SIST EN 50708-2-3:2022
(Main)Power transformers - Additional European requirements - Part 2-3: Medium power transformer - Accessories
Power transformers - Additional European requirements - Part 2-3: Medium power transformer - Accessories
This document describes lists of typical accessories used for liquid and dry type Medium Power Transformers (≤3150kVA). It defines the interface between the transformer's terminals, including cable boxes, and the power grid.
Leistungstransformatoren - Zusätzliche europäische Anforderungen - Teil 2-3: Mittelleistungstransformatoren - Zubehör
Transformateurs de puissance - Exigences européennes supplémentaires - Partie 2-3 : Transformateurs de moyenne puissance - Accessoires
Le présent document décrit des listes des accessoires types utilisés pour les transformateurs de moyenne puissance (≤ 3 150 kVA) à diélectrique liquide et de type sec. Il définit l’interface entre les bornes du transformateur, y compris les boîtes à câbles, et le réseau d’alimentation.
Močnostni transformatorji - Dodatne evropske zahteve - 2-3. del: Srednji močnostni transformatorji - Pribor
Ta dokument opisuje sezname tipičnega pribora, ki se uporablja za srednje močnostne transformatorje (≤ 3150 kVA) vlažnega in suhega tipa. Določa vmesnik med terminali transformatorja, vključno s kabelskimi omaricami in električnim omrežjem.
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN 50708-2-3:2022
01-november-2022
Močnostni transformatorji - Dodatne evropske zahteve - 2-3. del: Srednji
močnostni transformatorji - Pribor
Power transformers - Additional European requirements - Part 2-3: Medium power
transformer - Accessories
Transformateurs de puissance - Exigences européennes supplémentaires - Partie 2-3 :
Transformateurs de moyenne puissance - Accessoires
Ta slovenski standard je istoveten z: EN 50708-2-3:2022
ICS:
29.180 Transformatorji. Dušilke Transformers. Reactors
SIST EN 50708-2-3:2022 en,fr
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST EN 50708-2-3:2022
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SIST EN 50708-2-3:2022
EUROPEAN STANDARD EN 50708-2-3
NORME EUROPÉENNE
EUROPÄISCHE NORM September 2022
ICS 29.180
English Version
Power transformers - Additional European requirements -
Part 2-3: Medium power transformer - Accessories
Transformateurs de puissance - Exigences européennes Leistungstransformatoren - Zusätzliche europäische
supplémentaires - Partie 2-3 : Transformateurs de moyenne Anforderungen - Teil 2-3: Mittelleistungstransformatoren -
puissance - Accessoires Zubehör
This European Standard was approved by CENELEC on 2022-08-15. CENELEC members are bound to comply with the CEN/CENELEC
Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC
Management Centre or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the
same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the
Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Türkiye and the United Kingdom.
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2022 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN 50708-2-3:2022 E
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SIST EN 50708-2-3:2022
EN 50708-2-3:2022 (E)
Contents Page
European foreword . 3
Introduction . 4
1 Scope . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Service conditions . 5
5 Electrical characteristics . 5
6 Design requirements . 5
6.1 Liquid immersed transformers . 5
6.1.1 Type of liquid preservation system . 5
6.1.2 Terminals . 6
6.1.3 Terminal markings . 6
6.1.4 Distance between bushings . 6
6.1.5 Wheels . 6
6.1.6 Filling hole . 7
6.2 Dry-type transformers . 7
6.2.1 Terminals . 7
6.2.2 Terminal markings . 7
6.2.3 Wheels . 7
6.2.4 Enclosure. 7
7 Accessories . 7
7.1 Liquid immersed transformers . 7
7.2 Dry-type transformers . 9
Bibliography . 10
2
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SIST EN 50708-2-3:2022
EN 50708-2-3:2022 (E)
European foreword
This document (EN 50708-2-3:2022) has been prepared by CLC/TC 14 “Power transformers”.
The following dates are fixed:
• latest date by which this document has to be (dop) 2023-08-15
implemented at national level by publication of
an identical national standard or by
endorsement
• latest date by which the national standards (dow) 2025-08-15
conflicting with this document have to be
withdrawn
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CENELEC shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national committee. A
complete listing of these bodies can be found on the CENELEC website.
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EN 50708-2-3:2022 (E)
Introduction
This part of the EN 50708 series deals with the accessories.
For the purpose of this document, the requirements of the general EN 50708-1-1:2020 apply.
This document contains particular requirements for specific transformers or transformer applications, which
are based on the requirements of the general EN 50708-1-1:2020.
This document should be considered in conjunction with the requirements of the general parts.
The particular requirements of the different sub parts of EN 50708
...
SLOVENSKI STANDARD
oSIST prEN 50708-2-3:2020
01-oktober-2020
Močnostni transformatorji - Dodatne evropske zahteve - 2-3. del: Srednji
močnostni transformatorj - Pribor
Power transformers - Additional European requirements - Part 2-3: Medium power
transformer - Accessories
Transformateurs de puissance - Exigences européennes supplémentaires - Partie 2-3 :
Transformateurs de moyenne puissance - Accessoires
Ta slovenski standard je istoveten z: prEN 50708-2-3
ICS:
29.180 Transformatorji. Dušilke Transformers. Reactors
oSIST prEN 50708-2-3:2020 en,fr
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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oSIST prEN 50708-2-3:2020
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oSIST prEN 50708-2-3:2020
EUROPEAN STANDARD DRAFT
prEN 50708-2-3
NORME EUROPÉENNE
EUROPÄISCHE NORM
August 2020
ICS
English Version
Power transformers - Additional European requirements - Part 2-
3: Medium power transformer - Accessories
Transformateurs de puissance - Exigences européennes To be completed
supplémentaires - Partie 2-3 : Transformateurs de moyenne
puissance - Accessoires
This draft European Standard is submitted to CENELEC members for enquiry.
Deadline for CENELEC: 2020-10-30.
It has been drawn up by CLC/TC 14.
If this draft becomes a European Standard, CENELEC members are bound to comply with the CEN/CENELEC Internal Regulations which
stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
This draft European Standard was established by CENELEC in three official versions (English, French, German).
A version in any other language made by translation under the responsibility of a CENELEC member into its own language and notified to
the CEN-CENELEC Management Centre has the same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the
Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are aware and to
provide supporting documentation.
Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without notice and
shall not be referred to as a European Standard.
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2020 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Project: 70485 Ref. No. prEN 50708-2-3 E
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prEN 50708-2-3:2020 (E)
1 Contents
2 European foreword . 4
3 Introduction . 5
4 1 Scope . 6
5 2 Normative references . 6
6 3 Terms and definitions . 6
7 4 Service conditions . 8
8 5 Electrical characteristics . 8
9 6 Design requirements . 8
10 6.1 Liquid immersed transformers . 8
11 Type of liquid preservation system and degree of sealing . 8
6.1.1
12 6.1.2 Terminals . 8
13 6.1.3 Terminal markings . 8
14 6.1.4 Distance between bushings . 8
15 6.1.5 Rollers . 9
16 6.2 Dry-type transformers . 9
17 Terminals . 9
6.2.1
18 6.2.2 Terminal markings . 10
19 6.2.3 Rollers . 10
20 6.2.4 Enclosure . 10
21 7 Accessories . 10
22 7.1 Liquid immersed transformers . 10
23 7.2 Dry-type transformers . 11
24 8 Cable box for Liquid immersed transformers . 11
25 Transformers with cable boxes on the high-voltage and/or low-voltage
8.1
26 side . 11
27 8.1.1 General consideration . 11
28 8.1.2 Provision for cable box Type 1 connections . 11
29 8.1.3 Provision for cable box Type 2 . 11
30 8.1.4 Transformer requirements . 12
31 8.1.5 Distance between bushings . 13
32 8.1.6 Tests . 13
33 8.2 Transformers with cable boxes on the high-voltage and/or low-voltage side
34 - Cable boxes type 1 . 18
35 8.2.1 General consideration . 18
36 8.2.2 Electrical requirements and clearances . 18
37 8.2.3 Design considerations . 20
38 8.2.4 Tests . 21
39 8.2.5 Earthing of cable boxes . 21
40 8.3 Transformers with cable boxes on the high-voltage and/or low-voltage side
41 -Cable boxes type 2. . 21
42 8.3.1 General consideration . 21
43 8.3.2 High-voltage connections . 22
44 8.3.3 Low-voltage connections . 23
45 8.3.4 Design considerations . 24
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46 8.3.5 Tests . 25
47
3
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48 European foreword
49 This document (prEN 50708-2-3:2020) has been prepared by CLC/TC 14 “Power transformers”.
50 This document is currently submitted to the Enquiry.
51 The following dates are proposed:
• latest date by which the existence of this (doa) dor + 6 months
document has to be announced at national
level
• latest date by which this document has to be (dop) dor + 12 months
implemented at national level by publication of
an identical national standard or by
endorsement
• latest date by which the national standards (dow) dor + 36 months
conflicting with this document have to be (to be confirmed or
withdrawn modified when voting)
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52 Introduction
53 This document defines the rules for the assessment of energy performance to ensure the product
54 conformity to the Commission Regulation (EU) No 548/2014 of 21 May 2014 and its amendment No
55 2019/1783 of 1 October 2019.
56 Regulation leads to have a minimum level of energy performances of power transformers.
57 NOTE In this document, the term Regulation refers to the Commission Regulation (EU) No 548/2014 of 21
58 May 2014 and its amendment No 2019/1783 of 1 October 2019.
59 For the purpose of this document, the requirements of the general EN 50708-1-1:2020 apply.
60 This document contains particular requirements for specific transformers or transformer applications,
61 which are based on the requirements of the general EN 50708-1-1:2020.
62 This document should considered in conjunction with the requirements of the general parts.
63 The particular requirements of the different sub parts of EN 50708 supplement, modify or replace
64 certain requirements of the general parts of EN 50708-1 and/or EN 50708-1-X being valid at the time
65 of publication of this document. The absence of references to the exclusion of a part or a clause of a
66 general part means that the corresponding clauses of the general part are applicable (undated
67 reference).
68 Requirements of other -X parts with X greater than 1 being eventually relevant for cases covered by
69 this document also apply. This document could therefore also supplement, modify or replace certain
70 of these requirements valid at the time of publication of this document.
71 The main clause numbering of each part follows the pattern and corresponding references of
72 EN 50708-1-1:2020. The numbers following the particular number of this document are those of the
73 corresponding parts, or clauses of the other parts of the EN 50708 series, valid at the time of
74 publication of this document.
75 In the case where new or amended general parts with modified numbering were published after the
76 sub part was issued, the clause numbers referring to a general part in sub parts might no longer align
77 with the latest edition of the general part. Dated references should be observed.
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78 1 Scope
79 This document describes lists of typical accessories used for liquid and dry type Medium Power
80 Transformers (≤3150kVA). It defines the interface between the transformer's terminals, including
81 cable boxes, and the power grid.
82 2 Normative references
83 The following documents are referred to in the text in such a way that some or all of their content
84 constitutes requirements of this document. For dated references, only the edition cited applies. For
85 undated references, the latest edition of the referenced document (including any amendments)
86 applies.
87 EN 50180, Bushings above 1 kV up to 36 kV and from 250 A to 3,15 kA for liquid filled transformers
88 EN 50216-4, Power transformer and reactor fittings - Part 4: Basic accessories (earthing terminal,
89 drain and filling devices, thermometer pocket, wheel assembly)
90 EN 50336, Bushings for transformers and reactor cable boxes not exceeding 36 kV
91 EN 50386, Bushings up to 1 kV and from 250 A to 5 kA, for liquid filled transformers
92 EN 50387, Busbar bushings up to 1 kV and from 1,25 kA to 5 kA, for liquid filled transformers
93 EN 50708-1-1:2020, Power transformers - Additional European requirements: Part 1-1: Common part
94 - General requirements
95 EN 50708-2-1, Power transformers - Additional European requirements: Part 2-1 Medium power
96 transformer - General requirements
97 EN 50708-3-1, Power transformers - Additional European requirements: Part 3-1 Large power
98 transformer - General requirements
99 EN 60076-1, Power transformers - Part 1: General (IEC 60076-1)
100 EN 60076-3, Power transformers - Part 3: Insulation levels, dielectric tests and external clearances in
101 air (IEC 60076-3)
102 EN IEC 60076-11, Power transformers - Part 11: Dry-type transformers (IEC 60076-11)
103 EN IEC 60076-22-7, Power transformers - Part 22-7: Power transformer and reactor fittings -
104 Accessories and fittings (IEC 60076-22-7)
105 EN 60529, Degrees of protection provided by enclosures (IP Code) (IEC 60529)
106 EN 62444:2013, Cable glands for electrical installations (IEC 62444:2010)
107 IEC/TR 60616, Terminal and tapping markings for power transformers
108 3 Terms and definitions
109 For the purposes of this document, the terms and definitions given in the EN 50708 series, EN 50336
110 and the following apply.
111 ISO and IEC maintain terminological databases for use in standardization at the following addresses:
112 — ISO Online browsing platform: available at https://www.iso.org/obp
113 — IEC Electropedia: available at http://www.electropedia.org/
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114 3.1
115 transformers with cable boxes, side mounted
116 transformer with electrical characteristics in the scope of this document, with facings on the
117 transformer tank side for provision of cable boxes Type 1
118 Note 1 to entry: These facings shall be on opposite sides of the transformer (as Figure 1).
119 3.2
120 transformers with cable boxes or similar, cover mounted
121 transformer with electrical characteristics in the scope of this document, with terminations mounted
122 on the tank cover
123 Note 1 to entry: The terminations exit in such a way as to provide for cables on opposite sides of the
124 transformer. The type of termination can be either cable box Type 1 or cable box Type 2 (as per Figures 3 or 4).
125 3.3
126 unit substation transformer, side mounted
127 transformer with electrical characteristics in the scope of this document, having facings on the
128 transformer tank side for provision of HV switchgear and LV equipment
129 Note 1 to entry: These facings shall be on the same side of the transformer (as per Figure 2).
130 3.4
131 unit substation transformer, cover mounted
132 transformer with electrical characteristics in the scope of this document, with terminations mounted
133 on the tank cover and enclosed in a flange box
134 Note 1 to entry: Figure 5 shows a typical arrangement.
135 3.5
136 cable boxes, Type 1
137 metallic box designed for receiving and protecting the ends of HV or LV cables so that the cable
138 dielectric can be effectively sealed against moisture damage, mechanical protection and against
139 accidental contacts
140 Note 1 to entry: A minimum protection of IP54 is required. These boxes are not specified in this section. A
141 higher protection, IP65, could be necessary to satisfy termination requirements.
142 3.6
143 cable boxes, Type 2
144 metallic or non-metallic enclosure designed to prevent accidental contact with live parts but without
145 mechanical protection of the ends of HV or LV cables
146 Note 1 to entry: The enclosure can be common to HV and LV terminations or be independent for HV and LV. A
147 protection between IP33 and IP55 is required and is subject to agreement between manufacturer and purchaser.
148 3.7
149 flange box
150 enclosure designed to provide flanges for mounting ancillary equipment on opposite sides of the
151 transformer as per Figures 5 and 6
152 Note 1 to entry: The box is mounted on the cover of the transformer.
153 3.8
154 fully insulated cable box
155 metallic cable box where those parts of the termination and bushing within the enclosure including
156 live metal parts and cable cores are insulated by oil or compound and allowance made for thermal
157 expansion
158 Note 1 to entry: The box is suitably sealed to contain the oil or compound and allows for their expansion due to
159 temperature changes.
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160 3.9
161 air insulated cable box
162 metallic cable box designed to protect the ends of the cables and bushings, providing a weatherproof
163 enclosure with a minimum rating of IP54
164 3.10
165 shrouded cable box
166 air filled cable box within the cable cores are terminated as in 3.9 with additional local insulation
167 enhancement, e.g. phase barrier, bushing protection or taping
168 Note 1 to entry: Enhancement can be achieved using insulated phase barriers.
169 4 Service conditions
170 EN 60076-1 applies.
171 5 Electrical characteristics
172 These shall comply with EN 50708-2-1.
173 6 Design requirements
174 6.1 Liquid immersed transformers
175 6.1.1 Type of liquid preservation system and degree of sealing
176 The type of liquid preservation system and the degree of sealing shall be indicated in the enquiry and
177 order.
178 6.1.2 Terminals
179 The terminations to be used can be of the following types:
180 a) open type bushings;
181 b) plug-in type bushings;
182 c) LV busbars;
183 d) cable boxes.
184 The requirements of the different types of terminations are described in the following standards:
185 EN 50180, EN 50386, EN 50387 and EN 50336.
186 6.1.3 Terminal markings
187 Terminal markings shall be in accordance with IEC/TR 60616 unless otherwise specified.
188 6.1.4 Distance between bushings
189 6.1.4.1 Distances between high-voltage liquid to air bushings
190 The bushings clearance shall meet the requirements of Table 1.
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191 Table 1 — Clearance and creepage distances
Rated voltage Type of enclosure Clearance Clearance Creepage
between live between live over insulator
metal of metal and earth
different phases
kV mm mm mm
12 Fully 45 32 *
insulated/shrouded
12 Air clearance 127 76 127
17,5 Fully 75 60
insulated/shrouded
17,5 Air clearance 165 102 153
24 Fully 100 75
insulated/shrouded
24 Air clearance 242 140 203
36 Fully 125 100
insulated/shrouded
36 Air clearance 356 222 305
192 NOTE The clearances in Table 1 are not those of EN 60076-3 and are reduced because these clearances
193 are used only in the box and not considered the polluted area and atmospheric area.
194 6.1.4.2 Preferred distance between centres of low-voltage bushings
195 For open type bushing, the distance between bushing can be defined as below:
196 — for currents up to 250 A 70 mm;
197 — for currents above 250 A and up to 2 000 A 150 mm;
198 — for currents above 2 000 A 165 mm.
199 Distances between centres are indicated in EN 50336 for LV cable box connexions made through
200 mono block bushing.
201 6.1.5 Rollers
202 When rollers are fitted, they shall comply with EN 50216-4.
203 For larger rated power this should be specified at the enquiry stage.
204 6.2 Dry-type transformers
205 6.2.1 Terminals
206 HV and LV terminals could be located on the upper side or middle part or lower side.
207 For easy understanding HV connecting leads side are fixed and used as reference side.
208 LV terminals could be on the same or on the opposite side referred to the HV leads.
209 Tapping could be on the same side or on the opposite side referred to the HV leads; preferred side is
210 on the same HV side.
211 At the enquiry stage the exact positions of HV leads/terminals, LV leads/terminals and tapping shall
212 be stated.
213 If in respect of leads with special dimensions and/or precise-exact dimensions and locations are
214 needed, this needed information shall be given at the enquiry stage and agreed between
215 manufacturer and purchaser.
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216 6.2.2 Terminal markings
217 Terminal markings shall be in accordance with IEC/TR 60616 unless otherwise specified.
218 6.2.3 Rollers
219 The dimensions of rollers are defined in EN 50216-4.
220 When rollers are fitted, information shall be given at the enquiry stage and agreed between
221 manufacturer and purchaser.
222 For larger rated power this should be specified at the enquiry stage.
223 6.2.4 Enclosure
224 Refers to EN IEC 60076-11.
225 7 Accessories
226 7.1 Liquid immersed transformers
227 Accessories shall be in accordance with the appropriate parts of EN IEC 60076-22-7 when applicable.
228 If not otherwise specified, transformers shall be fitted with the accessories marked with an “X” as
229 listed in Table 2. Accessories not crossed in this table are optional.
230 Special care should be taken to avoid conflicts between accessories which could be non-compatible.
231 Table 2 — List of accessories (not exhaustive)
Type Hermetically Breathing type Air cushion
sealed with conservator
Tap changer X X X
Rating plate X X X
Lifting device X X X
Filling hole and plug X X X
Rollers or skid chassis (Not applicable for X X X
pole mounted)
Oil level indicator(s) X X
Conservator draining plug(s) X X
Dehydrating breather(s) X
Gas and oil actuated relay(s) X X
Butterfly valve
Thermometer pocket
Pad-locking tap changer handle
Protective device
Conservator drain valve
Removable radiators instead of fixed radiator
Removable radiators insulating Butterfly
valve
Jacking pads
Pulling eyes
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232 7.2 Dry-type transformers
233 Accessories shall be in accordance with the appropriate parts of EN 50216-4 and EN IEC 60076-11
234 when applicable.
235 If no otherwise specified, transformers shall be fitted with the accessories listed in Table 3.
236 Table 3 — List of accessories
HV Terminal
LV Terminal
Earthing terminals
Warning plate
Lifting devices
Rollers or skid (Not applicable for pole mounted)
Rating plate
237 8 Cable box for Liquid immersed transformers
238 8.1 Transformers with cable boxes on the high-voltage and/or low-voltage side
239 8.1.1 General consideration
240 Medium power transformer could have different termination features.
241 The following constructional situations are possible.
242 i) Termination in open type (oil-air) bushings without protection. This is covered EN 50180,
243 EN 50386 and EN 50387 and this document.
244 ii) Termination in plug-in type bushings of inside or outside cone type. This is covered EN 50180
245 and this document.
246 iii) Termination in air filled or compound filled cable box or protective enclosure using air and/or
247 oil/compound oil to oil bushings, as defined in EN 50336.
248 iv) Flange boxes and similar solutions using open type bushings can also be used.
249 For the purposes of this document, unless is not specified, the terms and definitions given in
250 EN 50336 apply.
251 Definition of the cable box for 12kV and 24kV are given in Figure 1, 2 and 3. The definition of the
252 cable box for 36kV are subject of agreement between manufacturers and purchasers.
253 8.1.2 Provision for cable box Type 1 connections
254 Facings shall be provided for mounting HV and LV bushing assemblies and cable boxes, as detailed
255 in Figures 1, 2 and 3 of this document.
256 Fixing methods shall be provided on transformer facings positioned as defined on the appropriate
257 drawings given in Figures 1 and Figure 2.
258 8.1.3 Provision for cable box Type 2
259 Facings shall be provided for mounting HV and LV bushings assemblies with cable box Type 2 as
260 shown in Figures 4 and 5. The use of independent HV and LV enclosures shall be subject to
261 agreement between manufacturer and purchaser.
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262 8.1.4 Transformer requirements
263 8.1.4.1 Transformers with cable boxes, mounted on both sides
264 Limiting dimensions are indicated in Figure 1.
265 The underbase is generally in the form of skids, provided with axle holes.
266 Four jacking lugs shall be provided, if specified by the purchaser.
267 Two lifting fittings shall be provided of adequate section. These shall be positioned to facilitate lifting
268 in a reasonably upright position, taking into account the cable box weight. These weights to be given
269 by the purchaser if necessary.
270 Other accessories shall comply with Clause 7.1 and shall preferably be mounted on one end of the
271 tank and shall not be obstructed by coolers.
272 Unless otherwise agreed, two earthing terminals shall be fitted on the centre line, one below each
273 connection facing, with the connection hole placed on the lower part of the tank.
274 8.1.4.2 Transformers with cable boxes, cover mounted
275 8.1.4.2.1 General
276 There are no limiting dimensions.
277 The accessories shall comply with Clause 7.1.
278 8.1.4.2.2 Cable box Type 1
279 A cable box Type 1 shall be fitted to the high voltage flange. The termination of the low voltage shall
280 be as specified by the purchaser at time of enquiry.
281 One method of cover mounting cable boxes Type 1 is shown in Figure 3 of this document which
282 defines its own flange fitting that shall always be maintained.
283 8.1.4.2.3 Cable box Type 2
284 A cable box Type 2 is provided for either both high voltage and low voltage termination or only one of
285 them. This shall be agreed between manufacturer and purchaser.
286 One method of cover mounting cable boxes Type 2 is shown in Figure 4 of this document.
287 8.1.4.3 Unit substation transformer, with cable boxes mounted on the same side
288 8.1.4.3.1 General
289 Limiting dimensions are indicated in Figure 2.
290 A stable fixing for HV switchgear equipment can be requested by the purchaser, in a position as
291 indicated in Figure 2. The requirements of this fixing shall be capable of supporting an agreed load
292 and designed so as to not load the facing flange.
293 An LV bushing plate assembly shall be provided on a mounting pocket. The mounting pocket flange
294 face shall lie in the same plane as the face of the pocket provided for the HV ring main equipment.
295 The termination of the low voltage shall be specified by the purchaser.
296 The flange face of the mounting pockets of HV/LV shall be flat and sufficiently robust to prevent
297 distortion and oil leakage when the agreed equipment is bolted thereto.
298 The transformer tank with its cover shall be capable of withstanding the combined loads of the agreed
299 attached equipment without distortion. The transformer shall not be moved or lifted in this condition
300 and shall be stable.
301 Lifting fittings shall be provided on the transformer’s tank of adequate section to facilitate lifting that
302 transformer and fittings in a reasonably upright position, with or without the agreed attached
303 equipment.
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oSIST prEN 50708-2-3:2020
prEN 50708-2-3:2020 (E)
304 8.1.4.3.2 Unit substation transformer with flange boxes, cover mounted
305 The general arrangement in the case of common HV and LV flange box is shown in Figure 5. For
306 independent HV and LV enclosures, see 8.1.3. A typical flange for interfacing between the flange box
307 and Type 2 cable boxes is shown in Figure 6.
308 Dimension should be agreed between manufacturer and purchaser
309 The accessories shall comply with Clause 7.1.
310 8.1.5 Distance between bushings
311 The distance between bushings is defined in 6.1.4.
312 8.1.6 Tests
313 Type and routine tests of the transformers should be in accordance with EN 50708 series. The
314 transformer should be tested without cable boxes when it is possible. Typically cable boxes are left
315 on the transformer for testing and secondary insulation applied to meet required test levels if shrouded
316 cable boxes are used.
317 If it is required to test with boxes attached, then in the case of fully insulated air filled boxes it is allowed
318 to perform tests with the cable boxes filled with oil.
319 The fitting with oil is not allowed for the purpose of type testing air filled boxes.
320 Other test requirements should be required as a consequence of further sections of this document.
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oSIST prEN 50708-2-3:2020
prEN 50708-2-3:2020 (E)
321 Dimensions in millimetres
E
min.
For ≤ 12 kV 280
For ≤ 24 kV 360
E dimensions and HV
flange size are suitable
for fully insulated or
PLAN VIEW
shrouded cable boxes.
Shaded area indicates maximum protection beyond tank walls
SIDE VIEW
LV FLANGE HV FLANGES for ≤ 12 kV
Rating A B H
*C *D
kVA max. max. max.
160–200 1 350 1 050 1 200 1 100 1 550
230–315 1 680 1 145 1 320 1 320 1 750
400–500 1 700 1 220 1 320 1 320 1 830
630–800 1 830 1 320 1 320 1 320 1
...
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