grid code requirement in connecting solar pv rooftop for...
TRANSCRIPT
1
Grid Code Requirement in Connecting Solar PV
rooftop for various Plant Capacities
Dr. H. M. Wijekoon
Chief Engineer (Transmission Planning)
DGM (Transmission and Generation Planning ) Branch
Ceylon Electricity Board, P.O. 540,
Colombo 02
2
A grid code is a technical specification
which defines the parameters, a facility
connected to a public electric network
has to meet to ensure safe, secure and
economic proper functioning of the
electric system. The facility can be an
electricity generating plant, a consumer,
or another network.
What is a Grid Code?
3
NET METERING / NET ACCOUNTING ARRANGEMENT FOR PARALLEL OPERATION OF ON-GRID SMALL-SCALE RENEWABLE ENERGY FACILITIES
[NOT INTENDED FOR STAND ALONE OPERATION]
Distribution Transformer
Service Main to Consumer up to contract demand
AC/DC
Inverter
M
Consumer’s Main
Distribution Panel
Disconnection Switch with Visible Separation (should be able to be locked against
unauthorized operation)
Automatic Disconnection
During mains failure
Bi-directional
Meter
Visible Separation of
the circuit is required
Consumer
Load
Consumer’s Small-Scale Renewable Energy Facility up to contract demand 3phase
(Neutral to be
kept open at
all times)
N
Connection Arrangement for Scheme 1 and 2
4
Consumer
Load
NET METERING / NET ACCOUNTING ARRANGEMENT FOR PARALLEL OPERATION OF ON-GRID SMALL-SCALE RENEWABLE ENERGY FACILITIES
[NOT INTENDED FOR STAND ALONE OPERATION]
Distribution Transformer
Service Main to Consumer up to contract demand
AC/DC
Inverter
M
Disconnection Switch with Visible Separation (should be able to be locked against
unauthorized operation)
Automatic DisconnectionDuring mains failure
Bi-directional Meter
Consumer’s Small-Scale Renewable Energy Facility up to contract demand 3phase
(Neutral to be kept open at
all times)
N
M
Connection Arrangement for Scheme 3
5
HT Interconnection Arrangement
The inverter of the Solar PV system Shall run on Voltage control
mode and CEB official should check the mode at the inspection
Collect Application and Agreement from respective
Area Office
Submission of Application& Documents to respective
Area Engineer after the payment of initial review fee
Comply with CEB
Standards
Contact Applicant for Clarifications and
request Applicant to comply with standards
Net Energy Metering EstimateIssued to the Customer byArea Engineer after initial
review
Net Energy Metering Estimate
Payment by the Applicant
Joint Inspection by Area Engineer, Applicant and
Consulting Engineer after installation
Comply with CEB
Standards
Corrections as per the CEB Standards
Joint Testing, Commissioning by Area
Engineer, Consulting Engineer, and Customer
No
Yes
No
Yes
Application Process on Net Energy Meter Connection
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Application Procedure (HT Metering)
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Circular Instructions Circular No.: 2017/DCC/COM-11
o HT Metering solar should be treated differently from LT
metered and be connected to HT side of the distribution
network
o Customer has to install required step up transformer and other
required equipment for the connection
o The connection cost should be borne by the customer
o CEB guide for Grid Interconnection of Embedded Generators
2000, Part 1 & Part 2 (Annex 1 & Annex 2)
o Addendum to above guide is given for Solar PV Connection
(Annex 3)
o Decided to follow same procedure for all the DDs. Connection
procedure is given as Annex 4
GRID CONNECTION REQUIREMENT FOR LARGE SCALE ROOF TOP
SOLAR POWER PLANTS -ADDENDUM TO THE CEB GUIDE FOR GRID
INTERCONNECTION OF EMBEDDED GENERATORS, DECEMBER 2000
(ANNEXURE 3)
(1) Data requirement for grid impact studies
i. Single line diagram of the solar PV plant up to the main installation circuit breaker.
This shall include all the technical parameters related to the conductors, and step
up transformers of the power collector system.
ii. Details of voltage support facilities such as switched capacitors, static var
compensators and, dynamic var compensators including the intended power factors
for full MW range. (Curve depicting power factor Vs solar plant output power)
iii. PV plant model data from the manufacturer, format acceptable to SYNERGY /
PSS/E software, and general plant characteristics including power curve to conduct
simulation studies at 33/11 kV level.
iv. PV plant layout, as per micro siting, on a 1:10,000 map.
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Plant Monitoring
The developer of the PV plant should keep provision for monitoring the output of
the PV plant and the developer should be able to provide data on line as and when
requested by CEB for secure operation of the power system
On line Data Provision
The generating company should build the necessary data transmission facility to
provide following parameters to system control
(i)Status of the main circuit breaker of the PV plant
(ii) Active power export from the PV plant
(iii)Active power imported by the Solar PV plant
(iv)Reactive power import by the PV plant
(v)Reactive power export from the Solar PV plant
(vi)Solar Plant voltage at the main circuit breaker of the solar plant
(vii)Solar Irradiation level of the site.
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Connection Requirement
o The quality of power provided by the PV system is governed by practices
and standards on voltage, flicker, frequency, harmonics and power factor.
o Power quality parameters must be measured at the utility interface(PCC)
unless stated otherwise.
o At PCC, the power quality requirements must comply to CEB Distribution
Connection Code and this Technical Guidebook
a. The measurement before and after energizing the PV must be
taken and submitted to relevant office of the CEB for
approval by the developer.
b. All measurement at site will be done with the representative
from CEB.
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Normal Voltage Operating Range
Voltage Level Steady state voltage limits
LV (400 V, 230 V) 6% (0.94 PU to 1.06 PU)
11 kV 5% (0.95 PU to 1.05 PU)
33 kV 5% (0.95 PU to 1.05 PU)
Frequency Requirement
Frequency (Hz) System Conditions
50.5 - 52.0 Emergency
49.5 - 50.5 Normal
47.0 - 49.5 Emergency
Power Factor
The PV plant shall operate in the range of 0.90 leading to 0.90 lagging. The exact level
of reactive power support required from a PV plant will depend on the out come of
grid interconnection studies review in time to time.
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Power output variation in a day of 650 kW Hambantota
Power output variation in a day of 10 MW Hambantota
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3. Solar
Renewable Energy Resource Estimation
Sample Solar measurement data ( 1 minute time step) in
Kilinochchi.
0
200
400
600
800
1000
1200
1400
1
59
11
7
17
5
23
3
29
1
34
9
40
7
46
5
52
3
58
1
63
9
69
7
75
5
81
3
87
1
92
9
98
7
10
45
11
03
11
61
12
19
12
77
13
35
13
93
Sola
r Ir
rad
ian
ce (
W/m
2)
Mins
19th Jan 9th Feb 11th March
0
1,000
2,000
3,000
4,000
5,000
6,000
7,000
8,000
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Cap
acit
y (M
W)
Hours
Day1 Day2 Day3 Day4 Day5
Estimated output of a 10 MW Solar PV plant for consecutive
five days
16
Low Voltage Ride Through (LVRT) Capability
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Power Quality
The power quality depends on the interaction between the grid and solar plant . Thus
the grid connected solar plants do affect the power quality. Hence, power quality in
terms of voltage and frequency should be maintained as specified below.
The harmonics are as defined in IEEE -519 2014
Voltage Distortion Limits
Bus Voltage V at PCC Individual harmonics (%)Total Harmonic
distortion THD (%)
𝑽 ≤ 𝟏. 𝟎 𝒌𝑽 5.0 8.0
𝟏𝒌𝑽 ≤ 𝑽 ≤ 𝟔𝟗. 𝟎 𝒌𝑽 3.0 5.0
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Current Distortion Limits for system rated voltage 120 V through
69 kV
Maximum harmonic current distortion in percent of IL
Individual harmonic order (odd harmonics)a,b
𝐼𝑠𝑐/𝐼𝐿 3 ≤ ℎ< 11
11 ≤ ℎ< 17
17 ≤ ℎ< 23
23 ≤ ℎ< 35
35 ≤ ℎ< 50
TDD
20c 4.0 2.0 1.5 0.6 0.3 5.0
2050 7.0 3.5 2.5 1.0 0.5 5.0
20100 10.0 4.5 4.0 1.5 0.7 12
100<100
0
12.0 5.5 5.0 2.0 1.0 15
>1000 15.0 7.0 6.0 2.5 1.4 20
aEven harmonics are limited to 25% of odd harmonic limit above
bCurrent distortion that result in a dc offset e.g half wave converters are not allowed
cAll power generation equipment is limited to these values of currents distortions regardless
of actual ISC/IL
where ISC – Maximum short-circuit current at PCC
IL – Maximum demand load current (fundamental frequency components) at PCC under
normal operating condition
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DC Injection
The PV system shall not inject DC current greater than 1 % of the rated
inverter output current into the utility interface under any operating
condition.
Flicker
Distribution system
voltage level
Absolute short term
flicker index (Pst)
Absolute long term
flicker index (Plt)
LV systems 1.0 0.8
11 kV- 33 kV 0.9 0.7
Voltage unbalance
The unbalance voltage shall not exceed 1% for 5 occasions within
any 30 minute time period at the terminals of a user’s installation
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Controls
o The Solar PV plant shall provide the necessary controlling facility to limit the out
put variation of the solar PV plant by incorporating necessary controls.
o A large penetration of PV will increase current injection to the network.
o The output has to be reduced to avoid such situations.
o In future, the CEB will impose a limit on the penetration level after carrying out
a detail study.
o Further, the output of a solar PV plant will suddenly drop to very low value due
to cloud coverage.
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Protection Requirement
o It is preferable to use proven protection equipment supplied by a reputable
manufacturer with a track record in this type of application.
o The performance of all protection relays shall be within the scope of IEC
protection product family Standard IEC 60255.
o It is recommended that control and protection panels are soak tested (i.e.
the protection relay panels are energized for several hours or days) prior to
being put into operation.
o During the soak test the operation of the protection relays should be
checked periodically.
o Protection relays and the associated sensing circuits must be designed to
maintain accuracy and operation in fault conditions.
o Current and voltage transformers should be appropriately selected and
comply with product standards IEC 60185 and IEC 60186.
22
PV generating facilities shall be equipped with the following protective
functions to sense abnormal conditions on CEB distribution system
Generating facility should be automatically disconnected as given in this
guide from CEB distribution system or to prevent the generating facility
from being connected to CEB distribution system inappropriately.
Under Voltage
Over Voltage
Under Frequency
Over Frequency
PV active islanding detection (Non islanding inverter)
Protection Schemes
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The coordination of auto re-closure in CEB network
o PV tripping needs to be coordinated with the CEB feeder reclosing
practices to eliminate any possibility of out of phase reclosing.
o PV system shall cease to energize the CEB network circuit to which it
is connected prior to re-closure by the CEB network.
After the inverter tripping, no inverter reconnection will take place until
the CEB network voltage and frequency are maintained within the limits
for a stabilization period of 3 minutes.
The PV stabilization period starts once the inverter detects the voltage
and frequency to be within the normal range.
PV reconnecting time
Voltage disturbance
The inverter should sense abnormal voltage and respond according to the conditions given in following table.
Voltage (pu) Maximum trip time (sec)
V< 0.05 0.1 (100 msec)
0.05V0.5 0.2 (200 msec)
0.5V0.95 0.5 (500 msec)
0.95V1.05 Continuous
V >1.05 0.1 (100 msec)
When the inverter sense the voltage lies outside its operating limits, the recommended action shall be as given in following table
Frequency disturbance
The under frequency and over frequency levels and the corresponding inverter trip time shall be as follows:
a) When the utility frequency f < 47 Hz and f > 52 Hz
b) Trip time shall be less than 0.20 sec.
Islanding protection
During islanding, PV system shall cease to energize the grid in case of voltageand frequency situation stated above. During islanding detection, the PVsystem shall cease to energize the CEB network through the PCC within 0.5seconds of the formation of an island due to:
Safety issues Power quality problem Inverter technical limit
Fault current contribution
The fault current contribution by the inverter will be limited usually by inverter control.
Based on IEEE 1547, the short circuit current typically ranges between 100% and 200% of the rated inverter current.
The CEB will request the developer as and when required to reduce fault current contribution from PV plant.
PV interconnection must incorporate utility interface disconnect switch to allowdisconnection of PV system output from the interconnecting with CEB for safe utilityline works. The switch shall be manual, lockable, load break disconnect switch that:
a) Provide clear indication of switch positionb) Visible and accessible to maintenance and operational personnelc) Provide visual verification of the switch contact position when the switch is inopen position
Connection Arrangement
Q & A
20
40
60
80
100
47 48 49 50 51 5249.5 50.5 51.2
Fequency
Pow
er o
utpu
t(%
)Ramp = 10%/min
Ramp = 5%/sec
Power Curtailment Requirement
Limit
