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3 Phase: How to Calculate Line Voltage, Phase Voltage, Line Current & Phase Current in Star & Delta

Joe Robinson Training・22 minutes read

The video provides electrical principles training with accompanying worksheets, encouraging viewers to solve questions on phase voltage, line current, and phase current in star and Delta connections with different resistive loads and voltage supplies, demonstrating calculations step by step. The worksheet includes questions on calculating phase and line voltages, phase currents, and line currents in both star and Delta connections with varying resistance values and voltage supplies, showcasing the application of electrical principles in practical scenarios.

Insights

  • In star connection, the phase current is the same as the line current, making calculations simpler and more straightforward.
  • Transitioning from star to delta connection results in a significant increase in current, with the line current in delta connection being approximately three times that in star connection.

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Recent questions

  • How do you calculate phase voltage in a star connection?

    By dividing line voltage by square root of 3.

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Summary

00:00

Electrical Principals Training: Star vs Delta Connections

  • Video designed for electrical principals training, used with accompanying worksheet
  • Worksheet link provided in video description for viewers to download
  • Viewers encouraged to answer questions on worksheet and check against worked examples in video
  • Question 1: Three 25-ohm resistive loads in star to 415V supply, asked to calculate phase voltage, line current, and phase current
  • Voltage between phases in star connection is 415V
  • Resistance of each load is 25 ohms
  • Phase voltage calculated as 239.6V using VL divided by square root of 3
  • Phase current calculated as 9.582A using VP divided by resistance
  • Line current in star connection is same as phase current, 9.582A
  • Question 2: Same loads in Delta to 415V supply, asked to calculate phase voltage, line current, and phase current
  • Phase voltage in Delta connection is equal to line voltage, 415V
  • Phase current calculated as 16.6A using VP divided by resistance
  • Line current in Delta connection calculated as 28.75A using phase current multiplied by square root of 3
  • Current in Delta connection is approximately three times that in star connection
  • Question 3: Three 50-ohm resistive loads in star to 400V supply, asked to calculate phase voltage, line current, and phase current
  • Resistance of each load is 50 ohms
  • Phase voltage calculated as 230.9V using VL divided by square root of 3
  • Phase current calculated as 4.618A using VP divided by resistance
  • Line current in star connection is equal to phase current, 4.618A

15:48

Calculating Voltage and Current in Electrical Circuits

  • Question 4 involves connecting 50 ohm loads in Delta to a 400 volt supply, requiring calculation of phase voltage, line current, and phase current.
  • The resistance in the circuit is 50 ohms, with a line voltage of 400 volts.
  • Phase voltage equals line voltage, both at 400 volts.
  • Phase current is calculated using Ohm's law, resulting in 8 amperes.
  • Line current is found by multiplying phase current by root 3, yielding 13.86 amperes.
  • The final values are: resistance 50 ohms, line voltage 400 volts, phase voltage 400 volts, phase current 8 amps, and line current 13.68 amps.
  • Question 5 involves connecting three 220 ohm resistive loads in star to a 440 volt supply, necessitating determination of phase voltage, phase current, and line current.
  • The resistance is 220 ohms, with a line voltage of 440 volts.
  • Phase voltage is calculated as 254 volts.
  • Phase current is found using Ohm's law, resulting in 1.15 amperes.
  • Line current equals phase current, at 1.15 amperes.
  • Question 6 tasks connecting the same 220 ohm loads from question 5 in Delta to a 440 volt supply, requiring calculation of phase voltage, phase current, and line current.
  • The resistance remains at 220 ohms, with a line voltage of 440 volts.
  • Phase voltage is equal to line voltage, both at 440 volts.
  • Phase current is determined using Ohm's law, resulting in 2 amperes.
  • Line current is found by multiplying phase current by root 3, yielding 3.46 amperes.
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