Module 2

Session 3

Overcurrent Earth Fault and

Directional Protection

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 2

Topics covered –1

Th

Fuse current –time characteristic

Pre

Di

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 3Topics covered –2Cr Ty Tim

Gr

Co

Gr

Pri

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 4

HRC fuse Typical fuse elements

Fuse

EMSD Refresher Course -Dr. K.K. Li5

Module 2, Session 3

EMSD Refresher Course -Dr. K.K. Li6

Module 2, Session 3

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 7Th Heat is conducted away from the restricted sections of an element to regions where the current densities are lower and this increases the time needed to melt and vaporise the restrictions Th The pre-arcing periods are relatively long and heat transfer is not restricted to the elements Th

The current in the fuselink will cause the restrictions

to reach a steady state condition in which they are at

the melting point of the element material

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 8

Ev

On

The total interruption time for any given

condition is therefore made up of:

the pre-arcing period, and

the arcing period.

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 9Mi No Fu

I 2t

current

rated current

fusing minimum = factor Fusing Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 10

Standardized Time Current Zones for Fuse

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 11Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li

12Pre-arcing behaviour

Th

the pre-arcing periods are so short that the

heat energy dissipated from a fuselink during

such periods may be regarded as negligible

heat

specific its x volume small the of mass instant the at volume small the to supplied power = t d d θheat

sp.x volume small of mass dt

) + 1 ( R i = am 2t

0t θαθ∫

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 13Arcing behaviour A Th

dt C i + ) i L (dt d + ) R + R ( i = e t

c f c s ∫Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 14

Discrimination between fuses

Th

In

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 15Discrimination between fuses and MCB Th If t

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 16

EMSD Refresher Course -Dr. K.K. Li17 EMSD Refresher Course -Dr. K.K. Li18

Module 2, Session 3Module 2, Session 3

EMSD Refresher Course -Dr. K.K. Li19

Overcurrent Relays

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li20

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 21IDMTL Relay Draw out case Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li

22Types of overcurrent relays

Ins

Ti

Inv

Standard inverse characteristic

sec 1

14

.002.0−⎟⎟⎠⎞⎜⎜⎝⎛=set f I I t

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 23Ve Ex Lo sec 15.13−⎟⎟⎠

⎞⎜⎜⎝⎛=set f I I t sec

180

2−⎟⎟⎠⎞⎜⎜⎝⎛=set f I I t sec 1120−⎟⎟⎠

⎞⎜⎜⎝⎛=set f I I t Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 24

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 25

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 26

Co-ordination procedure –1

A

Th Th

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 27

Co-ordination procedure –2

Th

Th De Pe

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 28

Co-ordination procedure –3

W

M

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 29

Principles of time/current grading

Di

Di

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 30

Discrimination by both time and current

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 31

Relay Fault level (MVA)Discrim by time (s)Discrim by time/current

(s)H 98.70.250.07

J 1230.650.33K 1540 1.050.07L

3500

1.45

0.25

Module 2, Session 3

EMSD Refresher Course -Dr. K.K. Li

32

Relay Fault level (MVA)Discrim by time/current (s)

H 35.70.17J 98.70.42K 1230.86L

1250

0.39

Relay operating times at remote end of the protected sections

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 33

Grading Margin

Th Th Er Fin

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 34

Module 2, Session 3

EMSD Refresher Course -Dr. K.K. Li

35

Determination of grading margin

W

(s) 100

2'ts to t t E E t CB CT R +++⎥⎦

⎤

⎢

⎣⎡+=(s) 1002'ts to t t E t CB R +++⎥⎦

⎤⎢⎣⎡=Module 2, Session 3

EMSD Refresher Course -Dr. K.K. Li

36

In

Electromechanical

relay

Static relay

Typical basic timing

error (%)7.5 5.0Overshoot time (s)0.050.03Safety margin (s)

0.10

0.05

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 37

Co

It i

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 38

Earth Fault Protection

Th

A Fo

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 39

C T Magnetisation Curve

Module 2, Session 3

EMSD Refresher Course -Dr. K.K. Li

40

Impedance of Electro-mechanical Relays

Th Fo

An earth fault overcurrent relay has a rating of 1 A, with setting range from 20% to 80% at 10% steps. The burden of relay at setting current is 5 VA and the impedance of relay may be assumed pure reactive. The relay is supplied from 3 x 100/1 line C.T.s

Module 2, Session 3

EMSD Refresher Course -Dr. K.K. Li

41

CT Magnetisation Curve

05101520

25300

0.02

0.05

0.08

0.1

0.15

0.2

1

Im(A)

V m (V )

Module 2, Session 3

EMSD Refresher Course -Dr. K.K. Li

42

At

At

()A

I I A I V E j j

Z m m R 8.963100I graph from 056.025.68125.78.08125.78

.05

2op 22

=×+×===×=Ω==()A

I I A I V E j j

Z m m R 1.803100I graph from 067.033.8.136.0.136

.05

2op 22

=×+×===×=Ω==

Module 2, Session 3

EMSD Refresher Course -Dr. K.K. Li 43

320A

1A

25V

125Ω

20%

63.1A 0.1320V 80Ω25%59.7A 0.09916.67V 55.6Ω30%65.5A 0.085A 12.5V 31.25Ω40%80.1A 0.067A 8.33V 13.9Ω60%96.8A 0.056A 6.25V 7.8Ω80%I op I m E Z R I set Module 2, Session 3

EMSD Refresher Course -Dr. K.K. Li

44

Effective op current plot against current setting

0501001502002503003500%

20%

40%

60%

80%

100%

Relay Current Setting

A c t u a l C u r r e n t S e t t i n g

Module 2, Session 3

EMSD Refresher Course -Dr. K.K. Li

45

Earth Fault Protection for Resistance Earthed System

Th Ch Es

()

m I I ×+×=3Ratio CT I 2op Module 2, Session 3

EMSD Refresher Course -Dr. K.K. Li

46

Sensitive Earth Fault Protection

Us Th

The effective setting depends on the CT magnetizing characteristic and the impedance of CT at the current setting

Module 2, Session 3

EMSD Refresher Course -Dr. K.K. Li

47

Example 1

OC 1

200/5100/5

OC 2

A B I FL =280A

1500 kVA 11/0.38 kV

Fault Level=100 MVA

(5250A)

108A 100A 1.08 current operating its 100%,

or 5A setting 2 O/C If 102.3A overload) 30% (assume max =×===I O/C 2 setting = 100%, 0.1

Module 2, Session 3

EMSD Refresher Course -Dr. K.K. Li

48

150%

setting Current A 308 A 280x1.1 cable max ===I sec

0.62 or

sec 0.22 0.4 time operating 1 O/C graph)

(from 0.1x2.2 2 O/C of time Operating 20 52.5100

5250

≥+≥=>==set

f I I 5.173005250 ==set

f I I 0.26

T.M.0.62

T.M. x 35.2≥≥T.M. is set at 0.3

O/C Relay 1 setting = 150%, 0.3

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 49

Example 1

Module 2, Session 3

EMSD Refresher Course -Dr. K.K. Li

50

Example 2

1200/5400/51

2

I FL =350A

33/11 kV 20 MVA 16%333 kV

(1200MVA)

11 kV

100/511/0.38 kV 1500 kVA

380 V

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 51

TM

PS

Example 2

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 52

Example 3

600/1

1

2

33/11 kV 20 MVA 20%

33 kV

(1200MVA)11 kV

400/5 NI 100% 0.3

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 53

Example 3

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 54

Example 4

200/5200/5

1Fault Level 110 MVA

2100%IDMTL 100% 0.3Ext Inv

11 kV

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 55

Example 4

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 56

Example 5

11 kV

Fault Level=100 MVA

B 100A

OC

200/5A

I FL =160A

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 57

Example 5

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 58

Directional Relays

W Di Re Ap

EMSD Refresher Course -Dr. K.K. Li59

Module 2, Session 3

EMSD Refresher Course -Dr. K.K. Li60

Module 2, Session 3

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 61Directional relay connections 30°Connection (0°MTA)

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 62

60°Connection No. 1 (0°MTA)

EMSD Refresher Course -Dr. K.K. Li63

Module 2, Session 3

60°Connection No. 2 (0°MTA)

Module 2, Session 3

EMSD Refresher Course -Dr. K.K. Li90°Connection (30°MTA)

EMSD Refresher Course -Dr. K.K. Li65

Module 2, Session 3

90°Connection (45°MTA)

Module 2, Session 3

EMSD Refresher Course -Dr. K.K. Li66

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 67Directional Relay Applications Pa

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 68

Gr

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 69Pro Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 70

Directional earth fault relays

Di an

Th typ

Th tra

Fo an

Fo an

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 71Self Evaluation W W Ho Ho W W Ho

Application of directional relays

Module 2, Session 3EMSD Refresher Course -Dr. K.K. Li 72

Further Readings

W ap

W ne

‘N AR

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