oSIST prEN 50122-3:2021
(Main)Railway applications - Fixed installations - Electrical safety, earthing and the return circuit - Part 3: Mutual Interaction of AC and DC traction systems
Railway applications - Fixed installations - Electrical safety, earthing and the return circuit - Part 3: Mutual Interaction of AC and DC traction systems
1 - General
- adaptation of the Scope of this standard (include electrical safety related interface with vehicles, extension for electrified road transport – as shown above)
- Incorporate such small technical improvements from IEC 62128, made when transferring from previous version 50122-1, only insofar as these are essential for the coherence of the standard 50122-1
- Harmonize definitions with other railway standards (esp. EN 50119)
- check and redefine some definitions, harmonize with IEC 60050:
o Check and harmonize terms and definitions specific to railway terminology with IEC 60050 chapters 811 and 821. If modification of a definition is essential, consider harmonization with a recent definition used in a railway specific standard and which should postdate the IEC entry.
o Check and harmonize terms and definitions specific to electric shock with IEC60050 chapter 195 except where the terms and definitions in IEC 61140:2016 are appropriate and postdate IEC 60050 entry.
o Check and harmonise other terms and definitions with IEC 50050 where appropriate.
- Review and ensure the document accurately and consistently uses the correct ‘verbal forms for expressions of provisions’ (according to the Internal Regulations, Part 3, clause 7), the wording used is clear and achieves good differentiation between normative and informative content.
- Review and ensure the document’s content relating to the prevention of electric shock is harmonized with basic safety publication IEC/EN 61140. In particular, the IEC/EN61140 content on fundamental rules, terminology, protective provisions (i.e. basic protection, fault protection, enhanced protective provisions).
- Review and revise clause 1 to ensure that the document’s scope is clear and accurately stated, it is harmonised with the title and only aspects falling within this scope are included within the document’s normative content. This take note of the on-going SC9XC work on coordination between SC9XC / TC9X standards and in particular the scope of prEN 50488.
2 – Specific
- Review and modify clause 5 and harmonize its content with the relevant aspects of IEC61140, EN50124 series, prEN50488. Particular consideration to be given to the dimensioning of air clearance associated with protective provisions. This will take note of the on-going SC9XC work on coordination between SC9XC / TC9X standards.
- Review and revise clause 6, in particular the content on protective provisions to improve its alignment with basic safety publication IEC/EN 61140 content for this aspect.
- revision of Chapter 7
- Review and revise clause 10.5 to ensure that the content is fit for purpose and is coordinated with EN 50124, EN 50119 and EN5 0488 in particular, such that these standards will provide a coherent approach. This will take note of the on-going SC9XC work on coordination between these standards.
Bahnanwendungen - Ortsfeste Anlagen - Elektrische Sicherheit, Erdung und Rückleitung - Teil 3: Gegenseitige Beeinflussung von Wechselstrom- und Gleichstrombahnen
Applications ferroviaires - Installations fixes - Sécurité électrique, mise à la terre et circuit de retour - Partie 3: Interactions mutuelles entre systèmes de traction en courant alternatif et en courant continu
This European Standard specifies requirements for the protective provisions relating to electrical safety in fixed installations, when it is reasonably likely that hazardous voltages or currents will arise for people or equipment, as a result of the mutual interaction of AC and DC electric traction systems.
It also applies to all aspects of fixed installations that are necessary to ensure electrical safety during maintenance work within electric traction systems.
The mutual interaction can be of any of the following kinds:
– parallel running of AC and DC electric traction systems;
– crossing of AC and DC electric traction systems;
– shared use of tracks, buildings or other structures;
– system separation sections between AC and DC electric traction systems.
Scope is limited to basic frequency voltages and currents and their superposition. This European Standard does not cover radiated interferences.
This European Standard applies to all new lines, extensions and to all major revisions to existing lines for the following electric traction systems:
a) railways;
b) guided mass transport systems such as:
1) tramways,
2) elevated and underground railways,
3) mountain railways,
4) trolleybus systems, and
5) magnetically levitated systems, which use a contact line system;
c) material transportation systems.
The standard does not apply to:
d) mine traction systems in underground mines;
e) cranes, transportable platforms and similar transportation equipment on rails, temporary structures (e.g. exhibition structures) in so far as these are not supplied directly or via transformers from the contact line system and are not endangered by the traction power supply system for railways;
f) suspended cable cars;
g) funicular railways;
h) procedures or rules for maintenance.
The rules given in this European Standard can also be applied to mutual interaction with non-electrified tracks, if hazardous voltages or currents can arise from AC or DC electric traction systems.
Železniške naprave - Stabilne naprave električne vleke - Električna varnost, ozemljitev in povratni tokokrog - 3. del: Medsebojno vplivanje med izmeničnimi in enosmernimi sistemi vleke
General Information
RELATIONS
Standards Content (sample)
SLOVENSKI STANDARD
oSIST prEN 50122-3:2020
01-januar-2021
Železniške naprave - Stabilne naprave električne vleke - Električna varnost,
ozemljitev in povratni tokokrog - 3. del: Medsebojno vplivanje med izmeničnimi in
enosmernimi sistemi vlekeRailway applications - Fixed installations - Electrical safety, earthing and the return circuit
- Part 3: Mutual Interaction of AC and DC traction systemsBahnanwendungen - Ortsfeste Anlagen - Elektrische Sicherheit, Erdung und Rückleitung
- Teil 3: Gegenseitige Beeinflussung von Wechselstrom- und GleichstrombahnenApplications ferroviaires - Installations fixes - Sécurité électrique, mise à la terre et circuit
de retour - Partie 3: Interactions mutuelles entre systèmes de traction en courant
alternatif et en courant continuTa slovenski standard je istoveten z: prEN 50122-3
ICS:
29.120.50 Varovalke in druga Fuses and other overcurrent
nadtokovna zaščita protection devices
29.280 Električna vlečna oprema Electric traction equipment
oSIST prEN 50122-3:2020 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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oSIST prEN 50122-3:2020
EUROPEAN STANDARD DRAFT
prEN 50122-3
NORME EUROPÉENNE
EUROPÄISCHE NORM
November 2020
ICS 29.120.50; 29.280 Will supersede EN 50122-3:2010 and all of its
amendments and corrigenda (if any)
English Version
Railway applications - Fixed installations - Electrical safety,
earthing and the return circuit - Part 3: Mutual Interaction of AC
and DC traction systems
Applications ferroviaires - Installations fixes - Sécurité Bahnanwendungen - Ortsfeste Anlagen - Elektrische
électrique, mise à la terre et circuit de retour - Partie 3: Sicherheit, Erdung und Rückleitung - Teil 3: Gegenseitige
Interactions mutuelles entre systèmes de traction en Beeinflussung von Wechselstrom- und Gleichstrombahnen
courant alternatif et en courant continuThis draft European Standard is submitted to CENELEC members for enquiry.
Deadline for CENELEC: 2021-02-19.
It has been drawn up by CLC/SC 9XC.
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.
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oSIST prEN 50122-3:2020
prEN 50122-3:2020 (E)
1 Contents
2 1 Scope ..................................................................................................................................................... 4
3 2 Normative references ........................................................................................................................... 5
4 3 Terms and definitions .......................................................................................................................... 5
5 4 Hazards and adverse effects ............................................................................................................... 5
6 4.1 General .................................................................................................................................................. 5
7 4.2 Electrical safety of persons ................................................................................................................. 5
8 5 Types of mutual interaction to be considered .................................................................................. 5
9 5.1 General .................................................................................................................................................. 5
10 5.2 Galvanic coupling ................................................................................................................................ 6
11 5.2.1 AC and DC return circuits not directly connected ......................................................................... 6
12 5.2.2 AC and DC return circuits directly connected or common........................................................... 6
13 5.3 Non-galvanic coupling ......................................................................................................................... 6
14 5.3.1 Inductive coupling ............................................................................................................................. 6
15 5.3.2 Capacitive coupling .......................................................................................................................... 7
16 6 Zone of mutual interaction .................................................................................................................. 7
17 6.1 General .................................................................................................................................................. 7
18 6.2 AC .......................................................................................................................................................... 7
19 6.3 DC .......................................................................................................................................................... 8
20 7 Touch voltage limits for the combination of alternating and direct voltages ................................ 8
21 7.1 General .................................................................................................................................................. 8
22 7.2 Touch voltage limits for long-term conditions .................................................................................. 8
23 7.3 AC system short-term conditions and DC system long-term conditions ...................................... 9
24 7.4 AC system long-term conditions and DC system short-term conditions .................................... 10
25 7.5 AC system short-term conditions and DC system short-term conditions ................................... 11
26 7.6 Workshops and similar locations ..................................................................................................... 11
27 8 Technical requirements and measures inside the zone of mutual interaction ............................ 12
28 8.1 General ................................................................................................................................................ 12
29 8.2 Requirements if the AC railway and the DC railway have separate return circuits .................... 12
30 8.2.1 General ............................................................................................................................................. 12
31 8.2.2 Return circuit or parts connected to the return circuit located in the OCLZ and/or
32 CCZ of the other system ................................................................................................................. 12
33 8.2.3 Common buildings and common structures ............................................................................... 13
34 8.2.4 Inductive and capacitive coupling ................................................................................................. 14
35 8.3 Requirements if the AC railway and the DC railway have common return circuits and
36 use the same tracks ........................................................................................................................... 14
37 8.3.1 General ............................................................................................................................................. 14
38 8.3.2 Measures against stray current ..................................................................................................... 14
39 8.3.3 Common structures and common buildings ............................................................................... 14
40 8.3.4 Exceptions ....................................................................................................................................... 15
41 8.3.5 Design of overhead contact line .................................................................................................... 15
42 8.3.6 Inductive and capacitive coupling ................................................................................................. 15
43 8.4 System separation sections and system separation stations ....................................................... 15
44 Annex A (informative) Zone of mutual interaction ..................................................................................... 16
45 Annex B (informative) Analysis of combined voltages ............................................................................. 21
46 Annex C (informative) Analysis and assessment of mutual interaction ................................................. 26
47 Annex ZZ (informative) Relationship between this European Standard and the essential
48 require-ments of EU Directive 2016/797/EU [2016 OJ L138] aimed to be covered ...................... 27
49 Bibliography .................................................................................................................................................... 28
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50 European foreword
51 This document (prEN 50122-3:2020) has been prepared by CLC/SC 9XC “Electric supply and earthing sys-
52 tems for public transport equipment and ancillary apparatus (Fixed installations)”.
53 This document is currently submitted to the Enquiry.54 The following dates are proposed:
• latest date by which the existence of this docu- (doa) dor + 6 months
ment 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 endorse-
ment
• latest date by which the national standards (dow) dor + 36 months (to be confirmed or
conflicting with this document have to be with- modified when voting)drawn
55 This document will supersede EN 50122-3:2010 and all of its amendments and corrigenda (if any).
56 prEN 50122-3:2020 includes the following significant technical changes with respect to EN 50122-3:2010:
57 — harmonization with EN 50122-1:2020.58 This document has been prepared under a mandate given to CENELEC by the European Commission and
59 the European Free Trade Association, and supports essential requirements of EU Directive(s).
60 For the relationship with EU Directive(s) see informative Annex ZZ, which is an integral part of this document.
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61 1 Scope
62 This document specifies requirements for the protective provisions relating to electrical safety in fixed installa-
63 tions, when it is reasonably likely that hazardous voltages or currents will arise for people or equipment, as a
64 result of the mutual interaction of AC and DC electric power supply traction systems.
65 It also applies to all aspects of fixed installations that are necessary to ensure electrical safety during mainte-
66 nance work within electric power supply traction systems.67 The mutual interaction can be of any of the following kinds:
68 — parallel running of AC and DC electric traction power supply systems;
69 — crossing of AC and DC electric traction power supply systems;
70 — shared use of tracks, buildings or other structures;
71 — system separation sections between AC and DC electric power supply traction systems.
72 The scope is limited to basic frequency voltages and currents and their superposition. This document does not
73 cover radiated interferences.74 This document applies to all new lines, extensions and to all major revisions to existing lines for the following
75 electric power supply traction systems:76 a) railways;
77 b) guided mass transport systems such as:
78 1) tramways,
79 2) elevated and underground railways,
80 3) mountain railways,
81 4) trolleybus systems, and
82 5) magnetically levitated systems, which use a contact line system;
83 c) material transportation systems.
84 The document does not apply to:
85 d) electric traction power supply systems in underground mines;
86 e) cranes, transportable platforms and similar transportation equipment on rails, temporary structures (e.g.
87 exhibition structures) in so far as these are not supplied directly or via transformers from the contact line
88 system and are not endangered by the traction power supply system for railways;
89 f) suspended cable cars;90 g) funicular railways;
91 h) procedures or rules for maintenance.
92 The rules given in this document can also be applied to mutual interaction with non-electrified tracks, if haz-
93 ardous voltages or currents can arise from AC or DC electric traction power supply systems.
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94 2 Normative references
95 The following documents are referred to in the text in such a way that some or all of their content constitutes
96 requirements of this document. For dated references, only the edition cited applies. For undated references,
97 the latest edition of the referenced document (including any amendments) applies.
98 prEN 50122-1:2020, Railway applications - Fixed installations - Electrical safety, earthing and the return circuit
99 - Part 1: Protective provisions against electric shock100 prEN 50122-2:2020, Railway applications - Fixed installations - Electrical safety, earthing and the return circuit
101 - Part 2: Provisions against the effects of stray currents caused by DC traction systems
102 3 Terms and definitions103 For the purposes of this document, the terms and definitions given in prEN 50122-1:2020 apply.
104 ISO and IEC maintain terminological databases for use in standardization at the following addresses:
105 — ISO Online browsing platform: available at https://www.iso.org/obp106 — IEC Electropedia: available at http://www.electropedia.org/
107 4 Hazards and adverse effects
108 4.1 General
109 The different requirements specified in prEN 50122-1 and prEN 50122-2, concerning connections to the return
110 circuit of the AC railway, and connections to the return circuit of the DC railway, shall be harmonized in order
111 to avoid risks of hazardous voltages and stray currents.112 Such hazards and risks shall be considered from the start of the planning of any installation which includes
113 both AC and DC railways. Suitable measures shall be specified for limiting the voltages to the levels given in
114 this document, while limiting the damaging effects of stray currents in accordance with EN 50122-2.
115 Additional adverse effects are possible, for example:116 — thermal overload of conductors, screens and sheaths;
117 — thermal overload of transformers due to magnetic saturation of the cores;
118 — restriction of operation because of possible effects on the safety and correct functioning of signalling sys-
119 tems;120 — restriction of operation because of malfunction of the communication system.
121 These effects should be considered in accordance with the appropriate standards.
122 4.2 Electrical safety of persons123 Where AC and DC voltages are present together the limits for touch voltage given in Clause 7 apply in addition
124 to the limits given in prEN 50122-1:2020, Clause 9.125 5 Types of mutual interaction to be considered
126 5.1 General
127 Coupling describes the physical process of transmission of energy from a source to a susceptible device.
128 The following types of coupling shall be considered:129 a) galvanic (conductive) coupling;
130 b) non-galvanic coupling;
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131 1) inductive coupling;
132 2) capacitive coupling.
133 Galvanic coupling dominates at low frequencies, when circuit impedances are low. The effects of galvanic
134 coupling are conductive voltages and currents.135 The effects of inductive coupling are induced voltages and hence currents. These voltages and currents de-
136 pend inter alia on the distances, length, inducing current conductor arrangement and frequency.
137 The effects of capacitive coupling are influenced voltages into galvanically separated parts or conductors. The
138 influenced voltages depend inter alia on the voltage of the influencing system and the distance. Currents re-
139 sulting from capacitive coupling are also depending on the frequency.140 NOTE As far as the capacitive and inductive coupling are concerned, general experience is that only the influence of
141 the AC railway to the DC railway is significant.142 5.2 Galvanic coupling
143 5.2.1 AC and DC return circuits not directly connected
144 A mutual interaction between the return circuits is possible by currents through earth caused by the rail poten-
145 tial of both AC and DC railways, for example return currents flowing through the return conductors, earthing
146 installations of traction power supply substations and cable screens.147 In case a conductive parallel path to the return circuit exists in the influenced system, various effects are
148 possible. In case a vehicle forms part of the parallel path, return current of the influencing railway system can
149 flow through the propulsion system of the traction unit. The same effects are possible when the return current
150 of the influencing system flows, for example, through the auto-transformer and substation transformer of an
151 auto-transformer system or through booster transformers or other devices.152 An electric shock with combined voltages can occur when parts of the return circuits or conductive parts which
153 are connected to the return circuits by voltage limiting devices are located in the overhead contact line zone
154 of the other railway system, see 8.2.2.155 5.2.2 AC and DC return circuits directly connected or common
156 In addition to the effects described in 5.2.1 current exchange will be increased where AC and DC return circuits
157 are directly connected or common.158 EXAMPLE Direct connections can be railway level crossings, common tracks, system separation sections, etc.
159 Currents flowing between the AC railway and the DC railway can create mutual interaction between the return
160 circuits.161 Both return circuits are at the same potential at the location of the connection. A short-circuit within the AC
162 system can cause a peak voltage on conductive structures connected to the return circuit of the DC railway.
163 The same effects apply for conductive structures connected to it directly or via a voltage limiting device (VLD).
164 The voltage across the voltage limiting device can trip the device without a fault on the DC side.
165 The connection of the return circuit of the DC railway to the earthed return circuit of the AC railway increases
166 the danger of stray current corrosion.167 For requirements for fixed installations see 8.3.
168 5.3 Non-galvanic coupling
169 5.3.1 Inductive coupling
170 An AC voltage can be induced on a DC contact line system and on the DC system’s return circuit. This effect
171 needs to be considered in case the DC railway is within the zone of mutual interaction.
172 Consequently an AC voltage can occur within the DC substation at the busbars versus earth (i.e. at the rectifier
173 or in the feeder cubicles).174 Interaction can occur in terms of impermissible touch voltages. See Clause 7.
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176 5.3.2 Capacitive coupling
177 Within small distances an AC voltage can be influenced on a DC contact line system when it is isolated with a
178 disconnector or circuit-breaker open. The possibility shall be considered that the flash-over voltage of the
179 insulators or of the surge arrestors can be reached.180 Distance depends inter alia on geometry and voltage.
181 An AC voltage can occur within the DC substation at the DC busbars versus earth, i.e. in the feeder cubicles.
182 Interaction can occur in terms of impermissible touch voltages. See Clause 7.
183 6 Zone of mutual interaction184 6.1 General
185 The AC railway affects the DC railway and vice-versa by galvanic, inductive and/or capacitive coupling (see
186 Clause 5). The zone of mutual interaction indicates a distance and a length of parallelism between an AC
187 railway and a DC railway (see Annex A). The limits of zone of mutual interaction are based on the limits of the
188 touch voltage given in Clause 7.189 If a zone of mutual interaction exists the requirements given in this document shall be fulfilled.
190 In general no generic values can be given for the zone of mutual interference. An assessment based on local
191 circumstances has to be made. However when the distance between both AC and DC railways is less than
192 50 m a zone of mutual interaction is assumed. Distances in excess of 50 m are dealt with in 6.2 and 6.3.
193 NOTE For information on analysis and assessment of zone of mutual interaction, see Annex C.
194 6.2 AC195 In case of an AC railway influencing a DC railway the zone of mutual interaction is based on voltages coupled
196 galvanically and inductively into the affected system. In this Subclause effects of capacitive coupling are neg-
197 ligible.198 For planning purposes the zone of mutual interaction has to be investigated either by calculation or by the
199 following procedure.200 Where the following preconditions apply the limit of the distance between AC and DC railway is 1 000 m:
201 — double track line, where only the four running rails of the AC railway are used for the return circuit;
202 — the inducing current is 500 A per overhead contact line (1 000 A in total);
203 — the length of parallelism between AC and DC railway is 4 km;204 — the soil resistivity is 100 Ωm;
205 — the rated frequency is 50 Hz;
206 — the affected system is insulated versus earth along its entire length and connected to earth at one end
207 only;208 — screening effects of other parallel metallic objects have not been taken into account.
209 Where other preconditions apply the dimension of the zone of mutual interaction shall be calculated.
210 A method for the calculation is given in Annex A.211 NOTE The example above is based on a 35 V limit for AC with a time duration longer than 300 s.
212 In case a DC railway is within the zone of mutual interaction of an AC railway, the level of voltages or currents
213 coupled into the DC system is not necessarily too high; in this case further analysis of the situation shall be
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215 6.3 DC
216 For the effects of DC railway systems on AC railway systems the dimension of the zone of mutual interaction
217 can be neglected due to the steep voltage gradient in the soil, caused by the insulated rails.
218 However if the possibility of a voltage transfer exists, either permanently or temporary, due to a galvanic con-
219 nection towards conductive or partly conductive parts, the zone of mutual interaction is given by the dimensions
220 of those parts. In this case the level of voltages or currents coupled into the AC system is not necessarily too
221 high; further analysis of the situation shall be carried out.222 7 Touch voltage limits for the combination of alternating and direct voltages
223 7.1 General224 The limits given in 7.2 to 7.6 are based on touch voltage only and shall not be exceeded. Other effects with
225 respect to electrical installations are not taken into account.226 Limits for electrical installations cannot be given in a generic way and should be addressed separately if nec-
227 essary, depending on the sensitivity of the affected installations.228 Where either an alternating or a direct voltage is present the touch voltage limits given in prEN 50122-1 apply.
229 The direct and the alternating components of a combined voltage u(t) for time duration in excess of 1 s are
230 calculated as follows:a+T
U = ⋅ u(t)⋅ dt
231 (1)
a+T
U = ⋅ (u(t)−U ) ⋅ dt
232 (2)
ac dc
233 where
T = 1 s;
t is the time;
u(t) is the combined voltage;
U is the direct component of combined voltage;
U is the alternating component of combined voltage.
234 NOTE 1 Formula (1) gives the moving average value of the direct component, and Formula (2) gives the moving r.m.s.
235 value of the alternating component.236 Only for short-duration phenomena ≤ 1 s the following definitions for alternating voltage and direct voltage are
237 used:238 — U is defined as that part of the combined voltage that is caused by the DC system;
239 — U is defined as that part of the combined voltage that is caused by the AC system.
240 NOTE 2 Further information on combined voltages is given in Annex B.241 NOTE 3 Long-term conditions are associated with operation conditions and short-term conditions are associated with
242 fault conditions or for example switching operations.243 7.2 Touch voltage limits for long-term conditions
244 The following approach shall be used to check whether the combined voltage is permissible:
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245 1) the alternating part of the combined voltage shall not exceed the maximum permissible alternating body
246 voltage as given in prEN 50122-1:2020, Table 7 for the applicable duration;247 2) the direct part of the combined voltage shall not exceed the maximum permissible direct body voltage as
248 given in prEN 50122-1:2020, Table 9 for the applicable duration;249 3) the combined voltage is permissible if it is within the envelope as given for the applicable duration in
250 Figure 1;251 4) for time durations in excess of 1 s the combined peak value (see explanation in Annex B) shall be less
252 than 2 × √2 times the maximum permissible alternating body voltage as given in prEN 50122-1:2020, Ta-
253 ble 7 for the applicable duration irrespective of frequency content.254 EXAMPLE Assuming the maximum permissible direct touch voltage of 120 V being present in the DC system the
255 alternating voltage limit is 35 V, see Figure 1. Assuming the maximum permissible alternating touch voltage of 60 V being
256 present in the AC system the direct voltage limit is 85 V, see Figure 1.257
258 The curves given in the graph are based on the r.m.s. values as given in prEN 50122-1.
259 Figure 1 — Maximum permissible combined effective touch voltages260 (excluding workshops and similar locations) for long-term conditions
261 7.3 AC system short-term conditions and DC system long-term conditions
262 The following approach shall be used to check whether the combined voltage is permissible:
263 1) the short-duration alternating part of the combined voltage shall not exceed the maximum permissible
264 alternating touch voltage as given in prEN 50122-1:2020, Table 8 for the applicable duration;
265 2) the direct part of the combined voltage shall not exceed the maximum permissible direct touch voltage as
266 given in prEN 50122-1:2020, Table 10 for the applicable duration;267 3) the combined voltage is permissible if it is within the envelope as given for the applicable durations in
268 Figure 2.---------------------- Page: 11 ----------------------
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269
270 The curves given in the graph are based on the r.m.s. values as given in prEN 50122-1.
271 Figure 2 — Maximum permissible combined effective touch voltages272 under AC short-term conditions and DC long-term conditions
273 EXAMPLE An example of the use of Figure 2 is given in Annex B.
274 7.4 AC system long-term conditions and DC system short-term conditions
275 The following approach shall be used to check w
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