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\journal{ Electric Power Systems Research}

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\begin_body

\begin_layout BeginFrontmatter
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\begin_layout Title
Distance Protection Zone 3 Misoperation During System Wide Cascading Events:
 The Problem and a Survey of Solutions
\end_layout

\begin_layout Author
A.M.
\begin_inset space ~
\end_inset

Abdullah
\begin_inset Flex CorAuthormark
status open

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cor1
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\end_inset


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status open

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rvt
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\begin_layout Email
ahmad.abdullah@cu.edu.eg
\end_layout

\begin_layout Author
K.
\begin_inset space ~
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Butler-Purry
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status open

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focal
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\size normal
With 
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\size default

\backslash
fnref
\series default
\size normal
 and you refer to the author footnotes.
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\begin_layout Email
klbutler@tamu.edu
\end_layout

\begin_layout Corresponding author
Corresponding author
\begin_inset Argument 1
status open

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cor1
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\end_layout

\begin_layout Address
Department of Electrical Power and Machines, Cairo University, Gizah, Egypt,
 12613
\begin_inset Argument 1
status collapsed

\begin_layout Plain Layout
rvt
\end_layout

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\end_layout

\begin_layout Address
Department of Electrical and Computer Engineering, Texas A&M University,
 College Station, TX, 77843
\begin_inset Argument 1
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focal
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\end_layout

\begin_layout Abstract
Distance relay zone 3 misoperation has been responsible for major blackouts
 around the world.
 Zone 3 misoperation generally occurs under system wide cascading events
 such as the 2003 Northeastern US-Canada blackout or under stressed system
 conditions such as the 2015 Turkish blackout.
 This paper explains the problem of zone 3 distance protection misoperation.
 The paper then proceeds to survey the literature for possible solutions
 to increase distance relay security to prevent distance protection misoperation.
 Three categories of solutions were proposed in literature to address the
 problem of zone 3 distance protection misoperation.
 The first one is anticipation and prevention of misoperation in the planning
 stage.
 The second one is communication assisted protection schemes that use remote
 measurements to enhance relay security.
 The last one uses local data to enhance distance relay security.
 
\end_layout

\begin_layout Keywords
Distance protection zone 3 
\begin_inset ERT
status collapsed

\begin_layout Plain Layout


\backslash
sep
\end_layout

\end_inset

 blackouts 
\begin_inset ERT
status collapsed

\begin_layout Plain Layout


\backslash
sep
\end_layout

\end_inset

 cascading events 
\begin_inset ERT
status collapsed

\begin_layout Plain Layout


\backslash
sep
\end_layout

\end_inset

 misoperation 
\begin_inset ERT
status collapsed

\begin_layout Plain Layout


\backslash
sep
\end_layout

\end_inset

 security 
\end_layout

\begin_layout EndFrontmatter

\end_layout

\begin_layout Section
Introduction
\begin_inset CommandInset label
LatexCommand label
name "sec:Introduction"

\end_inset


\end_layout

\begin_layout Standard
With the deregulated market structure in the United States and Europe, grid
 operators are under more pressure to reap more profits of existing infrastructu
re due to increased competition.
 The grid is thus increasingly operated near the threshold of stability.
 Failure of the grid, better known as blackouts, carries catastrophic economic
 and societal sequences.
 Large blackouts tend to be due to either extreme natural events such as
 hurricanes or a series of events called cascading failures 
\begin_inset CommandInset citation
LatexCommand citep
key "Hines2009"

\end_inset

.
 In this paper, we only focus on cascading events.
 Those events can be any of the following: line tripping, overloading of
 other lines, malfunctions of protection systems, power oscillations and
 voltage instability 
\begin_inset CommandInset citation
LatexCommand citep
key "Yamashita"

\end_inset

.
 The reason that is considered in this paper is distance protection misoperation
 which is a contributing factor in seventy percent of all cascading events
 
\begin_inset CommandInset citation
LatexCommand citep
key "Chen2005"

\end_inset

.
 If not discovered and mitigated in an early stage, cascading events generally
 lead to a complete blackout.
 With today’s society much dependence on electricity as a form of energy,
 preventing such damage is of high importance.
 
\end_layout

\begin_layout Standard
Cascading failures are defined as “a sequence of dependent failures of individua
l components that successively weaken the power system” 
\begin_inset CommandInset citation
LatexCommand citep
key "Baldick"

\end_inset

.
 Since the 2003 US-Canada blackout, cascading events have drawn much attention
 in the industrial and academic community.
 Even though the world has witnessed many blackouts prior to the 2003 blackout
 
\begin_inset CommandInset citation
LatexCommand citep
key "Hines2009"

\end_inset

, the dramatic causes and consequences of the 2003 blackout have left industrial
 and academic community with the burden of exploring this phenomenon in
 more detail.
 To understand the severity of the 2003 blackout 
\begin_inset CommandInset citation
LatexCommand citep
key "Liscouski2004"

\end_inset

, it sufficient to say it had caused the loss of 62 GW which caused the
 lights to turn off for more than 51 million people in the eastern interconnecti
on.
 Considering the many components and the bits and pieces involved, a domino
 effect of events evolved slowly (hours) or fast (seconds) according to
 the region causing a degradation of the integrity of the system leading
 ultimately to a complete blackout.
 The main reason of the 2003 blackout was distance relay misoperation.
 Daunting efforts had to be exerted to gain more knowledge and understanding
 of the underlying phenomenon.
 
\end_layout

\begin_layout Standard
Relays by design act quickly to remove the fault from the system by disconnectin
g faulted lines.
 However, sometimes relays fail to perform such function which is considered
 a protection system misoperation.
 Of all protection system misoperations that lead to cascading events, this
 paper focuses exclusively on distance protection misoperation.
 A protection system misoperation is defined as 
\begin_inset Quotes eld
\end_inset

a failure to operate as intended for protection purposes
\begin_inset Quotes erd
\end_inset

 
\begin_inset CommandInset citation
LatexCommand citep
key "NERCMisoperation"

\end_inset

.
 Various categories are given for misoperation in 
\begin_inset CommandInset citation
LatexCommand citep
key "NERCMisoperation"

\end_inset

.
 However, in this paper the word misoperation will be used exclusively to
 mean only one of them, namely, an operation in which a protection system
 trips a healthy line due to heavy loading when no fault exists.
 In other words, other causes of distance protection misoperation such as
 power swing are not considered in this paper.
 Notable cascading events 
\begin_inset CommandInset citation
LatexCommand citep
key "Yamashita,Novosel2004"

\end_inset

 begin with lines that were tripped due to actual faults.
 The tripping of those faulty line causes the current flowing in those lines
 to be redistributed to adjacent lines.
 Those lines may be overloaded and thus tripped incorrectly -protection
 misoperation- which may trigger a sequence of cascading events that might
 ultimately lead to a blackout.
 It should be noted that regardless of the initial triggering events- whether
 a fault or not- that cause cascading events, historically those cascading
 events were triggered under stressful system conditions 
\begin_inset CommandInset citation
LatexCommand citep
key "Liscouski2004,Kosterev1999"

\end_inset

.
\end_layout

\begin_layout Standard
As mentioned in 
\begin_inset CommandInset citation
LatexCommand citep
key "Yamashita"

\end_inset

, one of the effective ways to prevent cascading events is to specify potential
 undesirable relay operations ahead of time.
 In this paper, we show that even though distance protection misoperation
 can be anticipated ahead of time, prevention of this misoperation is not
 possible with distance protection principle only because the distance protectio
n principle is not able to be selective in some regions of its operation.
 
\end_layout

\begin_layout Standard
The paper is organized as follows: Section 
\begin_inset CommandInset ref
LatexCommand eqref
reference "sec:Typical-Distance-Protection"

\end_inset

 provides a sample distance relay that is set according to NERC standards.
 Once this relay is set according to NERC directives, it will be explained
 in the same section that the relay may still misoperate under various operating
 conditions.
 Anticipation and detection of distance relay misoperation in the planning
 stage is described 
\begin_inset CommandInset ref
LatexCommand formatted
reference "sec:Detection-and-mitigation-of-cascading-events-in-the-planning-stage"

\end_inset

.
 
\begin_inset CommandInset ref
LatexCommand formatted
reference "sec:Communication-Assisted-Schemes"

\end_inset

 provides an overview of the communication assisted schemes that have been
 proposed to eliminate the distance protection misoperation.
 Lastly, 
\begin_inset CommandInset ref
LatexCommand formatted
reference "sec:Modifications-to-Local"

\end_inset

 offers a survey on the methods that were suggested in literature to enhance
 the distance protection security using local data only.
 
\end_layout

\begin_layout Section
The Distance Protection Misoperation Problem
\begin_inset CommandInset label
LatexCommand label
name "sec:Typical-Distance-Protection"

\end_inset


\end_layout

\begin_layout Standard
On August 14th of 2003 
\begin_inset CommandInset citation
LatexCommand citep
key "Liscouski2004"

\end_inset

, the US eastern interconnection suffered one of the largest blackouts in
 the recent US history.
 Three 345 kV transmission lines sagged into untrimmed trees during the
 hot summer days.
 The tripping of those lines caused another 345 kV transmission line to
 carry substantial system load.
 The heavy loading of this last line coupled with relatively low system
 voltage, caused the distance relay to confuse a heavy loading situation
 for uncleared zone 3 fault as the impedance entered the third zone of protectio
n which in turn resulted in tripping of the heavily loaded line.
 The tripping of the healthy yet heavily loaded line worsened system conditions
 leading to a chain of events that ultimately led to system collapse.
 Also, on March 31st of 2015 
\begin_inset CommandInset citation
LatexCommand citep
key "2015Turkish"

\end_inset

, the Turkish grid suffered the worst blackout ever recorded since 1999
 when an earthquake caused a complete shutdown of the grid.
 On the contrary to the 1999 earthquake, the 2015 blackout was caused by
 a impedance protection misoperation that tripped a heavily loaded line
 on the 400 kV transmission level even though there was no fault on the
 tripped line or anywhere in the transmission network.
 As can be seen from the examples in 
\begin_inset CommandInset citation
LatexCommand citep
key "Liscouski2004,2015Turkish"

\end_inset

 in which distance protection misoperation have been the main cause of the
 blackouts or in 
\begin_inset CommandInset citation
LatexCommand citep
key "Abdullah"

\end_inset

 in which distance protection misoperation have been studied in the IEEE
 118 bus system , a distance protection misoperation is characterized by
 a distance protection system seeing a heavy load on a line as a fault.
 This confusion arises from the fact that the impedance measured by the
 impedance protection system coincides with that of a fault.
 The reason for the heavy load can be due to load shifting after a fault
 as in the 2003 US-Canada blackout 
\begin_inset CommandInset citation
LatexCommand citep
key "Liscouski2004"

\end_inset

 or due to lines out of service for maintenance causing one line to carry
 substantial system power transfer as in the 2015 Turkish blackout 
\begin_inset CommandInset citation
LatexCommand citep
key "2015Turkish"

\end_inset

 or due to any unforeseen reasons.
 
\end_layout

\begin_layout Standard
To illustrate that this confusion is not tied up with certain system conditions
 but rather inherent insecurity in the distance protection principle, the
 single line diagram shown in Figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:System-Configuration-for-formulating-problem"

\end_inset

 is used to formulate the problem in general terms.
 It will be shown below that this insecurity always exists and the degraded
 system conditions only excite it; that is, for some regions in the impedance
 protection zone the protection system is not able to be selective between
 a fault and non-fault condition.
 Without the degraded system conditions, it is highly unlikely that a distance
 protection misoperates.
 Even though, degraded system conditions can be anticipated in the planning
 stage, the system operator will have nothing in hand to prevent a distance
 protection misoperation if local function of the distance protection is
 used alone.
 It is important to keep in mind that distance protection systems are set
 locally with the help of the impedance of adjacent lines without any informatio
n about the system load until the coordination study phase.
 In the coordination study phase, the transmission line owner checks all
 settings against applicable standards.
 This is explained in detail in 
\begin_inset CommandInset citation
LatexCommand citep
key "thompson2015transmission"

\end_inset

.
 In the following paragraphs, we will set up the relay settings first then
 discuss what happens in system wide cascading events.
\end_layout

\begin_layout Standard
In Figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:System-Configuration-for-formulating-problem"

\end_inset

, the distance protection relay that will be studied is the relay at point
 A of line A-C.
 Line A-C is connected to three (3) lines, namely C-M, C-N and C-P.
 The number of lines connected to line A-C will not affect zone 1 or zone
 2 settings but will affect zone 3 settings.
 As will be seen below, tripping in Zone 3 becomes more insecure with more
 lines connected to line A-C as zone 3 reach becomes larger.
 To simplify the analysis, all lines are assumed to have the same impedance
 as well as the short circuit level.
 However, as will be explained below, this simplification does not affect
 the generality of the problem formulation.
 The impedance and the rating of the lines are 
\begin_inset Formula $60$
\end_inset

 
\begin_inset Formula $\varOmega$
\end_inset

 and 3000 Amp, respectively and are taken from 
\begin_inset CommandInset citation
LatexCommand citep
key "NERC2003"

\end_inset

.
 The setting of zone 1 is assumed to be 0.85 of the line impedance.
 Zone 2 setting is assumed to be 1.2 of the line impedance.
 However, some consideration is needed to set the third zone.
 The third zone has to be set such that it can protect the longest adjacent
 line (assumed to be line C-P in this case) and to protect 20% beyond that
 line to provide backup to the remote circuit breakers.
 In case of a bolted three phase fault on line C-P and assuming that the
 short circuit contributions of all buses is given in Figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:System-Configuration-for-formulating-problem"

\end_inset

 by 
\begin_inset Formula $I_{index}$
\end_inset

 where 
\begin_inset Formula $index$
\end_inset

 is the bus name (being M , N, A or P), the voltage at distance protection
 system at A can be written as given in equation 
\begin_inset CommandInset ref
LatexCommand formatted
reference "eq:VoltageAtRelat"

\end_inset

.
\begin_inset Float figure
placement h
wide false
sideways false
status collapsed

\begin_layout Plain Layout
\align center
\begin_inset Graphics
	filename SysExample.PNG
	scale 60

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption Standard

\begin_layout Plain Layout
System Configuration for formulating the problem
\begin_inset CommandInset label
LatexCommand label
name "fig:System-Configuration-for-formulating-problem"

\end_inset


\begin_inset Argument 1
status open

\begin_layout Plain Layout
System Configuration for formulating the problem
\end_layout

\end_inset


\end_layout

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Standard
\begin_inset Formula 
\begin{equation}
V_{A}=I_{A}\times Z_{A}+Z_{P}\times\left(I_{M}+I_{A}+I_{N}\right)\label{eq:VoltageAtRelat}
\end{equation}

\end_inset


\end_layout

\begin_layout Standard
The impedance that is seen by the relay A can then be written as in 
\begin_inset CommandInset ref
LatexCommand formatted
reference "eq:ApparentImpedanceAtRelay"

\end_inset


\end_layout

\begin_layout Standard
\begin_inset Formula 
\begin{equation}
Z_{R}=\frac{V_{A}}{I_{A}}=Z_{A}+Z_{P}\left(1+\frac{I_{M}+I_{N}}{I_{A}}\right)\label{eq:ApparentImpedanceAtRelay}
\end{equation}

\end_inset


\end_layout

\begin_layout Standard
Equation 
\begin_inset CommandInset ref
LatexCommand formatted
reference "eq:ApparentImpedanceAtRelay"

\end_inset

 will only be applicable to faults on line C-P, if we need to include 20%
 for the line that is beyond bus P, then the impedance 
\begin_inset Formula $Z_{P}$
\end_inset

 in 
\begin_inset CommandInset ref
LatexCommand formatted
reference "eq:ApparentImpedanceAtRelay"

\end_inset

 has be replaced by 
\begin_inset Formula $1.2\times Z_{P}$
\end_inset

.
 Using the data in 
\begin_inset CommandInset citation
LatexCommand citep
key "NERC2003"

\end_inset

 and assuming all lines are identical as well as their short circuit contributio
n, then the setting of zone 3 will be 
\begin_inset Formula $Z_{A}+3.6\times Z_{P}=4.6\times Z_{A}$
\end_inset

.
 The three zones are plotted in Figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Distance-Relay-characteristic"

\end_inset

.
 
\begin_inset Float figure
placement !h
wide false
sideways false
status collapsed

\begin_layout Plain Layout
\align center
\begin_inset Graphics
	filename impedance form.PNG
	scale 60

\end_inset


\begin_inset Caption Standard

\begin_layout Plain Layout
\begin_inset Argument 1
status open

\begin_layout Plain Layout
Distance protection characteristic 
\end_layout

\end_inset

Distance protection characteristic for system in Figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:System-Configuration-for-formulating-problem"

\end_inset

 
\series bold

\begin_inset CommandInset label
LatexCommand label
name "fig:Distance-Relay-characteristic"

\end_inset


\end_layout

\end_inset


\end_layout

\end_inset

 
\end_layout

\begin_layout Standard
After setting up the relay locally, applicable standards and directives
 need to be applied to the settings for compliance purposes.
 This step involves running worst case power flow in the summer peak case.
 The most notable directive is the load encroachment.
 The load encroachment zone is an area of the protection zone in which the
 load impedance “ encroaches” –intrudes- upon the fault impedance.
 Load encroachment will obviously cause misoperation and should be removed
 from the zone of protection 
\begin_inset CommandInset citation
LatexCommand citep
key "NERC2003"

\end_inset

.
 To plot the load encroachment zone according to NERC directives 
\begin_inset CommandInset citation
LatexCommand citep
key "NERCMisoperation,NERC2003,NERCLoadability"

\end_inset

, the load zone should include the point which corresponds to 150% line
 loading and 0.85 per unit voltage.
 Thus the load encroachment locus of the distance relay at A will consist
 of two parts.
 The first part will be an arc of circle of radius given in equation 
\begin_inset CommandInset ref
LatexCommand formatted
reference "eq:LoadImpedance"

\end_inset

 which is given as arc 
\series bold
RIT
\series default
 in Figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:System-Configuration-for-formulating-problem"

\end_inset

.
 This arc 
\series bold
RIT
\series default
 corresponds to the least impedance that the relay should not issue a trip
 command for.
 The other characteristic load lines will be two lines making an angle of
 
\begin_inset Formula $\pm30^{\circ}$
\end_inset

 with the x-axis (
\begin_inset Formula $\pm30^{\circ}$
\end_inset

 represents the power factor of the line under worst case loading condition)
\end_layout

\begin_layout Standard
\begin_inset Formula 
\begin{equation}
Z_{load}=\frac{V_{A}}{I_{A}}=\frac{\frac{345kV}{\sqrt{3}}\times0.85}{1.5\times3000}=57\varOmega\label{eq:LoadImpedance}
\end{equation}

\end_inset


\end_layout

\begin_layout Standard
The orange hashed area 
\series bold
RLQT
\series default
 is the load encroachment area.
 NERC directives 
\begin_inset CommandInset citation
LatexCommand citep
key "NERCMisoperation,NERC2003,NERCLoadability"

\end_inset

 states that this load encroachment zone has to be removed from the relay
 operating zone.
 It can be seen at once that if the impedance seen by the relay lies within
 the solid green area 
\series bold
URI
\series default
 then a relay may confuse this operating point for a fault since the point
 lies already in zone 3.
 This confusion arises if the fault resistance is high enough to cause the
 fault point to lie within the solid green area 
\series bold
URI
\series default
.
 In Figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Distance-Relay-characteristic"

\end_inset

, this fault resistance ranges from 
\begin_inset Formula $30$
\end_inset


\begin_inset Formula $\varOmega$
\end_inset

 to 
\begin_inset Formula $90$
\end_inset


\begin_inset Formula $\varOmega$
\end_inset

.
 The fault resistance can be obtained by measuring the distance between
 the diameter 
\series bold
AB
\series default
 of zone 3 circle to point 
\series bold
R
\series default
 and 
\series bold
U
\series default
 of the green zone.
 If it is known in advance that the fault resistance calculated cannot be
 attained along the route of the transmission line, then the risk of misoperatio
n is nonexistence and the green area can be removed from zone 3 without
 affecting the security or reliability of the distance protection system.
 However, fault resistance along the route of the transmission line is not
 known in advance.
 Also, one should note that solid state and electromechanical relays can
 not be programmed, only microprocessor relays can.
 This really means that older relays will have to comply with NERC standards
 by disabling zone 3 altogether.
 It is shown in 
\begin_inset CommandInset citation
LatexCommand citep
key "Horowitz2006"

\end_inset

 that disabling zone 3 in some cases will force protection engineers to
 provide back up protection solutions to remote circuit breakers.
 This might involve a considerable cost.
 Additionally, not all countries around the world have standards as strict
 as NERC, so the solid green area 
\series bold
URI 
\series default
exist in the zone of protection without regard from the protection engineer.
 Lastly, even if the relay complies with NERC directives, an impedance can
 still fall anywhere in zone 3, not only the solid green area 
\series bold
URI,
\series default
 under stressed system conditions as Phadke and Horowitz pointed out in
 their paper 
\begin_inset CommandInset citation
LatexCommand citep
key "Horowitz2006"

\end_inset

.
 This shows clearly the impedance protection is inherently insecure under
 stressed system conditions.
 
\end_layout

\begin_layout Standard
Attention is now given to the assumptions stated in the beginning.
 It was assumed that all lines have the same impedance and all of them are
 contributing equal currents to the fault.
 It can be seen at once from Figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Distance-Relay-characteristic"

\end_inset

 that this assumption is not restricting the generality of the problem formulati
on.
 Because in any case the green area 
\series bold
URI
\series default
 will exist due to the load profile under stressed conditions.
 Additionally, the fault contribution of the transmission lines will only
 affect the diameter 
\series bold
BA
\series default
 of zone 3 which will only affect point 
\series bold
U
\series default
.
 Point 
\series bold
U
\series default
 correspond to the max fault resistance.
 Stated differently, there will always be an overlap between the dynamic
 rating of the line and zone 3 and the short circuit levels from nearby
 lines will only affect the size of the overlap (area 
\series bold
URI)
\series default
 not the overlap itself.
 Lastly, to derive equations 
\begin_inset CommandInset ref
LatexCommand formatted
reference "eq:VoltageAtRelat"

\end_inset

 and 
\begin_inset CommandInset ref
LatexCommand formatted
reference "eq:ApparentImpedanceAtRelay"

\end_inset

, a three phase fault has been assumed.
 This is due to the fact that line overload is three phase phenomenon.
 However, it should not be hard to be able to envision a single line to
 ground fault causing the same effect if one important line is operated
 with only one phase due to a line to line fault under heavy loading conditions.
 
\end_layout

\begin_layout Standard
It should be apparent from the description above that the major issue that
 is faced by traditional impedance protection system is that the steady
 state impedance corresponding to a heavy load is coincident to the impedance
 under a fault on a remote line to which the distance protection system
 provides backup protection.
 It could be argued that impedance protection should be supervised by other
 steady state protection principles to enhance its selectivity, i.e, the
 ability to differentiate between a load and a fault current.
 However, other protection principles -such as over current protection-
 that can make the distinction between a load and a fault depend on the
 anticipated power flow for operation while the problem in hand is different.
 The confusion that is seen by the distance protection is because the power
 flow under system wide cascading failures changes considerably from the
 planned power flow.
 In other words, the load encroachment zone has to be set for system wide
 cascading scenarios that are not known in advance, which is close to impossible
 undertaking.
 One of the authors 
\begin_inset CommandInset citation
LatexCommand citep
key "Horowitz2006"

\end_inset

 states this fact as:
\end_layout

\begin_layout Standard

\shape italic
"The overwhelming thrust of the NERC rules and other instructions regarding
 the application of zone 3 elements has been to prevent its operation during
 emergency conditions.
 Although this is a desirable goal, it should be recognized that even with
 all the intelligence available to modern computer relays, the problem of
 distinguishing a fault from a heavy load in a relatively short time and
 using only the current and voltage signals available to the relay can not
 be solved in every single imaginable (and some unimaginable) power system
 scenarios"
\shape default
.
\end_layout

\begin_layout Section
Detection and mitigation of zone 3 misoperation in the planning stage
\begin_inset CommandInset label
LatexCommand label
name "sec:Detection-and-mitigation-of-cascading-events-in-the-planning-stage"

\end_inset


\end_layout

\begin_layout Standard
Most Independent System Operators (ISOs) 
\begin_inset CommandInset citation
LatexCommand citep
key "ERCOTNodal,CaisoPlanning"

\end_inset

 today use N-1 criterion to judge whether the system is secure after the
 removal of one line in planning stage.
 However, given that zone 3 distance protection misoperation is not triggered
 until two or three lines go out of service 
\begin_inset CommandInset citation
LatexCommand citep
key "Liscouski2004"

\end_inset

, the distribution of power flow is hard to be taken into account in the
 planning stage as it would mean performing N-2 and N-3 contingency analysis
 which is expensive computationally.
 Thus, it is increasingly hard to assess protection system capability under
 the most stressful system conditions.

\shape slanted
 
\shape default
Due to that, the authors in 
\begin_inset CommandInset citation
LatexCommand citep
key "li2007operation,li2008sensitivity"

\end_inset

 provided an efficient method to study the sensitivity of zone 3 under various
 operating conditions without the need for performing large number of power
 flow studies.
 In 
\begin_inset CommandInset citation
LatexCommand citep
key "li2007operation,li2008sensitivity"

\end_inset

, the authors define a linearized impedance margin of a distance relay using
 system voltages, injected power and shunt susceptance.
 The impedance margin is defined as the distance between the measured impedance
 locus in the R-X plane to the boundary of the operating characteristic
 of the relay and is shown in Figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Impedance-margin-and"

\end_inset

.
 By doing so, the relays that may misoperate can be anticipated ahead of
 time in an efficient manner in the planning stage using simple formulas.
 However, it is shown in the paper that if the changes in the voltages or
 power injections are electrically far away from the relay under study,
 a situation that always exists in wide area cascading scenarios, the error
 in the analysis becomes unacceptable especially for long lines.
 
\begin_inset Float figure
wide false
sideways false
status collapsed

\begin_layout Plain Layout
\align center
\begin_inset Graphics
	filename IMpedance margin.PNG
	scale 60

\end_inset


\begin_inset Caption Standard

\begin_layout Plain Layout
Impedance margin and impedance locus plot for a distance relay during a
 wide area cascading scenario
\begin_inset CommandInset label
LatexCommand label
name "fig:Impedance-margin-and"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

\begin_layout Standard
In 
\begin_inset CommandInset citation
LatexCommand citep
key "aghamohammadi2016new"

\end_inset

, the authors propose blocking zone 3 of certain distance relays ahead of
 time based on offline simulations.
 The authors propose that the system operator perform contingency analysis
 using credible historical contingencies in planning stage to observe the
 impedance trajectory at each distance relay in the system.
 The contingency scenarios to be performed have to include more than one
 contingency to create an impedance trajectory.
 The relays that misoperate during each contingency scenario due to the
 impedance trajectory entering zone 3 when no fault conditions exist should
 be short listed.
 Of those relays that are short listed, certain relays are selected such
 that their zone 3 protection will be disabled.
 The relays that will be disabled are common to all contingency scenarios
 and are selected based on a specific criterion explained in the paper.
 However, the contingency scenarios can be hard to design in the planning
 stage for modern power systems that have thousands of buses.
 Additionally, disabling zone 3 effectively disables backup protection for
 remote circuit breaker which is a situation that should be avoided unless
 another form of backup is available.
 
\end_layout

\begin_layout Standard
The authors in 
\begin_inset CommandInset citation
LatexCommand citep
key "Song2007"

\end_inset

 proposed certain indices that can accurately gauge the severity of system
 conditions and the likelihood of cascades in real time.
 An index that is used to monitor distance relays is also proposed.
 If the indies associated with the distance relays exceed their threshold,
 then distance protection misoperation is about to occur and the system
 operator has the option to stop distance relays from operation.
 However, in practice only N-1 contingencies are studied and thus the severity
 index is chosen based on these cases.
 Nevertheless, if the system enters N-2 or N-3 contingency conditions, tuning
 of the “severity” threshold will be a difficult task computationally.
 
\end_layout

\begin_layout Standard
Lastly, distance protection co-ordination has been explored in 
\begin_inset CommandInset citation
LatexCommand citep
key "ravikumar2008approach,ravikumar2009approach"

\end_inset

.
 An SVM for each relay is trained using the impedance trajectory that is
 seen by the relay during fault conditions.
 The impedance trajectory is obtained by using a transient stability program.
 SVM is then trained for various scenarios to distinguish zone 1, zone 2
 and zone 3 faults.
 Training scenarios include cases for different fault types at different
 distances away from the relay that has the SVM and at different fault resistanc
es.
 Testing scenarios for SVM include faults that have not used in training.
 By ensuring that the relays are well co-coordinated under various contingency
 conditions, unnecessary trip could be avoided.
 However, the impedance trajectory will depend on the system topology at
 the time of fault occurrence and this has not been taken into consideration
 in 
\begin_inset CommandInset citation
LatexCommand citep
key "ravikumar2008approach,ravikumar2009approach"

\end_inset

 which could lead to large offline training set.
 
\end_layout

\begin_layout Standard
Due to the fact that distance protection co-ordination requires large amount
 of offline simulations by performing many contingency conditions, the authors
 in 
\begin_inset CommandInset citation
LatexCommand citep
key "tasdighi2016automated"

\end_inset

 introduced the idea of 
\begin_inset Quotes eld
\end_inset

distance of impact
\begin_inset Quotes erd
\end_inset

 to automate the distance protection co-ordination.
 However, the authors use the super computer to perform their computations
 at the first stage.
 Once the distance of impact of each relay has been calculated, co-ordination
 of the distance relays becomes straight forward.
 A shortcoming of the distance co-ordination approach is that even though
 it can ensure that distance relays never overreach for faults beyond their
 reach, little research has been performed to study whether the co-ordination
 can ensure that relays will not misoperate under heavy loading conditions.
 
\end_layout

\begin_layout Standard

\series bold
As can be seen above, anticipation detection  of distance protection misoperatio
n in the planning stage is a hard task.
 To be able to fully prevent distance protection misoperation, an N-x, where
 x is greater than 1, contingency analysis need to be done.
 Even though this could be done for small benchmark systems, contingency
 analysis, under uncertain load and generation, is computationally intensive
 for large system consisting of thousands of buses.
 Many ISOs may not have access to supercomputers to run such intensive computati
ons.
 
\end_layout

\begin_layout Section
Communication Assisted Schemes
\begin_inset CommandInset label
LatexCommand label
name "sec:Communication-Assisted-Schemes"

\end_inset


\end_layout

\begin_layout Standard
The 2003 blackouts pointed out the importance of having events along with
 the time they occurred.
 Investigators spent much of their time trying to match up the waveforms
 to reconstruct the sequence of events that led to the blackout.
 It was then apparent that to facilitate the transfer and comparison of
 waveforms, all samples need to have a time stamp for this purpose.
 Phasor Measurement Unit (PMU) or synchrophasor technology was then recommended
 to address this shortcoming 
\begin_inset CommandInset citation
LatexCommand citep
key "Liscouski2004"

\end_inset

.
 By the time of 2003 blackout, state estimation was a very mature field,
 but PMUs opened new areas for the application of state estimation by reducing
 the time needed to do state estimation due to wide spread deployment in
 the transmission network.
 A PMU measures the positive sequence voltage and current (both the magnitude
 and angle), which opens new areas for adaptive relaying and wide area control
 and protection.
 In typical distance protection schemes, the relay is only applied to a
 single transmission line.
 However, in a wide area protection scheme, a complete area (several transmissio
n lines) can be protected using selected PMU devices without the need to
 apply PMUs to each single bus in the system.
 By transferring information in between PMUs in the power system, accurate
 decision regarding the nature of the impedance falling in zone 3 can be
 made and misoperation can be avoided.
\end_layout

\begin_layout Standard
With the introduction of PMUs, several fault detection and locations methods
 have been proposed.
 The salient feature of PMU detection schemes 
\begin_inset CommandInset citation
LatexCommand citep
key "Joe-Air2000"

\end_inset

 is that using the communication links to transfer data between the two
 ends of the lines, several conclusions can be drawn regarding whether the
 line is undergoing abnormal conditions.
 A salient feature of the PMU algorithm is the ability to monitor the status
 of the line and compute the parameters of the line online in a very accurate
 way.
 
\end_layout

\begin_layout Standard
Due to the fact that zone 3 of distance relays may not be able differentiate
 between heavy line load and an actual fault on the system, the authors
 in 
\begin_inset CommandInset citation
LatexCommand citep
key "Lim2008"

\end_inset

 proposed that a tool be installed at the control center, also known as
 Independent System Operator (ISO), to continuously supervise the operation
 of zone 3 elements.
 The tool will consist of two modules, a central control unit (CCU) and
 several regional control units (RCUs) as shown in Figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:RCU-and-CCU"

\end_inset

.
 The CCU will be installed in the ISO while the RCUs will be installed at
 select individual substations.
 The CCU measures the line outage distribution factors and generation shift
 factors for the entire power grid and sends all factors to the individual
 RCUs.
 RCUs use local measurements at the substation and communicate with one
 another.
 The individual RCUs will differentiate between faults and transfer of power
 flow and supervise distance relays based on the information received from
 the CCU and other RCUs.
 Even though this solution might be able to prevent all zone-3 misoperations,
 it needs considerable cost to construct the communication infrastructure
 that is needed to transmit the data between the individual substation and
 the ISO.
 
\begin_inset Float figure
wide false
sideways false
status collapsed

\begin_layout Plain Layout
\align center
\begin_inset Graphics
	filename IEEE14BusSystemB.jpg
	scale 70

\end_inset


\begin_inset Caption Standard

\begin_layout Plain Layout
RCU and CCU of the solution in 
\begin_inset CommandInset citation
LatexCommand citep
key "Lim2008"

\end_inset


\begin_inset CommandInset label
LatexCommand label
name "fig:RCU-and-CCU"

\end_inset

 
\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

\begin_layout Standard
The authors in 
\begin_inset CommandInset citation
LatexCommand citep
key "dutta2014transmission"

\end_inset

 uses synchronized samples from both ends of the line to check whether the
 transmission line has been tripped successfully or not.
 The instantaneous power from both line ends are calculated.
 It is shown in the paper that after fault inception, the instantaneous
 power at both ends becomes positive.
 This hold true even under systems with week infeed.
 The method is applicable to all systems other than radial systems.
 However, due to the need to transfer data between both ends, significant
 cost may be incurred to establish such algorithm across each transmission
 line in the grid.
 The approach that has been proposed in 
\begin_inset CommandInset citation
LatexCommand citep
key "dutta2014transmission"

\end_inset

 has been validated using field data in 
\begin_inset CommandInset citation
LatexCommand citep
key "esmaeilian2015transmission"

\end_inset

.
 
\end_layout

\begin_layout Standard
In 
\begin_inset CommandInset citation
LatexCommand citep
key "navalkar2011secure"

\end_inset

, distributed PMUs are used to reach a definitive decision about the existence
 of the fault in the system using a synchrophasor state estimator (SynSE).
 The SynSE is used to detect network topology changes as well as determine
 the fault locations as shown in Figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Protection-logic-ofSYNSE"

\end_inset

.
 However, the grid has be completely observable by PMUs.
 Thus, siting PMUs has to be done carefully to not create unobservable islands
 under stressed system conditions and certain contingency conditions.
 
\begin_inset Float figure
wide false
sideways false
status collapsed

\begin_layout Plain Layout
\align center
\begin_inset Graphics
	filename SynSE.tif
	scale 50

\end_inset


\begin_inset Caption Standard

\begin_layout Plain Layout
Protection logic of the paper in 
\begin_inset CommandInset citation
LatexCommand citep
key "navalkar2011secure"

\end_inset


\begin_inset CommandInset label
LatexCommand label
name "fig:Protection-logic-ofSYNSE"

\end_inset

 
\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

\begin_layout Standard
In 
\begin_inset CommandInset citation
LatexCommand citep
key "Kundu2014"

\end_inset

 synchrophasors are proposed to supervise zone 3 operation.
 Specific indices are proposed to assert the fault using the currents which
 result in a very robust zone 3 distance protection system.
 The algorithm forms a super node from the certain groups of PMUs.
 By summing the current going into the super node, a decision can be reached
 whether a disturbance exists or not.
 If a disturbance is detected, another logic is invoked to determine whether
 it is a fault for the group of PMUs with the higher deviation.
 The logic that is invoked after disturbance detection is impedance based.
 A weighted fault detection index is defined for this purpose.
 The weights used to define the index depend on the reach of the respective
 zone 3 distance protection relay.
 If after disturbance detection, the weighted fault index is exceeded, a
 fault in zone 3 is declared and the relay is restrained from operation.
 However, to fully take advantage of the method, strategically located PMUs
 have to exist in the system which makes the approach highly dependent on
 the topology and any transmission system upgrades.
 Additionally, certain contingency conditions can cause some faults not
 to be detected due to the location of the PMUs.
 
\end_layout

\begin_layout Standard
In 
\begin_inset CommandInset citation
LatexCommand citep
key "Garlapati2013"

\end_inset

, agents are used to aid zone 3 relay elements without enforcing a decision.
 In this scheme, each impedance relay will have the capability to communicate
 with other agents in the network that protect the same transmission line.
 If the majority of the agents informs the local distance relay that the
 impedance in its zone 3 reach is actually due to a fault, then the local
 distance relay should be energized and a trip command has to be issued.
 An optimization approach is set up such that the communication delay between
 the various agents are less than 1 second, which is the time of operation
 of zone 3.
 A similar approach has been proposed in 
\begin_inset CommandInset citation
LatexCommand citep
key "haj2014intelligent"

\end_inset

 where agents are installed everywhere without the optimization approach.
 
\end_layout

\begin_layout Standard
In 
\begin_inset CommandInset citation
LatexCommand citep
key "Neyestanaki2015"

\end_inset

, a limited number of PMUs are used to determine the faulted line as well
 as the location of the fault.
 An optimization approach is used to locate a set of PMUs such that the
 observability is independent of the generator models.
 A backup protection zone is then constructed using the lines and buses
 between each PMU such that a line in not included in two regions.
 The sum of zero and positive sequence currents are used as discriminant
 for fault detection and location.
 If the sum is not zero then the area will be flagged as having a fault.
 Next comes the task of identifying the faulted line.
 For the area that is flagged as having a fault, a distance quantity will
 be calculated for each line within the area, i.e., each line will be assumed
 faulted and a distance quantity will be calculated.
 If the distance quantity falls between 0 to 1 then the faulted line will
 be determined.
 If more than one line is found to be faulted, an estimation of relative
 residual error is made and the line with the minimum residual error will
 be selected as the faulted line.
 It is clear from this description that two faults within any protected
 zone or cross country faults will be detected as one fault only.
 And even though one of the two faults may have not been cleared, the algorithm
 may not be able to detect such situation.
 
\end_layout

\begin_layout Standard
In 
\begin_inset CommandInset citation
LatexCommand citep
key "Eissa2010"

\end_inset

, a backup wide area protection scheme is proposed.
 Short window DFT is used to extract the phasor information from the three
 phase voltages and currents.
 In this scheme, the absolute difference of the bus angles and currents
 are used to detect the fault.
 The minimum voltage magnitude establishes the closest bus to the fault
 and the maximum current angle difference between the buses establishes
 the faulted lines.
 However, for the method to work, the minimum voltage threshold has to be
 established.
 It is shown in the paper that a voltage threshold less than 0.95 means that
 there is a fault on a system.
 This immediately points out that in case of voltage instability conditions,
 the method can operate erroneously.
\end_layout

\begin_layout Standard
In 
\begin_inset CommandInset citation
LatexCommand citep
key "He2011"

\end_inset

, another wide area protection scheme is proposed.
 The solution consists of two components: a fault element identification
 (FEI) and a fault area detection (FAD).
 The FEI is used to identify the faulted element in the zone being protected.
 After that, the fault isolation is realized by coordination among area
 circuit breakers breakers.
 As part of the FEI, the measured voltage and current of one terminal of
 the protected area are used to estimate the voltages at the other end.
 If an internal fault occurs within the zone being monitored, then the estimated
 value will be different from the measured value at that bus causing a fault
 to be detected.
 On the other hand, the faulted area is detected through FAD.
 The substations that are within the faulted area need to send the information
 to the central control room.
 Afterwords, the central control room will search the suspected faulty lines
 and identify actual faulty lines quickly.
 The use of FAD concept reduces the communication overhead required by the
 scheme.
 The overall structure of the solution is shown in Figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:The-concept-of-FAD"

\end_inset

.
 
\begin_inset Float figure
placement h
wide false
sideways false
status collapsed

\begin_layout Plain Layout
\align center
\begin_inset Graphics
	filename FAD.tif
	scale 50

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption Standard

\begin_layout Plain Layout
The concept that is given in 
\begin_inset CommandInset citation
LatexCommand citep
key "He2011"

\end_inset

.
 A select number of substations will be included in the communication network.
 
\begin_inset CommandInset label
LatexCommand label
name "fig:The-concept-of-FAD"

\end_inset


\end_layout

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Standard
The authors in 
\begin_inset CommandInset citation
LatexCommand citep
key "lin2016countermeasures"

\end_inset

 use PMUs, that are in place as part of a wide area protection scheme, to
 detect the power flow transfer due to the removal of faulted line from
 service.
 In 
\begin_inset CommandInset citation
LatexCommand citep
key "lin2016countermeasures"

\end_inset

, the load flow transfer to a line can be calculated using the network topology
 via the distribution factors.
 If the measured power flow transfer significantly mismatches the calculated
 power flow transfer, then a fault will be declared.
 Based on that detection, zone 3 is adaptively adjusted to prevent misoperation
 which eliminate distance protection zone 3 misoperation.
 
\end_layout

\begin_layout Standard

\series bold
Even though PMU based schemes and wide-area based schemes can offer attractive
 solutions to eliminate the problem of distance protection misoperation,
 these solutions require significant communication infrastructure cost.
 Additionally, the power grid is a critical infrastructure and the cybersecurity
 risk may be eminent if the grid is brought online for communications purposes.
 
\end_layout

\begin_layout Section
Modifications to Local Distance Protection
\begin_inset CommandInset label
LatexCommand label
name "sec:Modifications-to-Local"

\end_inset


\end_layout

\begin_layout Standard
In addition to using PMUs for fault detection and assisting zone 3 tripping,
 various authors proposed making changes to the way impedance relays operate.
 In these methods, the authors proposed additional criteria to assist distance
 protection in order to assert that fault exists within the relay reach
 using local data.
 
\end_layout

\begin_layout Standard
Local measurements are used in 
\begin_inset CommandInset citation
LatexCommand citep
key "Nayak2015"

\end_inset

 to assist zone-3 tripping.
 The authors proposed to distinguish three phase faults from system overloads.
 The DC decaying component and the line load angle are used to determine
 whether a fault has occurred within the reach of local distance relay.
 The DC decaying fault component is reconstructed from the measured currents
 in all three phases.
 Since the fault is three phase, a DC decaying component must exist in one
 of the phases.
 A transient monitoring function will then be defined to be the maximum
 of all three phases DC decaying components in one cycle.
 Also, for the three phase to be asserted, the line load angle has to be
 greater than 50 degrees.
 Both the monitoring function as well as the line load angle has to be true
 for a three phase fault to be declared.
 The drawback of this method is that the fault must have significant decaying
 DC component which makes it challenging for certain fault incipient angles
 and transmission line lengths as a significant decaying DC component can
 only occur when the fault occurs at certain incipient angles and under
 certain X/R ratios.
 Additionally, the paper assumes the angle between the current and the voltage
 at the relay to be more than 50 degrees as a fault indicator.
 However, it has been pointed out in 
\begin_inset CommandInset citation
LatexCommand citep
key "Horowitz2006"

\end_inset

 that under stressed system conditions the angle may indeed exceed that
 threshold with no fault on the system.
 Also, if the swing frequency in the system is anticipated to be larger
 than 5 Hz, threshold selection for transient monitoring becomes a hard
 task which could mislead the scheme to confuse power system swing for three
 phase faults.
 Lastly, the effect of fault resistance has not been studied in the paper.
 Fault resistance can potentially cause trouble setting the threshold for
 the transient monitoring function as it affects the DC decaying component.
\end_layout

\begin_layout Standard
In 
\begin_inset CommandInset citation
LatexCommand citep
key "Jonsson2003"

\end_inset

 the rate of change of voltage is used as a trip restraint to supervise
 distance protection misoperation.
 The idea is that fault occurrence or fault clearing causes the voltage
 seen by the relay to change drastically.
 The authors propose if the local relay senses that the system voltage is
 stressed according to the conditions listed in 
\begin_inset CommandInset citation
LatexCommand citep
key "vu1999use"

\end_inset

, the rate of voltage change 
\begin_inset Formula $(\Delta V/\Delta t)$
\end_inset

 will be used to assert whether a fault has occurred and cleared within
 zone 3 protection using two thresholds for both fault occurrence and fault
 clearing.
 Additionally, the authors proposed to use a thermal loading monitoring
 function to decide whether the maximum conductor temperature has been reached.
 The temperature monitoring function will start operation after the fault
 has been detected.
 If the temperature monitoring function declares that the line temperature
 has reached maximum limit, the line will be tripped whether the fault has
 been cleared or not.
 However, for the trip command to be secure, large amount of offline simulations
 need to be carried out to know the worst case rate of change of voltage.
 The major disadvantage of the method is that under voltage instability,
 the 
\begin_inset Formula $(\Delta V/\Delta t)$
\end_inset

 criterion is not exclusive property for faults as pointed in 
\begin_inset CommandInset citation
LatexCommand citep
key "Sharifzadeh2014"

\end_inset

 since under voltage instability, a sudden generator tripping could cause
 the same 
\begin_inset Formula $(\Delta V/\Delta t)$
\end_inset

.
 
\end_layout

\begin_layout Standard
Since it is hard to distinguish between evolving pre-blackout event and
 short circuit conditions using magnitude of voltage, another trip restraint
 quantity, namely 
\begin_inset Formula $(\Delta I/\Delta V)$
\end_inset

 has been used along with 
\begin_inset Formula $(\Delta V/\Delta t)$
\end_inset

 criterion to trip zone 3 securely in 
\begin_inset CommandInset citation
LatexCommand citep
key "Sharifzadeh2014"

\end_inset

.
 The 
\begin_inset Formula $(\Delta I/\Delta V)$
\end_inset

 threshold value has also been obtained using offline simulations.
 The disadvantage of the method in 
\begin_inset CommandInset citation
LatexCommand citep
key "Sharifzadeh2014"

\end_inset

 is that neither contingency analysis nor system loading levels have been
 taken into consideration.
\end_layout

\begin_layout Standard
The use of fault generated high frequency components has also been investigated
 in literature 
\begin_inset CommandInset citation
LatexCommand citep
key "Probert"

\end_inset

.
 Such usage can give a more precise answer whether a fault has occurred
 thus making tripping in zone 3 more secure.
 In 
\begin_inset CommandInset citation
LatexCommand citep
key "Perera2011"

\end_inset

, the energy of the first three current levels and the third approximation
 is used to train a probabilistic classifier.
 The energy is calculated using certain levels of the discrete wavelet transform
 of the three phase currents.
 Using this energy features, a decision is made whether a transient signal
 if due to a fault or non-fault condition on a line.
 A simpler online transient classifier has been proposed in 
\begin_inset CommandInset citation
LatexCommand citep
key "abdullah2016towards"

\end_inset

, where the transient events occurring on the transmission lines nearby
 any distance relay are identified.
 Modal transformation is used to transform the phase currents into modal
 currents.
 The discrete wavelet transform coefficients of the aerial modes 
\begin_inset CommandInset citation
LatexCommand citep
key "hedman1965propagation"

\end_inset

 are combined in a certain manner to train a feedforward neural network
 to classify those transients.
 However, the major drawbacks of both 
\begin_inset CommandInset citation
LatexCommand citep
key "Perera2011"

\end_inset

 and 
\begin_inset CommandInset citation
LatexCommand citep
key "abdullah2016towards"

\end_inset

 is that they cannot be used to tell whether the fault is within the relay
 protection reach even though they can tell whether a fault has occurred
 in the network.
 These papers can only be useful if a method is found to use the transient
 classification as an entrance point to determining whether the fault is
 within the protection reach of the relay but this has not been done in
 literature to the best of our knowledge.
\end_layout

\begin_layout Standard
Various adaptive zone 3 settings were also investigated in literature where
 zone 3 reach is adjusted based on local information.
 In 
\begin_inset CommandInset citation
LatexCommand citep
key "zadeh2008artificial,zadeh2011adaptive"

\end_inset

, ANN has been used to predict the correct load blinder under various system
 conditions.
 The load blinder is then combined with the zone 3 settings to block any
 undesirable tripping.
 The load blinder is only activated under balanced conditions to make sure
 that the heavy loading is not confused for unbalanced fault conditions.
 The load blinder is determined based on offline simulations.
 The simulations take into account the loading level of the power system,
 fault incipient angle, source impedance ratio, fault resistance and fault
 location.
 The features used to train ANN is the active and reactive power, voltage
 as well as the rate of change of both the voltages and currents seen at
 the relay terminal as shown in Figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Creation-of-adaptive"

\end_inset

.
 A simple line connected to another line with a load in between is used
 to test the method which is a disadvantage of the method.
 Also, the effect of the system topology wasn't studied.
 It is also foreseen that the inclusion for contingency analysis in ANN
 training will require large offline simulations and will make load blinder
 selection difficult task.
 Additionally, only three phase fault currents has been used to train the
 ANN and in case a single line to ground fault occurs and cause the features
 to be different than the ones used in training, the method is expected
 to fail because ANN is known to have bad generalization capabilities 
\begin_inset CommandInset citation
LatexCommand citep
key "zurada1992introduction"

\end_inset

.
 
\begin_inset Float figure
wide false
sideways false
status collapsed

\begin_layout Plain Layout
\align center
\begin_inset Graphics
	filename loadblinder.tif
	scale 70

\end_inset


\begin_inset Caption Standard

\begin_layout Plain Layout
Creation of adaptive load blinder in 
\begin_inset CommandInset citation
LatexCommand citep
key "zadeh2011adaptive"

\end_inset

 
\begin_inset CommandInset label
LatexCommand label
name "fig:Creation-of-adaptive"

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

\begin_layout Standard
In 
\begin_inset CommandInset citation
LatexCommand citep
key "Nikolaidis2016,Nikolaidis"

\end_inset

, the authors propose changing zone 3 reach during emergency conditions
 to prevent distance protection misoperation if certain system conditions
 are met.
 If those system conditions are met, zone 3 protection reach will be shrunk
 to zone 2 which in turn gives maximum security.
 During stressed system conditions, the impedance seen by the local relay
 approaches the original zone 3 border, whether this border is MHO characteristi
cs or polygonal one.
 The authors propose to define a fourth protection zone, called third zone
 proximity area (TZPA), as well as a fifth protection zone, called third
 zone modification area (TZMA), to change zone 3 protection reach based
 on certain criteria.
 The TZMA is a region within TZPA but closer to zone 3 protection zone.
 The authors provided rules on how to set both TZMA and TZPA.
 Once the impedance enters this TZPA and crosses zone 3 fast enough, the
 fault will be declared.
 However, if the impedance enters TZPA and stays within TZPA, the TZMA logic
 will be put into action.
 Zone 3 protection will be shrunk to zone 2 if the impedance crosses TZMA
 within a minute.
 This one minute is used to adjust for restorative corrective forces of
 the gird such as generator excitation controls and transformer load tap
 changer.
 In summary, zone 3 protection will only be changed if the impedance crosses
 TZMA with a certain rate within a specified time delay once it starts changing
 in TZPA.
 These ideas are illustrated in Figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:TZMA-and-TZPA"

\end_inset

.
 Although, the approach is very promising, a fast evolving system instability
 could mislead the scheme.
 Additionally, it can be seen that the approach proposed sacrifices dependabilit
y for security as evident by shrinking zone 3; if a fault occurs within
 the original zone 3 protection zone beyond the original zone 2 reach after
 zone 3 protection zone is shrunk, the approach proposed by the authors
 will rely heavily on the closest relay and circuit breaker to clear the
 fault.
 However, if this relay or circuit breaker fails to clear the fault, the
 fault will go uncleared worsening the already stressed system conditions.
 Lastly, the proposed algorithm will fail definitely in case the impedance
 stays within TZPA, suddenly jumps to original zone 3 due to zone 3 fault
 before the time delay expires then stays in zone 3 after fault clearing
 due to line heavy loading conditions.
 
\begin_inset Float figure
wide false
sideways false
status collapsed

\begin_layout Plain Layout
\align center
\begin_inset Graphics
	filename TZPA.PNG
	scale 60

\end_inset


\begin_inset Caption Standard

\begin_layout Plain Layout
TZMA and TZPA of the method in 
\begin_inset CommandInset citation
LatexCommand citep
key "Nikolaidis2016"

\end_inset


\begin_inset CommandInset label
LatexCommand label
name "fig:TZMA-and-TZPA"

\end_inset

 
\end_layout

\end_inset


\end_layout

\begin_layout Plain Layout

\end_layout

\end_inset


\end_layout

\begin_layout Standard
Lastly, the authors in 
\begin_inset CommandInset citation
LatexCommand citep
key "ma2016adaptive"

\end_inset

 proposed to identify power flow overload based on a newly proposed concept.
 This concept is based on the phasor relationships in the complex phasor
 plane.
 The paper only differentiates between three phase faults and overloads
 as overloads are three phase balanced phenomenon.
 Since the paper only aims to distinguish three phase faults from overload,
 any three phase fault on a transmission line can be analyzed without the
 need of information from the other end of line.
 This is due to the fact that the arc voltage is not affected by the infeed
 fault current making the fault point grounded through the arc resistance.
 This property is used to derive the criterion to differentiate between
 three phase faults and overloads based on an impedance criterion that can
 be adaptively adjusted using the measured phase angle between the voltage
 and current at the relay location as well as a constant safety factor.
 However, the method is not applicable when a three phase fault occurs within
 the distance relay reach during an overload condition.
 Additionally, it is assumed that all three phase to ground faults involve
 arc without the consideration of the other situations when three phase
 downed conductors cause such faults which in turn could cause some of the
 assumptions used in deriving the impedance criterion to be invalid.
 
\end_layout

\begin_layout Standard

\series bold
In summary, the use of rate of change of voltages and currents can prevent
 the problem of distance protection misoperation in most occasions but does
 not fully prevent it.
 Other methods use previous operational experience with distance relays
 to propose solutions to the problem of distance protection misoperation.
 However, system conditions and scenarios that were not previously encountered
 could mislead those proposed solutions.
 The use of high frequency fault generated transients seems to be a promising
 area but it is scarcely researched in literature.
\end_layout

\begin_layout Section
Conclusion
\end_layout

\begin_layout Standard
The problem of distance protection misoperation has been presented.
 Various approaches to solve the problem have been surveyed and organized
 into three main categories.
 The methods in each category have been explained.
 Additionally, the advantages and disadvantages of each method have been
 pointed out.
 
\end_layout

\begin_layout Standard
The first category is anticipation of distance protection misoperation in
 the planning stage.
 In this category, distance protection misoperation could be anticipated
 day ahead based on the forecasted load and generation as well as contingency
 conditions.
 However, due to the large size of modern day power systems, such anticipation
 is computationally intensive.
 
\end_layout

\begin_layout Standard
The second category is communication assisted protection schemes.
 The main idea in this category is that using information from both ends
 of the line or information from various substations in the network, a blocking
 command can be issued to the affected distance relay.
 Nevertheless, these communication assisted protection schemes have not
 found wide industry acceptance due to cybersecurity risks as well as the
 economic cost that is required to build such systems.
 
\end_layout

\begin_layout Standard
The third category is modification of the local distance protection function
 using local information.
 The main idea in this family of solutions is that using operational system
 experience as well as the local data, one can tell with certainty that
 a distance relay is about to misoperate.
 By detecting such conditions, a blocking command can be issued to guard
 the relay against misoperation.
 Nevertheless, the methods in this last category may fail under system condition
s that were not taken into consideration while developing these methods.
 
\end_layout

\begin_layout Standard
The most appropriate method to mitigate zone 3 misoperation is dependent
 on what is the most important factor for the utility company.
 For example, one utility company may prefer a communication-assisted scheme
 using remote measurements to eliminate the possibility for distance protection
 misoperation while accepting the cybersecurity vulnerabilities that are
 introduced.
 Another utility may not be willing to accept the cybersecurity risks or
 the cost of constructing such scheme and requires a solution using local
 measurements or minimum remote measurements.
 The authors think that methods which use local relay data are worthy of
 research attention as cybersecurity threats are becoming a major concern.
 
\end_layout

\begin_layout Standard
\begin_inset CommandInset bibtex
LatexCommand bibtex
bibfiles "References_used_in_proposal,newlit"
options "bibtotoc,IEEEtran"

\end_inset


\end_layout

\end_body
\end_document