Basics of CBs

8/14/2019 Basics of CBs

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X MER

ACB B C ACB

MCCBACBACB

TOCCP

TOMCC1

TOMCC2

TOETP

TOEM.LIGHT

TOUTILITYMCC

MCCB SDF SDF

Basics of Low Voltage System & Circuit Breakers

G

ACB

ACB

B C ACB

X MER


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How to calculate system fault level

T/F rating 1000 kVA

IFL of the transformer 1391 amps kVA x 1000

1.732 x 415

Isc of the transformer 27,825 amps IFL0.05

So the fault level at T/F terminals works out to be 27.8 kA

Similarly the fault level at the generator terminal works out to be 8.7 kA


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Effects of addition of T/F in parallel

T/F rating 1000 kVA

IFL of the transformer 1391 amps kVA x 1000

1.732 x 415

Isc of the transformer 55,650 amps IFL2 x 0.05

So the fault level at T/F terminals works out to be 55.7 kA


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Considerations for the fault level calculations

1. What is the size of the transformer

2. How many transformers are in parallel

3. Size of the Captive Generator, if used

4. Are all these units used in parallel ?

5. Any large size motor fed from the main bus ?


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Criterion for Breaker selection

1. Full load current of the transformer / Generator

2. Fault level at the point of installation

3. Other issues such as

1. 3 pole / 4 pole

2. Manual / motorized

3. Type of the release

4. Any other points .


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Terminologies associated with breakers

1. ICM Rated making capacity (expressed as peak value)

2. ICU Rated ultimate breaking capacity (expressed as rms value)

3. ICS Rated service breaking capacity (expressed as rms value)

4. ICW Rated short time withstand capacity (expressed as rms value)

5. ICC Rated short time withstand capacity for non automatic breakers

(expressed as rms value)

Test sequence ICU = O t CO (t = 3 min)

ICS = O t CO t - CO (t = 3 min)


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Types of breakers

1. Medium of arc quenching - Oil

- Air,

- Vacuum

2. Principle of operation - Current zero type of breakers

- Current limiting breakers


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What is current limiting ?

A principle where short circuit currentis interrupted before it reaches thefirst peak.

Current limitationin to Sentron VL

10 ms4 ms t

iProspectivecurrent


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Advantages of current limiting

1. Faster fault clearing

2. Lower let through value

3. Devices subjected to lesser stresses

4. Enhanced protection levels with

Cascading

5. ProperDiscrimination possible

Current limitationin to Sentron VL

10 ms4 ms t

iProspectivecurrent


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What is Cascading ?

Cascading refers to the technique of series connection of

protective devices,which results in enhanced breaking capacity.


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What is Cascading ?

Isc = 35 kA

3VL, 630 A ,45 kAIsc = 40 kA

VL160X, 100A, 40 kA

VF100, 100A, 18 kA


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CascadingChart

U p s t r e a m

M C C B fr a

B r . C a p .

( I c u )

V F 1 0 0 V L 1 6 0 x V L 1 6 0 x V L 1 6 0 V L 2 5 0 V L 2 5 0 V L 4 0 0

1 8 k A 4 0 k A 4 0 k A 4 0 k A 4 0 k A 4 0 k A 4 5 k A

R e l e a s e T M T M T M T M / E T UT M / E T UT M / E T UT M / E

R a t in g s 1 0 0 A 1 0 0 A 1 6 0 A 1 6 0 A 2 0 0 A 2 5 0 A 3 1 5 A

V F 1 0 0 T M 1 8 k A 1 0 0 A

4 0 k A 1 0 0 A

7 0 k A 1 0 0 A4 0 k A 1 6 0 A

7 0 k A 1 6 0 A

4 0 k A 1 6 0 A

7 0 k A 1 6 0 A

4 0 k A 2 0 0 A 4 0 k A

7 0 k A 2 0 0 A 5 0 k A

4 0 k A 2 5 0 A 4 0 k A 4 0 k A

7 0 k A 2 5 0 A 5 0 k A 7 0 k A

4 5 k A 3 1 5 A 4 5 k A 4 5 k A

7 0 k A 3 1 5 A 5 0 k A 7 0 k A

4 5 k A 4 0 0 A 4 5 k A 4 5 k A 4 5 k A 4 5 k A

7 0 k A 4 0 0 A 5 0 k A 7 0 k A 7 0 k A 7 0 k A

4 5 k A 6 3 0 A 4 5 k A 4 5 k A 4 5 k A 4 5 k A 5 0 k A 5 0 k A

7 0 k A 6 3 0 A 5 0 k A 7 0 k A 7 0 k A 7 0 k A 7 0 k A 7 0 k A

5 0 k A 8 0 0 A 5 0 k A 5 0 k A 5 0 k A 5 0 k A 5 0 k A 5 0 k A 5 0 k A

7 0 k A 8 0 0 A 5 0 k A 7 0 k A 7 0 k A 7 0 k A 7 0 k A 7 0 k A 7 0 k A

T M / E

D o w n s tr e a m M C C B f r a m e

V L 1 6 0 x T M

V L 2 5 0 T M / E

T M

T M / E

T M / E

V L 6 3 0

V L 8 0 0

T M / E

T M / E

E T U

V L 1 6 0 x

V L 1 6 0

V L 2 5 0

V L 4 0 0

V L 4 0 0


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What is Discrimination ?

Discrimination implies that the protective devices

closest to the point of fault will operate in the quickest possible

manner to avoid any wide spread shut down.


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What is Discrimination ?

Isc = 35 kA

3VL, 630 A ,45 kAIsc = 40 kA

VL160X, 100A, 40 kA

VF100, 100A, 18 kA


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Types of Discrimination

1. Current based

2. Time based

3. Energy based

4. Logic based (ZSI)

1. Partial Discrimination

2. Total Discrimination


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DiscriminationChart

U p s t r e

M C C B

B r . C a .

( I c u )

5 S X4 5 S X4 5 S X4 V F 1 0 0 V L 1 6 0 xV L 1 6 0 xV L 2 5 0 V L 2 5 0

1 0 k A 1 0 k A 1 0 k A 1 8 k A 4 0 k A 4 0 k A 4 0 k A 4 0 k A

R e le a s e T M T M T M T M T M T M T M / E T UT M / E

R a t in g s u p t o 2 0 A2 5 / 3 2 A4 0 - 6 3 A1 0 0 A 1 0 0 A 1 6 0 A 2 0 0 A 2 5 0 A

V F 1 0 0 T M 1 8 k A 1 0 0 A 3 . 8 k A 3 . 0 k A 2 .1 k A

4 0 k A 1 0 0 A 1 0 k A 9 .1 k A 4 .8 k A

7 0 k A 1 0 0 A 1 0 k A 9 .1 k A 4 .8 k A4 0 k A 1 6 0 A 1 0 k A 9 .1 k A 4 .8 k A 1 2 k A

7 0 k A 1 6 0 A 1 0 k A 9 .1 k A 4 .8 k A 1 2 k A

4 0 k A 2 0 0 A 1 0 k A 1 0 k A 6 . 5 k A 1 8 k A 2 5 k A

7 0 k A 2 0 0 A 1 0 k A 1 0 k A 6 . 5 k A 1 8 k A 2 5 k A

4 0 k A 2 5 0 A 1 0 k A 1 0 k A 6 . 5 k A 1 8 k A 2 5 k A 2 5 k A

7 0 k A 2 5 0 A 1 0 k A 1 0 k A 6 . 5 k A 1 8 k A 2 5 k A 2 5 k A

4 5 k A 3 1 5 A 1 0 k A 1 0 k A 1 0 k A 1 8 k A 4 0 k A 4 0 k A 3 2 k A 2 6 k A


4 5 k A 4 0 0 A 1 0 k A 1 0 k A 1 0 k A 1 8 k A 4 0 k A 4 0 k A 3 2 k A 2 6 k A7 0 k A 4 0 0 A 1 0 k A 1 0 k A 1 0 k A 1 8 k A 4 0 k A 4 0 k A 3 2 k A 2 6 k A





V L 1 6 0 T M

D o w n s t r e a m M C B / M C C B f r a m e

V L 6 3 0 T M / E

V L 2 5 0 T M / E

V L 4 0 0 T M / E

V L 1 6 0 T M

V L 2 5 0 T M / E

V L 8 0 0 E T U

V L 4 0 0 T M / E

Basics of CBs

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