A three phase circuit breaker is rated at 2000 MVA, 33 kV. The symmetrical breaking current is: 

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NMDC Junior Officer Electrical 24 April 2022 Official Paper
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  1. 20 kA
  2. 60 kA
  3. 80 kA
  4. 35 kA

Answer (Detailed Solution Below)

Option 4 : 35 kA
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Detailed Solution

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Breaking capacity of a circuit breaker

The rated breaking capacity is defined as the maximum fault current a circuit breaker can successfully interrupt without being damaged.

It is always expressed in KVA and the current corresponding to breaking capacity is known as the breaking current.

The breaking current is given by:

where, Ib = Breaking current

MVA = Breaking capacity

VL = Line-to-line voltage

The relationship between making and breaking current is:

where, Im = Making current

Ib = Breaking current

Calculation

Given, Breaking capacity = 2000 MVA

VL = 33 kV

Ib = 34.9 kA (OR) 35 kA

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