Requirements for the connection of generators above 16 A per phase - Part 1: Connection to the LV distribution system

The purpose of this Technical Specification is to provide technical guidance on the requirements for
generating plants which can be operated in parallel with a distribution network.
For practical reasons, this Technical Specification refers to the distribution system operator in case
settings have to be defined and/or provided, even when these settings are to be defined and/or
provided by another actor according to national and European legal framework.
NOTE 1 This includes European network codes and their national implementation, as well as further national
regulations.
NOTE 2 Further national requirements especially for the connection to the distribution network and the
operation of the generating plant can apply.
The requirements of this Technical Specification apply to all generating plants, electrical machinery
and electronic equipment, irrespective of the kind of primary energy source and irrespective of the
presence of loads in the producer’s network that meet all of the following conditions:
– converting any primary energy source into AC electricity;
– connected to a LV distribution network and rated at more than 16 A per phase;
– intended to operate in parallel with this distribution network under normal network operating
conditions.
NOTE 3 Generating plants rated up to and including 16 A per phase are covered by EN 50438.
NOTE 4 Generating plants connected to a MV distribution network fall into the scope of CLC/TS 50549-2.
Unless stated differently by the DSO generating plants connected to a medium voltage distribution
network with a maximum apparent power up to 100 kVA can comply with this Technical Specification
as alternative to the requirements of CLC/TS 50549-2. A different threshold may be defined by the
DSO.
This Technical Specification defines connection requirements.
This Technical Specification recognizes the existence of National Standards, Network Codes, and
specific technical requirements of the DSOs. These should be complied with.
Excluded from the scope are:
– the selection and evaluation of the point of connection;
– power system impact assessment;
– connection assessment;
– island operation of generating plants, both intentional and unintentional, where no part of the
distribution network is involved;
– active front ends of drives feeding energy back into the distribution network for short duration;
– requirements for the safety of personnel as they are already adequately covered by existing
European Standards.

Anforderungen für zum Parallelbetrieb mit einem Verteilnetz vorgesehene Erzeugungsanlagen – Teil 1: Anschluss an das Niederspannungsverteilnetz über 16 A je Phase

Diese Technische Spezifikation legt die technischen Anforderungen für den Anschluss von Erzeugungsan-lagen fest, die parallel mit einem öffentlichen Verteilungsnetz betrieben werden können. Diese Technischen Spezifikation soll als Referenz in einer Anschlussgenehmigung herangezogen werden, die zwischen einem VNB und einem Erzeuger getroffen wird.  Die Anforderungen dieser Technischen Spezifikation beschränken sich auf den elektrischen Teil der Anlage, unabhängig von der verwendeten Primärenergiequelle. Diese Technischen Spezifikation gilt für alle dreiphasigen Erzeugungseinheiten, welche die folgenden Bedin-gungen – entweder als Einzelanlage oder als Gruppe von mehreren Anlagen mit einem gemeinsamen An-schlusspunkt – erfüllen: •   Umwandlung einer beliebigen Primärenergie in Wechselstrom; •   Bemessungsströme größer 16 A je Phase und Anschluss an ein Niederspannungsnetz; •   Anlagen, die unter normalen Netzbetriebsbedingungen ständig parallel mit einem öffentlichen Ver-teilungs¬netz betrieben werden sollen; ANMERKUNG   Erzeugungsanlagen bis 16 A je Phase werden durch die EN 50438 abgedeckt. Diese Technischen Spezifikation legt die Anschlussbedingungen und ein Verfahren für die Konformitäts¬prü-fung fest. Der Inselnetzbetrieb von Erzeugungsanlagen – beabsichtigt oder unbeabsichtigt – bei dem kein Teil des öffentlichen Verteilungsnetzes betroffen ist, liegt nicht im Anwendungsbereich dieser Technischen Spezifika-tion. Die Personensicherheit liegt nicht im Anwendungsbereich dieser Technischen Spezifikation. Diese Norm anerkennt die Existenz von nationalen Normen und Grid Codes: diese müssen eingehalten wer-den. Nur wenn keine nationalen Normen und Grid Codes vorhanden sind, sollen die Anforderungen dieser Technischen Spezifikation zur Anwendung kommen.

Prescriptions pour le raccordement de générateurs de plus de 16A par phase - Partie 1: Connexion au réseau de distribution BT

L'objet de la présente Spécification Technique est de fournir des instructions techniques pour le raccordement des centrales de production pouvant fonctionner en parallèle avec un réseau de distribution public. La présente Spécification Technique est destinée à être utilisée comme référence technique dans les contrats de raccordement entre les GRD et les producteurs d'électricité. Les exigences contenues dans la présente Spécification Technique s'appliquent uniquement aux machines et au matériel, quelle que soit la source d'énergie primaire. La présente Spécification Technique s'applique à toutes les unités de production triphasées qui satisfont à toutes les conditions qui suivent en tant qu'unité de production individuelle ou en tant que groupe d'unités de production ayant un point de raccordement commun: •   convertissant toute source d'énergie primaire en électricité en courant alternatif; •   est raccordé(e) au réseau BT et assigné(e) à plus de 16 A par phase; •   est destiné(e) à fonctionner en parallèle avec un réseau de distribution public dans des conditions de fonctionnement normales. NOTE   Les générateurs assignés à 16 A inclus par phase sont couverts par la norme EN 50438. La présente Spécification Technique définit les exigences applicables aux interconnexions ainsi qu'une procédure d'essai de conformité.  Le fonctionnement en îlotage de centrales de production, qu'il soit intentionnel ou non, dans lequel aucune partie du système de distribution public n'est impliquée, est en dehors du domaine d'application de la présente Spécification Technique.  La sécurité du personnel est en dehors du domaine d'application de la présente Spécification Technique.  La présente Spécification Technique reconnaît l'existence de normes et de codes nationaux applicables aux réseaux: ceux-ci doivent être respectés. Il convient que les exigences de la présente Spécification Technique s'appliquent uniquement en l'absence de ces normes et codes nationaux.

Zahteve za priklop generatorjev za toke nad 16 A na fazo – 1. del: Priklop na nizkonapetostni distribucijski sistem

Namen te tehnične specifikacije je zagotoviti tehnična navodila o zahtevah za generatorje, ki jih je mogoče upravljati hkrati z razdelilnim omrežjem.
Zaradi praktičnih razlogov se ta tehnična specifikacija nanaša na upravljavca razdelilnega omrežja,
kadar je treba nastavitve opredeliti in/ali zagotoviti, tudi kadar mora te nastavitve opredeliti in/ali zagotoviti drug udeleženec v skladu z nacionalnim in evropskim pravnim okvirom.
OPOMBA 1: To zajema evropske omrežne kodekse in njihovo nacionalno izvajanje ter tudi dodatne nacionalne predpise.
OPOMBA 2: Uporabiti je mogoče dodatne nacionalne zahteve, zlasti za povezavo z razdelilnim omrežjem in delovanjem generatorja.
Zahteve iz tega tehničnega standarda se uporabljajo za vse generatorje, električne stroje in elektronsko opremo, ne glede na vrsto vira primarne energije in ne glede na prisotnost obremenitev v omrežju proizvajalca, ki izpolnjujejo naslednje pogoje:
– pretvarjanje katerega koli vira primarne energije v izmenični tok;
– povezava z nizkonapetnostnim razdelilnim omrežjem z nazivno vrednostjo več kot 16 A na fazo;
– namenjeni so za uporabo skupaj s tem razdelilnim omrežjem v običajnih pogojih delovanja
omrežja.
OPOMBA 3: Generatorji z nazivno vrednostjo do vključno 16 A na fazo so zajeti v standardu EN 50438.
OPOMBA 4: Generatorji, povezani s srednjenapetostnim omrežjem, so zajeti v področju uporabe standarda CLC/TS 50549-2.
Razen če upravljavec razdelilnega omrežja navede drugače, je mogoče, da so generatorji, povezani v srednjenapetostno razdelilno
omrežje z največjo navidezno močjo do 100 kVA, skladni s to tehnično specifikacijo kot alternativo zahtevam iz CLC/TS 50549-2. Upravljavec razdelilnega omrežja lahko opredeli drugačen prag.
Ta tehnična specifikacija določa zahteve za priključitev.
V tej tehnični specifikaciji se upošteva obstoj nacionalnih standardov, omrežnih kodeksov in
posebnih tehničnih zahtev upravljavcev razdelilnih omrežij. Te zahteve naj bi se upoštevale.
Ta standard ne zajema:
– izbire in ocene točke povezave;
– ocene učinka napajalnega sistema;
– ocene povezave;
– ločenega delovanja generatorjev, namernega in nenamernega, kadar ni vključen noben del
razdelilnega omrežja;
– aktivnih sprednjih delov pogonov, ki energijo za kratek čas usmerjajo nazaj v razdelilno omrežje;
– zahtev za varnost osebja, ker so že ustrezno zajete v veljavnih evropskih standardih.

General Information

Status
Withdrawn
Public Enquiry End Date
17-Jun-2010
Publication Date
15-Mar-2015
Withdrawal Date
24-Jan-2022
Current Stage
9900 - Withdrawal (Adopted Project)
Start Date
24-Jan-2022
Due Date
16-Feb-2022
Completion Date
25-Jan-2022

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Standards Content (Sample)

SLOVENSKI STANDARD
SIST-TS CLC/TS 50549-1:2015
01-april-2015
Zahteve za priklop generatorjev za toke nad 16 A na fazo – 1. del: Priklop na
nizkonapetostni distribucijski sistem
Requirements for the connection of generators above 16 A per phase - Part 1:
Connection to the LV distribution system
Prescriptions pour le raccordement de générateurs de plus de 16A par phase - Partie 1:
Connexion au réseau de distribution BT
Ta slovenski standard je istoveten z: CLC/TS 50549-1:2015
ICS:
29.160.20 Generatorji Generators
29.240.01 2PUHåMD]DSUHQRVLQ Power transmission and
GLVWULEXFLMRHOHNWULþQHHQHUJLMH distribution networks in
QDVSORãQR general
SIST-TS CLC/TS 50549-1:2015 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST-TS CLC/TS 50549-1:2015

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SIST-TS CLC/TS 50549-1:2015

TECHNICAL SPECIFICATION CLC/TS 50549-1

SPÉCIFICATION TECHNIQUE

TECHNISCHE SPEZIFIKATION
January 2015
ICS 29.160.20
English Version
Requirements for generating plants to be connected in parallel
with distribution networks - Part 1: Connection to a LV
distribution network above 16 A
Prescriptions relatives au raccordement de générateurs de Anforderungen für den Anschluss von
plus de 16A par phase - Partie 1: Connexion au réseau de Stromerzeugungsanlagen über 16 A je Phase - Teil 1:
distribution BT Anschluss an das Mittelspannungsverteilungsnetz
This Technical Specification was approved by CENELEC on 2014-09-15.

CENELEC members are required to announce the existence of this TS in the same way as for an EN and to make the TS available promptly
at national level in an appropriate form. It is permissible to keep conflicting national standards in force.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.



European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2015 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
 Ref. No. CLC/TS 50549-1:2015 E

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Contents Page
Foreword.3
1 Scope .4
2 Normative references .4
3 Terms and definitions .5
4 Requirements on generating plants . 13
4.1 General . 13
4.2 Connection scheme . 14
4.3 Choice of switchgear . 14
4.4 Normal operating range . 15
4.5 Immunity to disturbances . 17
4.6 Active response to frequency deviation . 19
4.7 Power response to voltage variations and voltage changes . 20
4.8 EMC and power quality . 25
4.9 Interface protection . 25
4.10 Connection and starting to generate electrical power . 30
4.11 Active power reduction on set point . 31
4.12 Requirements regarding single fault tolerance of interface protection system and
interface switch . 31
5 Conformance test procedure . 31
Annex A (informative)  Interconnection requirements . 32
A.1 General . 32
A.2 Network integration . 32
A.3 Clusters of single-phase generating units . 33
Annex B (informative) Loss of Mains and overall power system security . 34
Annex C (informative) Examples of protection strategies . 35
C.1 Introduction . 35
C.2 Example strategy 1 . 36
C.3 Example strategy 2 . 40
Annex D (normative) Abbreviations . 42
Bibliography . 43

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Foreword

This document (CLC/TS 50549-1:2015) has been prepared by CLC/TC 8X "System aspects of
electrical energy supply".
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC [and/or CEN] shall not be held responsible for identifying any or all such
patent rights.
This Technical Specification relates to both future European Network Codes and current technical
market needs. Its purpose is to give detailed description of functions to be implemented in products.
This Technical Specification is also intended to serve as a technical reference for the definition of
national requirements where European Network Codes requirements allow flexible implementation.
The stated requirements are solely technical requirements; economic issues regarding, e.g. the
bearing of cost are not in the scope of this document.
CLC/TC 8X plans future standardization work in order to ensure the compatibility of this Technical
Specification with the evolution of the legal framework.

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1 Scope
The purpose of this Technical Specification is to provide technical guidance on the requirements for
generating plants which can be operated in parallel with a distribution network.
For practical reasons, this Technical Specification refers to the distribution system operator in case
settings have to be defined and/or provided, even when these settings are to be defined and/or
provided by another actor according to national and European legal framework.
NOTE 1 This includes European network codes and their national implementation, as well as further national
regulations.
NOTE 2 Further national requirements especially for the connection to the distribution network and the
operation of the generating plant can apply.
The requirements of this Technical Specification apply to all generating plants, electrical machinery
and electronic equipment, irrespective of the kind of primary energy source and irrespective of the
presence of loads in the producer’s network that meet all of the following conditions:
– converting any primary energy source into AC electricity;
– connected to a LV distribution network and rated at more than 16 A per phase;
– intended to operate in parallel with this distribution network under normal network operating
conditions.
NOTE 3 Generating plants rated up to and including 16 A per phase are covered by EN 50438.
NOTE 4 Generating plants connected to a MV distribution network fall into the scope of CLC/TS 50549-2.
Unless stated differently by the DSO generating plants connected to a medium voltage distribution
network with a maximum apparent power up to 100 kVA can comply with this Technical Specification
as alternative to the requirements of CLC/TS 50549-2. A different threshold may be defined by the
DSO.
This Technical Specification defines connection requirements.
This Technical Specification recognizes the existence of National Standards, Network Codes, and
specific technical requirements of the DSOs. These should be complied with.
Excluded from the scope are:
– the selection and evaluation of the point of connection;
– power system impact assessment;
– connection assessment;
– island operation of generating plants, both intentional and unintentional, where no part of the
distribution network is involved;
– active front ends of drives feeding energy back into the distribution network for short duration;
– requirements for the safety of personnel as they are already adequately covered by existing
European Standards.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
EN 60255-127, Measuring relays and protection equipment  Part 127: Functional requirements for
over/under voltage protection (IEC 60255-127)
EN 61000-4-30, Electromagnetic compatibility (EMC)  Part 4-30: Testing and measurement
techniques  Power quality measurement methods (IEC 61000-4-30)

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 Part 1: Fundamental principles, assessment of
HD 60364-1, Low-voltage electrical installations
general characteristics, definitions (IEC 60364-1)
HD 60364-5-551, Low-voltage electrical installations  Part 5-55: Selection and erection of electrical
equipment  Other equipment  Clause 551: Low-voltage generating sets (IEC 60364-5-551)
IEC 60050, International Electrotechnical Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60050 and the following
apply.
3.1
active factor
for a two-terminal element or a two-terminal circuit under sinusoidal conditions, ratio of the active
power to the apparent power
Note 1 to entry:  In a three phase system, this is referring to the positive sequence component of the
fundamental.
Note 2 to entry:  The active factor is equal to the cosine of the displacement angle.
[SOURCE: IEV 131-11-48, modified]
3.2
basic insulation
insulation of hazardous-live-parts which provides basic protection
Note 1 to entry:  This concept does not apply to insulation used exclusively for functional purposes.
[SOURCE: IEV 195-06-06]
3.3
basic protection
protection against electric shock under fault-free conditions
[SOURCE: IEV 195-06-01]
3.4
cogeneration
combined heat and power (CHP)
combined generation of electricity and heat by an energy conversion system and the concurrent use of
the electric and thermal energy from the conversion system
3.5
converter connected generating technology
technology where a generating unit is connected to a distribution grid through a converter including
doubly fed induction machine based technology (DFIG)
3.6
design active power
P
D
maximum AC active power output at an active factor of 0,9 or the active factor specified by the DSO
for a certain generating plant or generating technology
3.7
directly coupled generating technology
technology where a generating unit is connected to a distribution grid without any converter
3.8
disconnection
separation of the active parts of the main circuit of the generating plant or unit from the network with
mechanical contacts providing at least the equivalent of basic insulation

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Note 1 to entry:  Passive components like filters, auxiliary power supply to the generating unit and sense lines
can remain connected.
Note 2 to entry:  For the design of basic insulation all voltage sources should be considered.
3.9
displacement angle
φ
under sinusoidal conditions, phase difference between the voltage applied to a linear two-terminal
element or two-terminal circuit and the electric current in the element or circuit
Note 1 to entry:  In a three phase system, this is referring to the positive sequence component of the
fundamental.
Note 2 to entry:  The cosine of the displacement angle is the active factor.
3.10
distribution network
electrical network, including closed distribution networks, for the distribution of electrical power from
and to third parties connected to it, to and from a transmission or another distribution network, for
which a DSO is responsible
3.11
distribution system operator
DSO
natural or legal person responsible for the distribution of electrical power to the public and for
operating, ensuring the maintenance of and, if necessary, developing the distribution network in a
given area
Note 1 to entry:  In some countries, the distribution network operator (DNO) fulfils the role of the DSO.
3.12
downstream
direction in which the active power would flow if no generating units, connected to the distribution
network, were running
3.13
droop
ratio of the per-unit change in frequency (Δf)/f (where f is the nominal frequency) to the per-unit
n n
change in power (ΔP)/ P (where P is the reference power at the instance when the frequency
ref ref
reaches a frequency threshold):
s= - (Δf/f ) / (ΔP/P )
n ref
[SOURCE: EV 603-04-08]
3.14
fundamental components of a three-phase system
3.14.1
phasor
representation of a sinusoidal integral quantity by a complex quantity whose argument is equal to the
initial phase and whose modulus is equal to the root-mean-square value
Note 1 to entry:  For a quantity a(t) = A √2 cos(ωt +Ө ) the phasor is A exp jӨ .
0 0
Note 2 to entry:  The similar representation with the modulus equal to the amplitude is called "amplitude phasor".
Note 3 to entry:  A phasor can also be represented graphically.
[SOURCE: IEV 131-11-26, modified]

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3.14.2
positive sequence component of the fundamental
for a three-phase system with phases L1, L2 and L3, the symmetrical sinusoidal three-phase set of
voltages or currents having frequency equal to the fundamental frequency and which is defined by the
following complex mathematical expression:
1
2

X = (X + aX + a X )
1 L1 L2 L3
3
j2π/3
where a = e is the 120 degree operator, and X , X and X are the complex expressions of the
L1 L2 L3
fundamental frequency phase quantities concerned, that is, current or voltage phasors
Note 1 to entry:  In a balanced harmonic-free system, only positive sequence component of the fundamental
π π
jθ j(θ+4 /3) j(θ+2 /3)
exists. For example, if phase voltage phasors are symmetrical U = Ue , U = Ue and U = Ue then
L1 L2 L3
π π π π
jθ j2 /3 j(θ+4 /3) j4 /3 j(θ+2 /3) jθ jθ jθ jθ
U = (Ue + e Ue + e Ue )/3 = (Ue + Ue + Ue )/3 = Ue .
1
[SOURCE: IEV 448-11-27]
3.14.3
negative sequence component of the fundamental
for a three-phase system with phases L1, L2 and L3, the symmetrical sinusoidal three-phase set of
voltages or currents having frequency equal to the fundamental frequency and which is defined by the
following complex mathematical expression:
1
2
X = (X + a X + aX )
2 L1 L2 L3
3
j2π/3
where a = e is the 120° operator, and X , X and X are the complex expressions of the
L1 L2 L3
fundamental frequency phase quantities concerned, that is, current or voltage phasors
Note 1 to entry:  Negative sequence voltage or current components may be significant only when the voltages or

currents, respectively, are unbalanced. For example, if phase voltage phasors are symmetrical U = Ue , U =
L1 L2
π π π π π
j(θ+4 /3) j(θ+2 /3) jθ j4 /3 j(θ+4 /3) j2 /3
Ue and U = Ue then the negative sequence component U = (Ue + e Ue + e
L3 2
π π π
j(θ+2 /3) jθ j2 /3 j4 /3
Ue )/3 = Ue (1 + e + e )/3 = 0.
[SOURCE: IEV 448-11-28]
3.14.4
zero sequence component of the fundamental
for a three-phase system with phases L1, L2 and L3, the in-phase sinusoidal voltage or current
component having the fundamental frequency and equal amplitude in each of the phases and which is
defined by the following complex mathematical expression:
1
X = (X +X +X )
0 L1 L2 L3
3
where X , X and X are the complex expressions of the fundamental frequency phase quantities
L1 L2 L3
concerned, that is, current or voltage phasors
[SOURCE: IEV 448-11-29]
3.15
generating plant
sum of generating units connected at one point of connection, including auxiliaries and all connection
equipment
Note 1 to entry:  This definition is intended to be used for verification of compliance to the technical requirements
of this standard. It may be different to the legal definition of a plant.

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3.16
generating plant controller
intelligence which ensures the fulfillment of performance requirements at the point of connection
(POC) towards a generating plant, usually by utilizing external measurement signals from the POC to
generate reference to a sub structure e.g. the generating units
3.17
generating unit
smallest set of installations which can generate electrical energy running independently and which can
feed this energy into a distribution network
Note 1 to entry:  For example, a combined cycle gas turbine (CCGT) or an organic rankine cycle (ORC) after a
combustion engine is considered as a single generating unit.
Note 2 to entry:  If a generating unit is a combination of technologies leading to different requirements, this has to
be settled case by case.
Note 3 to entry:  A storage device operating in electricity generation mode and AC connected to the distribution
network is considered to be a generating unit.
3.18
interface protection relay
combination of different protection relay functions which opens the interface switch of a generating unit
and prevents its closure, whichever is appropriate in case of:
• a fault on the distribution network (with reference to POC voltage level);
• an islanding situation;
• the presence of voltage and frequency values outside the corresponding regulation values
3.19
interface protection system
a protection system that acts on the interface switch
3.20 Interface protection system timing
3.20.1
energizing quantity
energizing quantity by which the protection function is activated when it is applied under specified
conditions
Note 1 to entry:  See also Figure 1.
[SOURCE: IEV 442-05-58, modified]
3.20.2
start time
duration of the time interval between the instant when the energizing quantity of the measuring relay in
reset condition is changed, under specified conditions, and the instant when the start signal asserts
Note 1 to entry:  See also Figure 1.
[SOURCE: (EN 60255-151, modified]
3.20.3
time delay setting
intentional delay that might be adjustable by the user
Note 1 to entry:  See also Figure 1.
3.20.4
operate time
duration of the time interval between the instant when the energizing quantity of a measuring relay in
reset condition is changed, under specified conditions, and the instant when the relay operates
Note 1 to entry:  See also Figure 1.

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Note 2 to entry:  Operate time is start time plus time delay setting.
[SOURCE: IEV 447-05-05, modified]
3.20.5
disconnection time
sum of operate time of the protection system and the opening time of the interface switch
Note 1 to entry:  See also Figure 1 where the CB opening time indicates the opening time.
3.20.6
reset time
duration of the time interval between the instant when the energizing quantity of a measuring relay in
operate condition is changed, under specified conditions, and the instant when the relay resets
Note 1 to entry:  See also Figure 1.
[SOURCE: IEV 447-05-06 modified]
3.20.7
disengaging time
duration of the time interval between the instant a specified change is made in the value of the input
energizing quantity which will cause the relay to disengage and instant it disengages
Note 1 to entry:  See also Figure 1.
[SOURCE: IEV 447-05-10]

Figure 1  Main times defining the interface protection performance
3.21
islanding
situation where a section of the distribution network, containing generation, becomes physically
disconnected from the rest of distribution network and one or more generating units maintain a supply
of electrical energy to the isolated section of the distribution network

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3.22
low voltage (LV) distribution network
electric distribution network with a voltage whose nominal r.m.s. value is U ≤ 1 kV
n
3.23
maximum active power
P
max
maximum AC active power output that the generating unit or the sum of all the generating units in a
generating plant is designed to achieve under normal operating conditions
Note 1 to entry:  This maximum power is defined by a measurement with 10 min averaging.
3.24
maximum apparent power
S
max
maximum AC apparent power output that the generating unit or the sum of all the generating units in a
generating plant is designed to achieve under normal operating conditions
Note 1 to entry:  This maximum power is defined by a measurement with 10 min averaging.
3.25
momentary active power
P
M

the actual AC active power output at a certain instant
3.26
nominal frequency
f
n
frequency used to designate and identify equipment or a power system
Note 1 to entry:  For the purpose of this standard, the nominal frequency f is 50 Hz.
n
[SOURCE: IEV 151-16-09, modified]
3.27
nominal voltage
U
n
voltage by which a supply network is designated or identified and to which certain operating
characteristics are referred
3.28
observation time
time during which all the voltage and the frequency values are observed to be within a specified range
prior to a generating plant connection to the distribution network or start to generate electric power
3.29
operation in parallel with the distribution network
situation where the generating plant is connected to a distribution network and operating
3.30
point of connection
POC
reference point on the electric power system where the user’s electrical facility is connected
Note 1 to entry:  For the purpose of this standard, the electric power system is the distribution network.
[SOURCE: IEV 617-04-01]

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3.31
power factor
under periodic conditions, ratio of the absolute value of the active power P to the apparent power S:

|𝑃|
𝜆 =
𝑆
Note 1 to entry:  Under sinusoidal conditions, the power factor is the absolute value of the active factor.
[SOURCE: IEV 131-11-46]
3.32
power system stability
the capability of a power system to regain a steady state, characterized by the synchronous operation
of the generating plants after a disturbance
[SOURCE: IEV 603-03-01]
3.33
primary energy source
non-electric energy source supplying an electric generating unit
Note 1 to entry:  Examples of primary energy sources include natural gas, wind and solar energy. These sources
can be utilized, e.g. by gas turbines, wind turbines and photovoltaic cells.
3.34
producer
party who already has or is planning to connect an electricity generating plant to a distribution network
3.35
producer’s network
electrical installations downstream from the point of connection owned/operated by the producer for
internal distribution of electricity
3.36
protection relay
measuring relay which detects faults or other abnormal conditions in a power system or of a power
equipment
Note 1 to entry:  A protection relay is a component part of a protection system.
Note 2 to entry:  An interface protection relay is a protection relay acting on the interface switch.
[SOURCE: IEV 447-01-14]
3.37
protection system
an arrangement of one or more protection equipments, and other devices intended to perform one or
more specified protection functions
Note 1 to entry:  A protection system includes one or more protection equipments, instrument transformer(s),
wiring, tripping circuit(s), auxiliary supply(s) and, where provided, communication system(s). Depending upon the
principle(s) of the protection system, it may include one end or all ends of the protected section and, possibly,
automatic reclosing equipment.
Note 2 to entry:  The circuit-breaker(s) are excluded.
[SOURCE: IEV 448-11-03]

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3.38
rated current
maximum continuous AC output current which a generating unit or generating plant is designed to
achieve under normal operating conditions
[SOURCE: 415-04-03, modified]
3.39
reference voltage
value specified as the base on which residual voltage, thresholds and other values are expressed in
per unit or percentage terms
Note 1 to entry:  For the purpose of this standard, the reference voltage is the nominal voltage or the declared
voltage of the distribution network.
[SOURCE: EN 50160, 3.18, modified]
3.40
single fault tolerance
built-in capability of a system to provide continued correct execution of its function in the presence of a
single fault
[SOURCE: IEV 394-33-13, modified]
3.41
switch
device for changing the electric connections among its terminals
[SOURCE: IEV 151-12-22]


Figure 2  Electricity generating plant connected to a distribution network
(schematic view of switches)
3.41.1
main switch
switch installed as close as possible to the point of connection, for protection against internal faults
and disconnection of the whole plant from the distribution network
Note 1 to entry: See also Figure 2.

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3.41.2
interface switch
switch (circuit breaker, switch or contactor) installed in the producer’s network, for separating the
part(s) of the producer’s network containing at least one generation unit from the distribution network
Note 1 to entry:  See also Figure 2.
Note 2 to entry:  In some situations, the interface switch may be used to enable island operation of part of the
producer’s network, if technically feasible.
3.41.3
generating unit switch
switch installed electrically close to the terminals of each generating unit of the generating plant, for
protection and disconnection of that generating unit
Note 1 to entry:  See also Figure 2.
3.42
temporary operation in parallel with the distribution network
conditions in which the generating plant is connected to a distribution network, during defined short
periods, to maintain the continuity of the supply voltage and to facilitate testing
3.43
transmission system operator
TSO
natural or legal person responsible for operating, ensuring the maintenance of and, if necessary,
developing the transmission system in a given area and, where applicable, its interconnections with
other power systems, and for ensuring the long-term ability of the power system to meet reasonable
demands for the transmission of electricity
3.44
voltage control system
automatic control system of a generating unit or generating plant which counteracts network voltage
changes, for instance but not only, by adjusting reactive power output accordingly
3.45
...

SLOVENSKI STANDARD
oSIST-TS CLC/prTS 50549:2010
01-maj-2010
Zahteve za priklop generatorjev za toke nad 16 A na fazo na nizkonapetostni
distribucijski sistem ali na srednjenapetostni distribucijski sistem
Requirements for the connection of generators above 16 A per phase to the LV
distribution system or to the MV distribution system
Prescriptions pour le raccordement de générateurs de plus de 16 A par phase au réseau
de distribution BT ou au réseau de distribution MT
Ta slovenski standard je istoveten z: CLC/prTS 50549:2010
ICS:
29.240.01 2PUHåMD]DSUHQRVLQ Power transmission and
GLVWULEXFLMRHOHNWULþQHHQHUJLMH distribution networks in
QDVSORãQR general
oSIST-TS CLC/prTS 50549:2010 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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oSIST-TS CLC/prTS 50549:2010

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oSIST-TS CLC/prTS 50549:2010
 DRAFT
TECHNICAL SPECIFICATION
CLC/prTS 50549

SPÉCIFICATION TECHNIQUE
March 2010
TECHNISCHE SPEZIFIKATION

ICS


English version


Requirements for the connection of generators above 16 A per phase
to the LV distribution system or to the MV distribution system



Prescriptions pour le raccordement de
générateurs de plus de 16 A par phase au
réseau de distribution BT ou au réseau de
distribution MT




This draft Technical Specification is submitted to CENELEC members for comments prior to the voting meeting
of 2010-10-27.

Deadline for CENELEC: 2010-06-18.

It has been drawn up by CLC/TC 8X.

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, Romania, Slovakia, Slovenia,
Spain, Sweden, Switzerland and the United Kingdom.

Warning : This document is not a Technical Specification. It is distributed for review and comments. It is subject
to change without notice and shall not be referred to as a Technical Specification.


CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

Central Secretariat: Avenue Marnix 17, B - 1000 Brussels


© 2010 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Project: 20863 Ref. No. CLC/prTS 50549:2010 E

Draft for Enquiry

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1 Foreword
2
3 This draft Technical Specification was prepared by WG 03 - Requirements for connection of
4 generators to distribution networks of the Technical Committee CENELEC TC 8X, System aspects for
5 electrical energy supply.
6
7 It is circulated for comments prior to the voting meeting foreseen on 2010-10-27 in accordance with
8 the Internal Regulations, Part 2, Subclause 11.3.3.2.
9 __________
10
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11 Contents
12
13
14 1 Scope .5
15 2 Normative references .5
16 3 Definitions .5
17 4 Interconnection requirements .8
18 4.1 network integration .9
19 4.2 connection scheme .9
20 4.2.1 Choice of switchgear . 11
21 4.3 Voltage and frequency tolerances . 11
22 4.3.1 Continuous operation . 12
23 4.3.2 Low frequencies . 12
24 4.3.3 High frequencies . 13
25 4.4 Starting, synchronisation and reconnection . 13
26 4.4.1 Plants using rotating machines . 13
27 4.4.2 Plants using static converters . 13
28 4.5 Response to normal voltage and frequency variations . 14
29 4.5.1 Power-frequency control . 14
30 4.5.2 Voltage control . 14
31 4.6 Response to abnormal voltage and frequency variations . 15
32 4.6.1 Abnormal voltage variations . 15
33 4.6.2 Abnormal frequency variations . 16
34 4.7 Short circuit power requirements . 16
35 4.8 Power quality . 17
36 4.9 Protection . 17
37 4.9.1 Protection which trips the interface switch . 17
38 4.9.2 Protection of the producer’s network . 18
39 4.9.3 Generating unit protections . 18
40 4.10 Coordination of protections . 19
41 4.11 Exchange of information . 19
42 5 Conformance test procedure . 20
43 5.1.1 Scope and object . 20
44 5.1.2 Measurement system requirements . 20
45 5.1.3 Requirements for simulated grid . 20
46 5.1.4 Test signals . 21
47 5.1.5 Step up signal . 21
48 5.1.6 Step down signal . 21
49 5.1.7 Phase step signal . 21
50 5.1.8 List of symbols . 21
51 5.1.9 Test reports . 22
52 5.2 Description of tests. 22
53 5.2.1 Starting. 22
54 5.2.2 Synchronisation . 23
55 5.2.3 Reconnection . 24
56 5.2.4 Power-frequency control . 24
57 5.2.5 Voltage control . 24
58 5.2.6 Abnormal voltage variations . 26
59 5.2.7 Abnormal frequency variations . 26
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60 5.2.8 Short-circuit power requirement . 27
61 5.2.9 Power quality . 27
62 5.2.10 Protection . 27
63 5.2.11 Loss of mains protection test . 28
64 5.2.12 Directional power protection function test. 29
65 Figures
66 Figure 1 - Electricity generating plant connected to a Public Distribution Network
67 (schematic view) . 10
68 Figure 2 - Voltage and frequency range tolerances . 12
69 Figure 3 - Fault-Ride-Through curve, Voltage at Point of Common Coupling . 15
70 Figure 4 - Active power reduction for over frequency conditions . 16
71 Figure 5 - Single phase equivalent circuit for loss of mains protection test . 28
72 Tables
73 Table 1 - Maximum allowable power reductions in case of low frequency on the grid . 13
74 Table 2 - Maximum allowable power reductions in case of high frequency on the grid . 13
75 Table 3 - Behaviour of generating plants providing dynamic grid support during grid faults . 15
76 Table 4 – Protections for generating plants connected to MV Public Distribution Network . 18
77 Table 5 – Protections for generating plants connected to MV Public Distribution Network . 18
78 Table 6 - Sequence of operation of the switches . 19
79 Table 7 - Sequence of operation of the protective devices in case of an individual line MV
80 connection . 19
81 Table 8 - Voltage dips to be tested . 26
82
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83 1 Scope
84 The purpose of this Technical Specification is to provide technical guidance for the connection of
85 generating plants which can be operated in parallel with a public distribution network.
86 The requirements of this Technical Specification only apply to electrical machinery and equipment,
87 irrespective of the kind of primary energy source.
88 This Technical Specification applies to all three-phase generating units that meet all of the following
89 conditions as an individual unit or as a cluster of units with a common point of connection:
90 • converting any primary energy source into AC electricity;
91 • connected to the LV network and rated at more than 16A per phase or connected to the MV
92 network;
93 • intended to operate permanently in parallel with a public distribution network under normal network
94 operating conditions.
95
96 This Technical Specification defines interconnection requirements and a conformance test procedure.
97 This Technical Specification is intended to be used as a technical reference in connection agreements
98 between DNOs and electricity producers.
99 Island operation of generating plants, both intentional and unintentional, is out of the scope of this
100 Technical Specification.
101 Safety of personnel is out of the scope of this Technical Specification.
102 2 Normative references
103 The following referenced documents are indispensable for the application of this document. For dated
104 references, only the edition cited applies. For undated references, the latest edition of the referenced
105 document (including any amendments) applies.
106 IEC 60050, International Electrotechnical Vocabulary
107 EN 50160, Voltage characteristics of electricity supplied by public distribution networks
108 3 Definitions
109 For the purposes of this document, the definitions given in IEC 60050 and the following definitions
110 apply.
111 3.1
112 connection agreement
113 written agreement between a producer and a DNO regarding the connection of a generating plant to a
114 Public Distribution Network
115 3.2
116 disconnection
117 separation of the active parts of the generator from the public distribution network by means of
118 mechanical contacts providing basic insulation at least
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119 3.3
120 Equipment Under Test (EUT)
121 generating unit and all associated equipment that is being subjected to the functional tests and
122 protection tests described in this Technical Specification
123 3.4
124 essential loads
125 electric loads close to the generating plant, which are deemed essential by the party installing the
126 generating plant
127 NOTE In case of islanding, essential loads may be supplied by the internal distribution network of the producer by opening
128 the interface switch.
129 3.5
130 general switch
131 switch installed as close as possible to the Point of Common Coupling (PCC), for protection and
132 disconnection of the whole plant from the distribution network
133 3.6
134 generating plant
135 set of generating units, circuits, equipment and auxiliary services for the production of electricity
136 NOTE A generating plant may include electric loads.
137 3.7
138 generating unit
139 set composed of one or more primary energy sources and one generator, to which the primary energy
140 sources supply their non-electric energy for conversion into electricity
141 3.8
142 generator
143 electric machine which converts non-electric energy (supplied by primary energy sources) into
144 electricity
145 3.9
146 generator switch
147 switch installed electrically close to the terminals of each generator of the generating plant, for
148 protection and disconnection of that generator
149 3.10
150 interconnection system
151 all equipment and functions (included the generator switch) used to connect a generating unit to a
152 public distribution network
153 3.11
154 islanding
155 condition in which the generating plant is supplying loads not connected to a public distribution
156 network
157 3.12
158 interface switch
159 switch installed in the producer’s network, for separation of a part of the producer’s network from the
160 public distribution network, in order to enable island operation of a part of the producer’s network
161 3.13
162 low voltage (LV) system
163 electric system with a nominal AC voltage less than 1 kV
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164 3.14
165 MV system
166 electric system with a nominal AC voltage 1 kV or more, but less than 35 kV
167 3.15
168 network
169 one or several electric systems which are outside the generating plant
170 3.16
171 network operation under normal conditions
172 stationary operating conditions where electricity demand is fully met without the ratings of any
173 component of the electricity network being exceeded
174 3.17
175 operation in parallel with the Public Distribution Network
176 situation where the generating plant is connected to and operating in synchronism with a public
177 distribution network
178 3.18
179 Point of Common Coupling (PCC)
180 point of a power network, electrically nearest to a particular network user, at which other network users
181 are, or may be, connected
182 3.19
183 point of connection
184 point on a public power supply system where a generating plant is, or can be connected
185 3.20
186 primary energy source
187 non- electric energy source supplying an electric generator
188 NOTE Examples of primary energy sources include gas turbines, wind turbines and photovoltaic cells.
189 3.21
190 producer
191 party planning to connect an electricity generating plant to a public distribution network
192 3.22
193 producer’s network
194 electrical installations owned/operated by the producer for internal distribution of electricity
195 3.23
196 protection
197 any function that automatically trips a switch when a given condition occurs
198 3.24
199 Public Distribution Network switch
200 switch installed electrically close to the interface between the producer’s network and the public
201 distribution network
202 3.25
203 reset ratio
204 ratio of the value of an electrical parameter that causes a protection function to reset and the value of
205 the same parameter that had triggered the protection to trip
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206 3.26
207 reset time
208 for a protection function in the trip state, the time lag from the input being removed and the output
209 circuit changing state
210 3.27
211 response time
212 time interval starting when a protection function is triggered and ending when the protection equipment
213 responds as expected
214 3.28
215 rotating generating plant
216 generating plant that, through rotating machinery, converts the primary energy source into electric
217 energy to be supplied to a network
218 3.29
219 Short Circuit Ratio (SCR)
220 ratio of the following quantities, referring to a synchronous generator:
221 - numerator: Open Circuit Field Current to obtain 1 p.u. Terminal Voltage,
222 - denominator: Short Circuit Field Current to obtain 1 p.u. Terminal Current
223 3.30
224 simulated grid
225 set of equipment, movable or immovable, for voltage and frequency testing, which simulates an
226 electric grid. Where appropriate, the grid itself can be employed instead of the simulated grid, provided
227 its integrity and the safety of operation are guaranteed
228 3.31
229 static generating plant
230 generating plant that, through static devices, converts the primary energy source into electric energy
231 to be supplied to the network
232 3.32
233 temporary operation in parallel with the Public Distribution Network
234 conditions in which the generating plant is connected to a public distribution network, during defined
235 short periods, to maintain the continuity of the supply voltage and to facilitate testing
236 3.33
237 trip time
238 time lag starting when the measured quantity (e.g. frequency, voltage, power) exceeds the trip
239 threshold and ending when the tripping command is issued
240 4 Interconnection requirements
241 This clause defines connection criteria of the generating plants to the public distribution network and
242 provides guidance for the selection of connection schemes and for the co-ordination of protection.
243 Three-phase generating plants (whether equipped with rotating or static generators) may be operated
244 in parallel with a public distribution network, subject to compliance with the requirements of this
245 Technical Specification. When the generating plant is composed of clusters of single-phase
246 generators, efforts should be made to ensure power balance between phases.
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247 The provisions of this Technical Specification are independent of the duration of generating unit
248 operation in parallel. It rests with the DNO to relax, if deemed appropriate, interconnection
249 requirements for an individual generator whose operation in parallel only lasts for a short time
250 (temporary operation in parallel). The relaxed requirements shall be recorded in the Connection
251 Agreement, along with the maximum allowable duration of the temporary operation in parallel. An
252 appropriate device shall automatically disconnect the generator as soon as the maximum allowable
253 duration has elapsed.
254 4.1 network integration
255 All generating plants shall meet the following connection requirements:
256 • the total installed power shall be compatible with the operating criteria agreed with the DNO;
257 • the connection of the generating plant shall not cause the short circuit current to exceed the
258 breaking and making capacity of any circuit breaker;
259 • the settings applied to the protection equipment shall be selected to ensure correct tripping of the
260 generator under fault conditions and stability against network disturbances as agreed with the
261 DNO;
262 • where the generating plant is connected to a public distribution network that is fitted with an auto-
263 reclose circuit breaker, the trip times of the generator switches shall be such that there is no risk of
264 an out of phase reclosure;
265 • the generating plant shall not cause the current carrying capacity of the lines and transformers to
266 be exceeded.
267 A connection agreement shall be reached between the DNO and the Producer, prior to connection.
268 The connection agreement shall include, but shall not be limited to, the following issues:
269 • maximum power to be installed in the generating plan;
270 • connection voltage level (MV or LV) at PCC (to be agreed upon between the producer and the
271 DNO, in compliance with national standards and regulations;
272 • contribution of the generating plant to short circuit curren;
273 • if appropriate, instantaneous power factor at PCC (loads, if any, are non included;
274 • operation and settings of automatic voltage power factor controller and power controller where
275 presen;
276 • single line diagram of installation with clearly marked connection point, installation boundary and
277 measuring poin;
278 • earthing arrangement of the generating plant (in compliance with national legislation, standards
279 and regulations;
280 • reconnection requirement;
281 • setting applied to the interface protection.
282 4.2 connection scheme
283 The plant shall be in compliance with national legislation, standards and regulations and agreed upon
284 between the producer and the DNO. The plant shall assure the following:
285 a) start up, operation and stop under normal network operating conditions, i.e. in the absence of
286 faults or malfunctions;
287 b) faults and malfunctions within the generating plant shall not impair the integrity of the public
288 distribution network;
289 c) co-ordinated operation of the interface switch with the generator switch, the general switch and the
290 public distribution network switch, for faults or malfunctions during operation in parallel with the
291 public distribution network;
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292 d) disconnection of the generating plant from the public distribution network by tripping the interface
293 switch in the following cases:
294  intentional opening of the public distribution network switch,
295  faults in the generating plant or on the public distribution network,
296  abnormal voltage or frequency (i.e. excursions outside of set limits).
297 In order to satisfy the above functions, co-ordinated but independent switches and protection
298 equipment shall be applied to each of the following sections of the generating plant, as shown in
299 Figure 1:
300 • generator;
301 • part of the producer’s network designed to run as an island (if required);
302 • the remaining part of the producer’s (i.e. all of the producer’s network less the island section;
303 • Public Distribution Network.
304
305 Figure 1 - Electricity generating plant connected to a Public Distribution Network
306 (schematic view)
307
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308 4.2.1 Choice of switchgear
309 4.2.1.1 Generals
310 Switches shall be chosen based on the characteristics of the system in which they are intended to be
311 installed; for this purpose, the short circuit current at the installation point shall be assessed, taking
312 into account, inter alia, the contribution of the generating plant being connected. All switches shall
313 comply with applicable European standards.
314 Unless otherwise stated in the connection agreement, a means of isolating the generating plant shall
315 be accessible to the DNO at all times.
316 4.2.1.2 General switch
317 Possible arrangements for the general switch include but are not limited to the following:
318 • for LV systems: automatic circuit-breaker or switch equipped with fuses;
319 • for MV systems: extractable circuit-breaker or circuit-breaker with a disconnector on the network
320 side.
321 4.2.1.3 Interface switch
322 The interface switch for LV systems can be composed of
323 • a circuit breaker, or
324 • a switch equipped with fuses.
325 For MV systems, the interface switch can be made of (e.g.)
326 • extractable circuit-breaker, or
327 • circuit-breaker with disconnectors on both sides.
328 If the whole of the load in the producer’s network is deemed essential, the functions of the interface
329 switch and the general switch may be provided by a single switch.
330 4.2.1.4 Generator switch
331 The generator switch for LV systems can be made of (e.g.)
332 • automatic circuit-breaker, or
333 • switch equipped with fuses.
334 For MV systems, the generator switch can be made of
335 • extractable circuit-breaker, or
336 • circuit-breaker with a disconnector on the network side.
337 The generator switch shall be installed at a sufficiently short distance from the terminals of the
338 generator; the arrangement shall be made in such a way that the dangers of short-circuit and of fire
339 are limited.
340 If the generating plant is composed of a single generating unit and is not intended for island operation,
341 the functions of the generator switch and the interface switch may be provided by a single switch.
342 4.3 Voltage and frequency tolerances
343 A generating unit must be resilient to the maximum deviations of voltage and/or frequency at the Point
344 of Common Coupling (PCC), while reducing the maximum power as little as possible.
345 The requirements governing reactive power in case of voltage fluctuations are described in more detail
346 in 4.5.2.
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347 In the full-load frequency range from 49,5 Hz to 50,2 Hz the generating unit must stay connected until
348 voltage protection trips.
349 For parallel operation with the Public Distribution Network, automatic start-up and synchronisation is
350 allowed when the voltage and the frequency are within the “normal continuous operation” area, as
351 shown in Figure 2.
352
353
354 Figure 2 - Voltage and frequency range tolerances
355 4.3.1 Continuous operation
356 The area of normal continuous operation in the full-load frequency range is the nominal operational
357 voltage ± 10 %.
358 At voltages -5 % < U ≤ -10 % and +5 % > U ≥ +10 % the generating unit shall provide voltage
n n
359 support according to 4.5.2.
360 At voltages below U - 10 % or above U + 10 % the generating unit must stay connected with a
n n
361 minimum reduction of power until under or over voltage protection trips.
362 Where minimum reduction is required, the generating unit may produce what it is capable of.
363 4.3.2 Low frequencies
364 When the frequency is low (below 49,5 Hz) and if voltages at the PCC are within the full-load voltage
365 range, a generating unit must be able to supply power only reduced from the maximum power at
366 frequencies at the PCC as
...

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