importance of data collection with growing distributed ......transformer type typical application...
TRANSCRIPT
Project: Analysis of Indian distribution systems for the integration of high shares of rooftop PV
INTEGRATION OF RENEWABLE ENERGIES IN THE INDIAN ELECTRICITY SYSTEM (I-RE)
Final Workshop, 29-30 August 2017
Dr. Thomas Ackermann
Dr.-Ing. Eckehard Tröster
Importance of Data Collection with Growing Distributed Generation
Day 2, 3:00pm, 30 mins
MONITORING OF GENERATION CAPACITIES
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Number of generation sites increases from a few large power stations to hundreds of distributed sites. It is necessary to keep track of installed capacities to know the behavior that can be expected from the power system, both at transmission and distribution level!
Example: German regulatory agency keeps track
of all generators and publishes lists
• Generators
• Self consumption
• DSOs
• Large consumers
• Curtailment
• ….
BEFORE: LOAD ONLY DISTRIBUTION GRID
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Knowing the load here allows to adequately
assess conditions in the LV grid.
Unidirectional power flow: Voltage drop only, control at MV/HV transformer sufficient Simply measuring the load at different transformers allows to get a good idea of voltage and flows in the grid.
Knowing the load and voltage here may allow
to adequately assess conditions in the MV and
LV grid.
AFTER: PROSUMER DISTRIBUTION GRID
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Power flow may be reversed – especially reversal on one of multiple parallel feeders is hard to predict without measurements. And how many PV units are installed in this grid anyway, and what can they do? → Need for data collection increases!
500 kW load here may be 500 kW load, or 1000
kW load and 500 kW generation, or… what is
going on below?
Same here, only in MW.
How should we set the voltage controls?
This feeder may generate more than it consumes…
… this one may consume more. Who knows?
How is the voltage? Do we need to take action?
INTEGRATION ISSUES
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(This transformer station did not catch on fire because of distributed generation)
MV grid
MV grid
MV grid
MV grid
Thermal overload Critical voltage
Parallel line at 1/2 length Parallel line at 2/3 length
Source: Uhlig, CIRED Workshop 2014
Voltage range violations Thermal overloading
Result: Network reinforcements may become necessary
… and how and when do I find out?
The best way of dealing with new problems is avoiding them in the first place.
→ Conduct measurements of operational data
→ Conduct studies to assess the impact of new generation
→ Know about the probable issues
→ Take action before actual problems occur
WHAT IS GOING ON IN THE GRID…
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STUDIES (1)
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I
V
V
I
• Load Flow Study Focus of grid integration studies at distribution grid level is the same for most cases: • Are any assets overloaded, and if yes, which?
• Is the voltage too high or too low anywhere in
the grid?
• How much distributed generation can be introduced before issues appear?
• What can be done to increase the hosting capacity for distributed generation?
Given an adequate grid model, load flow studies deliver that information.
Grid modelling requires input data from real life.
DATA: LINES AND CABLES
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Parameter Remarks
Length
Coordinates Start and end substation
Rated voltage Un [kV]
Essential parameters. Ampacity Ir [kA]
Rated short-time current [kA]
Conductor type OHL only. Can be used to calculate ampacity
and short time current, otherwise not strictly
necessary. Maximum allowed conductor sag
Max. Operational Temperature [°C]
Temperature Coefficient [1/°C]
Cable type Cable only. Can be used to calculate ampacity
and short time current, otherwise not strictly
necessary. Insulation
Topology (air or ground)
Resistance R’ [Ohm/km] This data is essential for modelling, but may not
be available to the grid operator. In this case, it
can be calculated if the conductor type and
OHL/cable topology is known.
Reactance X’ [Ohm/km]
Capacity C’ [µF/km]
Conductance G’ [µS/km]
Number of Circuits on Tower
OHL only. Strictly necessary if line impedance
data is unavailable, as it can be calculated from
these parameters
Number of Earth Wires on Tower
Symmetry of conductors on tower
Distance between towers
In a meshed grid, line impedances determine the flows. In a radial distribution grid, they impact losses and voltage on the feeders. Accurate data is crucial for grid modelling. → Generally, HV and MV data is available, but the data for LV cables/lines is often lacking!
DATA: TRANSFORMERS
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Parameter Remarks
Rated apparent power Sr [MVA] For three winding transformers, ratings may
vary for the three voltage sides
Rated primary voltage Ur_HV
Rated secondary voltage Ur_LV Three winding transformer data should also
include rated tertiary voltage
General winding configuration
Short circuit voltage uk [%] Necessary for the calculation of voltage drop
over loaded transformer
Commissioning date If data is unavailable, assumptions may be
based on the state of the art at the date of
commissioning/manufacture of the unit
Copper losses PCu [kW]
No-load current i0 [%]
No-load losses P0 [kW]
Transformer type Typical application
On-load tap changing, automatic
voltage control
HV/MV and MV/MV applications – voltage can
be continually controlled during operation
On-load tap changing, remote
controlled
HV/MV and MV/MV applications – voltage set
points can be changed remotely
On-load tap changing, manually
controlled
MV/MV and MV/LV applications – voltage set
points are typically changed only seasonally
Off-load tap changing MV/LV applications, ratio is re-set only at
revisions, if at all
Fixed ratio MV/LV applications, rare
Transformers, as branch elements, have an impact on flows and voltage similar to lines. OLTC transformers also control the voltage – the capabilities and control settings for those are important for a good model! The latter is also true for reactive compensators – data on those must be accurate as well.
DATA: SWITCHING STATES
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In case there are multiple different ways of supplying a feeder, these must be clearly specified: • What is the switching state
during normal operation?
• Under what conditions is it changed? Only emergency, or peak / off-peak, or seasonal?
• Can the switching states be altered to better accomodate distributed generation?
DATA: DIAGRAMS AND MAPS
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Knowing where lines and substations are is helpful: • Cross check line lengths
• Cross check load data
• Generate load data if missing
• Assess potential for distributed generation
• Determine reinforcement costs (dependent on
terrain)
Maps also allow for easier understanding of grid topology.
DATA: MEASURED DATA
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Data Typically available Additional requirements
Voltage, HV Voltage at all busbars
through SCADA system
Sufficient
Voltage, MV Voltage at secondary side
of HV/MV transformer
Sufficient for modelling. For model
validation, measurements from
other locations in the grid (feeder
end) may be useful. Voltage, LV None
Load, HV Power flow through
HV/MV transformer
Active and reactive power
measurements may be available,
can be used for model validation
Load, MV Peak load at MV/LV
transformers
Feeder load time series (active
power) are often available for MV.
For LV grids, only peak load may be
available, if at all.
Load, LV
Necessary for modelling (green): • Load of all branches • Voltage at last control instance (OLTC)
Good for validation (red): • Voltage measurements at different points
Setting up measuring infrastructure will also help to assess the grid state during real operation!
STANDARD LOAD PROFILES
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𝑓𝑐𝑜𝑖𝑛𝑐𝑖𝑑𝑒𝑛𝑐𝑒 = Load𝑖𝑛𝑖=1
Max (Load)𝑖𝑛𝑖=1
If only peak loads are available, standard load profiles can be used to estimate the load time series. → Standard procedure in many European countries, but not always available.
If customer peak loads are available, feeder peak load can be calculated using typical coincidence factors. → Standard procedure in many European countries. Factors can be determined from real time measurements at a higher level.
• Simulation results
LOAD FLOW MODEL
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• Load Flow Model
Voltage control regime
Measured or generic load profile
Transformer specs
Line and cable data
Switching configuration
Voltage of each point on the feeder
Loading of all elements
DATA COLLECTION AND GRID OPERATION
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Load PV
Load PV
Load PV
Load PV
OLTC
11 kV
33 kV
33 kV to 11 kV Transformer is controlled with discrete on load tap changers which keep voltage in range for multiple measurement points
Setting up measurements allow for better controllability of the grid during real life operation: • Simple: Analysis of historical measured data may identify
need for remedial action on a certain feeder
• More advanced: Data can be used for grid control in real time, see example of Wide Area Voltage Control – either manually or automatically controlled (SCADA)
• Data can also be used to assess quality of supply and improve it as necessary
• Storing data for several years can be advisable
Distributed PV integration requires a detailed
review of data management and data
collection approach
SUMMARY
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THANK YOU FOR YOUR ATTENTION!