feeder_protn - akhil
TRANSCRIPT
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ee er ro ec on
Akhil K G tkhil Kumar GuptaSr. Faculty Member PMI)
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Introduction
Fuse Coordination
Relay Coordination
Conclusion
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Fuses & Its CoordinationFuses & Its Coordination
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Feeder Protection
ensuring the safety of personnel working with electricalsys ems an or preven ng amage ue o var oustypes of faults such as over currents, short circuits andover vo tage etc.
A short circuit may melt a conductor, resulting in arcingand the possibility of fire ; the high electromechanicalforces associated with a short circuit also causemechanical stresses which can result in severe damage,a heav short circuit ma also cause an ex losion
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Feeder Protection
Used in Lower End Systems
IDMT O/C, Definite Time O/C, High Set O/C Relays used Extensivel used at Medium Volta e level and also at HV
EHV Systems as Backup Protection
Unit Protection (Pilot Wire Protection) Used for critical Medium Voltage Circuits like Long cable
feeders, Tie feeders etc. Also some times used for HV /EHV
applied
Primarily Longitudinal Differential Protection Supplemented by Backup Protection, usually IDMT O/C type
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Protection Co-ordination
protective devices is the prospective current
Prospective current is the current which would flow ata particular point in an electrical system if a shortcircuit of negligible impedance were applied
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Protection Co-ordination
protection system so that when fault occurs, minimumsec on o e sys em aroun e au s sconnec e
Protective devices are described by a timecurrentcharacteristic and in order to achieve co ordination
between protective devices, their timecurrentcharacteristics must be sufficiently separated so that afault downstream of both of rotective devicesoperates only the device nearest to the fault
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Protection Co-ordination
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Fuses
use s e mos common an w e y useprotective device in electrical circuits
Because element of fuse is of much smallercross sectional area than cable it protects(assuming of same material), element will
reach its melting point before the cable Larger the current, quicker the element melts If deterioration of element occur it o erates
even faster, hence fail safe
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Fuses
sem -enc ose or rew rea e use
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Cartr idge type
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Cut Section of Fuse
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Fuses
Silver element, specially shaped, enclosed in a barrel of insulating material, filled with quartz
Advantages Correct rating and characteristic fuse always fitted to a
Arc and fault energy contained within insulating tube prevents damage
Normally sealed therefore not affected by atmosphere hence gives more stable characteristic reliable grading
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Design of Fuse Elements
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Fuses ,
at the notches when an overcurrent flows and this results in a number of controlled arcs in series
The voltage across each arc contributes to the total voltage across the fuse, and this total voltage results in the current fallin to zero and because the number of arcs is limited the fuselink voltage should not be high enough to cause damage
elsewhere in
the
circuit
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Fuses
in shorter times so short that current will be cut off before it reaches its eak value o eration < 5 ms
Hence serious overheating and electromagnetic forcesin the system can be avoided
Extremely high breaking
capacity of up to 100KA,also known as HRC (highrupturing capacity) fuses
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Fuses
Simple & Economical Ver Fast O eration
Current Time Characteristic
Limits fault energy Disadvanta es
Require close coordination
Poor sensitivity for earth faults Cause single phasing Inconvenient of replacement
can be set to trip on as little as 5% over current while thefuse has a fusing factor of about 1.75)
Fusing factor = minimum fusing current current rating16
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Selection of Fuses
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Selection of Fuses
Fuses can be used as either for overload and short circuit protection or for short circuit protection
Fuse se ect on gu e ne or motor app cat on Fuse should not blow during running Fuse should not blow during starting
12 x Ie for 10 msec & 6 x Ie for Motor Starting Time
Coordination with Starter
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Selection of Fuses- Case Study
Motor data M1 S. C. Induction motor
50 HP, IRM = 70 A, ILR = 6 x IRM Starting method : D.O.L. Starting time = 15 sec
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Selection of Fuses
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Coordination with Starter
Type 1 Coordination Requires that, under short circuit conditions, the contactor
or s ar er s a cause no anger o persons or ns a a on an
may not be suitable for further service without repair andreplacement of parts
Type 2 Coordination
or starter shall cause no danger to persons or installation andshall be suitable for further use. The risk of contact welding is
z , w u umeasures to be taken as regards the maintenance of theequipment
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Type 2 Coordination
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Type 2 Coordination
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Rela sRela s
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Definite Current Relay
Relay operates instantaneously when the current reaches a
predetermined value.
t me
Definite
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current
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Definite Time Relay
Relay operates after a definite time delay when the current
reaches a pre-determined value.
time
Definite
currentDefinite
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current
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Over Current Relays
Definite Time
Normal Inverse
IDMT
T
I
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IDMT O/C Relays
. . . . RELAYS Current/time tripping characteristic
equation of IDMT (Inverse Definite Minimum Time) Over Current relays
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IDMT O/C Relays
applications
there is substantial reduction in the fault current as thedistance from the power source increases
Extremely Inverse Characteristic is particularly suitable
in grading with fuses Long Inverse Characteristic is primarily used for
overload protection or earth fault protection in
resistance grounded system IDMT relays provide both time and current grading to achieve
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IDMT O/C Relays
is usually represented on a lo arithmic scale and ives
the operating
time
at
different multiples of setting current, for the maximum Time Multiplier
TMS is adjustable giving a
characteristics
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IDMT O/C Relays
5A, 2.2sec, IDMT and having a relay setting of 125%, TMS =0.6. It is connected to a supply circuit through a CT 400/5 ratio. The au curren s .
Solution The pick up value of the relay is 5A but since the rela settin is 125% therefore the o eratin current of the relay is 5 X 1.25 = 6.25A
The PSM
(Plug
Setting
Multiplier)
of
the
relay,
PSM = 4000 / (6.25 x 80) = 8(PSM = Prim Current / Relay Current Setting X CT Ratio)
. u v , = 3.2 secSince TMS is 0.6 actual o eratin time of the rela is 1.92s
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Relay Coordination Methods
Methods used to achieve correct relay co ordination are
Time grading
Current grading
Combination of Time and Current grading
The common aim of these methods is to give correctdiscrimination so that each method isolate only the
faulty section of the power system network, leavingthe rest of the system undisturbed
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Time Grading
pera ng me o e pro ec on s ncrease rom e ar en o the protected feeder towards the generating source
The time difference between two adjacent relay is usually
approximately 0.5 s, this is provided to cover operating time of CBs & errors
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Time Grading
When fault occur beyond B, all relays come into action as fault current flows through all of them, the least time setting is for re ay B, ence re ay B operates a ter . 5 s; B at B opens an clears the fault, with this, all other relays (C, D and E) reset
If relay or CB at B fails to operate, fault remains un cleared, in this case, relay C will operate after 0.65 s and trip CB at C, if the CB at C also fails to operate, then relay D will operate after 1.05 s
, high and it should be cleared very quickly, but time grading method takes longest time to open the CB near the source, i.e.
e more severe au s e mos e aye
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Feeder Protection
Relay R1 Current Setting =100% (100A Prim) = = = . , Operating Time @ PSM20 & TMS0.10 = 0.22 S (i.e.2.2 x 0.1)
Relay R2 Current Setting = 100% (150A Prim) TMS selected = 0.25, PSM = 3000/ 150 = 20 Operating time @ PSM30 & TMS0.25 = 0.55S (i.e. 2.2 x 0.25)
Grading Margin between Relay R1 / R2 = 0.55 0.22 = 0.33 S
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Current Grading
It relies
on
the
fact
that
the
fault
current
varies
with
the
position
of the fault because of the difference in impedance values
etween t e source an t e au t Relays are set to pick up at progressively higher values of
current towards the source and rela s em lo ed are hi h set (high speed) instantaneous over current relays
The operating time is kept same for all the relays protecting the
i erent sections
Advantage compared to time graded system is that the
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Current Grading
at F2, since the distance between these points may be only a few meters, corresponding to a change in fault current of approx ma e y .
The magnitude of fault current cannot be accurately determined as all the circuit arameters ma not be known sometimes
During a fault, there is a transient condition and the
performance of
the
relay
is
not
accurate
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Feeder Protection
Relay R1 Current Setting = 100% (100A Prim) = = = . , Operating time @ PSM30 & TMS0.10 = 0.22 S (i.e. 2.2 x 0.1)
RELAY R2 Current Setting = 100% (750A Prim) TMS selected = 0.10, PSM = 3000/750 = 4 Operating time @ PSM4 & TMS0.10 = 0.50 S (i.e. 5 x 0.10)
Grading margin
between
Relay
R1
/ R2
= 0.50
0.22
= 0.28
S
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Discrimination by Time and Current
, to the fact that the more severe faults are cleared in the longest operating time. On the other hand, discrimination by current can be applied only where there is appreciable impedance
between the two circuit breakers concerned ,
proportional to the fault current level and the actual
characteristic is
a function
of
both
time
and
'current'
settings
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Grading Margin in IDMT O/C Relays
u Grading Margin (t)
Rela timin Error + 7.5% for EM 5% for Numerical Version)
Relay Over shoot (40 60 ms for EM, N.A. for Numerical
C.B. Trip time (40 60 ms)
Safety Margin Recommended Grading Margin: 0.3 0.4s for EM & 0.2 0.3s for Numerical Version
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NON-DIRECTIONAL IDMT O/C RELAY
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DIRECTIONAL IDMT O/C RELAY
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DIRECTIONAL IDMT O/C RELAY
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DIRECTIONAL IDMT O/C RELAY
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DIRECTIONAL IDMT O/C RELAY
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DIRECTIONAL IDMT O/C RELAY
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DIRECTIONAL IDMT O/C RELAY
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DIRECTIONAL IDMT O/C RELAY
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DIRECTIONAL IDMT O/C RELAY
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DIRECTIONAL IDMT O/C RELAY
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DIRECTIONAL IDMT O/C RELAY
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DIRECTIONAL IDMT O/C RELAY
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DIRECTIONAL IDMT O/C RELAY
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DIRECTIONAL IDMT O/C RELAY
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DIRECTIONAL IDMT O/C RELAY
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Fuse Coordination
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Fuse Coordination
u u The operating time of a fuse is a function of both the
,
which follows an I 2t law, so, to achieve proper co ordination between two fuses in series it is necessar to ensure that the total I 2t taken by the smaller fuse is
less than
the
pre
arcing
I 2
t value
of
the
larger
fuse
It has been established by tests that satisfactory grading between the two fuses will generally be
achieved if
the
current
rating
ratio
between
them
is
greater than two
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Fuse Coordination
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Fuse Coordination
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Fuse Coordination
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Fuse Coordination
u y For grading inverse time relays with fuses, the basic
backs up
the
fuse
and
not
vice
versa If the fuse is upstream of the relay, it is very difficult to
maintain correct discrimination at high values of fault current because of the fast operation of the fuse
e re ay c aracter st c est su te or coor nat on with fuses is normally the extremely inverse (EI)
2
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IDMT Relay Coordination
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IDMT Relay Coordination
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IDMT Relay Coordination
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IDMT Relay Coordination
Rate Current = 87.5 A 66KV 525 A 11KV S.C. Current for Fault on LV side (assuming infinite source)
t
= 525 x 100 / 10 = 5250 A (11 KV side) = 87.5 x 100 10 = 875A 66 KV side
IDMT Relay with Normal Inverse Characteristic (IEC)
Operating time (t) = (0.14 / ( I0.02
1) ) x TMSwhere I = Plug Setting Multiplier (PSM) t @ PSM 10 / TMS 1.0 = 3.0s
t @
PSM
20
/ TMS
1.0
= 2.2s
t @ PSM 8.75 / TMS 1.0 = 3.16s
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IDMT Relay Coordination
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IDMT Relay Coordination
O/C Setting= 1A (200A), TMS = 0.10, PSM=10500/200 >20
> =
11KV B/C
(R2) O/C Setting = 1A (600A), PSM= 5250/600 = 8.75
Desired Operating Time (DOT)= 0.22 + 0.30 = 0.52sOperating time @PSM 8.75 / TMS 1.0 = 3.16sTMS to achieve DOT of 0.52S = 0.52/3.16 = 0.16
11KV I/C (R3) e ng = , = = .
DOT = 0.52 + 0.30 = 0.82s . . .
TMS to achieve DOT of 0.82S = 0.82/3.16 = 0.2655
IDMT Relay Coordination
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e ay Coo d at o
O/C Setting = 1A (100A), PSM = 875 / 100 = 8.75
= + =
Operating time
@
PSM
8.75
/ TMS
1.0
= 3.16s
TMS to achieve DOT of 1.12S = 1.12 / 3.16 = 0.35Note:
Grading between Relay R3 & R4 is optional since it does not a ect own stream coor ination, i oregone, i entica TMS can be adopted for Relay R4 (TMS 0.26) with similar response time of 0.82s as relay R3, this would reduce the up stream fault
clearance time Grading margin of 0.3s is used considering EM IDMT relays,
w umer ca re ays, gra ng marg n can e re uce o . s, in view of reduced timing errors and no over shoot
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