first because
servicing costs are very low due to
the maintenance-free circuitbreakers, and secondly because
availability is increased because of
6
(PDF 6330) published in
ew
the high degree of reliability. With
type-tested retrofit solutions, replacement of the switchgear truck
only requires the power supply to be
interrupted briefly because no work
or only a very limited amount needs
to be performed on the existing
switchgear.
dieter.saemann@siemens.com
www.siemens.com
vol.108 (2009), issue 22-23
This article appeared in:
ew
Volume 108 (2009), Issue 22 – 23
Copyright © 2009 by
EW Medien und Kongresse GmbH
This reprint is published by:
Siemens AG
Energy Sector
Freyeslebenstrasse 1
91058 Erlangen, Germany
Siemens AG
Energy Sector
Power Distribution Division
Medium Voltage
Mozartstrasse 31c
91052 Erlangen, Germany
For more information, please contact
our Customer Support Center.
Phone: +49 180/524 70 00
Fax:
+49 180/524 24 71
(Charges depending on provider)
E-mail: support.energy@siemens.com
Power Distribution Division
Order No. E50001-E710-A355-X-4A00
TH 260-091064 481130 SD 1209X
All rights reserved.
Trademarks mentioned in this document
are the property of Siemens AG, its affiliates,
or their respective owners.
Subject to change without prior notice.
The information in this document contains general
descriptions of the technical options available, which
may not apply in all cases. The required technical
options should therefore be specified in the contract.
www.siemens.com/energy