Question
Download Solution PDFA three phase circuit breaker is rated 2000 MVA 33 kV. What will be the making current?
Answer (Detailed Solution Below)
Detailed Solution
Download Solution PDFBreaking 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:
\(I_b={MVA\over \sqrt{3}\times V_{L}}\)
where, Ib = Breaking current
MVA = Breaking capacity
VL = Line-to-line voltage
The relationship between making and breaking current is:
\(I_m=2.55\times I_b\)
where, Im = Making current
Ib = Breaking current
Calculation
Given, Breaking capacity = 2000 MVA
VL = 33 kV
\(I_b={2000\space \times 10^6\over \sqrt{3}\times 33\times 10^3}\)
Ib = 34.9 kA
The making current is given by:
\(I_m=2.55\times 34.9\)
Im = 89 kA
Last updated on Jun 24, 2025
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