Fault Level and Fault Current
Laxman Chaudhary
Senior Section Engineer Electrical at JKCement | Ex-UltraTech Cement , Heidelberg Cement India , Shree Cement | Electrical Graduate with Honors | 8 Years of Experience in Cement Plant Project, Operation & Maintenance
Fault level at any given point of the Electric Power Supply Network is the maximum current that would flow in case of a short circuit fault?.
Formula to Calculate Fault Level -
Fault MVA = (Transformer Rated MVA x 100) / Percentage Impedance
Fault Current = (Fault MVA) / ( 1.732 x Voltage in KV)
Please note that here Secondary Voltage will be considered in fault current formula due to fault will take place in secondary side.
Example= Suppose We have transformer which is rated at 25 MVA , percentage impedance is 11.9 , Primary and secondary voltage is 132 KV and 11 KV respectiely , fault MVA will be-
Fault MVA = (25 x 100) / 11.9
= 210 MVA ( This is maximum MVA during short circuit fault)
Now During fault maximum current -
Fault Current = (210) / ( 1.732 x 11 )
= 11 KA ( approximately )
Fault level for above transformer will be 210 MVA and 11 KA .
Note that Time is also considered to withstand with fault level.
HT switchgears are rated for 3 seconds and LT are rated for 1 seconds.
Senior Section Engineer Electrical at JKCement | Ex-UltraTech Cement , Heidelberg Cement India , Shree Cement | Electrical Graduate with Honors | 8 Years of Experience in Cement Plant Project, Operation & Maintenance
1 个月Percentage impedance (%Z) varies with transformer rating. It is not a fixed value across all transformers. The main factors affecting %Z include: 1. Transformer Rating (MVA): As the transformer's MVA rating increases, the percentage impedance typically increases to limit fault currents. 2. Voltage Level: Higher voltage transformers tend to have higher %Z to control short-circuit currents. 3. Design & Construction: The winding configuration, core design, and cooling method also influence %Z. 4. Application Requirement: Power system stability and fault current considerations affect the choice of %Z for different applications (e.g., generator transformers, distribution transformers). For example: A small distribution transformer (e.g., 500 kVA, 11 kV) may have %Z around 4–6%. A large power transformer (e.g., 100 MVA, 220 kV) may have %Z in the range of 10–15%. So, percentage impedance is varied with transformer rating rather than being fixed.
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1 个月Has the percentage impedance been varied with Transformer rating or kept fix(assumed) for voltage level