Dr . Pisupati S Subramanyam , Sr. Member IEEE, Professor, E.E.E. , V.B.I.T.,

1. DISTRIBUTED GENERATION GRID AND ISLANDING PROBLEM Dr . Pisupati S Subramanyam, Sr. Member IEEE, Professor, E.E.E. , V.B.I.T., HYDERABAD-501301.

2. DISTRIBUTED GENERATION GRID What is Smart Grid ? • The Smart Grid is a combination of hardware, management and reporting software, built atop an intelligent communications infrastructure. • In the world of the Smart Grid, consumers and utility companies alike have tools to manage, monitor and respond to energy issues. • The flow of electricity from utility to consumer becomes a two-way conversation, saving consumers money, energy, delivering more transparency in terms of end-user use, and reducing carbon emissions.

3. What is Smart Grid ? Contd. Modernization of the electricity delivery system so that it monitors, protects and automatically optimizes the operation of its interconnected elements – from the central and distributed generator through the high-voltage network and distribution system, to industrial users and building automation systems, to energy storage installations and to end-use consumers and their thermostats, electric vehicles, appliances and other household devices. The Smart Grid in large, sits at the intersection of Energy, IT and Telecommunication Technologies

4. Pillars of Smart Grid • Transmission Optimization • Demand Side Management • Distribution Optimization • Asset Optimization

5. Overview of Smart Grid 5

6. Smart Grid in Power Sector • Asset Management • HVDC and UHVAC etc. • Advance Metering Infrastructures • Asset Management etc. • Self Healing Grids • WAMS • Adaptive Islanding etc. • Transmission • Distribution • System Operations 6

7. Smart Grid in Power Sector • Asset Management • HVDC and UHVAC etc. • Advance Metering Infrastructures • Asset Management etc. • Self Healing Grids • WAMS • Adaptive Islanding etc. • Transmission • Distribution • System Operations 7

8. Distribution Changes • The current IEEE recommended industry practice (P1547) is to isolate all distributed generators (DGs) from the grid in the event of a fault in the grid. • This approach is adequate when the total capacity of the DGs is not significant and they can be removed without major impact on the system. • However it is expected that the penetration level of grid - • connected DGs will increase substantially over the next • few decades. • In addition, the number of Plugin Hybrid Electric • Vehicles ( PHEVs ) will increase in the near future. • Also micro grids will become popular in rural communities and commercial buildings.

9. Distribution Changes (Contd.) • Existing distribution systems have a simple power flow radially outwards from power stations. These will have to be modified. • The future distribution systems will have to be redesigned to accommodate the non radial nature of power flows in a more complex distributed generation environment. • The non-radial nature will make the existing over current • protection system unviable since the elements of the • system cannot be coordinated. • It is desirable that the DG protection systems should work in conjunction with the protection of networks, implying a paradigm shift in protection principles.

10. Distribution Changes (Contd.) • The installation of a large number of single phase DGs with different ratings will have severe impacts on power quality (PQ) due to the introduction of voltage imbalance and harmonics. • Require new solutions for control synchronization since all the distributed resources must work together • Require enhanced strategies for automation of distribution in terms of demand management • Require strategies for complex self reorganizing networks. • Require reactive power control strategies to provide acceptable voltage levels throughout the network.

11. Distribution Changes (Contd.) • The installation of a large number of Single phase DGs with different ratings will have severe impacts on power quality (PQ) due to the introduction of voltage imbalance and harmonics. • Require new solutions for control synchronization since all the distributed resources must work together • Require enhanced strategies for automation of distribution in terms of demand management • Require strategies for complex self reorganizing networks • Require reactive power control strategies to provide acceptable voltage levels throughout the network.

12. Sources of Renewable Energy • Wind turbines and wind farms • Solar photovoltaic (PV) cells • Solar-thermal energy • Fuel Cells • Geothermal • Wave and tidal energy • Biomass • Micro or mini hydro

13. DISTRIBUTED GENERATION ISLANDING • IMPLICATIONS ON POWER SYSTEM DYNAMIC PERFORMANCE • Islanding basics • Types of Islanding • Islanding detection methods • Disadvantages of Islanding • Anti Islanding Methods

14. What is islanding ? • Islanding refers to the condition in which a Distributed Generator (DG) continues to power a location even though electrical grid power from the electric utility is no longer present. • It is called Islanding as there is Power in a small area in the midst of a large area of no Power like an Island of Light in vast Sea of Darkness.

15. EXAMPLE:A grid supply line that has solar panels attached to it. • In the case of a blackout, the solar panels will continue to deliver power as long as brightness is sufficient. In this case, the supply line becomes an "island" with power surrounded by a "sea" of unpowered lines. • For this reason, solar inverters that are designed to supply power to the grid are generally required to have some sort of automatic anti-islanding circuitry in them.

16. For connecting Distribution Generating systems to the utility grid, several conditions have to be met. • These conditions are normally published by standardizing institutions such as IEC and IEEE but also by local (country) regulating authorities. • A very important requirement which is mandatory to distributed generators is their ability to detect islanding conditions. • Islanding refers to the condition of a distributed generator (DG) continuing to power a part of the grid even though power from electric utility is no longer present.

17. What is islanding ? [ Typical distributed system with Two DG’s

18. Islanding basics • Electrical inverters: Devices that convert direct current (DC) to alternating current (AC). • Grid-interactive inverters : Have the additional requirement that they produce AC power that matches the existing power presented on the grid. Grid-interactive inverter must match the voltage, frequency and phase of the power line it connects to.

19. If the grid is disconnected, the voltage on the grid line might be expected to drop to zero, a clear indication of a service interruption. However, consider the case when the house's load exactly matches the output of the panels at the instant of the grid interruption. In this case the panels can continue supplying power, which is used up by the house's load. In this case there is no obvious indication that an interruption has occurred. If the Grid Restores then Problem arises.

20. BOOBY TRAPS IN ISLANDING • Normally even when the load and production are exactly matched, the so-called "balanced condition", the failure of the grid will result in several additional transient signals being generated. • For instance, there will almost always be a brief decrease in line voltage, which will signal a potential fault condition. • However, such events can also be caused by normal operation, like the starting of a large electric motor.

21. Non-detection zone" (NDZ): • Methods that detect islanding without a large number of false positives is the subject of considerable research. • Each method has some threshold that needs to be crossed before a condition is consider to be a signal of grid interruption. • This Threshold is known as "non-detection zone" (NDZ), the range of conditions where a real grid failure will be filtered out.

22. TYPES OF ISLANDING 1. UNINTENTIONAL ISLANDING 2. Intentional Islanding

23. UNINTENTIONAL ISLANDING • Unintentional islanding can be dangerous to utility workers, who may not realize that the particular part of the network is still powered even though there is no power from the main grid. • Also, unintentional and non-controllable islanding can damage customer equipment, especially in situations of re-closing into an island. For that reason, distributed generators must detect islanding and immediately disconnect. • The probability of having islanding conditions is very small because, when the grid power is lost, the generated power (both active and reactive) of distributed generators has to match almost perfectly the power consumed by the loads including losses, otherwise the under/over voltage and under/over frequency • relays of generators would cease power generation.

24. INTENTIONAL ISLANDING • Lately there has been a lot of interests in MICRO GRIDS, i.e.distribution grids that can operate in controllable, intentional islanding conditions, decoupled from the main grid. • In case of such grids, islanding detection is still important in order to switch the control modes of distributed generators from power injection to voltage and frequency control during disconnection and opposite during reconnection to the main grid.

25. ISLANDING DETECTION METHODS • All distributed generators (DG), especially those connected to low voltage distribution grids are required to detect islanding conditions. The methods for detecting islanding are classified in three main categories: 1. Passive Methods 2. Active Methods 3. Communication based Methods.

26. Passive methods: • Based on grid monitoring • easy to implement but • have a large non-detection zone in the case local generation meets the load demand. • Active methods: • commonly used today, • may reduce the non-detection zone • but in the case of large amount of DGs installed, power quality problems are foreseen. • The communication based methods : • seldom used today mainly because of high cost of communication. However, if the islanding detection schemes can use the communication infrastructure to be deployed for smart grids, e.g.for metering, feeder automation, etc. the communication based methods will become cost competitive with the active methods without their weaknesses.

27. A. Passive methods • Passive methods are based on monitoring of grid variables by a dedicated algorithm residing in the control of distributed generator or outside in a dedicated device. Most passive methods are looking for abnormal changes in frequency, voltage or phase angle but also in some particular harmonics or the total • harmonic distortion (THD). • If the monitoring algorithm detects large or sudden changes of these variables at the point of connection with the utility grid, the inverter will trip. • The most common passive methods : • over/under voltage – monitors whether or not the grid voltage goes out of the limits established by the relevant • standards (see Fig. 1) over/under frequency – monitors whether or not the grid frequency goes out of the limits imposed by the relevant standards

28. A. Passive methods(Contd.) • monitoring rate of change of frequency (ROCOF) and voltage (ROCOV) ∙ • phase monitoring – monitors fast jumps of grid voltage phase ∙ • voltage harmonic – monitors selective (3rd, 5th, etc.) or total harmonic distortion (THD) of grid voltage [4], [5] • Passive methods are quite effective in majority of situations that may occur in the grid; however their non-detection zone (NDZ) does not cover situations when the power absorbed by the load matches almost perfectly the power generated by DG. • In such case, the variations in voltage, frequency or phase angle are lower than specified in the standard because the network remains balanced even though the connection with the main grid has been lost. Therefore, the DG would not trip even though an island has been formed. One can use a combination of passive methods and use multi-criteria decision making. In [6] the islanding detection algorithm uses passive methods including frequency and voltage monitoring and the most widely recognized methods like the Rate of Change of frequency (ROCOF), Voltage Vector Shift (VVS), and Voltage Unbalance. • However, passive methods are generally considered as in-sufficient anti-islanding protection

29. B. Active methods • Active methods appeared as a necessity to minimize the non-detection zone of islanding detection methods in conditions when generation matches load. • Normally, active methods inject a small disturbance to the utility grid and based on the grid response decide whether or not an island has formed. Disturbances in terms of shifts from normal values to grid voltage magnitude, frequency or phase angle can be added by the DG and,in case of grid connected situation, these disturbances should be corrected by the grid through the voltage and frequency control. However, if the voltage magnitude, frequency or phase angle follow the shift introduced by the DG, it is most likely that the grid has been disconnected,.Hence an island has been formed. • The most common active methods are using: • positive feedback inside the DG control – the controller tries to alter grid variables such as frequency, phase or voltage magnitude in order to perform: –a frequency jump or phase jump – the DG deliberately alters the frequency or phase of the injected • current in order to change the frequency or phase of the voltage. If grid frequency follows the inverter current, an island has formed and the PV inverter should disconnect

30. Out - Phase – Reclosing • What is reclosing / out – of – phase reclosing? • Produces transients which are potentially damaging to utility & customer equipments Figure 2 Phase voltages on source and DG side for a simulation of 180º out-of-phase reclosing [1] • Unusually high inrush currents in transformers

31. Active Anti - Islanding 1)Communication based schemes 2)Local detection schemes 1a) Transfer Trip Scheme

32. Power Line Signaling Scheme

33. Method of impedance measurement

34. Dynamic Impact of Anti-Islanding Measures Under voltage trip sensitivity • Undervoltages due to faults can lead to unnecessary DG tripping • With extensive DG penetration, simultaneous DG tripping due a fault can cause voltage collapse in the local system (voltage regulation equipment takes time to react)

35. Active Anti-Islanding Impact • Degradation of power quality and system stability as DG penetration becomes higher • Currently the local islanding detection methods virtually guarantee that the DG will be unable to provide grid support or improve grid stability when the grid is stressed anti-islanding protection disconnects the DG when it detects voltage and frequency excursions on the grid. • Because of the reclosing practice, anti-islanding techniques must trip DG’s within about 200 milliseconds before the breaker is reclosed. Failure to do so will lead to out-of-phase re-energization of the DG.

36. Anti-Islanding Today,Successful Islanding in the Future • Failure to trip islanded generators can lead to problems such as threats to personnel safety, out-of-phase reclosing, and degradation of power quality. • a wide-area measurement-based islanding detection scheme (IDS_WA) that uses time synchronized measurements to calculate the slip frequency and acceleration between two systems to detect islanded conditions. • The proposed scheme has significant advantages compared to traditional anti-islanding schemes, specifically when the power mismatch is minimal. Local-area measurement-based schemes (IDS_LA) complement the IDS_WA. AUTHORS:JohnMulhausen and Joe Schaefer, Florida Power & Light Company MangapathiraoMynam, Armando Guzmán, and Marcos Donolo, Schweitzer Engineering Laboratories, Inc.

37. http://zone.ni.com/wv/app/doc/p/id/wv-2658 Video:Smart-Grid Control Systems: Moving Towards a Self-Healing Grid Smart embedded systems that combine instrumentation, analytics, and control can make the grid more like the Internet – self-diagnosing and self-healing, distributed rather than centralized, and bidirectional rather than unidirectional. This session explains the fundamentals of smart-grid distribution and bidirectional power control systems and provides development tips and tricks for architecting a scalable control architecture with peer-to-peer communication between distributed nodes and fast hard real-time FPGA-to-FPGA control links. What is a distribution fault anticipation system? How do smart switches and reclosers detect problems and reroute power to isolate a fault? How do grid adaptive energy storage systems store and release energy at sub-cycle control loop rates?

38. Queries??? Thank you !