Download Technical Requirements for Connecting Wind

COMPANY STANDARD
EE 10421629 ST 7:2001
TECHNICAL REQUIREMENTS FOR CONNECTING
WIND TURBINE INSTALLATIONS TO THE POWER
NETWORK
Tehnilised nõuded elektrituulikute liitumiseks elektrivõrguga
EESTI ENERGIA AS
OFFICIAL PUBLICATION
FOREWORD
Company Standard EE 10421629 ST 7:2001 “Technical Requirements for Connecting Wind
Turbine Generator Systems to the Electrical Network” is a rework of the research work titled
“Theoretical Bases and Technical Requirements for Connecting Wind Turbines to the Substations
of the Electrical Network”, prepared by the Department of Electrical Power Engineering of the
Tallinn Technical University in 2001.
The research was prepared by the following working group:
Rein Oidram – Associate Professor, Ph.D. – project manager
Kalju Möller – Senior Research Fellow, Ph.D.
Peeter Raesaar – Associate Professor, Ph.D.
Eeli Tiigimägi – Associate Professor, Ph.D.
The following working group drafted the Standard and prepared the Standard for adoption:
Enno Saluvee – Support Services of Eesti Energia AS, head of the working group
Indrek Aarna – Support Services of Eesti Energia AS
Mati Kalda - Support Services of Eesti Energia AS
Rein Kraav – National Grid of Eesti Energia AS
Raivo Rebane – Distribution Network of Eesti Energia AS
Mati Roosnurm – Distribution Network of Eesti Energia AS
The Standard format is based on the EVS Instruction 4:2000 “Drafting and Presentation of
Standards”, drafted by the Estonian Centre for Standardisation.
The Standard has been approved and introduced by the Eesti Energia AS directive No 47 of 22
May 2001.
The Standard has been entered in the Eesti Energia AS Registry of Normative Documents, Ref.
No 30 of 22 May 2001.
The Standard shall serve as a guidance upon the connection of wind turbine generator systems and
wind farms to the electrical network of Eesti Energia AS.
© The rights of publication and copying belong to Eesti Energia AS.
II
CONTENTS
1. Scope .............................................................................................................................. 1
2. Referenced normative documents............................................................................... 1
3. Definitions...................................................................................................................... 2
3. Symbols, units and abbreviations................................................................................ 4
5. General technical requirements for the electrical network...................................... 5
5.1. Requirements arising from the transmitting capacity of the electrical network ..................5
5.2. Requirements for the WTGS power quality ........................................................................6
5.2.1. Steady-state voltage.......................................................................................................6
5.2.2 Flicker and voltage fluctuations ....................................................................................7
5.2.2.1. Procedure for the assessment of flicker emission due to the WTGS......................8
5.2.2.2. Procedure for the assessment of the relative voltage change due to the WTGS
switching operations................................................................................................................9
5.2.3 Permitted emission limits on harmonic currents ...........................................................9
5.2.4 Telecommunication line interference..........................................................................10
5.2.5 Interference in remote switching equipment...............................................................10
5.3. Requirements for relay protection and automation............................................................10
5.3.1. General ........................................................................................................................10
5.3.2. Avoidance of feeding from the WTGS only ...............................................................11
5.3.3. Automatic reclosing ....................................................................................................11
5.3.4. Automatic voltage regulation of the WTGS ...............................................................11
5.4. Stability requirements ........................................................................................................12
5.5. Requirements for telemechanics ........................................................................................12
5.6. Metrological requirements .................................................................................................12
6. Data to be submitted with the application for connection...................................... 13
6.1. General...............................................................................................................................13
6.2. Application for connection ................................................................................................14
6.3. General data on the WTGS ................................................................................................14
6.4. Rated data...........................................................................................................................14
6.5. Data on the WTGS tests.....................................................................................................14
6.5.1. General ........................................................................................................................14
6.5.2. Maximum permitted power.........................................................................................15
6.5.3. Maximum measured power.........................................................................................15
6.5.4. Reactive power............................................................................................................16
6.5.5. Voltage fluctuations ....................................................................................................16
6.5.6. Harmonics ...................................................................................................................17
7. Analysis of the application for connection ............................................................... 18
7.1. General principles of the checking of preconditions for the connection of the WTG
Systems to the electrical network ................................................................................................18
7.2. Simplified analysis of the application for connection........................................................18
III
COMPANY STANDARD
EE 10421629 ST 7:2001
TECHNICAL REQUIREMENTS FOR CONNECTING WIND TURBINE
INSTALLATIONS TO THE POWER NETWORK
Tehnilised nõuded elektrituulikute liitumiseks elektrivõrguga
1. Scope
This Standard relates to the technical requirements for the connection of wind turbine generator
systems and wind farms to the electrical network of Eesti Energia AS at high voltage (over 1,000
V).
If there is a contradiction between this Standard and other technical normative documents,
referred to in this Standard, guidance shall be taken from this Standard.
Any amendments to the technical requirements of the Standard shall apply also to the wind
turbine generator systems that are already connected.
2. Referenced normative documents
This Standard refers to the following documents:
Draft IEC 61400-21, Ed. 1
Wind turbine generator systems – Part 21: Measurement and
assessment of power quality characteristics of grid connected
wind turbines. IEC, 2000
EE 10421629 ST 8:2001
Vahelduvvoolu elektrienergia mõõtmine. Tehnilised nõuded
tehingutes kasutatavatele mõõtekompleksidele kõrgepingel.
Measuring of Alternating Current of Electric Power.
Technical Requirements for Fixed Measuring Systems Used
in the Transactions at High Voltage. Eesti Energia AS, 2001
Elektrijaamade liitumise
tehnilised tingimused Eesti
Energia ASi Jaotusvõrguga
Technical requirements for
the connection of power
plants to the Distribution
Network of Eesti Energia AS
Uute generaatorite
liitumistingimused
Requirements for the
connection of new generators
Eesti Energia AS, Distribution Network, 1999 (09.11)
Eesti Energia AS, National Grid, 1999 (05.11)
Eesti Energia AS
Ametlik väljaanne
1
Põhivõrguga liitumise,
võrguühenduse kasutamise
ning ülekande-, juhtimis- ja
muude teenuste osutamise
tüüptingimused
Standard conditions of
connection to the National
Grid, use of network
connection and provision of
transmission, control and
other services
IEC 61000-3-7
CCITT 1978
Eesti Energia AS, National Grid, 2001
Electromagnetic compatibility (EMC) - Part 3: Limits − Section
7: Assessment of emission limits for fluctuating loads in MV and
HV power systems – Basic EMC publication
Directives Concerning the Protection of Telecommunication
Lines Against Harmful Effects from Electric Lines, 1978
3. Definitions
In this Standard the following definitions are used:
3.1.
Wind turbine generator system (WTGS) – a system that is comprised of a wind turbine, drive,
generator, controller and tower and converts kinetic energy in the wind into electrical energy.
3.2.
Wind turbine generator systems (WTG Systems) – a general term, used if there is no need to
specify in the text of the Standard whether reference is made to the wind turbine generator system
or wind farm.
3.3.
Wind farm – an integrated unit comprised of several WTG Systems, as well as the buildings and
equipment connecting the WTG Systems to the connection point and interconnecting the WTG
Systems.
3.4.
Electrical network – an integrated unit for the transmission or distribution of electrical energy,
comprised of buildings and equipment.
Note 1. For the purpose of this Standard, the electrical network means the electrical network of
Eesti Energia AS, if not specified otherwise.
3.5.
Wind turbine generator system terminals – a point being a part of the WTGS and identified by
the WTGS supplier at which the WTGS may be connected to the power collection system.
3.6.
Cut-in wind speed – the lowest wind speed at hub height at which the WTGS starts to produce
power.
2
3.7.
Connection point – a precisely defined point of connection of customer’s electrical installation to
network operator’s network; if not agreed otherwise, the connection point shall define the
responsibility of the customer and network operator, and the service boundary of the electrical
installations.
3.8.
Switching operation – start-up or switching-over of generators.
3.9.
Flicker step factor – a normalised measure of the flicker emission due to a single switching
operation of the WTGS.
3.10.
Rated current – the current from the WTGS while operating at rated power and nominal voltage
and frequency.
3.11.
Rated apparent power – the apparent power from the WTGS while operating at rated power and
nominal voltage and frequency.
S n = Pn2 + Qn2
Here Pn is the rated (active) power and Qn is the corresponding reactive power.
3.12.
Rated reactive power – the reactive power from the WTGS while operating at rated power and
nominal voltage and frequency.
3.13.
Rated power – the maximum continuous (active) output power from the WTGS under normal
operating conditions.
3.14.
Normal operation – fault-free operation complying with the description in the WTGS manual.
3.15.
Voltage change factor – a normalised measure of the voltage change due to a switching
operation of the WTGS.
Note 2. The voltage change factor kU is similar to ki being the ratio between the maximum inrush
current and the rated current, though kU is a function of the network impedance phase angle. The
highest value of kU will be numerically close to ki .
3.16.
Continuous operation – normal operation of the WTGS, excluding start-up and shutdown
operations.
3.17.
Flicker coefficient for continuous operation – a normalised measure of the flicker emission
during the continuous operation of the wind turbine.
Note 3. The flicker coefficient for continuous operation is the same for a short-term (ten minutes)
and long-term period (two hours).
3
3.18.
Maximum permitted power – the ten-minute-average power that shall not be exceeded
irrespective of weather and network conditions.
3.19.
Maximum measured power – the maximum power (with a specified averaging time) observed
during the continuous operation of the WTGS.
3.20.
Wind turbine – a device which converts kinetic energy in the wind into rotating mechanical
energy of the WTGS shaft.
Note 4. In English a wind turbine is often denoted a WTGS.
3.21.
Rated wind speed – wind speed at which a wind turbine’s rated power is achieved.
3.22.
Network impedance phase angle – phase angle of network short-circuit impedance
ψ k = arctan( X k Rk )
Here Xk is the network short-circuit reactance and Rk is the network short-circuit resistance.
3.23.
Output power – electric active power delivered at the WTGS terminals.
3.24.
Flicker – a visual perception of variations, caused by the fluctuation of brightness of electric
lighting or by changing in time spectral distribution.
3. Symbols, units and abbreviations
∆U dyn
Un
ψκ
∆S
∆Udyn
c(ψκ ,va)
ci(ψκ ,va)
cos φ
d
EPlti
EPsti
ET
fh
h
Ii lub
In
kf(ψκ)
maximum permitted voltage change
network impedance phase angle (º)
apparent power change
dynamic voltage change
flicker coefficient for continuous operation
flicker coefficient of a single (i’th) WTGS
power factor
relative voltage change
long-term flicker emission limit
short-term flicker emission limit
wind turbine generator system
frequency of the h’th harmonic (Hz)
harmonic order
permitted continuous current of a single (i’th) network element (A)
rated current (A)
flicker step factor
4
ki
kU(ψκ)
N10
N120
Nwt
P0,2
P60
Plt
Pmc
Pn
Pst
Q0,2
Q60
Qmc
Qn
r
Rk
SET
Si
Si lub
Sn
Sn, i
Sk
Smax i
THD
THFF
U1
Uh
Un
va
Xk
ratio of maximum inrush current and rated current
voltage change factor
number of one type of switching operations within a 10-minute period
number of one type of switching operations within a 120-minute period
number of WTG Systems connected to a single connection point
maximum measured power (0.2-second-average value) (W)
maximum measured power (60-second-average value) (W)
long-term flicker emission (flicker disturbance factor)
maximum permitted power (W)
rated power (W)
short-term flicker emission (flicker disturbance factor)
reactive power (0.2-second-average value) at P0.2 (var)
reactive power (60-second-average value) at P60 (var)
reactive power at Pmc (var)
rated reactive power (var)
frequency of voltage changes (hour-1, min-1)
short-circuit resistance of the network (Ω)
power generated by the WTGS (V·A)
contractual apparent power of the i’th user of the medium voltage network (V·A)
maximum permitted power of the i’th element of the distribution network (V·A)
rated apparent power (V·A)
rated apparent power of a single WTGS (V·A)
short-circuit apparent power of the network (V·A)
peak apparent power of the fluctuating load
total harmonic distortion factor
telephone harmonic form factor
50 Hz component of the phase voltage (root mean square (RMS)) (kV)
the h’is harmonic of the voltage (root mean square) (kV)
nominal phase-to-phase voltage of the electrical network (V)
annual average wind speed (m/s)
short-circuit reactance of the network (Ω)
5. General technical requirements for the electrical network
5.1.
Requirements arising from the transmitting capacity of the electrical network
The requirements arising from the transmitting capacity of the electrical network are based on the
fact that in open 35 and 10 kV electrical networks, the direction of generated by the WTGS power
S ET is opposite to the direction of the power flows due to the consumer loads. This situation is
explained on Figure 1.
5
SET
35 kV
SET
SET
110 kV
SET
SET
10 kV
SET
SET
10 kV
SET
Power flows
in the electrical
Tarbijate
koormustest
tingitud
network
due
to
the consumer load
võimsusvood jaotusvõrgus
ET
SET
Elektrituuliku
võimsusvoog
Power flow from
the WTGS
Figure 1 – Power distribution in the electrical network with a WTGS
In addition to the thermal tolerance, the transmitting criterion in this case shall be the
permissibility of the difference between the power flows from the WTGS and any element i on the
path between the WTGS and the 110 kV electrical network.
S ET − S i ≤ S i lub
(1)
Provided that the power flows Si , due to the consumer loads, pose individually no thermal danger
to any element, the most dangerous overload may occur in a situation where consumer loads are at
minimum and the power of the WTG System(s) is at maximum.
Therefore, if Si ≈ 0, then
S ET ≤ S i lub
(2)
Consequently, the maximum power requirement for the WTG Systems to be installed shall be
based on the transmitting capacity of the element with the minimum permitted continuous load in
the existing distribution network, as follows:
S ET ≤ min ( Si lub ) = min ( 3 ×U n × I i lub )
(3)
In the case of lines, the minimum permitted power corresponds to the permitted current for the
line section with the minimum wire cross-section at the voltage level in question.
5.2.
Requirements for the WTGS power quality
5.2.1. Steady-state voltage
The operation of installation of WTG Systems in the electrical network may affect the steady-state
voltage in the connected network. It is required that load-flow calculations be conducted to ensure
that the WTG Systems do not bring the magnitude of the voltage outside the permitted limits.
During the load-flow analysis the impact of the WTG Systems shall be assessed as follows:
- at rated power, or
6
-
at active power P60 (60-second-average value) (kW) and reactive power Q60 (60-secondaverage value) (kvar), or
at active power P0.2 (0.2-second-average value) (kW) and reactive power Q0.2 (0.2-secondaverage value) (kvar).
The wind farm shall be assessed assuming its output power at the connection point. More
specifically, the ten-minute-average power values (Pmc and Qmc) and 60-second-average power
values (P60 and Q60) may be calculated by simple summation, and the 0.2-second-average values
may be calculated according to the following equations:
N wt
P0 ,2 Σ = ∑ Pn , i +
i =1
N wt
Q0 ,2 Σ = ∑ Qn , i +
i =1
5.2.2
N wt
∑( P
0 ,2 , i
i =1
N wt
∑( Q
0 ,2 , i
i =1
− Pn , i ) 2
(4)
− Qn , i ) 2
(5)
Flicker and voltage fluctuations
Flicker emission from the WTG Systems shall not exceed the permitted limits:
Pst ≤ EPst i
(6)
Plt ≤ EPlt i
(7)
Whereas the permitted emission limits at the connection point in question shall be as follows:
EPst i = 0,35
EPlt i = 0,25
The relative voltage change due to the WTG Systems shall be limited in accordance with the
following:
∆U dyn
d≤
(8)
Un
The permitted voltage change limits are given in Table 1
Table 1 – Permitted voltage change limits
r
(hour -1)
r≤1
1 < r ≤ 10
10 < r ≤ 100
100 < r ≤ 1000
∆Udyn /Un
(%)
at the voltage of 35 kV
at the voltage of 110 kV
and lower
and higher
4
3
3
2,5
2
1,5
1,25
1
7
5.2.2.1.
Procedure for the assessment of flicker emission due to the WTGS
Continuous operation
The flicker emission from a single WTGS during continuous operation shall be expressed as
follows:
S
Pst = Plt = c(ψ k , va ) × n
(9)
Sk
where
c(ψk, va) is the flicker coefficient of the WTGS for the given network impedance phase
angle, ψk at the connection point, and for the given annual average wind speed, υa
measured at the hub-height of the turbine at the site of the WTGS.
The WTGS flicker coefficient c(ψk, va) for the actual ψk and va at the installation site, shall be
found from the table of measuring results, applying linear interpolation.
If there are more than one WTGS connected to the connection point, the sum of their flicker
emission shall be estimated as follows:
Pst Σ = Plt Σ =
1
Sk
N wt
∑ (c (ψ
i
k
, va ) × S n , i ) 2
(10)
i =1
Switching operations
The flicker emission due to the switching operations of a single WTGS shall be estimated
applying the following equations:
Pst = 18 × N 100,31 × k f (ψ k ) ×
0, 31
Plt = 8 × N 120
× k f (ψ k ) ×
Sn
Sk
(11)
Sn
Sk
(12)
where
kf(ψk) is the flicker step factor of the WTGS for the given network impedance phase angle,
ψk at the connection point.
The WTGS flicker step factor kf(ψk) for the actual ψk at the installation site shall be found from the
table of measuring results, applying linear interpolation.
If there are more than one WTGS connected to the connection point, the sum of their flicker
emissions shall be estimated from the following equations:
Pst Σ
18  N wt
3, 2 
=  ∑ N10, i × (k f , i (ψ k ) × S n , i ) 
Sk  i =1

Plt Σ
8
=
Sk
0, 31
 N wt
3, 2 
 ∑ N120, i × (k f , i (ψ k ) × S n , i ) 
 i =1

8
(13)
0 , 31
(14)
where
N10, i and N120, i are the number of switching operations of the individual WTGS within a
10-minute and 2-hour period, respectively
kf, i(ψk) is the flicker step factor of the individual WTGS
Sn, i is the rated apparent power of the individual WTGS
5.2.2.2.
Procedure for the assessment of the relative voltage change due to the WTGS
switching operations.
The relative voltage change due to the switching operations of a single WTGS shall be estimated
applying the equation below:
S
d = kU (ψ k ) × n
(15)
Sk
The WTGS voltage change factor kU(ψk) for the actual ψk on the installation site, shall be found
from the table of measuring results, applying linear interpolation.
If there are more than one WTGS connected to the connection point, it is still unlikely that even
two of them will perform a switching operation at the same time. Hence, no summation effects
need to be taken into account to assess the relative voltage change of an installation consisting of
several WTG Systems.
If the applicant for connection has submitted a report on the power quality test results with no data
on the voltage change factor, the relative voltage change may be found from the Equation (15),
applying the voltage change factor value kU(ψk) = 1,0.
5.2.3
Permitted emission limits on harmonic currents
Harmonic currents must not cause voltage rise at the connection point.
Table 2 gives the permitted emission limits on odd harmonic currents in a continuous situation.
Within the same frequency range, the emission limits on even harmonic currents shall not exceed
25% of the values given in Table 2.
Table 2 – Permitted emission limits on odd harmonic currents
Harmonic order
Emission limits on harmonic currents with
respect to the current
4,0 %
2,0 %
1,5 %
0,6 %
0,3 %
5,0 %
h < 11
11 ≤ h < 17
17 ≤ h < 23
23 ≤ h < 35
35 ≤ h < 50
Total harmonic distortion factor (THD)
9
The total harmonic distortion factor (THD) shall be defined as:
THD = 100
5.2.4
Uh

∑
h=2  U1
50



2
(%)
(16)
Telecommunication line interference
The Telephone Harmonic Form Factor (THFF) shall be defined as:
THFF =
Fh = Ph × h ×
Uh


× Fh 
∑
h =1  U 1

50
2
fh
800
(17)
(18)
where
Ph is the relative interference at frequency fh in a telecommunication circuit as determined
from a psophometric weight factor according to CCITT (Directives Concerning the
Protection of Telecommunication Lines Against Harmful Effects from Electric Lines,
CCITT 1978).
The THFF factor shall not exceed 1% at the connection point.
5.2.5
Interference in remote switching equipment
The WTG Systems shall not generate noise more than –35 dB (0 dB = 0.775 V) in the frequency
range of (40…500) kHz, measured in the input of a standard remote switching device at the
connection point.
The measured frequency bandwidth shall be at least 2 kHz.
5.3.
Requirements for relay protection and automation
5.3.1. General
Upon the connection of the WTG Systems, the requirements for relay protection and automation
shall be complied with, based on the following documents of Eesti Energia AS:
- Technical requirements for the connection of power plants to the Distribution Network of
Eesti Energia AS
Requirements
for the connection of new generators
- Standard conditions of connection to the National Grid, use of network connection and
provision of transmission, control and other services.
In addition, the Network Operator shall specify the following requirements for the connection:
10
-
the need to upgrade the relay protection and automation of the electrical network in
connection with the increase in short-circuit currents and (or) introduction of a feeding
from several independent sources;
avoiding the feeding from the WTG Systems of the part of the network that has been
disconnected under an abnormal operation;
automatic reclosing, and automatic synchronisation of the WTG Systems;
the need for automatic voltage regulation of the WTG Systems;
avoidance or mitigation of start-up shocks in the case of WTG Systems with asynchronous
generators.
5.3.2. Avoidance of feeding from the WTGS only
If due to a fault in the electrical network (e.g. short-circuit) it is only the WTG Systems that
remain feeding the customers, these WTG Systems shall be instantly disconnected from the
electrical network in order to avoid non-permissible excessive deviations of voltage and frequency
of the electrical energy supplied to the customers in the respective part of the network.
The disconnection shall be conducted according to the values given in Table 3
Table 3 - The time limit set on the disconnection of the WTG Systems
Electrical energy
characteristic
Frequency
Voltage
Values
Time limit on
disconnection
s
< 47,0 Hz
≤ 0,3
> 53,0 Hz
≤ 0,3
< 85 % Un
≤ 10
> 106 % Un
≤ 60
> 110 % Un
≤ 0,5
5.3.3. Automatic reclosing
Given the transient nature of the majority of short-circuits, there shall be an automatic reclosing
following the tripping off of the short-circuit. For a successful reclosing, also the WTGS must be
tripped off instantly. The network operator shall define the duration of the voltage break of the
automatic reclosing.
5.3.4. Automatic voltage regulation of the WTGS
The need for the automatic voltage regulation of the WTGS may arise in the case of high-power
generators, as well as in the case when the WTGS is connected to the same substation’s busbars
that the customers are connected to. In order to reduce the voltage fluctuations due to the WTGS,
the introduction of current compensation on transformers’ automatic voltage regulators and (or)
readjustment may be required. The network operator shall perform the required calculations and
prepare the technical solutions.
11
5.4.
Stability requirements
A wind farm that is connected to the National Grid shall be able to withstand the following faults
in all operational situations, without losing its stability:
- a three-phase short-circuit on a random line or transformer, with a lasting interruption
of connection, with no reclosing;
Note 5. A typical fault: occurrence of a short-circuit, tripping off of the line/transformer,
no automatic reclosing. Typically, the tripping off of the short-circuit takes 0.5 seconds,
but may last longer in some places.
-
a two-phase short-circuit on a random line, with unsuccessful reclosing.
Note 6. A typical fault: occurrence of a short-circuit, tripping off of the line, unsuccessful
automatic reclosing with a lasting tripping off of the short-circuited line. Typically, the
tripping off of the short-circuit takes 0.5 seconds, and in the case of an unsuccessful
reclosing the tripping off of the short-circuit takes (0.1…0.15) seconds.
These requirements shall not apply to the faults, which are due to the radially- connected wind
farms, because a fault in the radial connection will disconnect the wind farm from the power
system.
The stability assessment shall be based on the actual time required for remedying the damage
identified by the relay protection.
Stability shall be assessed under both the normal operation and overhaul schemes.
The wind park shall withstand at least three faults within two minutes, without the connection
being interrupted. This requirement mainly aims at providing the WTG Systems a sufficiently
trouble-free auxiliary supply voltage.
5.5.
Requirements for telemechanics
The remote measuring and, if required, control of voltage, active power and reactive power at the
connection point of the WTG Systems shall be taken to the regional dispatch centre.
5.6.
Metrological requirements
At the connection point of the WTG Systems to the electrical network at least the following shall
be measured: the voltage and current of electrical energy, active power, reactive power, amount of
active power and amount of reactive power. The power and energy shall be measured in both
directions.
The said measuring shall comply with the Metrology Act and other legislation, rules and
normative documents on metrology valid in Estonia.
The issues, which are not regulated by the Metrology Act or other legislation and normative
documents valid in Estonia, shall be solved by way of co-ordination between the parties.
The site of measuring of electrical energy at the connection point shall comply with the
requirements of the Company Standard of Eesti Energia AS EE 10421629 ST 8:2001
“Measuring of Alternating Current of Electric Power. Technical Requirements for Fixed
Measuring Systems Used in the Transactions at High Voltage.”
12
The required accuracy classes of the measuring devices used in the transactions are given in
Table 4.
Table 4 - Required accuracy classes of the measuring devices used in the transaction
Nominal value
of the
measured
voltage
kV
6 … 35
110
Accuracy classes of electricity
meters
Accuracy class
of current
transformer
Accuracy class
of voltage
transformer
Active power
meter
Reactive power
meter
1,0
2,0
0,2 or 0,2S
0,2
0,5
1,0
0,2 or 0,2S
0,2
The requirements for the maximum permissible totalised error of the measuring of electrical
energy are given in Table 5.
Table 5 -The requirements for the maximum permissible totalised error of the measuring of
electrical energy at the load of (10…100) % of nominal load in the range of (0.8…1.0) of the
power factor cos φ
Nominal value
of the
measured
voltage
kV
6 … 35
110
Maximum permissible error under
verification requirements
±%
Active power
Reactive power
measuring
measuring
2,0
3,0
1,5
2,0
Maximum permissible error under
operational requirements
Active power
measuring
2,5
Reactive power
measuring
4,0
2,0
3,0
6. Data to be submitted with the application for connection
6.1.
General
The applicant for connection to the electrical network shall submit an application for connection
and the following general and technical data, as well as test results for each type of WTGS to be
installed:
- general data;
- rated data;
- data on the tests of the WTGS type.
The technical data and test results shall be submitted in the scope defined under Articles 6.3-6.6.
13
6.2.
Application for connection
The application for connection shall contain the following data:
- data about the applicant;
- desired installation-location;
- desired connection point;
- number of the WTG Systems;
- data on the tests of the WTG Systems (separately for each type).
6.3.
General data on the WTGS
Table 6
Wind turbine type (horizontal-axis or verticalaxis)
Number of blades (pcs)
Rotor diameter (m)
Hub height (m)
Blade control (pitch/stall)
Speed control (fixed/two-speed/variable)
Generator type and rating(s) (kW)
Frequency converter type and rating (kW)
Transformer type and rating (kVA)
6.4.
Rated data
Table 7
Rated power, Pn (kW)
Rated wind speed, vn (m/s)
Rated apparent power, Sn (kVA)
Rated reactive power, Qn (kvar)
Rated current, In (A)
Rated voltage, Un (V)
Times inrush current kI
Transformer transfer factor (kV/kV)
Note 7. Upon the connection to the National Grid, in addition to the data requested in Table 7 also
the data on generator’s electrical parameters shall be submitted in compliance with the document
of the National Grid of Eesti Energia AS “Requirements for the connection of new generators”.
6.5.
Data on the WTGS tests
6.5.1. General
The testing of the WTG Systems shall be based on the standard IEC 61400-21 (until the
publication of the standard, guidance shall be taken from the draft standard).
The organisation that conducts the tests shall be competent to do so.
14
The characteristics are valid for the specific configuration of the tested WTGS only. Other
configurations, including altered control parameters, that cause the wind turbine to behave
differently in terms of power quality, require separate assessment.
Data about the organisation that conducts tests and test description shall be submitted in the
following scope:
Table 8
Name of test organisation
Report number
WTGS type designation
WTGS manufacturer
Serial number of the WTGS tested
Table 9
Type of information
Description of the tested WTGS, including
settings of control parameters
Description of test site and network
connection
Description of test equipment
Description of test conditions
Note of exceptions to IEC 61400-21
Document name and date
Table 10
Author
Checked
Approved
Date of issue
6.5.2. Maximum permitted power
Table 11
Assessed value, Pmc (kW)
Normalised value, pmc = Pmc / Pn
6.5.3. Maximum measured power
60-second-average value
Table 12
Measured value, P60 (kW)
Normalised value, p60 = P60 / Pn
0.2-second-average value
Table 13
Measured value, P0,2 (kW)
Normalised value, p0,2 = P0,2 / Pn
15
6.5.4.
Reactive power
Table 14
Output power (% of Pn)
0
10
20
30
40
50
60
70
80
90
100
Output power (kW)
Reactive power (kvar)
Table 15
Assessed reactive power at Pmc (kvar)
Assessed reactive power at P60 (kvar)
Assessed reactive power at P0.2 (kvar)
6.5.5.
Voltage fluctuations
Continuous operation
Table 16
Network impedance phase angle, ψκ ( °)
Annual average wind speed, va (m/s)
6,0
7,5
8,5
10,0
30
Switching operations
Table 17
Type of switching operation
Max. number of switching operations, N10
Max. number of switching operations, N120
Network impedance phase angle, ψκ ( °)
Flicker step factor, kf(ψκ)
Voltage change factor, kU(ψκ)
50
70
Flicker coefficient, c(ψκ ,va)
85
Start-up at cut-in wind speed
30
Table 18
Type of switching operation
Max. number of switching operations, N10
Max. number of switching operations, N120
Network impedance phase angle, ψκ ( °)
Flicker step factor, kf(ψκ)
Voltage change factor, kU(ψκ)
50
70
85
Start-up at rated wind speed
30
16
50
70
85
In the case of the WTG Systems with more than one generator or with a divided winding
generator:
Table19
Type of switching operation
Worst case switching between generators
Max. number of switching operations, N10
Max. number of switching operations, N120
30
50
70
85
Network impedance phase angle, ψκ ( °)
Flicker step factor, kf(ψκ)
Voltage change factor, kU(ψκ)
6.5.6. Harmonics
Relevant only for the WTG Systems with a power electronic converter
Table 20
Output power Harmonic current
Order Output power Harmonic current Order
(kW)
(% of In)
(kW)
(% of In)
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
Table 21
Maximum total harmonic current distortion (% of In)
Output power at maximum total harmonic current distortion (kW)
17
7. Analysis of the application for connection
7.1.
General principles of the checking of preconditions for the connection of the WTG
Systems to the electrical network
While handling the application for the connection of the WTG Systems to the electrical network,
the values characterising the WTGS power quality shall be compared with the permitted limits.
The values characterising the WTGS power quality shall be found based on the submitted by the
applicant report, which contains data about the WTGS and power quality test results.
The fulfilment of preconditions for the connections shall be checked in detail based on the
comparison with the permitted emission limits and maximum permitted voltage change of the
submitted by the applicant parameters, or indicators calculated from these parameters.
It is assumed that one or several WTG Systems are to be connected, which power quality
characteristics have been measured in accordance with the recommendations of the IEC draft
standard IEC 61400-21. The defining for the medium and high voltage installations of permitted
flicker emission limits and maximum permitted voltage change shall be based on the principles
stipulated in Article 5.2.
Upon the assessment of the voltage fluctuation limit levels, guidance shall be taken from Section
7 of Part 3 of the international electromagnetic compatibility standard (IEC 61000-3-7) Assessment of emission limits for fluctuating loads in MV and HV power systems. In this
Enterprise Standard the IEC 61000-3-7 term “fluctuating load” has been replaced with the term
“fluctuating power”. In compliance with the international flicker standard IEC 61000-3-7, the
connected party shall take care that the emission from the WTGS at the connection point is below
the minimum established by the Electricity Company.
The electricity company and the connected party may co-operate, if required, in order to find
optimal methods for emission reduction. The connected party is responsible for implementing the
method.
7.2.
Simplified analysis of the application for connection
Upon a partial submission of test results referred to in Article 6 of this Standard, the possibilities
for connection shall be checked as follows:
S max i
≤ 0,1 %
Sk
(19)
where
Smax i is the peak apparent power of the fluctuating load
Sk is the short-circuit apparent power of the network at the connection point.
If there is data available about the frequency of power changes, the connection of the fluctuating
power can be accepted without further analysis, provided that the maximum relative power
changes with respect to the short circuit power (∆S/Sk)max at the connection point are within the
limits given in Table 22. The limits depend on the number of voltage changes per minute, r
(voltage drop with the subsequent recovery counts as two changes).
18
Table 22 - Limits on the relative power change, dependant on the number of changes per
minute
(∆S/Sk)max
(%)
0,1
0,2
0,4
r
(min−1)
r > 200
10 ≤ r ≤ 200
r < 10
Power changes ∆S may be lower or higher than or equal to the rated power Sn of the respective
device (e.g. in the case of an engine or WTGS account shall be taken of the apparent power at the
start-up, and ∆S may be 3-8 Sn). Genrally,
∆S = ki × Sn
(20)
whereas the following requirement shall be met:
S k ≥ 25 ki × S n
(21)
where
Sk is the short-circuit power of the network
Sn is the rated apparent power of the WTG Systems
ki is the ratio of the maximum inrush current and rated current of the WTG Systems.
19