CLC/TS 50549-1:2015

SLOVENSKI STANDARD
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
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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

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.

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

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:
X = (X + aX + a X )
1 L1 L2 L3
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 .
[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:
X = (X + a X + aX )
2 L1 L2 L3
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
jθ
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:
X = (X +X +X )
0 L1 L2 L3
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.

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

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]
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
voltage change
variation of the r.m.s value of a voltage between two consecutive levels sustained for definite but
unspecified durations
[SOURCE: IEV 161-08-1, modified]
3.46
voltage variation
increase or decrease of r.m.s. voltage normally due to load variations in load and/or generation
[SOURCE: EN 50160, 3.34, modified]
4 Requirements on generating plants
4.1 General
This clause defines requirements on generating plants to be operated in parallel with the distribution
network. Where settings have to be provided or a range of configurability is given, these configuration
and settings may be provided by the DSO respecting the legal framework. Where no settings are
provided by the DSO, the stated default settings shall be used; if no default settings are given, it rests
with the producer to choose settings or to deactivate the function.
The provisions of Clause 4 are independent of the duration the generating unit operates in parallel
with the distribution network. It rests with the DSO to relax, if deemed appropriate, the requirements
for an individual generating unit or plant whose operation in parallel only lasts for a short time
(temporary operation in parallel). The relaxed requirements shall be agreed between the DSO and the
producer, along with the maximum allowable duration of the temporary operation in parallel. For the

short-term parallel operation an appropriate device shall automatically disconnect the generating unit
or plant as soon as the maximum allowable duration has elapsed.
If different requirements on the generating plant/units interfere with each other following hierarchy in
descending order shall be applied:
a) generating unit protections including for prime mover if technically justified and agreed between the
producer and the DSO;
NOTE E.g. the generating unit protection may not trip prior to the interface protection without consent of the
DSO.
b) interface protection (see 4.9) and protections against faults internal to the generating plant;
c) remote control command on active power limitation;
d) local response to overfrequency (see 4.6.1);
e) remote control commands (P and/or Q set points or control modes);
f) local reactive power (see 4.7.2) and/or active power (P(U) see 4.7.3) controls.
The system shall be designed that under foreseeable conditions the self-protection does not trip prior
to interface protection.
Besides the requirements of Clause 4, further requirements apply for connecting a generating plant to
the distribution network, e.g. assessment of the point of connection. However, this is excluded from
the scope of this Technical Specification; some guidance is given in the informative Annex A.
4.2 Connection scheme
The generating plant shall be in compliance with the requirements of the DSO. Different requirements
may be subject to agreement between the producer and the DSO depending on the power system
needs.
Inter alia, the generating plant shall assure the following:
a) synchronization, operation and disconnection under normal network operating conditions, i.e. in
the absence of faults or malfunctions;
b) faults and malfunctions within the generating plant shall not impair the normal functioning of the
distribution network;
c) co-ordinated operation of the interface switch with the generating unit switch, the main switch and
switches in the distribution network, for faults or malfunctions within the generating plant or the
DSO network during operation in parallel with the distribution network;
d) disconnection of the generating plant from the distribution network by tripping the interface switch
according to 4.9.
In order to satisfy the above functions, co-ordinated but independent switches and protection
equipment may be applied to each of the following sections of the generating plant, as shown in the
example in Figure 2.
4.3 Choice of switchgear
4.3.1 General
Switches shall be chosen based on the characteristics of the power system in which they are intended
to be installed. For this purpose, the short circuit current at the installation point shall be assessed,
taking into account, inter alia, the contribution of the generating plant.

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4.3.2 Interface switch
Switches shall be power relays, contactors or mechanical circuit breakers each having a breaking and
making capacity corresponding to the rated current of the generating plant and corresponding to the
short circuit contribution of the generating plant.
The short-time withstand current of the switching devices shall be coordinated with maximum short
circuit power at the point of connection.
In case of loss of auxiliary supply power to the switchgear, a secure disconnection of the switch is
required immediately.
Where means of isolation (according to HD 60364-5-551) is not required to be accessible to the DSO
at all times, automatic disconnection with single fault tolerance according to 4.12 shall be provided.
NOTE 1 For PV-inverters, further requirements are stated in EN 62109-1 and EN 62109-2 with respect to
the interface switch.
The function of the interface switch might be combined with either the main switch or the generator
switch in a single switching device. In case of a combination, the single switching device shall be
compliant to the requirements of both, the interface switch and the combined main switch or generator
switch. As a consequence, at least two switches in series shall be present between any generating
unit and the POC.
NOTE 2 This does not refer to the number of series-connected switches in order to assure single fault
tolerance as required in clause 4.12 but to the number of different switching devices itself.
4.4 Normal operating range
4.4.1 General
Generating plants when generating power shall have the capability to operate in the operating ranges
specified below regardless the topology and the settings of the interface protection.
4.4.2 Operating frequency range
The generating plant shall be capable to operate continuously when the frequency at the point of
connection stays within the range of 49 Hz to 51 Hz.
In the frequency range from 47 Hz to 52 Hz the generating plant should be capable to operate until the
interface protection trips. Therefore, the generating plant shall at least be capable to operate in the
frequency ranges and for the duration as for the minimum requirement indicated in Table 1.
NOTE 1 In later editions of this document a more stringent requirement might be introduced in order to take into
account the functioning of subnetworks (temporarily) operating as an island.
Respecting the legal framework, it is possible that for some synchronous areas more stringent time
periods and/or frequency ranges are required by the DSO. Nevertheless, they are expected to be
within the boundaries of the most stringent requirements as indicated in Table 1.
NOTE 2 For small isolated distribution networks (typically on islands) even more stringent periods and
frequency ranges can be required.

Table 1  Minimum time periods for operation in underfrequency and overfrequency situations
Time period for operation Time period for
operation
Minimum requirement
Most stringent
Frequency Range requirement
47,0 Hz – 47,5 Hz not required 20 s
a
47,5 Hz – 48,5 Hz 30 min 90 min
a a
48,5 Hz – 49,0 Hz 30 min 90 min
49,0 Hz – 51,0 Hz Unlimited Unlimited
a
51,0 Hz – 51,5 Hz 30 min 90 min
51,5 Hz – 52,0 Hz not required 15 min
a
Respecting the legal framework, it is possible that longer time periods are required by the relevant
authority in some synchronous areas.

4.4.3 Minimal requirement for active power delivery at underfrequencies
A generating plant shall be resilient to reductions of frequency at the point of connection while
reducing the maximum active power as little as possible.
The admissible active power reduction due to underfrequency below 49,5 Hz is limited by a reduction
rate of 10 % of the momentary power P per 1 Hz frequency drop as given by the full line in Figure 3.
M
Respecting the legal framework, it is possible that a more stringent power reduction characteristic is
required by the relevant authority. Nevertheless this requirement shall be limited to an admissible
active power reduction due to underfrequency below 49,0 Hz with a reduction rate of 2 % of the
momentary power P per 1 Hz frequency drop as indicated by the dotted line in Figure 3.
M
Figure 3  Maximum allowable power reduction in case of underfrequency
4.4.4 Continuous operating voltage range
The generating plant when generating power shall be capable to operate continuously when the
voltage at the point of connection stays within the range of 85 % U to 110 % U In case of voltages
n n
below U , it is allowed to reduce the apparent power to maintain the current limits of the generating
n
plant. The reduction shall be as small as technically feasible.
For this requirement all phase to phase voltages and in case a neutral is connected, additionally all
phase to neutral voltages are evaluated.

- 17 - CLC/TS 50549-1:2015
NOTE The stated reduction is an absolute minimum requirement. Further power system stability aspects
might be relevant. In later versions of this document, constant power output within the operating range might be
required. In this context, the different priority of active and reactive power for voltage stability in distribution
networks might be considered.
The producer shall take into account the typical voltage rise and voltage drop within the generating
plant.
4.5 Immunity to disturbances
4.5.1 General
The following withstand capabilities shall be fulfilled regardless the topology and the settings of the
interface protection.
NOTE An event on the HV and EHV transmission network can affect numerous small scale units on MV and
LV level. Depending on the penetration of dispersed generation, a significant loss of active power provision can
be caused.
4.5.2 Rate of change of frequency (ROCOF) immunity
With regard to the rate of change of frequency withstand capability, the generating unit shall be able to
operate with rates of change of frequency up to 2,5 Hz/s.
4.5.3 Low voltage ride through (LVRT)
4.5.3.1 General
Generating plants shall contribute to overall power system stability by providing also immunity towards
dynamic voltage changes.
The following clause describes the standard required immunity for PV plants.
NOTE 1 In future revised editions of this Technical Specification the LVRT immunity might be required for all
types of generating and connection technologies.
The requirements apply to all kinds of faults (1ph, 2ph and 3ph).
NOTE 2 A more distinctive differentiation for 1ph, 2ph and 3ph faults is under consideration.
NOTE 3 These requirements are independent of the interface protection settings. Disconnection settings of the
interface protection relay always overrule technical capabilities. So, whether the generating plant will stay
connected or not will also depend upon those settings.

4.5.3.2 PV generating plant
Figure 4  Low voltage ride through capability for converter technology connected generating
unit
The generating plant shall be capable to stay connected to the distribution network as long as the
voltage at the point of connection remains above the voltage-time diagram of Figure 4. The voltage is
relative to U . The smallest phase to neutral voltage or if no neutral is present the smallest phase to
n
phase voltage shall be evaluated.
NOTE 1 According to the legal framework, the relevant authority defines the FRT characteristic. Nevertheless,
this requirement is expected to be limited to the most stringent curve, indicated in Figure 4.
NOTE 2 This means that not only the generating units shall comply with this LVRT requirement but also all
elements in a generating plant that might cause its disconnection.
For the generating unit, this requirement is considered to be fulfilled if it stays connected to the
distribution grid as long as the voltage at its terminals remains above the defined voltage-time
diagram.
After the voltage returned to continuous operating voltage range, 90 % of pre fault power shall be
resumed as fast as possible, but at the latest within 5 s.
4.5.4 High voltage ride through (HVRT)
Generating plants shall be capable to stay connected if the voltage at the terminals goes beyond the
upper limit of the continuous operating voltage range:
a) up to 120 % U for a duration of 100 ms; and
n
b) up to 115 % U for a duration of 1 s.
n
The highest phase-neutral voltage or if no neutral is present the highest phase-phase voltage shall be
evaluated.
- 19 - CLC/TS 50549-1:2015
Figure 5  High voltage ride through capability
NOTE 1 This means that not only the generating units shall comply with this HVRT requirement but also all
elements in a generating plant that might cause its disconnection.
NOTE 2 These requirements are independent of the interface protection settings. Disconnection settings of the
interface protection relay always overrule technical capabilities. So, whether the generating plant will stay
connected or not will also depend upon those settings.
NOTE 3 This is a minimum requirement. Further power system stability aspects might be relevant. The
technical discussion is still ongoing. A voltage jump of +10 % of U from any stable point of operation is
n
considered, resulting in high voltage situations for many seconds. In later editions of this document, more
stringent immunity might be required.
4.6 Active response to frequency deviation
4.6.1 Power response to overfrequency
The generating unit shall be capable of activating active power response to overfrequency at a
programmable frequency threshold f at least between and including 50,2 Hz and 52 Hz with a
programmable droop in a range of at least 2 % to 12 %. The droop reference P is P , the actual AC
ref M
output power at the instant when the frequency reaches the threshold f . The resolution of the
frequency measurement shall be +/- 10 mHz or less. After activation, the active power frequency
response shall be delivered with an accuracy of ± 10 % of the nominal power.
NOTE 1 Respecting the legal framework, it is possible that, alt
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