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Metal Enclosed and Pluggable Surge Arresters
for Vm = 72.5kV
R. B. Grund, Pfisterer Kontaktsysteme, and M.S. Zerrer, Pfisterer Kontaktsysteme

Abstract—Surge arresters are a vital component for network
safety. At Medium voltage networks (Vm ≤ 52kV), dry type
pluggable surge arresters are known and widely used. This
solution has now been taken to the next voltage level, Vm =
72.5kV. This paper discusses the general function, application in
GIS and transformers, as well as testing.
Fig. 1. Pluggable System
Index Terms—Surge Arrester, High Voltage, Dry Type, PlugIn
I. INTRODUCTION
S
urge arresters are a main component in securing a high
voltage network. There are three types of overvoltage that
can occur. [1] Voltage swells and overvoltage may occur
during load rejection or earth connection faults. The duration
lies between 0.1 seconds and several hours. In general the
surge is of no danger to the network operation, however it is an
important information for dimensioning of the arrester.
Switching overvoltage occur during switching procedures and
consist mostly of heavily damped oscillations with frequencies
up to several kHz. Lightning overvoltage can reach very high
values endangering the systems safety.
In order to minimize these risks damaging the network,
surge arresters are widely used. As we see a major change in
replacing air insulated systems by cable systems -mainly in
urban areas, places with lack of space and areas of high
security level - surge arresters should meet the same
expectation in reliability, lifetime and securing aspects.
Therefore a pluggable, metal enclosed surge arrester was
developed tested and is now available for service.
II. MODULAR SETUP UTILIZING PLUGGABLE COMPONENTS
Flexibility as well as modular setup and completely metal
enclosed and therefore secure networks are getting more and
more important. This can only be achieved by using pluggable
components. These components allow separate manufacturing
and testing.
Such a connecting system consists of two main parts, the
socket and the connector as shown in Fig. 1. The socket is
fitted into a switchgear or transformer. The cable connector is
fitted onto an XLPE or EPR insulated cable.
The socket design includes a high voltage stress relief which
is located inside the cast resin body connected to the high
voltage contact element. Furthermore a capacitive voltage tap
is optionally integrated in the socket.
The separable connector which is plugged into the socket
consists of the contact element an insulating part including the
electrical stress relief and a metallic housing.
The cable connector is a familiar product which is mainly
used in the common sense of a cable accessory. Nevertheless
most options are achieved whilst viewing the socket as an
interface. An interface for testing, operation (as part of a cable
system), operation (as part of an air insulated system) or as a
connecting point for a surge arrester.
Fig. 2. Surge arrester Size 4 Vm = 72.5kV
This solution offers the flexibility and security directly at
the hot spot of the equipment.
The system above 72.5 kV is classified according to
different sizes. These sizes do mainly refer to the cables
dimensions. The interface is standardized whereas a size 4
socket complies to a size 4 connector, size 4 current testing
connector, size 4 test joint and a size 4 surge arrester.
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Fig. 3. Size Classification, Dry Type plug-in- Connector
III. SETUP AND FUNCTION OF SURGE ARRESTER
The dry type surge arrester consists of a contact element
relevant for low resistance connection to the socket, utilizing
contact lamellas. This type of contact allows a reliable
interconnection for the operating idle current of the surge
arrestor as well as the high impulse current in case of the surge
arrestor has to secure from overvoltage. The insulation part of
the plug-in system between high voltage and earthed parts is
made of silicone.
The main part, regarding the function of a surge arrestor are
specific metal oxide resistor tablets. These MO-tablets are
used as a non linear component with a very low leakage
current during operation. The tablets are connected to the male
part of the plug-in system and are insulated by a silicone body.
This insulating body includes field controlling elements. The
head armature includes a bursting disk for pressure relief and a
turnable head for the re-direction of the gas, in the event of a
failure according to IEC 60099-4. The housing is made of
glass-fiber reinforced resin and allows enormous mechanical
strength as well as protection of the silicon body against
environmental conditions. The silicone body itself is protected
and touch-proof. A special arrangement of the earthing path
allows connecting monitoring devices or discharge counters if
desired.
more substituted by encapsulated systems. In the event of an
Overvoltage impulse, started e.g. by a lightning, the wave is
travelling at the high voltage line. The amplitude of that signal
is mainly influenced by the intensity of the lightning as well as
the distance between the position of the lightning stroke and
the location of the transformer. Furthermore, every change of
the surge impedance of the line, e.g. between the air insulated
line and the underground cable, causes reflections and phase
inversions of the traveling wave. This could lead to
interferences, causing the amplitude to increase. This wave,
travelling along the cable conductor of a cable system could
hit into a transformer, causing damage if the insulating
coordinates of the transformer is below the amplitude of that
wave. One possibility to reduce the risk is achieved by adding
a surge arrester at the connecting point between the air
insulated line to the ground cable systems. This is a preferred
position, because the transformers connections and the cable
impedance mismatch, which usually doubles the amplitude of
the incoming traveling wave.
This leads to additional effort in calculating the network
and the specific surge arrester due to additional influences by
cable impedance, cable length, transformer impedance, as well
as external sources. The optimum would be the positioning of
a surge arrester directly at the transformer, possibly as near as
possible to the transformer core. The pluggable solution offers
this functionality, an additional socket is to be integrated in the
transformer body, connected to the transformer core. The
surge arrester assembled by a simple plug-in process is then
being assembled and positioned directly at the so called “hot
spot”.
V. APPLICATION SWITCHGEAR
In view of cable systems, a gas insulated switchgear is an
additional connecting point for surge arresters. This demand is
generally met by adding an gas insulated department including
Metaloxyd tablets. One disadvantage of this well known
technique is an additional need for SF6 as well as additional
space requirement. As SF6 is known as the strongest green
house gas[4], switchgear manufactures must reduce it to a
minimum.
Furthermore an additional gas compartment needs to be
separated, monitored in view of moisture and must include a
bursting relief.
Fig. 4. Cut View of surge arrester Size 4
The arresters main insulation is pure silicone, there is no
insulation liquid or insulation gas such as SF6 included.
IV. APPLICATION TRANSFORMER
Transformers are one of the main components with the need
to be secured against overvoltage. Conventional surge arresters
are positioned at an air insulated environment parallel to
conventional bushings.
As space saving is getting more important and due to safety
issues, these air insulated switchyards are getting more and
A Dry Type Plug-in surge arrester requires an additional
socket in the existing compartment. Assembly of the surge
arrester is a simple plug-in process. In the event of an
Overvoltage at which the surge arrester blows up massive load
of energy is distributed. This causes the surrounding of the
MOx tablets to be affected as well. Utilizing an SF6 insulated
arrester generally results in or replacement of the GIS
compartment as well as the Spacers. In comparison a
pluggable surge arrester can be replaced without gas works
resulting in a reduced back in service time.
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VI. TECHNICAL DATA
Surge arrester are selected according to different aspects
such as
Highest system voltage Vm

Handling of Neutral point (solid earth, …)

Voltage swells and overvoltage (environment)

Nominal Discharge Current

Energy absorption

Safety factors
These factors lead to the electrical definitions of the surge
arrester suitable for the network.
TABLE I.
MCOV RATINGS AND RESULTING RESIDUAL VOLTAGES
VII. DETERMINATION OF TEMPORARY OVERVOLTAGE TIME
CHARACTERISTIC (TOV)
Due to networks setup and external influences, voltage
swell as well as overvoltage might be unavoidable. Thermal
stress on the metal oxide resistor tablets is the result. The
maximum allowable limits regarding time and overvoltage can
be determined according to a so called TOV- chart (Fig. 5).
This information is crucial for networks operator to know the
allowed limits for safe network operation. This measurement is
therefore obligatory to pass a Type Test according to IEC
60099-4 [3]. Measurement is performed on a thermal
equivalent consisting of a single tablet in its original
configuration as shown in Fig. 6. This test configuration is
thermally insulated at the top and the bottom to guarantee a
thermal behavior which is equivalent or worse to the original
configuration.
Fig. 6. Test setup for TOV
In operation an overvoltage could occur in a state of a
maximum nominal thermal stress. Therefore pre-stress is part
of the actual TOV measurement:
The samples are preheated to 60°C (140°F). After
preheating, two long duration current impulses are applied to
reach the required energy according to IEC 60099-4 [3]. The
time interval between the impulses has to be between 50s and
60s. Within less than 0.1s after the application of the second
impulse, the temporary power-frequency overvoltage VTOV has
to be applied for the duration tTOV. Then the elevated
continuous operating voltage VMCOV’ has to be applied to
prove the thermal stability. Power dissipation of the thermal
equivalent must decrease or stay stable during application of
VMCOV’. VMCOV’ is the elevated continuous operating voltage
according to IEC 60099-4 [3].
This measurement is to be repeated with several pairs of
VTOV and tTOV. As these values should be as high as possible it
is the aim to get the values as near as possible to the physical
limits without thermal runaway.
To determine the overall power dissipation of the arrester
during pre-stress the energy level is monitored and calculated.
Vref is measured before and after each measurement block to
ensure no physical damage of thermal equivalent. With several
measurement pairs of VTOV and tTOV the following chart (Fig.5)
is determined.
1,4
1,3
1,2
V/V C

1,1
1
0,9
continuous operating voltage Vc
0,8
0,1
1
10
100
t [s]
Fig. 5. Power frequency versus TOV
1000
10000
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VIII. REFERENCES
References:
[1]
[2]
[3]
[4]
ABB, Wettingen, July 1999, Application Guidelines Overvoltage
Protection
Prof. Hinrichsen, Siemens, February 2011, Surge Arrester Handbook
IEC 60099-4, SURGE ARRESTERS - PART 4: METAL-OXIDE SURGE
ARRESTERS WITHOUT GAPS FOR A.C. SYSTEMS
P. Forster, P., V. Ramaswamy et al.: Changes in Atmospheric
Constituents and in Radiative Forcing. In: Climate Change 2007: The
Physical Science Basis. Contribution of Working Group I to the Fourth
Assessment Report of the Intergovernmental Panel on Climate Change.
Cambridge University Press, Cambridge und New York 2007, pg. 212
IX. BIOGRAPHIES
Ruben Grund (M’1980) was born in
Stuttgart. He graduated from the University of
Applied Science Esslingen holding a degree of
electrical Engineering.
He works in the field of cable accessories focusing
on Plug-able systems.
Directed Research on a UHF PD diagnosis system
for a corporate- sponsored doctoral student.
Michael Zerrer (M’1976) was born in
Kirchheim Teck . He graduated from the
University of Stuttgart holding a degree of
electrical Engineering. He worked in the field of
automotive EMC measurement at the University
of Stuttgart during his PhD.
Since two years he is Head of R&D at
PFISTERER.