feeder_protn - akhil

8/11/2019 Feeder_Protn - Akhil

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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 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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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

25

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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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)

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IDMT Relay Coordination


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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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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



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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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