2003 09-08 joeck icefa fuse protection in transformer pole substation

2003-09-08 ICEFA, Seventh International Conference on Electrical Fuses and their Applications
Jurata
FUSE PROTECTION OF TRANSFORMER POLE SUBSTATION IN
POLAND
Józef Ossowicki(1)
, Remigiusz Joeck(2)
Instytut Elektrotechniki Oddział w Gdańsku(1)
, 80-557 Gdańsk, ul. Narwicka 1
ENERGA SA(2)
, 80-557 Gdańsk, ul. Marynarki Pol. 130, remigiusz.joeck@energa.pl
Abstract: The transformers protection in pole substations MV/LV 15/0,4 kV or 20/0,4 kV, is closely connected
with the protection of complete substation. In Poland, on the MV side mainly expulsion fuses are used but on
the LV side are used current limiting fuses with t-I characteristic gG or gF. It was proved that transformers rated
up to 400 kVA could be effectively and inexpensively protected by fuses against results of overloads and short-
circuits.
Keywords: protection, transformer pole substation, expulsion fuses, overload, short-circuits, t-I characteristic
1. Introduction
Correct protection of transformer pole substation
MV/LV against overloads and short-circuits, has an
essential influence on consumers supply continuity
and safety of people or animals situated close to the
substations. In Poland MV pole substations with
typical rated voltage of 15/0,4 kV or 20/0,4 kV are
mainly situated on the terrains of: agriculture, small
industrial plants or other consumers. They are built as
free–standing constructions with solutions depending
on local conditions. Many years of domestic
maintenance experiences proved [4] that the cheapest
as well as effective transformer protection in these
substations on the MV and LV side against results of
overloads and short-circuits, are properly selected
fuses [1, 3, 8, 10, 11]. In Poland for 40 years for
protection of three-phase transformers rated up to
400 kVA on the 15 kV or 20 kV side, where
prospective short-circuit current does not exceed 3,15
kA [4, 8, 19], were used domestic expulsion fuses
(fig. 1A). For protection of larger transformers or in
case of larger short-circuit currents there are used
limiting fuses (fig. 1B).
Voltage, rated current and breaking capacity of a
fuse are selected according to the basic rules, taking
into consideration permissible transformer overloads.
The permissible operation overload is essential in the
case of distribution transformers. It was accepted that
distribution oil transformer overloads with current
1,5 InT and 1,3 InT should not lasted longer than
adequately 2 and 10 h [5]. Due to the fact that the
transformer has thermal time-constant larger than
series connected conductors and apparatus, all circuit
elements [5] should have the rated current larger than
transformer e.g. In ≥1,25InT. This rule applies also
secondary transformer circuit.
At the beginning of the 70-ties there was a
tendency in Western Europe, especially in France to
simplify transformer pole substation by
eliminating protections on the MV side. Many
fuses were removed what was explained that they
operate due to not justified reasons. It was soon
apparent that the fuses lack of was the reason of
many transformers faults which were dangerous for
surrounding. There were stated cases of oil leaks and
even oil ignition which is an unacceptable ecological
danger for the environment.
Considering different ways of transformer pole
substation protection, the transformers faults
statistics should be observed. Statistics from different
countries could differ a lot, because they concern
transformers produced, installed, protected and

Jurata
supervised according to the rules of specific technical
education. Polish observations of 6 000 distribution
transformers from period 1990 – 1992, proved that
every year 1% of them are damaged, c.a. 2/3 faults
are internal short-circuit of HV windings, from these
windings to core or oil tank, and also between HV
winding and LV winding [5]. (Undoubtedly, the
newest domestic transformers have several times
lower fault rates). Similar German observation [1] of
600 000 oil distribution transformers, proved that
average fault rate was ten times lower because every
year 0,1% transformers were damaged. Despite a
small fault amount in the latest years, due to the
ecological requirements, there is an observed
noticeable comeback to protection of transformer
pole substations by fuses. It was proved by
experimental testing [2] carried out on single-phase
transformer substations models, rated 50 and 100
kVA. The testing aim was an explanation of MV
fuses operation without reasons especially during
atmospheric discharges. The good example could be
the co-operation between French power engineers
and SIBA company where the new fuse construction
was developed [20]. It enables easy fuse links
replacement by hot stick from the ground level
(without pole climbing).
On the contrary to West Europe experiences, in
Poland almost for 10 years there is a tendency to
eliminate MV fuses in pole substations which are
rated lower than 400 kVA [6, 12]. It is a result of too
many unjustified reasons of expulsion fuse
operations, caused probably by information lack in
catalogues how to select properly these fuses
considering operation co-ordination with fuses on the
LV side. For example in the catalogue [19] there are
presented recommended expulsion fuse nominal
currents for transformer protection on the rated
voltage of 15 kV. The maximum nominal currents of
fuses with gG characteristic which can be used on the
0,4 kV side there were not mentioned.
2. Fuse selection in transformer pole
substations
In Poland are used three variants of transformer
substation protection by fuses (fig. 1).
A B C
Fig. 1. Protection methods of transformer pole substations MV/LV
gG or gF
T
MV
gG or gF
T
MV
LV/gG
gG or gF
T
MV
LV/gTr

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The protection method should be selected according
to nominal transformer power and prospective short-
circuit current on the MV side.
• A – On the MV side are used expulsion fuses
when nominal transformer power is not larger
than 400 kVA and prospective short-circuit
current does not exceed 3,15 kA (unless the
expulsion fuses producer proves that his fuses
can be used for protection of transformers with
larger nominal power or in network with larger
prospective short-circuit current).
• B – On the MV side are used classic current
limiting fuses when prospective short-circuit
current is larger than 3,15 kA or when nominal
transformer power exceeds 400 kVA.
• C – Is used when nominal transformer power
is larger than 630 kVA and does not exceed
1000 kVA.
Typical transformer pole substation (fig. 2)
consists of a transformer (T) with nominal power not
exceeding 250 kVA supplied from MV network
usually through expulsion fuses (1), and surge
arresters (not shown on the fig. 2).
Fig. 2. Typical diagram of transformer pole substation ( overvoltage protection is not shown )
In the new products offered among other
producers by ZRE Gdańsk [18] one of MV fuse base
insulator is also a surge arrester. On the
transformers secondary side, in the LV part,
particular outgoing feeders are protected by fuses (2)
with t-I characteristic gG or fast gF in case of rural
network when shock prevention is required.
3. Protection on the MV side
The tasks of MV fuses in transformer pole substation
are:
• protection of the substation part between fuses
connections and transformer clamps against
results of short-circuits,
• transformer protection against: oil tank fault, oil
leak and possible its ignition due to the short-
circuit inside transformer caused by e.g.
insulation breakdown,
• cut-off of two and three-phase short-circuits when
they appears on the secondary transformer side,
on the substation part between bushings and fuse
entrance clamps or fuse load switches on the
particular outgoing feeders (fig. 2).
Fuses for transformers protection should have big
enough operation current If0,1 with prearcing time of
MV
15 kV
1
20 A
T
250 kVA
LV
gG or gF
0,4 kV 2

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0,1 s regarding making current holding and
selectivity with protections on the secondary side.
Relative value (with reference to nominal current of
fuse-link In should fulfil the condition (1) [16]
25,0
1,0
100
7 





⋅≥ n
n
f I
I
I
(1)
Fuses should have relatively small prearcing
current If10 in time 10 s due to detection of turn to
turn short-circuit on the secondary transformer side
and selectivity with preceding protections, so the
condition (2) [16] should be fulfilled
6
10
≤
n
f
I
I
(2)
MV fuses should be selected according to the
following:
• Their nominal short-circuit breaking
capacity declared by producer should be not
lower than prospective short-circuit current in
the installation place.
• They should not operate during transformer
switching on in any phase time. It is a
convention [5, 8] that prearcing time at current
12 InT ≥ 0,1 s ; and at current 25 InT ≥ 0,01s. In
their catalogues fuse producers usually describe
type and values of fuse nominal currents which
should be used for transformers protection.
• Their t-I characteristic in prearcing time
(starting from overload to short-circuit in whole
range) should run above t-I characteristic of LV
fuse cut-off for the biggest nominal current of
fuse situated in LV switchgear (fig. 3). Usually
it is accepted that it is the close current to
nominal transformer current InT.
• They should operate in a period shorter than
1 s, if two or three-phase short-circuit on the
secondary transformer side in the substation
part between bushings and LV fuses clamps
appear (fig. 2);
• The maximum value of Joule integral I2
t of
MV fuse cut-off should not exceed 105
A2
s. This
condition is caused by durability of transformer
tank to bursting when internal short-circuit
occurs in the transformer [10].
Requirements mentioned above are easily met in
domestic expulsion fuses [4, 17, 19].
On the Fig. 3, continuous lines present prearcing
t-I characteristics of expulsion fuses for rated voltage
of 15 kV (have been produced in Poland for many
years). Dashed lines show the characteristics
(calculated to the 15 kV side) of maximum fuse
disconnection time (characteristic gG) permitted by
Polish Standard [14]. Fuses from many producers are
in use in Poland. Their t-I characteristics sometimes
differ a lot but all of them should be placed in
required band shown in Polish Standard [14]. Due to
their variety maximum characteristics of permissible
disconnection times should be chosen in the
selectivity analysis. The greatest approach between
these characteristics, occurs when short circuit
current on the 0,4 kV side calculated to the 15 kV
side is ca. 2,5In of expulsion fuse.

Jurata
Fig. 3. Example of t-I characteristics of: prearcing domestic expulsion15 kV fuses (continuous lines); gG fuse
disconnection calculated to the 15 kV side (dashed lines). Explanations in the text …
In Table 1 it is shown an example of properly selected domestic expulsion fuses which protect the transformers
rated 63 ÷ 400 kVA. On the 0,4 kV side there are used fuses with gG characteristic.
Table 1. Example of fuse selection in transformer pole substations 15/0,4 kV
Transformer
rated power
[kVA]
Nominal voltage 15 kV Nominal voltage 0,4 kV
Transformer
rated current [A]
Fuse rated
current [A]
Transformer
rated current [A]
Fuse rated*)
current [A]
63
100
160
250
400
2,43
3,85
6,20
9,60
15,40
6
10
16
20
25
91,0
144,5
231,0
361,0
578,0
63
125
200
315
400
*) It is the largest rated current of gG fuse-link which assures selective fuse operations.

Jurata
4. Protection on the LV side
• Fuse selection and protection method of
transformer pole substation on the LV side
depends mainly on nominal transformer power,
less on fuse type or prospective short-circuit
current on the MV side.
• To protect transformers rated up to 400 kVA
against results of overloads and short-circuits,
properly selected fuses on outgoing feeders in
LV switchgear (fig. 1A) should be satisfied,
because in opinion of experienced people there
is a low probability of exceeding permissible
transformer overloads by current 1,3 InT during
10 h and current 1,5 InT during 2 h.
• To protect transformers larger than 400
kVA should be used a protection on the
entrance to the LV switchgear. For this purpose
fuses with transformer characteristic gTr are the
most suitable [17] (fig. 1C). Their advantages
are that they enable full using of permissible
transformer overload [9] and better limit short-
circuit current than fuses with gG characteristic.
5. Conclusions
• Many years of maintenance experiences in West
Europe concerning use of classic limiting fuses
and Polish experiences in use MV expulsion
fuses, point at that the cheapest and also most
effective way of transformer protection and other
parts of substation, against results of overload and
short-circuit are properly selected fuses.
• For transformer protection on the MV side with
nominal power not exceeding 400 kVA, when
prospective short-circuit currents do not exceed
3,15 kA, domestic expulsion fuses are
recommended [18].
• Transformers larger than 400 kVA should be
protected by classic short-circuit current limiting
fuses when prospective short-circuit current
exceeds 3,15 kA on the MV side.
• The mistakes in maintenance can be avoided if
expulsion fuse links are marked by transformer
nominal power and not by nominal current,
according to the standard DIN/VDE [17] for LV
fuse links with gTr characteristic.
• The MV fuses task is to protect transformers
against results of internal short-circuit (oil tank
damage, oil leak and possible its ignition due to
short-circuit occurred inside the transformer) and
cut-off of two and three-phase short-circuit when
it appears on the primary or secondary side in the
substation part between transformer clamps and
fuses.
• Due to the introduction of a new standard PN-IEC
60282-2 [14], some technical parameters of
domestic expulsion fuses (especially for rated
current of 6A) should be corrected and catalogues
completed with necessary technical data,
especially Joule integral I2
t in prearcing time and
during cut-off is what is needed for designers and
users for proper fuses application.
6. References
[1] Hampel W. ; Hartmann E.; Karlscheur
W.;Tenberge W.: „Schutz von
Verteilungstransformatoren“,
Elektrizitätswirschaft, Jg. 91 (1992), Heft 25 z.
1660-1663
[2] Hamel A.; Paquette M.; St-Jean G.: “Nuisance
Fuse Operation on MV Transformers During
Storms”, IEEE Transactions on Power Delivery,
Vol. 5, No. 4, November 1990
[3] Hartmann E.: „Verhalten und Schutz von
Verteilungstransformatoren“, CIRED 89
[4] Kacprzak B.; Hyrczak A.: “Service experience
of new high-voltage expulsion fuses at rural
outdoor networks”, CIRED 1989, s. 76-79
[5] Lipski T.; Musiał E.: „Bezpieczniki topikowe i
ich zastosowania”, Rozdz.8.4.

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Podręcznik przygotowany do druku
[6] Michniewski R.: „Eksploatacja stacji
transformatorowych 15/0,4 kV słupowych
uproszczonych w ZE Toruń S.A.”, Biul. Infor.
PTPiREE, nr 2/96
[7] Ossowicki J.; Sibilski H.: „Zabezpieczenia
rozdzielnic pierścieniowych średniego
napięcia”, WE 2000, nr 9
[8] Ossowicki J.: „Nowoczesne zabezpieczenia
transformatorów rozdzielczych”,
Przedsiębiorstwo ENERGO- EKO- TECH
Poznań - Kiekrz paźdz. 2000
[9] Ossowicki J.: „Bezpieczniki topikowe o
charakterystyce gTr w stacjach
transformatorowych”, Biul. Infor. PTPiREE nr
3/2002
[10] Planzlaff K.P., Schemmann B.: „Prűfung des
Verhaltens bei inneren Fehlern im
Transformatorenraum bei nicht begehbaren
Ortsnetzstationen“, Elektrizitätswirtschafft, Jg.
89(1990) Heft 16/17
[11] Popeck C.A., Lewis W.A. and Allen G. D.: “The
Application of Current Limiting to
Distribution Circuit Protection”, USA 1977
[12] „STANDARDY TECHNICZNE
OBOWIĄZUJĄCE DLA URZĄDZEŃ SN i
nN EKSPLOATOWANYCH W ENERDZE
GDAŃSKIEJ KOMPANII
ENERGETYCZNEJ”, S.A. Gdańsk styczeń
2002
[13] PN-92/E-06110: „Bezpieczniki topikowe
wysokiego napięcia. Bezpieczniki ograniczające
prąd”
[14] PN-HD 630.2.1. S5: 2003 (U) „Bezpieczniki
topikowe niskonapięciowe. Część 2-1:
Wymagania dodatkowe dotyczące
bezpieczników przeznaczonych do wymiany
przez osoby wykwalifikowane (przeznaczone
głównie do stosowania w przemyśle). Sekcja od
I do V: Przykłady typowych znormalizowanych
bezpieczników”
[15] PN-IEC 60282-2: „Bezpieczniki topikowe
wysokonapięciowe. Bezpieczniki gazo-
wydmuchowe”, listopad 1999
[16] IEC Publ. 787: “Application guide for the
selection of fuse-links of high voltage fuses for
transformer circuit applications”, 1983
[17] DIN/VDE 0636-201/A10 z października 1997.:
„Niederspannungssicherungen (NH-System)
Teil 2: Zusätzliche Anforderungen an
Sicherungen zum Gebrauch durch
Elektrofachkräfte bzw. elektrotechnisch
unterwiesene Personen (Sicherungen
überwiegend für den industriellen Gebrauch).
Hauptabschnitte I bis V“
[18] Katalog firmy ZRE Gdańsk:
„Wysokonapięciowy zespół zabezpieczający
typu WZZ”
[19] Katalog firmy ZRE Gdańsk: „Wkładka
bezpiecznikowa gazowydmuchowa
napowietrzna typu WBGN”
[20] Katalog firmy SIBA: „HH –Sicherungseinsätze
HH 1- 03/00“

2003 09-08 joeck icefa fuse protection in transformer pole substation

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2003 09-08 joeck icefa fuse protection in transformer pole substation