7. Percent Impedance at 85°C With Base kVA and Voltage Transformer Impedance is the opposition to current flow caused by the transformer's internal resistance and leakage reactance. •
Expressed as a percentage of rated voltage at 85 o C, typically 2% to 10% for distribution transformers 85°C matters since impedance is temperature- dependent: It’s standardized at 85°C, the typical operating temperature of a liquid-filled transformer
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Ensures consistent comparison across manufacturers and models and reflects real-world performance under load conditions It’s important because it is used in design and operation of the transformer • Short-circuit protection: Higher impedance limits fault current, protecting downstream equipment •
Voltage regulation:Affects how much voltage drops under load. Lower impedance = tighter regulation Parallel operation: Matching impedance is critical when connecting multiple transformers together as in a three-phase bank
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Used to: •
Used in coordination studies, fault analysis, and system design Transformer sizing, breaker selection, and load balancing
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