The document presents a review of protection schemes for active distribution systems. It begins with an introduction to topics like distributed generation, microgrids, and the challenges of protecting active distribution networks. It then summarizes various proposed protection schemes that employ techniques such as communication-based protection, voltage-based protection, adaptive protection, differential protection, overcurrent protection, distance protection, and multi-agent protection. The document concludes by suggesting a hybrid protection scheme is needed and presenting some preliminary simulation results testing different protection schemes on IEEE test feeders with and without distributed generation.

1. A Review of Protection Schemes for
Active Distribution Systems
PRESENTED BY: UMAIR SHAHZAD
Ph.D. STUDENT,
DEPARTMENT OF ELECTRICAL & COMPUTER ENGINEERING,
UNIVERSITY OF NEBRASKA-LINCOLN
Umair Shahzad and Dr. Sohrab Asgarpoor

2. Topics Covered
 Introduction
 Distributed Generation
 Microgrids
 Protection Schemes for Active Distribution Networks
 Phasor Measurement Units (PMUs)
 Suggested Protection Scheme
 Preliminary Simulations and Results
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3. Introduction
Due to the increasing popularity and demand for cleaner sustainable
energy, along with major blackout incidents around the world, distributed
generation (DG) has emerged as a possible alternative to fossil fuels.
Concept of active distribution systems has evolved.
Introduction of DG creates some hurdles for the electrical power network.
System Voltage Profile, Power Quality, Security, Power Flow Control,
Frequency Control, and System Protection.
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4. Passive vs. Active Networks
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5. Distributed Generation (DG)
IEEE defines DG as the “generation of electricity by the facilities that are
sufficiently smaller than central generating plants to allow interconnection at
nearly any point in a power system”.
Electric Power Research Institute (EPRI) defines DG as “smaller power sources
that can be aggregated to provide power necessary to meet regular demand”.
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6. DG Types (according to power rating)
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7. DG types (according to coupling)
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8. Microgrids and Microsources
Microgrid
According to the U.S. Department of Energy (DOE), a microgrid is “a group of interconnected
loads and distributed energy resources within clearly defined electrical boundaries that acts as a
single controllable entity with respect to the grid (and can) connect and disconnect from the grid
to enable it to operate in both grid-connected or islanded mode.”
Microsources
Sources connected to microgrids are called micro sources. They include photovoltaic (PV) arrays,
wind turbines, micro turbines ,synchronous generators, combined heat and power (CHP) plants,
flywheels, fuel cells, super capacitors, induction generators, electric vehicles and battery energy
storage systems.
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9. Microgrid: Modes of Operation
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Grid Connected Mode
Critical Loads
Non-Critical Loads

10. Microgrid: Modes of Operation
Islanded Mode
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Critical Loads

11. Review of Protection Schemes for Active
Distribution Networks
Protection using Communication
Voltage-based Protection
Adaptive Protection
Differential Protection
Overcurrent Protection
Distance Protection
Multiagent Protection
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12. Protection using Communication
Protection scheme employing digital relays and a communication system
The primary protection in grid-connected mode is based on a differential communication
scheme where each feeder segment trips the switching device on both ends of a faulted feeder.
Under islanded mode, the scheme detects high impedance faults.
Errors and Mismatches in CT.
High cost of switching devices and relays.
Protection scheme employing a central computer
In this scheme, a central computer is used to regulate the settings of protective devices upon
receiving data about network topologies and distributed generation connections or
disconnections. This action is performed to maintain coordination between various devices.
Assumption of existing protective devices been updated to their digital counterparts.
Vulnerability to cyber attacks due to communication.
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13. Ethernet Ring communication
In this scheme, a Ethernet ring communication for linking the microgrid management center and
protective devices in the microgrid system is utilized. Each protective device reports information
such as current, voltage, circuit breaker status etc. at its location.
High cost and non-availability of sufficient communication channels impedes practical
implementation.
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14. Schematic of Protection using
Communication
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15. Voltage-based Protection
Protection using disturbed voltage signal
In this scheme, communication is employed to transfer voltage signals between any
two relays to recognize the fault zone. The process basically consists of three steps.
1. Supply voltages are converted from abc frame to dq frame.
2. The disturbance signal is determined by using disturbed dq values. This signal
characterizes the deviation of supply voltages from a set reference. The
greater the value of this signal, the greater the disturbance. The disturbance
signal is an indicator that disturbance is present in the system.
3. Disturbed signal is passed and processed through a low pass filter (LPF) and a
hysteresis comparator (HYS). Lower and upper limits of a comparator
determine fault detection sensitivity.
No consideration of high impedance faults and symmetrical faults.
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16. Block Diagram for Voltage-based
Protection
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17. Adaptive Protection
In adaptive protection techniques, the calculated relay settings are stored in a database
according to network topology. When there is a change in topology, the relays update their
values from the database system.
Scheme for low-voltage microgrid
An adaptive protective scheme for a low voltage microgrid where a communication network
connects a microgrid management system and various components of the microgrids is
proposed.
The microgrid management system detects any change in microgrid configuration and sends
appropriate settings to protective devices.
Possibility of communication failures has been neglected.
The scheme does not allow the plug and play of DG sources.
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18. Schematic for Adaptive Protection
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19. Differential Protection
Protection using differential zone
A differential protection scheme for protection of microgrids in islanded operation is proposed.
Instead of the conventional differential line protection scheme, the scheme uses the concept of
differential zone protection.
An algorithm for appropriate placement of sensors and relays is also devised.
The scheme has not been tested experimentally.
Protection using differential current
A protection scheme based on differential current is proposed. It employs overcurrent relays
and communication links in a microgrid having converter-based and directly coupled DG sources.
The scheme is ineffective under unbalanced load conditions.
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20. Schematic for Differential Protection
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21. Overcurrent Protection
Overcurrent (OC) protection is one of the most effective and efficient methods when applied to
traditional radial distribution networks. Combined with a directional element, they form a strong
entity to protect the distributed grid in grid-connected mode .
Protection in the presence of wind turbines
The IEEE 13 bus system with wind turbines as DG sources (in islanded mode) is used to observe a
three-phase fault .
The locations of DGs were changed to observe the variations in fault current levels.
Directional over current relays were used to counter the bidirectional flow of the current.
The scheme does not consider other types of DG.
Penetration levels of DG are fixed.
Only a three-phase fault is considered.
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22. Block Diagram for Overcurrent Protection
(Passive Systems)
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GRID

23. Diagram for Directional Overcurrent
Protection (Active Systems)
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Grid DG
DOC
Relay

24. Distance Protection
This protection offers high selectivity, particularly when applied to transmission lines. Impedance at each relay
location is calculated by dividing the voltage at the relay location by the current flowing through it.
Usually, three zones are defined for the region to be protected.
 Protection using Mho characteristics
The scheme uses distance relaying with Mho characteristics in a microgrid protection plan. According to the
designed protection criteria, Zone 1 covers 80% of the protected line; and Zone 2 covers the entire line plus 50%
of the subsequent line.
The designed scheme may lead to a redundant operation scenario due to violation of coordination rules.
Protection on a MV microgrid
A distance protection scheme is simulated on a MV microgrid using DIgSILENT PowerFactory software. Different
modes of the network are analyzed and tested. Wind turbines are used as source of DG.
Variations of fault currents seen by forward relays are much larger than backward relays.
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25. Schematic for Distance Protection
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80%
240%
120%

26. Multiagent Protection
A typical multiagent is a combination of hardware and software agents distributed in the
network which collectively work to achieve a desired global goal. In this case, the goal is the
protection of the power system.
Three layers: Equipment Layer, Substation Layer and System Layer.
The overcurrent relays are in the equipment layer. It is the lowest layer which also contains the
measurement (management), protector, performer, and mobile agent.
The substation layer communicates with the equipment layers and sends the information to the
system layer. The substation layer includes region, mobile, and management agents.
The system layer is the highest layer which monitors the entire network by communication with
substation layer.
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27. Multiagent Protection
Protection using Java Agent Development Framework
A fault diagnosis method for an active distribution system using the concept of multiagent
systems is suggested.
Java Agent Development Framework (JADE) has been utilized to implement the proposed
multiagent system.
The proposed method is verified using a modified 32 node active distribution system.
Only a single kind of DG is tested on this scheme.
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28. Schematic for Multiagent Protection
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29. 10/26/2017 A REVIEW OF PROTECTION SCHEMES FOR ACTIVE DISTRIBUTION SYSTEMS 29
Summary of Protection Schemes

30. Phasor Measurement Units (PMUs)
A phasor measurement unit (PMU) is a device which measures the electrical waveforms on the
grid using a common time source for synchronization.
Time synchronization allows synchronized real-time measurements of multiple remote
measurement points on the grid.
The receiver section receives the Global Positioning System (GPS) transmission which then
delivers a phase-locked sampling clock pulse to the analog to digital converter mechanism.
The sampled data is transformed to a complex number which characterizes the sampled
waveform phasor.
Phasors of the three phases are merged to give the positive sequence measurement.
Computation of the discrete Fourier transform (DFT) enables the signal (voltage or current) to
be measured.
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31. Schematic for PMU
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32. Phasor Measurement Units
PMUs are an excellent way of measuring real time magnitude and the phase angle of voltages
and currents at various points in the system.
Very effective when applied to real time control and protection applications.
The communication network needed to support this technology is expensive.
It is difficult to visualize and monitor huge amount of output data.
Algorithms are computationally heavy.
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33. Suggested Protection Scheme
A single scheme cannot accurately protect an active distribution system.
A hybrid scheme integrating traditional schemes (overcurrent, distance etc.) and modern
schemes (employing PMUs, IEDs and real time communication and control ) is a likely solution.
The choice of scheme will depend on the type of microgrid structure, type and control of DG
sources, cost and required reliability, selectivity, sensitivity, security and speed.
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34. Drone: Another Possibility
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35. SIMULATION WORK (performed on DIgSILENT PowerFactory)

36. IEEE 13 Bus Radial Distribution System
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37. IEEE 13 Bus Radial Distribution System
 Different types of DG sources (SG, IG, DFIG, PV) are connected at Bus 675, 634 and 632
 Short circuit analysis
 Protection schemes (overcurrent, distance) designed for IEEE-13 bus network (without and
with DG)
 Only three phase fault (LLL) is considered as it is typically the most severe
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38. Protection Schemes: IEEE 13-Bus Radial System (without DG)
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39. Coordination of OC Relays : IEEE 13-Bus Radial System (without DG)
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40. Comprehensive Protection: IEEE 13-Bus Radial System (without DG)
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41. Distance Protection: IEEE 13-Bus Radial System (without DG)
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42. Distance Relay Tripping Times
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LLL Fault @Bus 632 (within Protection zone) LLL fault @Bus 680 (outside protection zone)

43. Protection Schemes: IEEE 13 Bus Radial System (with DG)
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44. Weakly-Meshed IEEE 13 Bus System
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Tie Breaker

45. Radial vs. Meshed
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Therefore, based on minimum fault current contributions, it is recommended to install PV type DG at Buses 675 and
632 and IG at Bus 634 (for both radial and meshed system).

46. Conclusions
Protection of active distribution networks present many challenges.
Conventional overcurrent protection works correctly only for radial systems.
Protection coordination is affected due to bidirectional power flows in active distribution
systems.
It is important to take into account IEEE-1547 standards while designing the protection
schemes for active distribution networks.
The aim of the presentation was to comprehensively review the existing protection schemes
related to active distribution systems.
A lot of work has been done in this direction but there is still a lot more to be explored to
overcome the critical protection problems and improve the existing works.
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47. ANY QUESTIONS?
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THANK YOU FOR YOUR ATTENTION!