1_Basic Protection Principles

8/17/2019 1_Basic Protection Principles

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The year of Profitable Growth

Basic ProtectionPrinciples


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Power Transmission and Distribution

Power AutomationProgress. It‘s that simple.

Overcurrent-time protection

Definite-time

overcurrent-

protection

Inverse-timeovercurrent-protection

t

I I

N I

> I

>>

t2

t1

t

I I N

t

I I N


3/15

3



Differential protection

Load condition

Fault condition

Load condition

Fault condition

I A I B

I C

I A I B

I C

Line

Busbar

Istart - Iend = 0 ∆I = 0

Istart - Iend≠ 0 ∆I ≠ 0

IA + IB + IC ≠ 0 ΣI ≠ 0

IA + IB + IC = 0 ΣI = 0


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Overvoltage - Undervoltage

U >

UN

U <

Overvoltage

Undervoltage


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Time grading

t = 700 ms

t = 400 ms

t = 100 ms

I>

I>

I>

I > I > I >


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t

t

t

t

I>>

I>

OFF

IE>>

IE>

IL1

IL2

IL3

IE

Valid for all devices with 4 input transformers

OFF

Function definite-time-protection


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IL1

IL2

IL3

(IE)

OFF

I>> t

I> t

suitable for all types of neutral-point connection

I>>

I>

I>>

I>

IL1

IL2

IL3

IE

IE is calcuated,

(min. 0.1 x IN)and equipped with

timer

Function definite-time-protection (three current inputs)


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Function definite-time protection (three current inputs)

I>> t

I> t OFF

OFF

t

t

L2 is calculated

I>>

I>

I>>

I>

IL1

IL2

IL3

IE

IL2

IL1

IL3

(IE)


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t [sec]

0.5

1.0

1.5

2.0

x IN0.5 1.0 1.5 2.0 2.5

I> I>>

Tripping area

Tripping characteristic curve of a two-step definite-time protection

Definite-time protection, Characteristic curves


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x IN0.5 1.0 1.5 2.0 2.5

t [sec]

0.5

1.0

1.5

2.0

Tripping characteristic curve of an inverse-time protection

Characteristic curves:

IECANSI British Standard

Inverse-time protection, Characteristic curves


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IL1

UL1

OFF&

I>> t

Direction

I> t

Instantaneous zone (I>>) directional

Back-up zone (I>) non-directional

Directional definite-time-protection


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I1

I2

I3

I4

I5

Measuring principle of differential protection devices

Kirchhoff law: I1 + I2 + I3 + I4 + I5 = 0

Current direction definition , .


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Power AutomationProgress. It‘s that simple. 1 (1) 2 (2)

Setting of the differential protection at a line / cable

1 + 2 - - 0

0, 1 + 2 - /

2.5.. 4 ≥ 0.15..0.2 , ( )

1 500 , 2 -300 , , 500 , 50

2,5 / , 0.25

/, 500 / 500 + (-300 / 500) 1.0 - 0.6 0.4

/ , -

I2

CT2

IDiff

Voltage

source U1

CT1 Voltage

source U2IC

I1


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IS = |I

1| + |I

2|

Restraint current

IDiff = | I1+I2|

Differential current

Tripping area ->

trip

Restraint area -> No tripIDiff

>

Differential current due to line

capacity / cable capacity

Differential current due to linear

errors of the primary current transformers

Differential current due to non-linear

errors of the primary current transformers

k1=0.25

I1 I2

IDiff

k2=0.5

Possible differential

currentdue to errors

Tripping characteristic

Line differential protection: Resulting tripping characteristic


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Summed up currents: I M1 = 5•I 1 + 3•I 2 + 4•I 3 I M2 = 5•I 1 + 3•I 2 + 4•I 3

U1 = Rb • Ib1 U2 = Rb•Ib2

Measuring principle of the two pilot-wire differential protection

⇒ Voltage comparision:

Side 1 Side 2

7SD600 7SD600

Device 1 Device 2Twisted pair pilot wire

I 1

I 2 I 3 I 3 I 2 I 1

L1

L2

L3

I M1

I a

I a

I M2

I b2 I b1

Rb Rb

Ra

Ra

R/2

R/2

U1

U2

transformer

Summation Summation

transformer

1_Basic Protection Principles

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