1. What is Percent Impedance?

Percent Impedance (%Z) is a key parameter in transformer design and operation that represents the percentage of rated voltage required to circulate full-load current through the transformer's impedance. It indicates the voltage drop across the transformer under full load conditions.

2. How Does the Calculator Work?

The calculator uses the percent impedance formula:

Where:

• Impedance Voltage — Voltage required to circulate full-load current through transformer impedance (volts)
• Rated Voltage — Nominal operating voltage of the transformer (volts)

Explanation: The formula calculates the percentage relationship between the impedance voltage drop and the rated voltage of the transformer.

3. Importance of Percent Impedance Calculation

Details: Percent impedance is crucial for determining short-circuit current levels, voltage regulation, and system protection coordination. It helps in selecting appropriate protective devices and ensuring system stability during fault conditions.

4. Using the Calculator

Tips: Enter impedance voltage and rated voltage in volts. Both values must be positive numbers greater than zero for accurate calculation.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical percent impedance range for transformers?
A: Distribution transformers typically have %Z values between 2-6%, while power transformers may range from 5-15% depending on size and application.

Q2: How does percent impedance affect short-circuit current?
A: Lower %Z values result in higher short-circuit currents, while higher %Z values limit short-circuit currents but may cause greater voltage drop.

Q3: Why is percent impedance important for parallel operation?
A: Transformers with significantly different %Z values may not share load proportionally when operated in parallel.

Q4: How is impedance voltage measured?
A: Impedance voltage is measured by short-circuiting one winding and applying voltage to the other winding until rated current flows.

Q5: Does percent impedance change with transformer loading?
A: Percent impedance is generally constant for a given transformer and does not vary significantly with loading conditions.