DOC and DEF for EHV Syst em

Tutorial on Distance and Over Current Protection

Int roduct ion

• DOC and DEF are used in majority of the utility
as Main 2 protection for 220 kV line
• e
n

• gh

•
under fuse fail condition
Tutorial on Distance and Over Current Protection

DOC Set t ing Philosophy

• For 220 kV and 132 kV line with only one main
distance protection DOC must be set in such a
w T)

• uch

as per

ERPC finalized philosophy) .

Tutorial on Distance and Over Current Protection

DOC Set t ing Philosophy

• I nstantaneous DOC can be used at 400 kV side
of I CT set such that

d.
Tutorial on Distance and Over Current Protection

DEF Set t ing Philosophy

• For 220 kV and 132 kV line with only one main
distance protection, DEF (I DMT) must be set in

w
•
t F
(I DMT) is coordinated with Zone 3 time (as per ERPC finalized
philosophy) .
Tutorial on Distance and Over Current Protection

DEF Set t ing Philosophy

• I nstantaneous DEF can be used at 400 kV side
of I CT set such that

d.
 Tutorial on Distance and Over Current Protection

Sample Set t ing Calculat ion

315 M VA
Zps=0.12 pu
15000 MVA

ault
ault
Tutorial on Distance and Over Current Protection

DOC Set t ing

• Line
▫ I p = 1.5*I rated = 1.5*580 =870 A.

Top tzone3 + Δt 1.0 s

▫ TMS = 0.12 s (Considering NI curve)
Tutorial on Distance and Over Current Protection

DEF Set t ing

• Line
▫ I e = 0.2*I rated = 0.2*580 =116 A.

elay
al

•
umed

Top tzone3 + Δt 1.0 s

▫ TMS = 0.35 s (Considering NI curve)
 Tutorial on Distance and Over Current Protection

Inst ant aneous Set t ing calculat ion

315 M VA
Zps=0.12 pu
15000 MVA

•
• I nrush Current = 8*450 = 3600 A
• I p>> = Highest of the above two = 4200 A (Set
value).
Tutorial on Distance and Over Current Protection

Concluding Remarks
• Recommended philosophy for setting distance
relay are well established and can provide fairly

•
dy
 Duration spectra of Main effects
Electrical Electrical System Prime Energy
Switching machine & Governin mover resource
Transients System g & load energy dynamics
Dynamics Controls supply
system
dynamics
Over
Voltages

Fault
Transients

µs/ms Few Seconds Several Days to

seconds to minutes minutes weeks

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Transient Phenomena
µs I nit ial t ransient , Recovery Volt age

Scale ms Sw it ching surges, Fault t ransient s

Several cycles Ferro - resonance

Surge period
Dynam ic per iod
St eady St at e per iod

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 Si m u l a t i o n Ca se s

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W h y Lo a d f l o w st u d y f o r
p r o t e ct i o n e n g i n e e r ?

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 Pow er f low t o know
1. Nor m al load cur rent
2. Worst cont ingency load current

Plug set t ing based on t his inf orm at ion

1. St eady st at e m axim um volt age

2. St eady st at e m inim um volt age

Volt age r elay set t ing based on t his inf o.

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Fa u l t si m u l a t i o n t o a i d
p r o t e ct i o n e n g i n e e r

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 Fault calculat ion t o det erm ine
1. Fault curr ent f rom various sour ces
2. Post fault volt age
3. Ear t h f ault curr ent
4. Pr im ar y and back up relay cur rent
5. Tem por ary over volt age ( during
single line t o ground f ault )

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Eart h f ault relay oper at ion - Ex plained

No sour ce in t his part of t he net w or k

Eart h fault r elay picks up, because of t r ansf orm er

Vect or group
 Fault st udy

1. Sym m et r ical AC cur rent

2. DC of f set curr ent
3. Asym m et rical AC curr ent

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 DC of f set cur r ent
1. Maxim um at volt age zer o
2. Minim um at volt age m ax im um

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W h a t m a ch i n e i m p e d a n ce
t o co n si d e r f o r f a u l t st u d y
a n d r e l a y - co o r d i n a t i o n ?

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 Sust ained fault at t he m achine t erm inal
1. I nit ial Sub-t r ansient current .
2. I nt er m ediat e t r ansient cur rent .
3. Final st eady st at e curr ent .

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St a b i l i t y st u d y si m u l a t i o n
a n d i t s i m p o r t a n ce

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 St abilit y st udy
1. To det er m ine t he crit ical clear ing t im e
2. To f ind t he volt age and f r equency var iat ion in t he gr id.
3. Helps in r elay set t ing calculat ions

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 Frequency plot

1. Under f requency and over f r equency relay set t ing

2. Oper at e t he syst em around designed values.

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 Par allel line, one line t r ips

1. Direct ional over cur rent relay should not oper at e

f or t he healt hy line.
2. Ther e should not be load encroachm ent

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 I nit ial point

Final point

Term inologies

1. Load encroachm ent

2. Pow er sw ing

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 I m pedance seen by t he dist ance relay

1. Helps in dist ance relay set t ing calculat ions

2. Re-shaping t h e relay charact erist ic t o avoid
t hird zone load encroachm ent

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 Fault cleared in 0.1 seconds

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Fault cleared in 0.3 seconds

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 Fault cleared in 0.5 seconds

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 Out of st ep det ect ed
and gener at or t ripped

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 Pow er reversal in t he line
And t he syst em is saved.

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 Underst anding single pole aut o r e-closing f acilit y

Bot h t he lines car r y sam e cur rent

Healt hy line carr ies f ull load

Healt hy line cur rent

Unsuccessf ul re-closure, once again f ault

Fault ed line cur rent

Fault y line t rips

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Out of st ep operat ion
1. Out of st ep pr ot ect ion f or t he m achine
2. Pole slipping relay

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 Pr o t e ct i o n En g i n e e r
d e si g n s t h e r e l a y , b a se d
o n sy st e m b e h a v i o u r

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 Loss of ex cit at ion
1. Machine draw s ver y lar ge r eact ive pow er
2. Over heat ing of st at or
3. I f not pr ot ect ed, burning out of st at or

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Loss of excit at ion
1. I m pedance m oves f rom t he f irst
quadr ant
2. Set t les in a circle w it h dia xd and
of f set xd’/ 2
3. Of f set m ho r elay det ect s t he f ault

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Loss of excit at ion r elay
1. Off set m ho r elay
2. Off set of x d’/ 2
3. Diam et er of x d

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 W h y cu r r e n t l i m i t i n g
r e a ct o r f o r ca p a ci t o r
b a n k s?

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 Capacit or char ging

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 I nrush curr ent capacit or char ging

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 2 nd Har m o n ic an d 5 th
H a r m o n i c r e st r a i n t f o r
t r a n sf o r m e r d i f f e r e n t i a l
p r o t e ct i o n

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 Magnet izing inr ush curr ent

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 W h y t o p r o v i d e su r g e
a r r e st o r a n d RC ci r cu i t
f o r VCB sw i t ch i n g

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 VCB cur rent chopping and volt age raise pr oblem

Energy stored in the

Inductor = (1/ 2)* L* I * I
Energy stored in the
Capacitor = (1/ 2)* C* V* V

Voltage = I * sqrt(L/ C)

Solut ion : Pr ovide surge suppressor/ RC cir cuit or bot h

af t er t he VCB, close t o equipm ent

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Si m p h a t i c Ti p p i n g , w h a t
i t m e a n s?

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1. Volt age dip during t he f ault
2. Healt hy f eeder m ot or s st all or speed reduces
3. Once t he volt age r ecover s, lar ge curr ent dr aw n by
m ot ors
4. Healt hy f eeder m ay t rip
Fe r r o r e so n a n ce w h e n a n d
how ?

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 Ferroresonance (FR) TOV
An oscillating phenomena occurring in an electric
circuit which must contain at least:
1. a non-linear inductance
2. a capacitor,
3. a voltage source (generally sinusoidal),
4. low losses.
Transients, lightning over voltages, energizing or de-
energizing transformers or loads, occurrence or
removal of faults, etc...may initiate ferroresonance.
The main feature of this phenomenon is that more
than one stable steady state response is possible for
the same set of the network parameters.
Examples of systems at risk
from ferroresonance.

Contd.
Case study for predicting and
understanding of TOV and FR
1-pole 3-pole

HT side LR by opening CB2

 Voltage Current

FR existence when 2-poles opening of CB1

Conclusions
1. The various issues in the protection are
discussed
2. I t is concluded that close co-ordination
for protection department with other
departments are required.
3. The simulation tools help in learning the
protection aspects
4. Automated fault analysis system will help
in understanding the relay tripping
incidences better.

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 Discussions

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 Thank You

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Tripping Analysis - Met hodology
D N aja R,
ector,
t. Ltd
Tutorial on Distance and Over Current Protection

Cont ent s
• I mportance

•A

• Conclusion and Recommendations

Tutorial on Distance and Over Current Protection

Import ance
• Helps in identifying issues related to
▫ Commissioning errors (Eg CT polarity reversal)

•
f
• m
Tutorial on Distance and Over Current Protection

Sources of Dat a for Analysis

• COMTRADE files from
▫ Relay

•
on
• Observation
Tutorial on Distance and Over Current Protection

Analysis Approach
• Analyze every data to classify it as use full
“information” for fault analysis
• l
t
• A

▫ Relay trajectories (Eg. I mpedance and differential)

▫ Reasoning of obtained Waveforms and observations
Tutorial on Distance and Over Current Protection

Simulat ion Model

• The scenario can be reconstructed in simulation
platform

•V

•
Tutorial on Distance and Over Current Protection

Case St udy
Tutorial on Distance and Over Current Protection

Conclusion and Recommendat ions

• Modification in relay settings
• Correction of any commissioning related issues
• n

•
healthiness can be studied.
POWER SWING AND OUT-OF-STEP
CONSIDERATIONS ON
TRANSMISSION LINES

Tutorial on Protection
 Contents
Introduction
Definitions
Power-swing phenomena and their effect on
transmission line relaying
Power-swing detection methods
PSB and OST protection philosophy
Summary and conclusions

Acknowledgements: All contents are based on references [1] and [ 2]

2 © Power Research and Development Consultants Pvt Ltd

 I NTRODUCTI
NTRODUCTI ON
Changes in regulations and the opening of the power markets
are causing rapid changes in the way the power grid is
operated.
Large amounts of power are commonly shipped across a
transmission system that was not designed for such
transactions.
Independently owned and operated generating units are
being built in locations that may not be optimum for system
stability and system needs.
Power plant systems are being upgraded to get every
possible megawatt out.
The results of these upgrades often make the generating units
more susceptible to instability.

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 I mpact
The August 14, 2003 blackout in the Northeastern
United States and Southeastern Canada has led
to substantial scrutiny of many aspects of
transmission line protection. One of the more
difficult and commonly misunderstood issues
being addressed is that of power swing and out-of-
step protection applied to transmission lines.

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 DEFI NI TI ONS
Power Swing: a variation
in three phase power flow
which occurs when the
generator rotor angles are
advancing or retarding
relative to each other in
response to changes in load
magnitude and direction,
line switching, loss of
generation, faults, and
other system disturbances.

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 DEFI NI TI ONS

Pole Slip: a condition

whereby a generator, or
group of generators,
terminal voltage angles
(or phases) go past 180
degrees with respect to the
rest of the connected
power system.

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 DEFI NI TI ONS
Stable Power Swing: a power swing is
considered stable if the generators do
not slip poles and the system reaches a
new state of equilibrium, i.e. an
acceptable operating condition.

Unstable Power Swing: a power swing

that will result in a generator or group of
generators experiencing pole slipping
for which some corrective action must
be taken.

Out-of-Step Condition: Same as an

unstable power swing.

Electrical System Center or Voltage

Zer o: it is the point or points in the
system where the voltage becomes zero
during an unstable power swing.
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 POWER-SWI NG PHENOMENA AND
THEI R EFFECT ON
TRANSMI SSI ON LI NE RELAYI NG
1. Fundamental power-swing detection problem: The power grid
is a very dynamic network connecting generation to load via
transmission lines. Power systems under steady-state conditions
operate very close to their nominal frequency and typically
maintain absolute voltage differences between busses of 5%. The
system frequency on a 60 Hz system normally varies by less than
+/- 0.02 Hz.

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 2. Effect of power swings on tr ansmission line relays
and relay Systems

Zone 1 and Directional Comparison Blocking Scheme Characteristics

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 3. I mpedance measured by distance relays
dur ing power swings

Two Machine System

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11 © Power Research and Development Consultants Pvt Ltd
 Impedance trajectories at the Relay During a Power Swing for Different k values

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 POWER-
POWER-SWI NGDETECTI ON METHODS
1.Conventional r ate of change of impedance PSB and OST methods
a. Concentric Characteristic Schemes

PSB and OST

Concentric Distance
Relay Characteristics

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 b. Blinder Schemes.

Two-Blinder Scheme
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 C. Rdot Scheme

Conventional OST Relay

Y1 = (R-R1)<= 0

R-dot relay:
Y2 = (R-R1)+T1*dR/ dt <= 0

Wherein
Y1 and Y2 are control outputs
R: Apparent resistance
R1 and T1: Relay settings

Phase-plane Diagram I llustrating the Concept of R-dot Principle

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 2. Additional power swing detection methods

a. Continuous Impedance Calculation

Power swing detection with continuous impedance calculation

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 b. Swing-Center Voltage and its Rate of Change

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