Protection Technique for Complex Distribution Smart Grid Using Wireless Token Ring Protocol

1106 IEEE TRANSACTIONS ON SMART GRID, VOL. 3, NO. 3, SEPTEMBER 2012
Protection Technique for Complex Distribution Smart
Grid Using Wireless Token Ring Protocol
M. M. Eissa, Senior Member, IEEE
Abstract—Distributed generation is expected to increase sharply
as more and more renewable are integrated to power system with
the realization of smart grid, consequently complex distribution
smart grid is given. The traditional protection devices cannot
be able to protect complex power system configuration due to
many fault current loops will feed the fault point. Relays based on
standalone decisions cannot provide reliable and correct action
when used on a complex distribution system. This paper pro-
poses new protection philosophy using wireless technology. Data
sharing among relays to obtain reliable and accurate decision are
introduced. Wireless Token Ring Protocol (WTRP) as a wireless
local area network (LAN) protocol inspired by the IEEE 802.4
Token Bus Protocol is used for data sharing. WTRP is selected
to improve efficiency by reducing the number of retransmissions
due to collisions. WTRP architecture and protocol are described
to verify operation. MATLAB simulation program is used to
simulate the data exchange protocol between relays in a ring for
a specified amount of time.
Index Terms—IEEE802.4, smart grid, wireless communication,
wireless token ring protocol.
I. INTRODUCTION
THE GROWING environmental concern and various ben-
efits of high distributed generation (DG) have resulted
in significant increasing of DG in many distribution systems
worldwide.
The electrical grid is an aggregate of multiple networks and
multiple power generation suppliers with multiple operators
employing varying levels of communication. Smart grids in-
crease the automation and connectivity between the suppliers,
consumers, and networks that perform either long distance
transmission or local distribution tasks. A smart grid is a term
that covers modernization of both the transmission and dis-
tribution grids [1]. Smart grid technologies will enable power
systems to operate with larger amounts of renewable energy
resources that can solve many problems such as limitations in
the traditional infrastructure.
Utilities are also investing in intelligent smart grid distribu-
tion management systems (DMS) for their control centers. DMS
provides intelligent alarm processing and load management ap-
plications that better enable the safe operation of grids with high
Manuscript received February 14, 2011; revised June 24, 2011; August 25,
2011, November 17, 2011, February 01, 2012; accepted June 04, 2012. Date of
publication June 18, 2012; date of current version August 20, 2012. Paper no.
TSG-00041-2011.
The author is with the Electrical Power Engineering Department, Faculty
of Engineering, University of Helwan, Cairo 11421, Egypt (e-mail: mm-
meissa@yahoo.com).
Color versions of one or more of the figures in this paper are available online
at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/TSG.2012.2203833
Fig. 1. The electricity complex distributors in smart grid.
quantity of DG resources. DMS also help optimize a hetero-
geneous mix of connected DG resources, such as wind, solar,
bio-mass, fuel cell, etc. As more renewable DG resources are
installed, the interaction and combination of the individual gen-
eration sources may aggravate the impact.
Nowadays protection schemes used in distribution networks
have a significant lack of distributed resources and intelligent
networking capabilities [2]. These schemes for distribution
network protection use local information of voltage and current
signals, limited communication, and standalone decision to
make decisions. Some new protection schemes proposed for
smart grid based on voltage and current signals for nontapped
transformers in [3]–[7]. However, with a high connection of
distributed generation in low voltage busbars such as given in
Fig. 1 the system becomes complex and none of these protec-
tion schemes are able to be used. Many loops of fault current
will contribute the fault point and therefore, a malfunction of
those schemes is expected to happen.
The use of embedded generation and the need for higher net-
work reliability requires new protection scheme, which can cope
with bidirectional power flows and provide a more intelligent al-
location of fault on the network during normal and faulted oper-
ation. Fig. 1 shows a complex power system configuration with
different types of generators and tapped points. Robust power
system protection with reliable wireless communication is vital
for smart grid success and sustainability that:
• maintains high reliability standards while decreasing oper-
ating and maintenance costs;
• facilitates the use of new technologies along with existing,
older equipment.
1949-3053/$31.00 © 2012 IEEE

EISSA: PROTECTION TECHNIQUE FOR COMPLEX DISTRIBUTION SMART GRID USING WIRELESS TOKEN RING PROTOCOL 1107
Developing enhanced power system protection strategies must
become a priority. This will improve risk management, expe-
dite advanced technology applications, safeguard capital invest-
ments, and maximize overall smart grid potential. The conven-
tional protection schemes using communication channel have
drawbacks, such as malfunction due to line disconnection and
limited line length. The wireless networks are now becoming
by far the most popular choice for new network algorithm. The
wireless communication network allows the exchange of infor-
mation among the protection relays. The exchange of informa-
tion among the relays can assist the protective relays to make
the correct decision [8].
The paper introduces a new WTRP application for protecting
complex distribution system. WTRP architecture and protocol
are discussed. A MATLAB simulation program is used to sim-
ulate the data exchange protocol between two relays in a ring
during a specified amount of time. The paper shows the connec-
tivity management tables for many relays in different rings due
to events of fault conditions. One of the main features of using
the WTRP, the protection scheme does need to be updated due
to penetrate any kind of renewable resources at the buses.
II. COMPLEX GRID AND PRESENT PROTECTION SCHEMES
The pilot with a communication channel between terminals
by directional comparison systems have been widely used in
transmission lines protection for detecting and isolating faulted
sections. However, the operation of these algorithms is based on
difference between the measured currents at both ends of a trans-
mission line, which imposes a high demand on the communica-
tion channels bandwidth with high speed and reliability. The
key advantages over distance relays include better sensitivity
for high resistance faults, 100% line protection, and better per-
formance in the single-pole-tripping mode, particularly during
cross-country faults.
Fig. 2(a) presents part of distribution configuration system
with two parallel lines and several transformers tapped. The low
voltage busbars may be interconnected although in most appli-
cations, the tap feeds a radial load. Note that if the LV busbars
are networked with many DGs, some means of isolating a fault
on the LV side must be provided so as to prevent back feed for
a fault on the differentially protected line. It is assumed that the
current differential protection system monitors the currents only
in the main substations. Currents at the taps, either transformers
or lines, are not available to the relays [17], [18].
The line differential system is not sensitive enough to pro-
vide sufficient protection for the transformer; a direct transfer
trip must be actually sent by the transformer protection to the
relays in the main substations. For this reason, a reliable com-
munication is required from the tap to the main substations. An-
other problem caused by the removal of the zero-sequence cur-
rent is a differential error signal created in the healthy phases.
As a consequence, the healthy phases will overtrip on internal
faults. This is a straightforward consequence of the fact that the
relay, although phase segregated, responds to the negative- and
positive-sequence currents only and as such is not capable of
proper fault type identification based on the current differential
element. The pickup setting would have to take care of the dif-
ferential error currents. If the considered line is a parallel line
Fig. 2. The conventional protection scheme and the new proposed arrangement
of WTRP.
Fig. 3. The Carrier-sense multiple access protocol with collision avoidance
(CSMA/CS) and random time delay.
or has more than one tap and there are interconnections between
the low voltage sides of the transformers, then detailed short cir-
cuit studies are required to set the distance supervising functions
[17]–[19]. Conventional protection schemes used for protecting
complex distributed system, as one given in Fig. 3(a) cannot
properly work. Also, it will be very difficult to be coordinated.
The definition of protection reliability includes communi-
cation channels as part of the protection system. Therefore,
communication channels are considered to include all commu-
nications equipment required to deliver information from an
initiating relay at one location to a receiving relay at another
location. End-to-end delay is the total time delay from the
output of the initiating relay to the input of the receiving relay.

This delay includes any data buffering associated with digital
multiplex. For example, an End-to-End delay of one cycle
(16.67 ms) would be the sum of all the equipment and propaga-
tion delays existing between the two relays [20]. The maximum
end-to-end delay for any protection scheme is dependent on the
power system stability requirements.
Nowadays, there are many advanced communication tech-
niques that can be used to improve protection, control, speed
outage restoration, operation analysis, maintenance, and plan-
ning. These communication facilities also allow engineers to
exchange operation, test, and maintenance information with the
neighboring utilities, and access real-time and historical relay
information [8], [21], [22]. The wireless networks are now be-
coming by far the most popular choice for new network al-
gorithm [23]. The wireless communication network allows the
exchange of information among the protection relays. The ex-
change of information among the relays assists the protective
relays to make the correct decision. Fig. 2(b) shows the new
proposed WTRP arrangement using wireless communication
among relays.
III. WTRP ARRANGEMENT ON COMPLEX
DISTRIBUTION SYSTEM
Fig. 2(b) shows the deployment of relays on complex distri-
bution smart grid. Three rings are arranged to cover the power
system protection. Each ring will cover some numbers of re-
lays. Three rings are allowed to share information. WTRP is ro-
bust against single node failures, and recovers gracefully from
multiple simultaneous faults. One major challenge that WTRP
overcomes is that of partial connectivity. WTRP places man-
agement, special tokens, and additional fields in the tokens, and
adds new timers [12], [14], [15].
As explained above, the complex distribution system needs to
robust communication around the relays and protection schemes
that satisfy high sensitivity and coordination. Fig. 3(b) shows
the studied power system with many tapped transformers. Re-
lays 1 and 2 are used to protect line-1. Relays 3 and 4 are lo-
cated to protect line-2. The other relays (5, 6, 7, 8, 9, 10, 11–16)
are deployed to protect the tapped transformers. Each relay de-
ployed on the power system can use the directionality function
for one of the schemes described in [24]–[27]. The main relays
1 and 2 are communicating through WTRP-1 (Wireless Token
Ring Protocol for ring-1). Relays 3 and 4 are communicating
through WTRP-2 (Wireless Token Ring Protocol for ring-2).
The other relays deployed on the tapped points are commu-
nicating through WTRP-3 (Wireless Token Ring Protocol for
ring-3). The main features of using WTRP are obtaining ro-
bustness against single node failure and the support for flexible
topologies, in which relays can be partially connected and are
not connected to a master and have less number of retransmis-
sion due to collisions [28], [29].
Wireless Token Ring Protocol (WTRP) is a wireless LAN
protocol inspired by the IEEE 802.4 Token Bus Protocol [9].
The protocol guarantees bounded delay and a share of band-
width to all stations in the network. An earlier version of this
token ring protocol has been implemented by [10], [11] and
used for the automated highway project. The paper introduces
first time application for protecting complex smart grid using
the WTRP technology.
As in the IEEE 802.4 [11] standards, WTRP is designed to
recover from multiple simultaneous failures. One of the biggest
challenges that the WTRP overcomes is partial connectivity.
To overcome the problem of partial connectivity, management,
special tokens, additional fields in the tokens, and new timers
are added to the protocol. When a node joins a ring, it is re-
quired that the joining node be connected to the prospective pre-
decessor and the successor. The joining node obtains this infor-
mation by looking up its connectivity table. When a node leaves
a ring, the predecessor of the leaving node finds the next avail-
able node to close the ring by looking up its connectivity table.
WTRP is efficient in the sense that it reduces the number of re-
transmissions due to collisions. It is a distributed protocol that
supports many topologies since not all stations need to be con-
nected to each other or to a central station. WTRP is inspired by
the IEEE 802.4 token bus protocol, which in turn was motivated
by applications in factory automation [12]–[16]. The paper ad-
dresses the WTRP to be applied in the protection system.
Fig. 3 shows the carrier-sense multiple access protocol with
collision avoidance (CSMA/CA). Carrier sense multiple access
with collision avoidance (CSMA/CA) is a wireless network
multiple access method in which; a carrier sensing scheme
is used, a node wishing to transmit data has to first listen to
the channel for a predetermined amount of time to determine
whether or not another node is transmitting on the channel
within the wireless range. If the channel is sensed “idle,” then
the node is permitted to begin the transmission process. If the
channel is sensed as “busy,” the node defers its transmission for
a random period of time. Once the transmission process begins,
it is still possible for the actual transmission of application data
to not occur. As shown in the figure that before attempting a
transmission an adapter waits a random time, and this is one of
the main disadvantages of using Wi-Fi protocol.
Token Ring is a data-link layer protocol and fundamentally
different than Wi-Fi. Token Ring networks use a logical ring
topology. Token Ring’s MAC mechanism is called token
passing, and it is the reason for using of the ring topology. A
special packet called a token circulates around the ring until
a relay has data to transmit. This relay takes possession of
the token and proceeds to transmit its data. Only the relay
possessing the token can transmit data, making it impossible
for collisions to occur on a network that is functioning prop-
erly. After the data circulates around the ring, the transmitting
system is responsible for removing it from the network and
generating a new token.
Many studies are performed to compare WTRP stability and
saturation throughput with IEEE 802.11. Results show that
WTRP recovers quickly from failures, has higher throughput
because of lower collision probability, and allocates bandwidth
equally among stations. The consistency of the token rotation
time, regardless of the number of simultaneous transmissions,
leads to predictable medium access latency. These features
make WTRP attractive for real time applications. WTRP im-
proves efficiency by reducing the number of retransmissions
due to collisions, and all relays use the channel for the same
amount of time. Stations take turns transmitting and give up

the right to transmit after a specified amount of time. Medium
Access Control (MAC) enables multiple nodes to transmit on
the same medium. The main function of MAC is to control
the timing of the transmissions to increase the chances of
successful transmission. The MAC layer manages the ring and
the timing of the transmissions [12].
IV. TOKEN RINGS ARCHITECTURE
A. Overall System Architecture
The main components of the WTRP architecture are Medium
Access Control (MAC), Channel Allocator, Mobility Manager,
Admission Control Policer, and Management Information Base
(MIB). The protocol uses the ring topology where repeaters are
connected via a transmission medium to form a closed path.
Data are transmitted serially bit by bit through the transmission
media. Data are transmitted in packets [12], [13]. Medium Ac-
cess Control (MAC) enables multiple nodes to transmit on the
same medium. The function of MAC is to control the timing
of the transmissions to increase the chances of successful trans-
mission. The ring management involves the following:
• Each ring has unique ring address.
• A station can transmit data when it holds free token.
• A free token turns into a busy token followed by a packet
that will be transmitted.
• Managing the joining and the leaving operations.
The channel allocator chooses the channel on which the relay
should transmit data. If a large number of token rings exist in
proximity, their efficiency can be increased by achieving spa-
tial reuse through sensible channel allocation. The idea of spa-
tial reuse is one of the core ideas of the wireless cellular com-
munity [12], [13]. The Admission Control Manager controls
the number of stations that can transmit on the medium. Links
in the token ring are unidirectional. Each node has a down-
stream neighbor and an upstream neighbor. Topology resem-
bles point-to-point links forming a ring, but access to ring is
shared via tokens. A token is a special flag that circulates around
the ring. Each node receives token, then transmits it to its down-
stream neighbor. Every node eventually can transmit data when
it receives token. Suppose token was passed from source to des-
tination rather than around the ring as in token ring, some hosts
could be passed over indefinitely. When a node has a frame to
send, it takes token, and transmits frame downstream. Each node
receives a frame and forwards it downstream. Destination host
saves copy of frame, but keeps forwarding frame. Forwarding
stops when frame reaches original source. The Mobility Man-
ager decides when a relay can join or leave the ring. When a
mobile node is drifting away from a ring and into the vicinity of
another ring, at some threshold the Mobility Manager decides
to move to the next ring.
The object tree groups logically related objects together under
a subtree. Such a subtree is called a Management Information
Base (MIB). An example of a MIB is the Internet TCP/IP MIB.
The Management Information Base keeps the information that
each management module needs to manage the MAC module.
The system group contains general information about the net-
work node. The rest of the groups contain information about
the particular protocol to which they refer.
Fig. 4. Timing diagram of the WTRP and Token Frame.
B. Wireless Token Ring Protocol
Fig. 4(a) shows the protocol. The figure shows a number of
relays in the ring. is the time during which relay (
to ) transmits data when it gets the token, and before it releases
the token. is ranged from 0 to Token Holding Time .
A relay first sends its data during and if there is enough time
left, the relay decides to send invitation to other nodes outside
a token frame contains information for ring management with a
token time . Fig. 4(a) shows the “ ” that refers to the
signal propagation time.
Fig. 4(b) shows the token frame. Frame Control (FC) iden-
tifies the type of packet, such as Token, Solicit Successor, Set
Predecessor, etc. As shown in Fig. 4(b), the Source Address (SA)
is defined as the relay where the packet originates, Destination
Address (DA) determines the destination relay and Ring Address
(RA) is the ring to which the token belongs. Sequence number
(Seq) is initialized to zero and incremented by every relay when
it passes the token. Generation Sequence number (GenSeq) is
initialized to zero and incremented at every rotation of the token
by the creator of the token. Number of Nodes (NoN) in the token
frame is calculated by taking the difference of sequence num-
bers in one rotation. For wireless Token Ring Protocol (WTRP):
• It is a media access protocol, can be implemented over
802.11 protocol, and so the channel rate is the same as
Wi-Fi.
• Propagation delay as above.
• Time slot of this protocol is taken equal to token length.
• The expected value of data payload is from 0 to 2312 bytes.
The data frame is given as:
The first byte uses field and has a code as indicated to
identify that the token hold data information. The key for this
code is:

As shown, the data payload in the frame is undetermined its
length, due to the nature of transmission, because the user can
transmit any data during the Token Holding Time .
V. CONNECTIVITY TABLE OF RELAYS
Fig. 5(a) shows a part of power system with many relays lo-
cated to protect it. All relays are installed and shared informa-
tion in the ring. Assume that for a certain event of fault the
relays and operate and leave the ring. The required
is to explain how relays leave the ring and how the connec-
tivity table is established. The Connectivity Manager resident
on each node tracks transmissions from its own ring and those
from other nearby rings. By monitoring the sequence number of
the transmitted tokens, the Connectivity Manager builds an or-
dered list of relays in its own ring. The Connectivity Table of the
manager holds information about its ring. Two relays and
operate but they are still in the ring. Relay monitors the
successive token transmission from to before the token
comes back to . At time , transmits the token with se-
quence number , at time , transmits the token with the se-
quence number , and so on. will not hear the transmission
from and , but when it hears transmission from ,
will notice that the sequence number has been increased by
3 instead of 1. This indicates to that there were two relays
that it could not hear between and . The ring owner is
the relay that has the same MAC address as the ring address.
A station can claim to be the ring owner by changing the ring
address of the token that is being passed around.
Leaving the ring can be done with or without notification.
Suppose Relay wants to leave the ring as shown in Fig. 5(b).
It means that there is a fault and relay wants to trip and leave
the ring. first waits for the right to transmit data. Upon re-
ceipt of the right to transmit, sends the set successor packet
to its predecessor with the MAC address of its successor,
. If can hear , tries to connect with by
sending a set predecessor token. If cannot hear ,
will find the next connected node, in the transmission order, and
send it the set predecessor token. If fails, then station
recognizes the failure when it does not get the implicit acknowl-
edgement and tries to close the ring.
VI. DATA EXCHANGE PROTOCOL SIMULATION
USING MATLAB PROGRAM
The relays in power system are connected together in a ring.
When the first token ring relay comes online, the network gen-
erates a token. The token is a predetermined formation of bits
Fig. 5. The relay actions in a ring and the connectivity table.
(a stream of data) that permits a relay to put data. The token
travels around the ring polling each relay until one of the re-
lays signals that it wants to transmit data and takes control of
the token. A relay cannot transmit data unless it has possession
of the token; while the token is in use by a relay, no other relay
can transmit data. After the relay captures the token, it sends
a data frame, see Fig. 4(b) out on the network. The frame pro-
ceeds around the ring until it reaches the relay with the address
that matches the destination address in the frame. The destina-
tion relay copies the frame into its receive buffer and marks the
frame in the frame status field to indicate that the information
was received. The frame continues around the ring until it ar-
rives at the sending relay, where the transmission is acknowl-
edged as successful. The sending computer then removes the
frame from the ring and transmits a new token back on the ring.
Fig. 6 shows the connectivity table of one of the relays inside
the ring. The Connectivity manager resident on each node tracks
transmissions from its own ring and those from other nearby
rings. In Fig. 6, relay 5 monitors the successive token transmis-
sion from 6 to 7 before the token comes back to 5. At time 0, 5
transmits the token with sequence number 0, at time 1, 6 trans-
mits the token with the sequence number 1, and so on. By mon-
itoring the sequence number of the transmitted tokens, the con-
nectivity manager builds an ordered local list of stations in its
own ring and an unordered global list of stations outside its ring
(see Fig. 6). My Table is defined as the relays (R5 to R16) in the
ring. Other Table is defined as the relays (R1 and R2) outside
this ring.
Fig. 7 shows the studied power system with three different
rings that protect it. Ring-1 protects the section that includes
Relay-1 and Relay-2. Ring-2 protects the section that includes
Relay-3 and Relay-4. Ring-3 shows the relays from 5 to 16.
Three rings are available to talk together and with themselves as
well. The token ring technology is used in order to prevent the
collision of data between two relays that want to send messages
at the same time. This section explains the feature.
Ring owner is the relay with the same MAC as ring address.
A relay can claim to be the ring owner by changing the ring

Fig. 6. The connectivity Table of one of the relays inside a ring.
Fig. 7. Three multiple rings of the relay connectivity for each ring that protect
the power system.
address of the token that is passed around. In Fig. 7, the ring
address of each of three rings is the address of one of its relays.
The uniqueness of the MAC address allows the relays to distin-
guish between messages coming from different rings. The relay
is called the owner of the ring. In the example, the owner of ring
3 is relay 5. Because we assume that the MAC address of each
station is unique and the ring address is also unique.
The uniqueness of the address is important, since it allows
the relays to distinguish between messages coming from dif-
ferent rings. To ensure that the ring owner is present in the ring,
when the ring owner leaves the ring, the successor of the owner
claims the ring address and becomes the ring owner. The pro-
tocol deals with the case where the ring owner leaves the ring
without notifying the rest of the relays in the ring as follows.
The ring owner updates the generation sequence number of the
token every time it receives a valid token. If a relay receives
a token without its generation sequence number updated, it as-
sumes that the ring owner is unreachable and it elects itself to
be the ring owner. It is possible for a relay to belong to more
than one ring or to listen to more than one ring; this is called the
multiple ring management.
The successful token transmission relies on implicit ac-
knowledgement. An implicit acknowledgement is any packet
heard after token transmission that has the same ring address
as the relay. Another acceptable implicit acknowledgement is
any transmission from a successive node regardless of the ring
address in the transmission. A successive node is a relay that
was in the ring during the last token rotation. In other words,
successive relays are those present in the local connectivity
table. Each relay resets its timer (idle timer) whenever it re-
ceives an implicit acknowledgement. If the token is lost in the
ring, no implicit acknowledgement will be heard in the ring,
and the idle timer will expire. When the idle timer expires, the
relay generates a new token, thereby becoming the owner of
the ring.
Transmission proceeds in one direction along the ring. Each
relay has a unique successor and predecessor. The above ex-
planation can be summarized in the flowchart given in Fig. 8.
The figure shows the flowchart of the data exchange protocol
using MATLAB program. The data exchange simulation pro-
tocol of two relays in a ring is also shown in figure. The data
is shared in the ring among relays. Sometimes many rings are
suggested in the protection according to the protection zones.
The information can be shared among the rings for identifying
the fault zone and consequently the relays that should operate in
each ring. Refereeing to Fig. 8, assume many relays in the ring
and only two relays are talking inside the ring. When a node re-
ceives the data from the upper layer, it first checks whether the
next hop node is in the same ring or not based on the local ring
information.
Fig. 8 explains a token based data exchange protocol for ef-
ficient intraring data communications between two relays. The
maximum token holding time of each node is denoted by Max
Token Holding Time. When a node receives a token from its
predecessor, it first checks its intraring data buffer. If the buffer
is nonempty during the Max Token Holding Time, the token
holder node starts data transmissions, and passes the token to its
successor when Max Token Holding Time is reached. To ensure
token delivery, the token holder node will retransmit the token
if no acknowledgement (ACK) is received before the token re-
transmission timer is timeout.
If the maximum retry limit is reached, the token holder node
will report to the ring founder node that its current successor is
not reachable (the successor is in deep fading for a long time or
has left the ring due to mobility), and the ring founder node will

Fig. 8. Flowchart of the data exchange protocol using MATLAB program.
delete the successor from the ring and update the ring informa-
tion in the next coordination period. The token holder node then
attempts to connect to the next node since all nodes in the ring
have the ring topology information. After successfully passing
the token to the next node, the token holder node switches to
the ring member node status. If the intraring data buffer of the
token holder node is empty during Max Token Holding Time,
the token holder node will start a timer and keep checking the
buffer status. The token holder node will pass the token to its
successor if no data arrives before the timer expires. This is to
ensure the following nodes with intraring data packets can ac-
quire the token as soon as possible.
Unlike all other standard forms of LAN interconnects, Token
Ring maintains one or more common data frames that continu-
ously circulates through the network. These frames are shared
by all connected relays on the network as follows:
• A frame (packet) arrives at the next relay in the ring se-
quence that device checks whether the frame contains a
message addressed to it.
• If so, the relay removes the message from the frame. If not,
the frame is empty (called a token frame).
• The relay holding the frame decides whether to send a
message.
• If so, it inserts message data into the token frame and issues
it back onto the Ring.
Fig. 9. Studied configuration for two events of fault.
• If not, the relay releases the token frame for the next relay
in sequence to pick up.
These steps are repeated continuously for all relays in the
token ring. In this case, WTRP improves efficiency by reducing
the number of retransmissions due to collisions, and it is fair as
all relays use the channel for the same amount of time. Relays
take turns transmitting and give up the right to transmit after a
specified amount of time.
VII. POWER SYSTEM SIMULATION AND RELAY OPERATION
The studied configuration system shown in Fig. 9 is simu-
lated. The system includes 138 kV bus transmission system in-
terconnected with distribution system. Data for verifying the
proposed technique were generated by modeling the selected
system using the MATLAB. The directional relays are located
at each terminal of the two circuits and at tapped lines. At each
terminal the current signals with reference voltage are required
for calculating the directionality. A system frequency of 50 Hz
is used. Table I shows the parameters of the power system.
Fig. 9(a) shows the studied configuration system. A fault is
occurred at point F1 between relay-3 and relay-4. There are
many fault current loops will flow in the fault point. As shown
in Fig. 9(a), four loops of fault current are flowing (i.e., loop-1,
loop-2, loop-3, and loop-4). In this case the tapped transformers
will draw some load currents. The total load current appears to
the line conventional differential relay as an error signal. The

TABLE I
SYSTEM PARAMETERS
amount of load drawn from tapped connections is low as com-
pared with the power transferred between the main substations.
This provides the opportunity to restrain the differential relay by
the bias current. However, as the number of taps increases and
many renewable resources can penetrate the grid, the total load
current leaking from the differential zone may become quite
high; the conventional biased characteristic of the differential
relays does not help. However, the tapped currents are not in-
cluded into the current balance monitored by the differential re-
lays; faults on the low voltage side of the taped transformers
would create a differential signal and result in a malfunction.
On the other hand, if the low voltage busbars are networked
with any type of renewable resources, some means of isolating
a fault on the low voltage side must be provided so as to prevent
back feed for a fault on the differentially protected line.
As explained above such conventional protection techniques
cannot selectively detect these faults. There are many of prob-
abilities that tend to false operation. The proposed protection
technique based on token ring technology can select and identify
such faults properly. The above problem can be solved based on
shared data among relays.
Fig. 10(a) describes the overall relay operation. The case
given above is studied as a three phase internal fault occurred at
point F1. The scheme described in [25] is used to calculate the
directionality function for each relay. The MATLAB simulation
program is used to simulate the data exchange in a speciﬁed
amount of time for each relay in the ring. In this step, each
relay talks with other relays in the ring and the data are shared
around the rings. As explained above three zone of protec-
tion are talking. Rings WTRP-1, WTRP-2, and WTRP-3 are
formed. The table for each ring is constructed and labeled by
“Connectivity Table.” Each ring builds the relay connectivity.
The relay connectivity is realized with a combination of the
relays’ status with Forward (F) and Reverse (R) directions.
The three zone of protection can be classiﬁed as three rings
(Ring-2, Ring-3, and Ring-1). Ring-2 includes two relays (R3
and R4). Ring-2 builds the relay connectivity given in Table II.
Ring-3 includes a group of relays (R5 to R16). Ring-3 builds
the relay connectivity given in Table III. Ring-1 includes two
relays (R1 and R2). Ring-1 builds the relay connectivity given
in Table IV. Relays R8, R10, R15, and R13 are leaving Ring-3
to join Ring-2 with R3 and R4 and also relays R1 and R2 are
leaving Ring-1 to join Ring-2, see Table III. Table IV shows
Fig. 10. The relay operation and wireless reliability.
TABLE II
IEEE STANDARD FOR WIRELESS LAN MEDIUM ACCESS CONTROL (MAC)
AND PHYSICAL LAYER (PHY)

TABLE III
RING-2 CONNECTIVITY FOR A FAULT OCCURRED AT F1
TABLE IV
TABLE V
“My Table” that includes relays in the forward direction (R8,
R10, R15, and R13). Other relays (R1, R2, R3, and R4) are
identified to be in the forward directions which leave Ring-2
and Ring-1 to join Ring-3.
Table V shows Ring-1 connectivity and “My Table” that in-
cludes relays R1 and R2. Other relays R8, R10, R15, and R13
are joining Ring-1 and leaving Ring-3. Also, relays R3 and R4
are leaving Ring-2 to join Ring-1. From the connectivity tables
given from Table III, Table IV, and Table V, “My Tables” in-
cludes forward relays (R1, R2, R3, R4, R13, R15, R10, and R8).
On the other hand, relays with reverse direction and noted by
“R” will not join the ring and will be excluded. So, all relays
with forward decision will operate, but from point of view the
coordination program for the system reliability and stability the
relays R8, R10, R3, and R4 should trip their associated circuit
breakers and the other remaining relays send block signals.
Fig. 9(b) shows another case study for a three phase to ground
fault located at F2. There are many loops of fault current will
flow in the fault point. As shown in Fig. 9(b), four loops of fault
current are flowing (i.e., loop-1, loop-2, loop-3, and loop-4).
The conventional protection schemes cannot able to detect such
fault. There are many different relays can operate in same time
and the zone of protection cannot be selectively achieved. The
protection zone must cover the entire line including taps and a
portion of the high voltage windings of the transformers. It is to
be noted that the ability to protect a tapped power line without
measuring all the currents in the zone will cost the user in terms
of sensitivity and speed of performance. The proposed method
can avoid the differential error signals caused by the taps. The
proposed scheme does not depend on the differential principle
but on the data shared obtained from the relays status in the three
rings. The performance of the relays and the protocol scheme

TABLE VI
TABLE VII
TABLE VIII
are described in Fig. 10(a). In such a case, the proposed protec-
tion technique used for data sharing can selectively identify the
faulted zone.
Due to fault occurrence, the Relays R7, R9, R16, and R14 are
leaving Ring-3 to join Ring-2 with R3 and R4. Relays R1 and R2
are leaving Ring-1 to join Ring-2, see Table VI. In this case, “My
Table” includes relays R3 and R4 and “Other Table” includes
R14, R16, R9, R7, R1, and R2. Table VII shows “My Table”
that includes relays in the forward direction (R7, R9, R16, and
R14). Other relays are also in the forward direction (R1, R2,
R3, and R4) which leave Ring-2 and Ring-1 to join Ring-3. In
this case, “My Table” includes relays R7, R9, R16, and R14;
“Other Table” includes joining forward relays (R1, R2, R3, and
R4) from other rings.
Table VIII shows Ring-1 connectivity and “My Table” that
includes R1 and R2. Other relays R7, R9, R16, and R14 are
joining Ring-1 leaving Ring-3. Also, relays R3 and R4 are
leaving Ring-2 to join Ring-1. From the connectivity tables
given from the three tables (Tables VI, VII, and VIII), “My
Tables” should include relays R1, R2, R3, R4, R7, R9, R16,
and R14. On the other hand, relays with reverse direction and
noted by “R” will not join any ring and will be excluded. So,
all the relays with forward decision will operate, but from point
of view the coordination program for the system reliability
and stability relays R14, R16, R1, and R2 should trip their
associated circuit breakers and the other remaining relays send
block signals.

In regions where large blocks of power are being transferred
over double circuit EHV transmission lines, the occurrence of a
cross country fault, could initiate serious system stability prob-
lems, if the fault results in three phase trip of both lines. For
the power system depicted in Fig. 9(a) and (b), consider that a
simultaneous fault has occurred at F1 and F2. The fault was se-
lected as phase A to ground for line-1 and phase B to ground
for line-2. The operation would be a single phase trip on each of
the circuits, maintaining three phase ties between the two ends
of the lines, assuming that single pole tripping is used. Due to
fault occurrence, relays R1, R2, R3, R4, R10, R16, R13, and R8
are in forward direction and all the other relays are in reverse
directions. So, all relays with forward decision operate, but ac-
cording to the system reliability and stability relays R1, R2, R3,
and R4 should trip their associated circuit breakers and the other
remaining relays send block signals. Of course the coordination
program in selecting the priority of tripped relays is based on the
configuration system and should consider the system reliability
and stability.
VIII. QUANTITATIVE AND PRECISE ANALYSIS
As given above, the proposed technique is able to identify the
faulted relays and faulted zone using data sharing through their
own ring. The relays are also able to share information through
other rings. A list of faulted relays can be issued through “My
Tables.” For any type of fault on the complex grid the technique
is able to list the faulted relays. An accurate and proper decision
can be obtained through coordination schemes. From the above
discussion, the wireless communication can be affected by time
delay and reliability that can be discussed as follows:
1) Propagation delay or time delay effected only by the trans-
mission media, for wireless channel;
So the disturbance or retransmission does not effect on
it. Another time should be considered is the “Processing
Time.” It is the time that represents the time it takes for a
station to process a token. More precisely, it is the delay
between the end of reception of a token to beginning of
data or token transmission in reaction to the token recep-
tion. The time delay estimated for the max distance in the
studied configuration system is given by 100 s.
2) To better capture the reliability of wireless communica-
tion, we make use of reliability metric for wireless com-
munication: Packet Delivery Ratio. Packet Delivery Ratio
(PDR) is the probability of successfully receiving a packet
at the receiver after this packet is transmitted at the sender.
In practice, it is often calculated as a ratio of the number
of data packets received at the receiver to total number of
packets transmitted at the sender within some predefined
time window. As shown from the definition that the distur-
bance and retransmission of packets lead to reducing the
PDR and so reduce the reliability of system. A solution to
improve reliability of the proposed technology is given in
Fig. 10(b) and explained in the next section.
The following steps outline the algorithm with notations ,
which is the priority of the message to transmit. , which is
the priority of the token protocol; and , which is the receiver
reservation priority.
A relay waits for a free token with a less than or equal to
and then seizes it. If the free token has higher priority (i.e.,
), the relay can set the field to only if is
less than and is less than . A relay reserves the pri-
ority at a busy token by setting the to the field if the
is less than the . After seizing a token, the token indicator
bit is set to , the field is set to , is unchanged. When re-
leasing a free token, the field is set to the max ,
and the field is set to max . Each relay downgrades
the priority of a free token to a former level stored in a stack.
Reliability of wireless links can bring to errors. This tends to
high packet loss rate detrimental to transport-layer performance.
Mechanisms needed to reduce packet loss rate experienced by
upper layers. A solution to improve reliability can be achieved
as follows; when a Relay-B receives data packet from Relay-A,
Relay-B sends an Acknowledgement (ACK). If Relay-A fails to
receive an ACK, it retransmits the packet as given in Fig. 10(b).
The above technique is investigated and tested for 16 relays
located at different points on the smart grid. This number is de-
pendent on the token ring equipment that is used in the network.
Current standards list a maximum of 250 relays.
Calculating Latency: As shown in Fig. 4(a), after receiving
the token frame, relay is allowed to transmit packet up to a
and passes the token to its successor. Assume that there
are relays in a ring. Time that takes for one rotation of token is
bounded by Maximum Token Rotation Time where
the equality holds.
As a result, can be ranged from to token holding time
. A relay first sends its data during and if there is
enough time left, the relay decides to send invitation to other
nodes outside. A token frame contains information for ring man-
agement is given in (1).
(1)
where “ ” stands for prorogation time of a signal in the
medium and can be taken as 100 and .
There are 12 relays in Ring-3, 2 relays in Ring-1, and 2 other
relays in Ring-2. So, is calculated for the max number
of relays . The time delay estimated for the max
distance (30ML, the max distance between two relays) in the
studied configuration system is given by 100 . The other
values of the parameters used to obtain numerical results are
summarized in Table II. The system values are those specified
for IEEE Standard for Wireless LAN Medium Access Control
(MAC) and Physical Layer (PHY). is calculated as
. This means that every station gets chance
to transmit packet in a specific bounden time equal to 8296 .
is given by . So, (1) can be calcu-
lated as . This
means that all the relays can send their bits in a time not more
than 105.4 ms. This time is quiet superior for the protection
philosophy for sharing information among 12 relays compared
with the traditional distance relay that can take about this value
for one relay. However, traditional protection schemes with
communication channel are sharing status between two relays

in a time equal to 16.6 ms compared with 100 s in the applied
technology.
Calculating Throughput: Let be the normalized system
throughput which is the fraction of the time the channel is used
to transmit payload bits. is expressed as
(2)
where payload length and frame length. The value of S
can be calculated as follows; is given in Table , T
the time taken for one relay
. The frame length is
given by .
So, (2) can be calculated and result in 0.88. This means that
88% of the transmitted data is useful information. According to
Table II, if we use a network card with channel rate 1 Mbits/s,
the actual rate used in the transmission of information is al-
most 0.88 Mbits/s. In implementation experimentally WTRP
over LAN Card can be easily built.
IX. CONCLUSION
Wireless Token Ring Protocol (WTRP) is now widely applied
in the factory automation. The paper addressed WTRP to be
firstly applied for protection system. WTRP is a distributed pro-
tocol that supports many topologies since not all stations need to
be connected to each other or to a control station. WTRP is fair
in the sense that each relay takes a turn to transmit and is forced
to give up the right to transmit after transmitting for a specified
amount of time. To prove that WTRP suitable for real time appli-
cations, the performance of the data exchange protocol is simu-
lated using MATLAB program. The relay operation for fault de-
tection is also given through the management of the connectivity
tables for many cases of fault events. The WTRP arrangement
on a complex distribution system is also described. The results
showed that the new applied technology of WTRP can prop-
erly detect different events of faults for a complex distribution
smart grid. The clearing time of the relays can be estimated by
5 ms (time for calculating the directionality) plus time delay of
about taken for protocol action among three rings. This
time is based on a start timer given by the nodes to check the
buffer status, the Max Token Holding Time to receive ACK for
all relays and Token delivery among rings. Reliability of wire-
less communication, Latency and throughput are discussed in
the paper. The proposed wireless technology applied in the pro-
tection satisfies the communication requirements. The informa-
tion frame is circling the ring; no token is on the network, which
means that other stations wanting to transmit must wait. There-
fore, collisions cannot occur in Token Ring system. The infor-
mation frame circulates the ring until it reaches the intended
destination station, which copies the information for further pro-
cessing. The information frame continues to circle the ring and
is finally removed when it reaches the sending station. Token
ring is deterministic while it is possible to calculate the max-
imum time that will pass before any end station will be capable
of transmitting. These features and several reliability features
make Token Ring ideal for applications in which delay must be
predictable and robust network operation is important.
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