Energy and Power Engineering, 2013, 5, 927-931
doi:10.4236/epe.2013.54B177 Published Online July 2013 (http://www.scirp.org/journal/epe)
Multi-agent Based Protection on Highly Dominated
Distributed Energy Resources
Stephanus A. Ananda, Jyh-Cherng Gu
Department of Electrical Engineering, National Taiwan University of Science and Technology.
Received January, 2013
ABSTRACT
Highly penetration of Distributed Energy Resources (DER) on the grid systems nowadays makes the systems grow dy-
namically. The system become more complex and the protection system become more complicated. The protection re-
lay should accommodate the system changes according to the system conditions and topologies. As part of develop-
mental aspect of Distributed Artificial Intelligent, Multi Agent System (MAS) is a challenging method for improving
the intelligent properties of relay protection. This paper introduces the use of MAS approach on radial distribution sys-
tem protection dominated with DER using dispersed adaptive rule-based protection supported by distributed database
agent. The simulation results confirmed that the proposed algorithm can respond within 15.05 ms.
Keywords: Multi-Agent System; Power System Protection; Distributed Energy Resources
1. Introduction
As the economic growth, the electricity demands are in-
creased and the need of electrical power sources is grow-
ing. Along with the awareness of green energy and cost
minimization, the energy providers begin to look to new
strategy. They use small-scale power generator such as
micro turbine, wind turbines, photovoltaic, etc. and
placed them near to the load center along with end-user’s
“share power generator” to expand power sources capac-
ity and creates Distributed Energy Resources (DER) [1].
This DER has the advantage in maintaining system sta-
bility, increasing power quality and reliability of the sys-
tem, reducing the distribution cost, and provides supply
in islanding mode [2-4]. The renewable energy DER is
also considered can reduce the air pollutant emission [2].
With the DER connected in the system, it will create
subsystem called micro-grid.
Beside those all advantages, connecting DER on the
radial distribution system can affect the load flow in the
system and change the fault current direction and magni-
tude [5,6]. It will mitigate the sensitivity and selectivity
of existing relay and cause problems in protection system.
Protection coordination becomes more complicated.
Many papers investigated the impact of DER installation
on existing protection systems. Some of the problems
that were reported are false tripping, protection blinding
and unsynchronized in the automatic reclosing [5,7]. The
other problem is the DER that use power electronics (PE)
interfaces has current limiter that also limit the fault cur-
rents from the DER. Small micro turbine or combine heat
and power (CHP) also has limitation on fault current and
short period of time to achieve out of step condition [8].
This means relay protection must have different setting
for different grid condition. Oudalov [8] proposed adap-
tive relay protection scheme based on the SCADA sys-
tem to overcome this problem, meanwhile A.R.Haron, A.
Mohamed, and H.Shareef [3] proposed resetting over
current relay protection or using microprocessor relay
with artificial intelligent approach. Edward Coster, Jo-
hanna Myrzik and Wil Kling [5] proposed more modern
approach using Multi-Agent System (MAS) to get opti-
mal protection on micro-grid.
2. Multi Agent System Technology
2.1. Multi Agent System Technology
A summarizing from Stephen D.J.’s literature study
[9-11], Agent and Multi Agent concepts are originated
from computer science society. Many definitions about
agent can be found; it can clearly show the difficulty to
get satisfied definition about the agency. But among
many different definitions, they share the same basic
concepts those are the notion of agent, environment and
autonomy properties. According to Wooldridge, an agent
is: a software (or hardware) entity that situated in some
environment and is able to autonomously react to a
change in that environment. Environment is defined as
everything outside the agent and at least some part of the
environment can be observable and also can be alterable
by agent. Observable means agent can take the informa-

S. A. ANANDA, J.-C. GU
928
tion either physically from a sensor or by program invo-
cation in the computing environment [9]. Alterable
means the agent can change the environment either
physically by tripping the circuit breaker (CB) or storing
information in database. Wooldridge extend the defini-
tion to the agents become with intelligent agent by add-
ing flexible autonomy to the definition. Flexible auton-
omy means that the agent has three characteristics i.e. 1)
Reactivity, the agent ability to react due to the environ-
ment changing; 2) Pro-activeness, the agent ability to
take initiatives; 3) Social Ability, the agent ability to
communicate to other agents.
2.2. Multi Agent
Multi agent is a system composed by two or more agents
or intelligent agents communicates each other and work
synergistically to achieve the system goal, while also at
the same time each agent will try attaining the local goal
[9]. As part of Distributed Artificial Intelligent (DAI)
system, MAS is very attractive to use in distributed pow-
er system [12].
3. Multi-Agent Based Protection
3.1. Multi-Agent System Architecture
Unlike SCADA protection system that based on the cen-
tralized operation architecture, MAS has decentralized
architecture and creates distributed relay system structure.
Each agent will act as intelligent node that in collaborate
with other agents via communication infrastructure in
order to solve the problem in the power system protec-
tion. The agent itself can be a sensing unit, a protection
device, a processing unit or database unit [13].
Many different MAS structures, architectures and
agents configuration were proposed [12,14-20], but most
of them have similarity in hierarchical classification.
Generally they divide the structures into 3 layers. First
layer is the equipment layer that functions to get the data
from and send command to the power system (I/O func-
tion). The second layer is substation / coordination layer
that functions to coordinate and compute the process data
from the first layer. The third layer is system layer that
functions to collect and evaluate data.
3.2. Multi-Agent System in Protection Systems
In the multi agent-based protection systems, the closest
layer to the real equipment in the power systems is the
equipment layer. Equipment layer is the layer that usu-
ally composes by measurement agent like CT and PT
agent, performer agent like CB agent and protector agent
like bus agent, line agent, etc. The information gathered
by the measurement agents will be send to protector
agent. Protector agent will calculate the fault current and
then send the information to substation (coordination)
layer. Management agent in substation layer will receive
data from equipment layer and determine the fault type
and the fault location. Then management agent will iden-
tify the problem and finding the type of the solution (or
relay setting) should be used. Based on the solution
chosen, the management agent will send a command to
CB agent as a performer agent in the equipment layer
whether to open or close the CB contact. At the same
time management agent will send to the evaluation agent
in the system layer to be evaluated and back up. The
evaluation result will be reported to the user for system
improvement. Sometimes the evaluation agent can also
contribute to improve the problem solution in manage-
ment agent in the substation (coordination) layer.
The other agents also needed are database agent and
communication agent. Database agent usually concen-
trated in the second layer. Meanwhile, the communica-
tion agent should be merging to individual agent to en-
able every agent to communicate each other’s.
4. Proposed System
In the highly dominated DER, especially CHP type, the
generators have small inertia, so they easily out of step
when the short circuit occurs in the systems. The protec-
tion should response quickly to anticipate this problem.
To solve this problem, this paper proposes dispersed
adaptive rule-based protection supported with distributed
database agent. The proposed method is based on Ou-
dalov et al.’s centralized adaptive protection algorithm [8]
and P. C. Maiola [20]. The algorithm will be imple-
mented in the protection agent inside the equipment layer
supported by local database agent instead of concentrat-
ing it on single management agent.
4.1. Proposed Architecture
The proposed architecture of MAS based protection can
be seen in the Figure 1. In the equipment layer, IED
agents are used as combined function of CT agent, PT
agent, CB agent extend with local database agent and
local knowledgebase agent that formed by local coordi-
nation agent and local configurator agent that acted as
distributed database and distributed knowledgebase. Be-
cause this agent is used as Intelligent Electronic Device
(IED) so it named as IED agent and the structure can be
seen in Figure 2. The agents inside IED Agent are
named as unit for clarity.
Substation layer are consist of coordination agent and
configurator agent. Coordination agent is responsible for
identifying fault type and fault location according the
information received from IED Agents. Configurator
agent is an expert system that decides which solution or
relay setting should choose to overcome the problem and

S. A. ANANDA, J.-C. GU 929
also provide the back-up system protection scenario. The
Configurator agent will support by database agent to
store the data i.e. list of rules of the solution, grid topolo-
gies, etc.
System layer is consist of evaluation agent, that will
evaluate every condition occurs in the system. The agent
will calculate the system’s condition offline and evaluate
if the protection system already running properly and
efficiently.
Database Agent is agent that stores all the information
calculated by the other agent such as relay settings, con-
figuration / topology changing and also faults history. DF
(Directory Facilitator) Agent is agent that has a special
function to register the services. AMS (Agent Manage-
ment Server) is agent that has a special function to regis-
ter the all agents used in the MAS. Every agent will
communicate each other using TCP/IP protocol.
In the real system IED Agent (A01-A12) are installed
at the position of the CB (see Figure 3). Every IED
Agent will connect to other agents via TCP/IP commu-
nication protocol.
Figure 1. Block diagram of proposed MAS protection ar-
chitecture.
Figure 2. Block diagram of IED agent architecture.
Figure 3. Distribution feeder with DER and MAS protec-
tion.
4.2. Proposed Algorithm
In the beginning, all agents need to register their name
and function to AMS agent and DF agent respectively.
Every IED Agent should check and list the neighbor IED
Agents which are connected to them. This will perform
subsection topology.
After agent initialization finished, IED Agents will
start to measure and monitor the system current and vol-
tage every certain time via measurement unit (CT/PT)
and send to Protector Unit (see Figure 2). The Protector
Unit will calculate and determine the fault current and
maximum load current when a changing situation like
fault happens in the network. If faults occur Protector
Unit will send the information to the Local Coordination
Unit.
After receiving information from Protector Unit, Local
Coordination Unit will first check the network grid con-
dition is in islanding situation or grid connected by
checking the status of the agent at main breaker. Next
step, Local Coordination Unit will request information
from neighboring IED Agent. From all data gathered
Local Coordination Unit will determine and calculating
the fault type. All information will send to Local Con-
figuration Unit to get the “Relay Setting Configuration”.
After determined the relay setting, the Local Configura-
tion Unit will send the information to Local Coordination
Unit what condition should be achieved. The Local Co-
ordination Unit will send Trip Signal to CB through Per-
former Agent. The Local Coordination Unit will send the
report information to Coordination Agent of Substation
Layer.
In the Substation Layer, Coordination Agent will
gather data from every IED Agent in the whole system.
Coordination agent will check whether the fault is
cleared by IED Agent or not. If it is cleared, the Coordi-
nation Agent will capture the new topology and send all
information to Evaluation Agent in the System Layer for
evaluation.

S. A. ANANDA, J.-C. GU
930
If the fault condition still occur, the Coordination
Agent will calculate the fault location and send the in-
formation to Configuration Agent to get the “Relay Con-
figuration” list, that is the list of which relay will operate
and which relay will block according the situation. After
received the list, the Coordination Relay will send the
information to all IED Agents what condition should be
achieved and wait the confirmation from IED Agent if it
is done. If one or several Relay Agents failed to respond,
the Coordination Agent will send the request for back-up
planning list to the Configurator Agent and the new list
of “Relay Configuration” will be issued to Coordination
Agent. The “Relay Configuration” list is saved in the
Database Agent. The whole information will be send to
Evaluation Agent in the System Layer to evaluate. In the
Evaluation Agent all information will be evaluated and
reported to the operator. The proposed algorithm can be
seen in the flowchart in Figure 4.
Figure 4. Flowchart of the proposed algorithm.
5. Simulation and Results
5.1. Test System
The proposed algorithm is simulated on the test system
using Matlab-Simulink based on Figure 3. with three-
phase to ground fault occurred on F1 and F2. After ini-
tialization every agent will register the neighbor-agents
to create protection zones (Table 1). If the fault current
occurs, several agents will sense the fault current, first
the agent will check the islanding status, and then the
agent will compare the fault current to neighbor-agents
and determine which relay setting should be chosen from
the local database and trip the CB.
5.2. Simulation Results
The simulation result can be seen in Table 2. For the
fault at F1, agent A02 and A06 will sense the same fault
current so the agent will trip the CB at A02 and A06 to
isolate the faulted line. When the fault at F2, Agent A06,
A09-A12 sense the fault current and trip the correspond-
ing CB.
6. Conclusions
The presence of DER in the distribution system will give
many advantages to users and providers. In other hand
DER penetration in the radial distribution system will
change the power flow in the system and make the pro-
tection coordination become complicated. The possibility
of islanding operation is show that the relay setting
should be changed dynamically based on grid topology.
The small generator used in DER has limited fault
current and small inertia. This makes easily to get “out of
step” that means the protection should react fast. MAS’
concepts are used to distribute the adaptive algorithm in
equipment agents and reduce the operation time of the
whole protection system.
Table 1. Neighbor-agents for some agents.
Agent A02A06 A09 A10 A11 A12
A03A05 A10 A09 A09 A09
A04--- A11 A11 A10 A10
Neighbor-
Agents
A06--- A12 A12 A12 A11
Table 2. Simulation results.
Agents / CB Trip Time (milliseconds)
Fault
A02 A06 A09 A10 A11 A12
F1 3.75 32.5 NT NT NT NT
F2 NT 4.55 9.45 15.05 15 15
a. Other CB Agents are not trip.; b. NT means Not Trip.

S. A. ANANDA, J.-C. GU
931
The Simulation results show that the algorithm can
works selective and fast. The trip time is between 3.75 to
15.05 milliseconds.
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