Calculating Series Inductance and Input Voltage for Cable Testing
How can we calculate the series inductance required and the input voltage to the testing transformer for cable testing?
Given the data of a 15 kVA, 230 V/50 kV testing transformer with 6% leakage reactance and 2.5% resistance on a 100 kVA base, a cable needs to be tested at 200 kV using the transformer as a resonant transformer at 50 Hz. The charging current of the cable at 200 kV is 0.2 A. How can we determine the series inductance and input voltage needed for the testing transformer?
Series Inductance and Input Voltage Calculation
The series inductance required for the resonant transformer is calculated using the formula L = (1 / (2πf)) * (1 / C), where L is the series inductance in henries, f is the frequency in hertz, and C is the capacitance of the cable in farads. The input voltage to the testing transformer can be calculated using the turns ratio and the desired output voltage.
To calculate the series inductance required and the input voltage to the testing transformer, we need to understand the concept of resonant transformers and their application in cable testing.
A resonant transformer is used to generate high voltages at specific frequencies for testing purposes. In this case, the transformer is being used as a resonant transformer at 50 Hz to test a cable at 200 kV.
The series inductance is used to create a resonant circuit with the cable's capacitance, allowing for efficient power transfer. The series inductance required can be calculated using the formula:
L = (1 / (2πf)) * (1 / C)
Where:
L is the series inductance in henries
f is the frequency in hertz (50 Hz in this case)
C is the capacitance of the cable in farads
The input voltage to the testing transformer can be calculated using the turns ratio and the voltage rating of the transformer. The turns ratio is given as 230 V/50 kV, which means that for every 230 volts on the primary side, there will be 50,000 volts on the secondary side.
Therefore, the input voltage to the testing transformer can be calculated as:
Input Voltage = Turns Ratio * Output Voltage
Where:
Input Voltage is the voltage on the primary side of the transformer
Turns Ratio is the ratio of the number of turns on the primary side to the number of turns on the secondary side
Output Voltage is the desired output voltage (200 kV in this case)