Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Locked Locked
  • Replies 12 replies
  • Subscribers 36 subscribers
  • Views 2492 views
  • Users 0 members are here
Options
You may also be interested in
This discussion is locked.
You cannot post a reply to this discussion. If you have a question start a new discussion

Three phase voltage drop

Derek Eccles

For a balanced 3 phase system the supply authority, distributes 400v at the supply transformer.

The supply cables are 150m in length, so care is required to ensure the voltage drop does not become excessive at the customers terminals

Assuming there is a votage drop of 20v, across each cable at a particular balanced load, what voltage would the customer see at his terminals ?

I presume 360v ?

Regards, Derek

Parents
  • 0

    If this is a standard 3 phase 4 wire system, and is TRULY balanced, without third harmonics or other complications,

    Then I believe that a load connected between phases will see 360 volts, this being the nominal 400 volts less 20 volts in each phase conductor.

    A load connected between one phase and neutral will see 210 volts, this being the the nominal 230 volts, less 20 volts drop in the phase conductor. No voltage drop in the neutral conductor due to no neutral current in a perfectly balanced system.

    In practice there will be some imbalance and therefore some voltage drop in the neutral.

    Also as has been said, standard DNO substation transformers are 433 volts rather than 400. A privately owned transformer might be either 433 volts or 415 volts.

Reply
  • 0

    If this is a standard 3 phase 4 wire system, and is TRULY balanced, without third harmonics or other complications,

    Then I believe that a load connected between phases will see 360 volts, this being the nominal 400 volts less 20 volts in each phase conductor.

    A load connected between one phase and neutral will see 210 volts, this being the the nominal 230 volts, less 20 volts drop in the phase conductor. No voltage drop in the neutral conductor due to no neutral current in a perfectly balanced system.

    In practice there will be some imbalance and therefore some voltage drop in the neutral.

    Also as has been said, standard DNO substation transformers are 433 volts rather than 400. A privately owned transformer might be either 433 volts or 415 volts.

Children
  • 0 in reply to broadgage

    I am a bit confused, I would agree that each phase voltage will drop by 20v i.e. down to 210v.

    Not sure about how the line voltages are affected if at all i.e. if each line voltage drops by 20v, then the difference between them

    should still bt 400v ?

Join us to get the best from IET EngX.

Joining EngX lets you personalise your experience so you stay up to date on the topics that interest you, plus you’ll be able to make connections who are looking to collaborate, exchange ideas and more.

Join us Not now

Community Rules & Guidelines