**5.10 Detection of islanding**

It plays a major role in proper functioning of protective system. If differential relaying is adapted there is no necessity to detect islanding. However for the Control of micro grid operation and to maintain the power quality the control system for each DER has to be changed since the reference signal for frequency and voltage which is taken from the grid will not be available when the micro grid is isolated. There are different methods available in the literature for islanding detection such as rate of change of frequency, voltage, power factor, THD. Also the use of FFT or Wavelet transform of the terminal voltage will give out different spectrum when isolation takes place. Artificial intelligence techniques also have been employed for detection of islanding. Some new hybrid techniques employing these techniques can be found in Refs. [32–35].


**103**

*Microgrid Protection Systems*

**Year Title Ref** 

2006 Al-Nasseri H, Redfern MA, Li F. A voltage based protection for micro-grids containing power electronic converters. In: IEEE Power Engineering Society General Meeting; 2006.

p. 7

p. 6

2007 Nikkhajoei H, Lasseter RH. Microgrid protection. In: IEEE Power Engineering Society General Meeting; 2007. pp. 1-6

2008 Al-Nasseri H, Redfern MA. Harmonics content based protection scheme for microgrids dominated by solid state converters. In: 12th International Middle-East Power System Conference, 2008 (MEPCON 2008); 2008. pp. 50-56

Rajapakse AD, Agent-based protection scheme for distribution net-works with distributed generators. In: IEEE Power Engineering Society General Meeting; 2006.

2006 Perera N,

*DOI: http://dx.doi.org/10.5772/intechopen.86431*

**No.**

**Methodology Type of** 

[27] Here DER output voltage transformation from abc to dq frame is performed and then the deviations of these values from reference values are computed. Based on the difference the protective action is initiated. A communication link is provided between relays. (Voltage based protection schemes)

[38] Network is divided into several segments. Relay agents communicate through an asynchronous communication link. Time domain simulation is done using wavelets for fault location. Central data processing is not required as the decisions are done in a distributed manner.

[17] A static switch is placed at the point of common coupling. Entire system is divided into different zones. Makes use of symmetrical components and system residual current is used for protective action.

[28] Protection System is based on the measurement of amount of harmonic content present during the fault condition. For each type of fault a threshold value of THD is evaluated and set as a reference. Based on the measured value of harmonic content, required protective action will be initiated. (Voltage based protection schemes)

**faults discussed**

Balanced and unbalanced faults

Phase to ground and phase to phase to ground fault high impedance fault

Phase to ground and phase to phase faults

Balanced and unbalanced faults

**Micro grid features**

(i) Islanded mode (ii) Radial system (iii) Inverter based DER (iv) Constant MVA load (v) Overhead line with voltage level 11 kV/0.48 kV

(i) Both gridconnected and islanded mode (ii) D-DGs (iii) Constant MVA Load (iv) OHL radial 24.9 kV

(i) Islanded mode (ii) Radial system (iii) Inverter based DER (iv) kW load (v) 0.48 kV distribution voltage

(i) Islanded mode (ii) Radial system (iii) Inverter based DER (iv) Constant MVA load (v) Overhead line with voltage level 11 kV/0.48 kV **Remarks**

(i) Protection against high impedance faults is not considered (ii) Effect of single pole tripping is not explained (iii) Relay functioning depends on the communication link between the relays

(i) Requires only current measurements and these measurements need not be time synchronized (ii) Demands high speed communication for proper determination of fault section (iii) Poses challenges to avoid relay functioning during switching transients

(i) Protection against high impedance faults is not considered (ii) Effect of single pole tripping is not explained

(iii) Three phase faults are not discussed

(i) It is required to assess the reference THD values for different fault scenarios which would be challenging (ii) If any DER supplies a harmonic free voltage or with lesser harmonic content, protection system may fail. (iii) Variable fault impedances, large dynamic load switching poses sensitivity issues demand for proper settings of threshold limits of THD

#### *Microgrid Protection Systems DOI: http://dx.doi.org/10.5772/intechopen.86431*

*Micro-Grids - Applications, Operation, Control and Protection*

**5.10 Detection of islanding**

**Year Title Ref** 

SM, Girgis AA. Development of adaptive protection scheme for distribution systems with high penetration of distributed generation. IEEE Transactions on Power Delivery. 2004;**19**(1):56-63

2005 Wan H, Li KK, Wong KP. A multi-agent approach to protection relay coordination with distributed generators in industrial power distribution system. In: Fortieth IAS Annual Meeting. Conference Record of the 2005 Industry Applications Conference, 2005. Vol. 2. IEEE; 2005. pp. 830-836

2004 Brahma

**No.**

relay with fixed operating time to provide backup protection. This system will not require any changes either in configuration or settings for faults in the micro grid or in the main grid. Also this is not affected by the number and location of DERs and

It plays a major role in proper functioning of protective system. If differential relaying is adapted there is no necessity to detect islanding. However for the Control of micro grid operation and to maintain the power quality the control system for each DER has to be changed since the reference signal for frequency and voltage which is taken from the grid will not be available when the micro grid is isolated. There are different methods available in the literature for islanding detection such as rate of change of frequency, voltage, power factor, THD. Also the use of FFT or Wavelet transform of the terminal voltage will give out different spectrum when isolation takes place. Artificial intelligence techniques also have been employed for detection of islanding. Some new hybrid

whether the micro grid is connected or isolated from the main grid.

techniques employing these techniques can be found in Refs. [32–35].

[36] Here protection scheme is developed for micro grids with Synchronous DERs operating in grid connected mode addressing the fuse to fuse, fuse to recloser co-ordination issues that arises due to large number of DERs. The relaying strategy is adaptable in view of temporary faults and permanent faults and extension of the scheme to additional feeders.

[37] Protective relay coordination using a multi agent communication approach is presented. It is capable of providing back up protection in case of primary protection failure in grid connected mode is developed. Make use of the Java agent Development Framework (JADE) platform for simulation of communication.

**Methodology Type of** 

**faults discussed**

Balanced and unbalanced faults

Fault type is not specified

**Micro grid features**

(i) Grid connected mode (ii) Radial system (iii) Synchronous based DER

(i) Grid connected mode (ii) Radial system (iii) Both synchronous based and inverter based DERs

**Remarks**

mode (ii) Protection in the islanded mode of operation is not included (iii) Works well when large number of DERs are connected in the micro grid. If the number DERs is less, it poses challenges.

(i) Applicable only in grid connected

(i) Applicable only in grid connected

mode (ii) Relay coordination is dependent on communication (iii) Capable of providing backup protection

**102**



**105**

*Microgrid Protection Systems*

**Year Title Ref** 

Kauhaniemi K, Laaksonen H. Novel protection approach for MV microgrid. In: CIRED 21st International Conference on Electricity Distribution; 6–9 June, 2011; Frankfurt; 2011. Paper No. 0430

2012 Samantaray SR, Joos G, Kamwa I. Differential energy based microgrid protection against fault conditions. In: IEEE PES Innovative Smart Grid Technologies (ISGT); 2012. pp. 1-7

2013 Ustun TS, Ozansoy C, Ustun A. Fault current coefficient and time delay assignment for microgrid protection system with central protection unit. IEEE Transactions on Power Systems. 2013;**28**:598-606

2014 Kar S, Samantaray SR. Timefrequency transform-based differential scheme for microgrid protection. IET Generation, Transmission & Distribution. 2014;**8**:310-320

2011 Voima S,

*DOI: http://dx.doi.org/10.5772/intechopen.86431*

**No.**

[42] This is an adaptive

[43] In this method, differential energy applying time frequency transform is used to initiate the protective action. On either end of the feeder, amount of spectral energy is found out. High impedance faults are also considered.

[44] In this method

communication based coordination has been presented. Amount of fault current contribution by any DG is represented as a coefficient. Selectivity of the relays is controlled by automatic adjustment of the current setting.

[45] The protection scheme identifies the fault current patterns based on the S transforms. Differential energy is computed considering both ends of the feeder and it is used for protective action.

protection scheme which uses tele-communication infrastructure. Network is divided into four different zones. IEDs used have directional over current protection function along with current and voltage measurements. To achieve proper selectivity, interlocking signal is sent along with the direction of fault. Applicability of distance relay also is presented.

**Methodology Type of** 

**faults discussed**

Specific type of fault details are not mentioned

Balanced and unbalanced faults

Balanced faults

Balanced and unbalanced faults

**Micro grid features**

(i) Islanded mode (ii) Radial system (iii) Inverter based DER (iv) Constant MVA load (v) Over head line with voltage level 20 kV

(i) Both gridconnected and islanded mode (ii) Both inverter and grid connected mode (iii) Constant MVA (iv) OHL radial and closed loop 25 kV distribution voltage

(i) Grid connected and islanded mode (ii) Inverter based and synchronous based DGs (iii) Radial system

(i) Both gridconnected and islanded mode (ii) Inverter based and synchronous DGs (iii) Constant MVA load (iv) OHL radial and closed loop 25 kV

**Remarks**

(i) High dependency on the communication infrastructure (ii) With reliable communication links it can be made adaptable to different modes of operation (iii) Details of simulation of different fault scenarios is missing

(i) Differential energy is used to recognize the fault

patters (ii) Makes use of both time and frequency data where as in other schemes only one data is used. (iii) Setting the threshold limit for the differential energy plays crucial

role

(i) Requires human input however it can be minimized if the structure of the network is obtained by running an automated algorithm (ii) Delay in the communication depends on the type of protocol used (iii) faults within the micro grid only are considered

(i) Results are compared with the current differential technique for all fault scenarios (ii) Differential energy is less sensitive to time synchronization errors compared to current difference

#### *Microgrid Protection Systems DOI: http://dx.doi.org/10.5772/intechopen.86431*

*Micro-Grids - Applications, Operation, Control and Protection*

**Methodology Type of** 

[39] These relays have the ability to operate for faults in both forward direction and reverse direction. Its operation is based on the measured admittance and has an inverse time characteristic. The protection system can operate for low fault currents also and thus provide protection under islanded mode also. It is possible to supply the load in islanded mode also. Network is divided into different

zones .

[40] In this method, digital relays are employed along with communication network. An additional line is added in the system to simulate the loop structure in this paper. A new modeling for high impedance fault simulation is presented.

[41] This protection scheme is based on current travelling waves. Here detection of the faults is done using busbar voltages and location of the fault is found out employing current travelling waves. No communication link is used. Based on the information available locally, protective relay

works.

**faults discussed**

Balanced and unbalanced faults

Balanced and unbalanced faults

(i) Grid connected and islanded mode (ii) Both inverter and synchronous based DGs (iii) Radial and loop structure (iv) 18 bus system with multiple DGs included (v) Unbalanced load is also included

Both gridconnected and islanded mode - - - 10/0.4 kV distribution voltage

**Micro grid features**

(i) Both gridconnected and islanded mode (ii) Inverter based-DGs (iii) Constant MVA (iv) OHL radial and closed loop (v) 11 kV

**Remarks**

offset (ii) Takes more time of operation for high impedance

faults

link

(i) Highly expensive and time synchronization is not considered (ii) Imbalance created between generation and demand due to line removal in the radial mode makes the protection challenging and calls for effective communication infrastructure and sensors. (iii) In case of communication failure, protection against high impedance faults is

at stake

(i) Method is independent of unbalance between the load and generation, level of fault current or power flow (ii) Simulation results are not presented

(iii) Does not use any communication

(i) fundamental frequency component extraction may lead to measurement errors due to harmonics and dc

**No.**

**Year Title Ref** 

2009 Dewadasa M, Ghosh A, Ledwich G. An inverse time admittance relay for fault detection in distribution networks containing DGs. In: 2009 IEEE Region 10 Conference (TENCON 2009); 2009. pp. 1-6

2010 Sortomme E,

2010 Shi S, Jiang B, Dong X, Bo Z. Protection of microgrid. In: 10th IET International Conference on Developments in Power System Protection (DPSP 2010); Managing the Change; 2010. pp. 1-4

Venkata M, Mitra J. Microgrid protection using communicationassisted digital relays. In: IEEE PES General Meeting; Providence, RI; 2010. p. 1

**104**



**107**

Micro Grids.

**Table 1.**

**6. Conclusions**

*Summary of research on protection of micro grids.*

*Microgrid Protection Systems*

**Year Title Ref** 

2018 Aghdam TS, Karegar HK, Zeineldin HH. Variable tripping time differential protection for microgrids considering DG stability. IEEE Transactions on Smart Grid

*DOI: http://dx.doi.org/10.5772/intechopen.86431*

**No.**

**Table 1** gives a consolidated picture of ongoing efforts for protection of

**Methodology Type of** 

[48] This method discusses the stability aspect also along with fault clearance. A multi agent approach along with the zoning principle is employed. For coordination and backup purposes each agent has three layers namely primary, backup and bus protection. The critical clearing time (CCT) curves of the DGs employed are analysed to establish the mechanism for checking the constraints on the CCT are developed.

**faults discussed**

Balanced fault

**Micro grid features**

(i) Both grid connected and islanded mode (ii) Modified CIGRE benchmark micro grid test system (iii) Synchronous DG (iv) 20 kV.

**Remarks**

DGs

(i) Micro grid has only synchronous

(ii) Specific type of fault is not mentioned (iii) Fuse tripping slower for the same fault current as the nominal current of the fuse increase. (iv) Settings of several differential layers depend on the fuse size for coordination.

A comprehensive review of various protection methods as applicable to micro grid protection is presented. DERs are becoming an integral part of distribution systems but the adequate changes necessary in the protection system has not yet picked up the pace. Lot of research is going on in this area to use the existing protective infrastructure justifiably without compromising on the safety aspect. It is apparent that well-built communication infrastructure is essential for meeting the requirement of micro grid protection. It is due to the fact that there are inevitable topological changes in the network due to the transition of micro grid operating mode from grid connected to islanded and vice versa. Also, the intermittent nature of the DER output and the fault limiting features of inverter fed DGs present several technical challenges to the micro grid protection engineers. Making the protective system to be adaptive is the need of the hour. But it involves lot of infrastructure development and is costly. Many methods based on directional O/C relays, distance relays and voltage based protection schemes have been proposed for effective implementation. However, effective utilization of the existing protective systems with minimal changes in the infrastructure appears to be possible with differential protection scheme. With the advancements in communication technology, micro grid

protection can be made adaptive in a cost effective manner.

### *Microgrid Protection Systems DOI: http://dx.doi.org/10.5772/intechopen.86431*


**Table 1.**

*Micro-Grids - Applications, Operation, Control and Protection*

[46] Using wavelet transforms a microprocessor based protection scheme is developed for grid connected mode of the micro grid with fault detection and classification. Cumulative sum of the high frequency details of power signal is computed and is compared against a threshold value to send the trip signal using the digital relay.

[47] Hilbert-Huang transform (HHT) has been employed to determine the differential energy in this method. To discriminate faults in islanded mode and in case of high impedance fault an appropriate setting for the differential energy is used as threshold

value.

[3] A comprehensive review of the micro grid protection techniques has been presented along with several case studies using different relays in different modes of operation employing synchronous based and inverter based DGs. The fault ride through capability also is discussed. DC microgrid protection is also discussed briefly.

**Methodology Type of** 

**faults discussed**

Balanced and unbalanced faults

Balanced and unbalanced faults

Balanced and unbalanced faults

**Micro grid features**

(i) Grid connected and disconnected mode (ii) Radial system (iii) Both Synchronous based and inverter based DERs

(i) Both grid connected and islanded modes (ii) Radial system (iii) Inverter based DERs

(i) Both grid connected and islanded modes (ii) Radial system and mesh system, voltage 12.47 kV (iii) Inverter based and synchronous based DERs

**Remarks**

(i) Fault location depends on the power signal high frequency details (Phfd)

(ii) Threshold value of Phfd depends on sampling frequency of the analog signal and the type of wavelet chosen

(i) Setting of proper threshold value is important to discriminate different fault conditions (ii) When noise is included in the signals protection becomes challenging

(i) DG ride through capabilities in islanded mode for different fault scenarios is presented. (ii) Effect of ECDG units on directional over current relays and distance relays is shown to be more than in case of differential relays. (iii) Frequency of fault current is shown to be dependent on the slip of induction machine. (iv) In case of DFIG based microgrid, response of the relay is shown to be dependent on the type of control strategy employed

**No.**

**Year Title Ref** 

2015 Kanakasabapathy P, Mohan M. Digital protection scheme for microgrids using wavelet transform. In: 2015 IEEE International Conference on Electron Devices and Solid-State Circuits (EDSSC). IEEE; 2015. pp. 664-667

2016 Gururani

3716

1353

2017 Hooshyar A, Iravani R. Microgrid protection. Proceedings of the IEEE. 2017;**105**(7):1332-

A, Mohanty SR, Mohanta JC. Microgrid protection using Hilbert–Huang transform based-differential scheme. IET Generation, Transmission & Distribution. 2016;**10**(15):3707-

**106**

*Summary of research on protection of micro grids.*

**Table 1** gives a consolidated picture of ongoing efforts for protection of Micro Grids.
