In a 3-phase system balanced star connected system, how many minimum watt-meters are sufficient to measure the total power?

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ALP CBT 2 Electrician Previous Paper: Held on 22 Jan 2019 Shift 1
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  1. 4
  2. 2
  3. 1
  4. 3

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Option 3 : 1
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 According to Blondel’s theorem:

  • When a system contains ‘N’ number of phases & ‘N+1’ wires, then ‘N’ number of watt-meters is required to calculate the total power of the system.
  • When a system contains ‘N’ number of phases & ‘N’ wires, then ‘N-1’ number of watt-meters is required to calculate the total power of the system.
  • In a 3-phase balanced and unbalanced star-connected system, two watt-meters are sufficient to measure the total power.
  • But if a 3-phase star connected system is balanced then only one wattmeter is sufficient to measure the total power.
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