grid integration study results & recommendations · day 1, 12:00, 60 mins . introduction delhi...

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 August 2017

Dr. Thomas Ackermann

Dr.-Ing. Eckehard Tröster

Grid Integration Study Results & Recommendations

Day 1, 12:00, 60 mins

Introduction

Delhi Simulation Results

• Urban Feeder

• Rural Feeder

Bhopal Simulation Results

• Urban Feeder

• Rural Feeder

Summary

Recommendations

CONTENT

2

Delhi urban Delhi rural 1 Delhi rural 2 Bhopal urban

Bhopal rural

Supplied from 33 kV 66 kV 66 kV 132/33 kV 33 kV

Dominant cable/line type

300XLPE cable, 5.7 MVA

Dog ACSR OHL, 5.7 MVA

Dog ACSR OHL, 5.7 MVA

Rabbit ACSR OHL, 2.9 MVA

Raccoon ACSR OHL, 3.8 MVA

Length OHL - 19.8 km 16.7 km 2.7 km 11.0 km

Length UG cables 3.1 km 10.9 km 2.6 km - -

Total length 3.1 km 30.7 km 19.3 km 2.7 km 11.0 km

Installed DT capacity

5.4 MVA 5.2 MVA 4.6 MVA 2.2 MVA 3.7 MVA

Peak load 2.5 MW 3.4 MW 3.0 MW 1.1 MW 1.6 MW

Expected main issues

Protection, reversed power flow

Voltage control, asset overloading (PV power plant)

Protection, reversed power flow

Voltage control

REMINDER: INVESTIGATED GRIDS COMPARISON OF RELEVANT 11 KV GRIDS

3

INCREASING PV GENERATION

4

Delhi urban Delhi rural Bhopal urban Bhopal rural

% of DT MW % of DT MW % of DT MW % of DT MW

20% 1.1 15% 1.5 30% 3.9 30% 10.9

50% 2.7 40% 3.9 50% 6.5 50% 18.2

75% 4.1 75% 7.4 75% 9.8 75% 27.2

100% 5.4 100% 9.8 100% 13.0 100% 36.3

150% 8.1 150% 14.7 150% 19.5 150% 54.5

Stepwise increase of installed PV generation

Bhopal: Including upstream PV and parallel feeders

Both rural feeders combined

RESULTS ON INCREASING PV PENETRATION

5

Loading Voltage

PV Penetration: 20 % of DTs

3.502.802.101.400.70-0.00 [km]

011k

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VVR

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1.14

1.08

1.03

0.97

0.92

0.86

[p.u.]

Voltage, Magnitude

1.1 pu

0.9 pu


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Loading Voltage


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011k

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1.14

1.08

1.03

0.97

0.92

0.86

[p.u.]

Voltage, Magnitude

1.1 pu

0.9 pu


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Loading Voltage


3.502.802.101.400.70-0.00 [km]

011k

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a..

2950

5059

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2950

1238

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2950

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1.14

1.08

1.03

0.97

0.92

0.86

[p.u.]

Voltage, Magnitude

1.1 pu

0.9 pu


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Loading Voltage


3.502.802.101.400.70-0.00 [km]

011k

V_V

a..

2950

5059

..

2950

5055

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2950

5059

..

2950

5059

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2950

1304

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2950

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2950

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2950

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2950

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2950

1238

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2950

1238

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2950

1238

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1.14

1.08

1.03

0.97

0.92

0.86

[p.u.]

Voltage, Magnitude

1.1 pu

0.9 pu


9

Loading Voltage


3.502.802.101.400.70-0.00 [km]

011k

V_V

a..

2950

5059

..

2950

5055

..

2950

5059

..

2950

5059

..

2950

1304

..

2950

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1.14

1.08

1.03

0.97

0.92

0.86

[p.u.]

Voltage, Magnitude

1.1 pu

0.9 pu

VOLTAGE RECORDING EXAMPLE

10

Voltage over feeder length

09:00:00


12:00:00


15:00:00

Max. voltage over time

Condense the information by using max. voltage without length information

From the simulations, two

specific result parameters

are taken for evaluation:

• Maximum Loading

• Maximum Voltage

The result includes the

11kV and for the Urban

Feeder also the 400 V

networks

RESULT EVALUATION

11

Simulation of a full day with

Maximum PV infeed profile

Minimum load

Evaluation of

Highest voltage

Highest loading

at every time step regardless of position in the grid

Peak loading and peak voltage get stored for each variation of installed PV

RESULT EVALUATION CRITERIA

12

Voltage

Loading Peak values

Peak values

VOLTAGE LIMIT DEFINITION

13

Rural Feeder: Relevant Voltage limit for PT+MV+DT = 1.06 pu

Voltage increase or drop allowed:

•1 % Tolerance 11 kV busbar of OLTC Transformer (66/33 kV – 11 kV)

•4 % at the 11 kV level

•1 % at the Distribution Transformer

•4 % at the 0.4 kV level

Total Drop = 1 + 4 + 1 + 4 = 10 %

Load PV

Load PV

Load PV

Load PV Urban Feeder Relevant Voltage limit for PT+MV+DT+LV = 1.1 pu

14

DELHI SIMULATION RESULTS

URBAN FEEDER

DELHI URBAN FEEDER MEASURE IMPLEMENTATION

15

Voltage

Loading Thermal limit of 100%

Voltage limit for LV ±10%

Voltage recommendation

for MV (±6%)

Scenario 1: PV equal distribution

DELHI RESULTS - URBAN FEEDER SCENARIO 1: PV EQUALLY DISTRIBUTED ALONG THE FEEDER WITH NORMAL LOAD

16

No issues with PV

No voltages issues up to ca. 120% PV

Base case violates loading of network elements (in this case a cable)

Suitable solutions:

• 07 cap pv

• 09 grid reinforcement

DELHI RESULTS - URBAN FEEDER SCENARIO 2: PV EQUALLY DISTRIBUTED ALONG THE FEEDER WITH ADAPTED LOAD

17

No issues with PV

DELHI RESULTS - URBAN FEEDER SCENARIO 3: PV WITH HIGHER PV PENETRATION AT THE END OF FEEDER WITH NORMAL LOAD

18

No issues with PV

DELHI RESULTS - URBAN FEEDER SCENARIO 4: PV WITH HIGHER PV PENETRATION AT THE END OF FEEDER WITH ADAPTED LOAD

19

No issues with PV

DELHI RESULTS - URBAN FEEDER SCENARIO 5: PV WITH CABLES CONVERTED TO CABLES WITH LOWER CROSS-SECTION

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No issues with PV

21

DELHI SIMULATION RESULTS

RURAL FEEDER

DELHI RESULTS - RURAL FEEDER SCENARIO 1: PV EQUALLY DISTRIBUTED ALONG THE FEEDER WITH NORMAL LOAD

22

No issues with PV

No issues with PV and storage peakShaving

Example: Choosing a solution

DELHI RESULTS - RURAL FEEDER SCENARIO 2: PV EQUALLY DISTRIBUTED ALONG THE FEEDER WITH ADAPTED LOAD

23

No issues with PV

DELHI RESULTS - RURAL FEEDER SCENARIO 3: PV ON ALL FEEDERS WITH A PV POWER PLANT CONNECTED

24

No issues with PV

DELHI RESULTS - RURAL FEEDER SCENARIO 4: PV WITH OHL CONVERTED TO CABLES WITH SIMILAR CROSS-SECTION

25

No issues with PV

26

BHOPAL SIMULATION RESULTS

URBAN FEEDER

BHOPAL RESULTS – URBAN FEEDER SCENARIO 1: ROOFTOP PV EQUALLY DISTRIBUTED ALONG THE FEEDER WITH NORMAL LOAD

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Voltage

Loading

No issues with PV

BHOPAL RESULTS - URBAN FEEDER SCENARIO 2: ROOFTOP PV EQUALLY DISTRIBUTED ALONG THE FEEDER WITH ADAPTED LOAD

28

Voltage

Loading

No issues with PV

29

Voltage

Loading

No issues with PV

BHOPAL RESULTS - URBAN FEEDER SCENARIO 3: ROOFTOP PV WITH HIGHER PV AT THE END OF FEEDER WITH NORMAL LOAD

BHOPAL RESULTS - URBAN FEEDER SCENARIO 4: ROOFTOP PV WITH HIGHER PV AT THE END OF FEEDER WITH ADAPTED LOAD

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Voltage

Loading

No issues with PV

31

Voltage

Loading

No issues with PV

BHOPAL RESULTS - URBAN FEEDER SCENARIO 5: ROOFTOP PV WITH OVER-HEAD-LINES CONVERTED TO CABLES WITH LOWER CROSS-SECTION

32

BHOPAL SIMULATION RESULTS

RURAL FEEDER

BHOPAL RESULTS – RURAL FEEDER SCENARIO 1: ROOFTOP PV EQUALLY DISTRIBUTED ALONG THE FEEDER WITH NORMAL LOAD

33

Voltage

Loading

No issues with PV

BHOPAL RESULTS - RURAL FEEDER SCENARIO 2: ROOFTOP PV EQUALLY DISTRIBUTED ALONG THE FEEDER WITH ADAPTED LOAD

34

Voltage

Loading

No issues with PV

BHOPAL RESULTS - RURAL FEEDER SCENARIO 3A: ROOFTOP PV WITH A PV POWER PLANT AT THE BEGINNING OF THE FEEDER

35

Voltage

Loading

No issues with PV

BHOPAL RESULTS - RURAL FEEDER SCENARIO 3B: ROOFTOP PV WITH A PV POWER PLANT AT THE MIDDLE OF THE FEEDER

36

Voltage

Loading

No issues with PV

BHOPAL RESULTS - RURAL FEEDER SCENARIO 3C: ROOFTOP PV WITH A PV POWER PLANT AT THE END OF THE FEEDER

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Voltage

Loading

No issues with PV

BHOPAL RESULTS - RURAL FEEDER SCENARIO 4: ROOFTOP PV WITH OVER-HEAD-LINES CONVERTED TO CABLES WITH SIMILAR CROSS-SECTION

38

Voltage

Loading

No issues with PV

39

RESULT SUMMARY

Impact Symbol

Measure increases hosting capacity from base case, above 100 %

Measure increases hosting capacity from base case but stays below 100 %

Measure has no effect O

Measure reduces hosting capacity from base case

RESULT ASSESSMENT

40

Measure

Scenario 1: PV equally distributed with normal load

Scenario 2: PV equally distributed with adapted load

Scenario 3: PV at the end of the feeder with normal load

Scenario 4: PV at the end of the feeder with adapted load

Scenario 5: PV at the end of the feeder with lower cable cross-section

base 90% 100% 75% 80% 55%

oltc 90% o 100% o 75% o 80% o 55% o

wide area control

90% o 100% o 75% o 80% o 50%

fixed PF 80% 85% 65% 70% 50%

qvchar 90% o 95% 70% 75% 55% o

cap pv 150% 150% 140% 150% 105%

storage own consumption

90% o 100% o 75% o 80% o 55% o

storage peakShaving

120% 130% 100% 115% 80%

dsm 90% o 100% o 75% o 80% o 55% o

grid reinforcement

150% 150% 150% 150% 150%

DELHI URBAN FEEDER RESULT OVERVIEW

41

Measure Scenario 2: PV equally distributed with normal load

Scenario 3: PV equally distributed with adapted load

Scenario 4: PV equally distributed with 3.5 MW PV power plant

Scenario 5: PV equally distributed with network fully cabled

Base 90% 110% 50% 70%

wide area control

105% 110% o 75% 100%

fixed PF 95% 105% 65% 95%

qvchar 105% 110% o 70% 90%

cap pv 150% 150% 70% 145%


90% o 110% o 50% o 70% o

storage peak shaving

125% 150% 70% 100%

dsm 90% o 110% o 50% o 70% o

grid reinforcement

150% 150% 150% 150%

DELHI RURAL FEEDER RESULT OVERVIEW

42

BHOPAL URBAN FEEDER RESULT OVERVIEW

43

Measure

Scenario 1: PV equally distributed normal load

Scenario 2: PV equally distributed adapted load

Scenario 3: PV at the end of the feeder normal load

Scenario 4: PV at the end of the feeder adapted load

Scenario 5: PV equally distr., cabled network

base 110 % 115 % 110 % 110 % 110 %

mvoltc 110% o 115% o 110% o 110% o 110% o

shunt V control

110% o 115% o 110% o 110% o 110% o

wide area control

110% o 115% o 105% 110% o 110% o

fixed PF 100% 105% 90% 95% 100%

qvchar 110% o 110% 105% 110% o 110% o

cap pv 145% 150% 140% 145% 145%


110% o 115% o 110% o 110% o 110% o

storage peakSh.

140% 150% 130% 135% 140%

grid reinf. 150% 150% 150% 150% 150%

Measure Scenario 1: PV equally distributed normal load

Scenario 2: PV equally distributed adapted load

Scenario 3C: PV equ. dist. with PV plant at end of feeder

Scenario 4: PV equally distributed, fully cabled network

base 100 % 105 % 65 % 105 %

mvoltc 105% 110% 65% o 105% o

shunt V control

90% 105% o 60% 100%

wide area control

100% o 110% 65% o 100%

fixed PF 90% 85% 60% 95%

qvchar 100% o 110% 65% o 100%

cap pv 125% 130% 85% 130%


100% o 115% 65% o 105% o

storage peakShaving

125% 140% 80% 130%

grid reinforcement

150% 150% 150% 150%

BHOPAL RURAL FEEDER RESULT OVERVIEW

44

• Grids in India are not very different from other grids in the world.

• PV systems with an aggregated capacity of up to 75% of the transformer rating can usually be connected without any further measures. In most cases 100% are actually possible.

• Above 75% the rural networks suffers predominately from over-voltage issues.

• Voltage issues can be solved with wide area control of the 66/11kV transformer and reactive power provision by the PV systems

• Above 75% in the urban network, mostly loading problems occur.

• As the lines are short there is less voltage drop across them.

• Above 75% line loading issues and above 100% distribution transformer overloading have to be considered critical

• Besides conventional network reinforcement, implementing peak-shaving battery systems is a possible solutions

GENERAL CONCLUSIONS

45

Peak shaving batteries • Needs to be procured and installed by the customer

• Would roughly double the price of the installation

• No grid parity for such a system

• Indian homes are already equipped with batteries that could be used for PV storage

• Additional incentive for batteries to operate in peak shaving mode

Capping of inverters • Cheaper solution, almost the same grid impact during extreme situations

• Possible to cap PV feed-in at 70 – 75 % of the maximum without losing more than 3 % of energy annually

• Solution is currently used for small rooftop PV units in Germany

PERFORMANCE OF TECHNICAL SOLUTIONS ACTIVE POWER MANAGEMENT

46

Additional incentive scheme required

Wide area control • Voltage rises induced by PV and drops caused by high load are detected and

alleviated

• The general quality of supply will be improved by improving the voltage profile

• Continuous measurements have to be made at multiple points resulting in a constant stream of operational data

• Estimated cost at 50,000 € per 110/20 kV transformer

Voltage control from PV inverters • Utilizes reactive power and increases loading

• In highly loaded grids, using a Q-V characteristic provides better results

• In grids with no loading issues, a fixed power factor of 0.95 lagging performed better

• If a large amount of PV power is located at one node in the grid, a Q-V characteristic performs better

PERFORMANCE OF TECHNICAL SOLUTIONS VOLTAGE CONTROL MEASURES

47

Overcurrent protection Short circuit current contribution of the units feeding in between the protection relay and the location of the fault have to be considered

Short circuit current of PV system is no larger than the rated current of the inverter

Simple solution:

Require the inverters to not feed in current at detection of a voltage drop (Zero-Current-Mode)

Collides with low voltage ride through capabilities

Short circuit current of all units on a feeder should be limited to

𝑰𝒔𝒄,𝒖𝒏𝒊𝒕 ≤ 𝑰𝒔𝒄,𝒎𝒊𝒏 − 𝑰𝒔𝒄,𝒕𝒓𝒊𝒈𝒈𝒆𝒓

PROTECTION

48

49

RECOMMENDATIONS

Studies • Great variety of results observed in this study

• High hosting capacity observed for both distribution grid areas

• Each grid area in India should be analysed independently

• Simple estimation approaches might be sufficient

• Simulation studies of example feeder is recommended to evaluate impact on grid operation

General technical requirements for PV systems • Compliance with international standards that limit emissions (Harmonics, Flicker,

DC currents)

• Generator protection to avoid damage and unintentional islanding

• Compatibility of fault behaviour and protection settings

RECOMMENDATIONS 1/4

50

Technology options • Automatic voltage control at 132/33, 220/66 or 220/33 kV should be

implemented

• Automatic voltage control at 66/11 or 33/11 kV is very beneficial, but not strictly required

• Under- and overvoltage can be efficiently eliminated using wide area control

• Voltage control by rooftop PV inverters through reactive power

• Can easily be required by the grid code and is highly recommended

• PV power plants connected to the 11 or 33 kV level should be equipped with active voltage control by Q-V characteristic

• Active power controllability should be required from all PV units

• Large centralized PV power plants should be remotely controllable

• Rooftop PV units should either be capped at 70 to 75 % of their maximum expected output, or be remotely controllable, or be equipped with a peak shaving storage (requires incentive)

RECOMMENDATIONS 2/4

51

Legal and regulatory framework • Remote control of PV units

• Requires legal framework of operation (When, who and how to use)

• Require voltage control capability from PV inverters, controlled by grid operator

• Active power curtailment requires agreed remuneration of lost energy

• Recommended to align the voltage control requirements with the German low voltage grid code, most PV systems already comply

• Capping of PV at 70 or 75 % would have to be specified in grid code and net metering scheme, and checked for legal complications

• PV batteries require incentives for installation and running them in peak shaving mode

• Grid code requirements should be developed in coordination transmission system operators

• Example: frequency response of PV units

RECOMMENDATIONS 3/4

52

Specific recommendations Delhi

Once the 66/11 and 33/11 kV transformers are upgraded to automatic voltage control, there are no specific recommendations that deviate from the previously stated.

Bhopal

Enable more control over the voltage control regimes

• Retrofit 132/33 kV transformers with automatic tap changing

• Equip 33/11 kV transformers with on-load tap changers

• Automatic voltage control should be used in new projects or when replacing old or damaged units

RECOMMENDATIONS 4/4

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THANK YOU FOR YOUR ATTENTION!

grid integration study results & recommendations · day 1, 12:00, 60 mins . introduction delhi...

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