NEUTRAL CURRENTS IN 3 PHASE SYSTEMS - WHERE DO THEY GO TO - WHY ARE THEY DIFFERENT TO SINGLE PHASE?
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- Опубліковано 10 вер 2024
- At LearnElectrics we have often been asked about neutral currents in three phase systems and how they appear to differ from single phase systems.
Examples of questions have included …
In a balanced 3 phase system, why are there no neutral currents
If we have a neutral current in a single phase installation, then where has it gone in a three phase system
If there is no neutral current then how do things work?
And we will also introduce Kirchoff’s Law to show what is happening and how we can use this to show how balanced a system might be, what will happen if we add a piece of equipment onto the system.
To view all of our videos type in LearnElectrics all one word into the UA-cam search bar.
This is video No.174 on our UA-cam channel where we have videos on a wide range of electrical topics.
Careful! The neutral current on a balanced 3 phase system is zero ONLY for linear loads, such as incandescent light bulbs. For non-linear loads, it can be 1.732 x the phase current. The NEC specifies either separate neutrals or a common neutral with 1.7 times the ampacity of each phase. I have seen neutrals on balanced fluorescent light systems burn. Doug Stell, MS(EE)
Thanks for your input, thanks for watching. Dave.
appreciate your input Mr. Stell.
By linear loads, do you mean strictly resistive?
Wow! This is very informative, thanks for sharing it with us Dave. It worth it and the best tutorial on the topic for me.
Lots more to come Daniel, thanks for the support. Dave.
Crikey, best explanation yet on this topic, will watch a couple of times then attempt to write it down in my own words, which is how I then manage to soak it into the memory bank and be able to recall it at with understanding from then on. Brilliant narration and clear graphic representation, many thanks for providing this content.
Glad it was helpful and thanks for watching. Dave.
Excellent presentation of the topic for non expert in this area. Many thanks.
Glad it was helpful and thank you for watching. Dave.
I love this kind gentleman, and thank you for sharing this brilliant information. Thank you.
Glad you enjoyed it and lots more to come. Dave.
for the first time in my life i understand what happen realy and what neutral means ...thanks a lot
That's good to know, the videos have done their job. It;s great when the light bulb comes on, isn't it. Every day is a school day, none of us stop learning. Good luck. Dave.
Beatifully explained
Thank you, appreciated.
Hello
I am a follower of your lessons and a big fan of them. I hope that you will show videos explaining the method of calculating the power factor, as well as the correct way to calculate the main breaker, and whether it should be larger than the service provider’s breaker, equal to it, or less in size than it.
sincerely
Khalid
Thank Khalid.
I have achieved what I want. Thank you🙏
That's good. Keep learning and thanks for watching.
Fantastic, thank you. Very much look forward to the balancing tutorial, coupled with PF issues & correction? possibly three tutorials there ;-)
Great suggestion, you intend keeping me busy. Thanks for your support, appreciated.
Howdy. Great.
Usually the neutral current is no larger than a phase current. The neutral cross section may be the same as a phase cross section. And thicker than 16 mm2 copper the neutral may be half the phase, yet at least 16 mm2.
It should be noted though, that early age frequency converters generated so much harmonic reactive current in the neutral that it needed be at least 25 mm2. Best check the specs before commissioning.
And there is a situation when the neutral will carry more current than any phase. This will theoretically happen if there is a heavily inductive load on one phase and a heavily capacitive on another phase. Best be aware of this possibility.
Capacitive loads are rare though. The Code does not recognize this case. What could produce capacitive loads ? Over-magnetized synchronous motors will generate capacitive loading. Some "bulb-head" may think connecting a capacitor bank to a receptacle removes spikes and harmonics from the mains and delivers clean sine wave to one's HiFi system. It does. Yes. But best be aware of the possibility of strong neutral currents.
Regards.
Thanks for the input, appreciated. Thank you for watching. Dave.
Thank you so much!.
You're welcome and thank you for your support.
Thanks again Dave I appreciate the knowledge shared 🙏blessings.
Thanks Anthony, appreciated. Dave.
Great explanation
Thanks for watching. Dave.
thank you
You're welcome, thanks for watching.
So question. When you go to motor say in an industrial setting. That one motor would be a balanced load since the 3 legs are just connected to one device. Im a first year apprentice trying to understand thanks, hunter
One motor on its own should be a balanced load, yes. thanks for watching.
Superb sir good explanation 🙏🙏🙏
Thank you Santosh, thanks for watching.
Spot on 👍
Thank you Brian, great support for the channel. Dave.
Thanks Dave--interesting video
Glad you enjoyed it David. Thanks for the support, Dave.
In the video you say something like not all 3 phase systems require a neutral. Can you make a video about why and when a neutral isn't needed?
A 3 ph electric motor, where the supply goes ONLY to the motor windings does not require a neutral as all phases are balanced. If the wiring to the motor also feeds something else, a control panel for instance, then a neutral is needed. Hope this helps. Dave.
In Norway we have been using 230V 3 phase IT distribution systems for 100 years. No neutral at all, none.
Great explanation.
It's a mystery however that so many people in England use SAT and STOOD indirectly.
They are SAT is not correct English. SAT is past tense. They are SITTING is the correct English.
Thanks for watching.
How about if you have 2 power source like AC & solar power, Is it okay to have different grounding system for solar inverters that is neutral grounded to metal case/housing then TNS output? Of course has an input of AC TNS also...
There is specific equipment available for this, installed to ensure that the point at which the incoming AC and the derived solar meet are compatible with each other and electrically safe. Dave.
Thanks Dave for sharing this with us. But, I've still some doubt about, what can neutral do to the supply if any currents flow along it (neutral) ?
Unless a 3 phase system is perfectly balanced then we will have neutral currents. They just go back to the transformer. Most 3 phase boards are not balanced which is why we should always try to make the neutral conductor the same size as the phase conductors.
Thinks so much for this explaine you are professor i wish if you can give me some books for electrical installation where i can download him thinks
Thank you Mohammed, great feedback. keep watching, keep learning, lots more to come. Dave.
Hi how are you. Useful topic.
I;m good and thanks for watching. Dave.
Need to do some work on this.
Learning is good, thanks for watching. Dave.
What happened when we lose neutral conductor in unbalanced 3 phase system?
What an excellent idea for another video. Lots of things can happen and its on the list now, Dave.
So out of 3 fellows any 1 fellow alternatively acts as drain pipe at any one point of time! My little brain says so!
FYI: After some tweaks I converted my single phase 240V variac into 2 phase 415V!
Thanks for watching, appreciated.
नमस्कार सर आपका चैनल इलेक्ट्रिक हेल्प के नेम से हैं सर मुझे आपकी हेल्प चाहीये अगर आप हेल्प कर दोगे तो सर जो थ्री फेज जनरेटR
हैं 50 केवीए मे उसकी पर फेज की रेटिंग 70 एम्पायर हैं वो हमारे पास हैं।। ओर हम लाइट डेकोरेशन विवाह शादी के अंदर काम चालू किया है न्यू न्यू तो जैसे हम एक फेज पर 45 एम्पायर लोड डाल दिया ओर एक फेज पर 35 एम्पायर लोड डाल दिया ओर एक फेज पर 15 एम्पायर लोड डाल दिया तो कोई दिकत आएगी क्या सर कुछ लोग बोलते है partek फेज का लोड बराबर रखना होगा नही तो अल्टीनेटर जल जाएगा ये क्या सिस्टम है सर
Thank you for watching.
i am here again
Good, I'm glad you're around. Thanks for watching and for the great comments. Dave.
This Chanel is Killing The text book … the table explains everything about 3 phases and neutral…
Thank you for the great feedback. We try our best. Thanks for watching. Dave.
Your channels is good but it.would be good if we got more.practicle examples. Explaining what is 3 phase in practical terms
Comments noted. I've put this on the list. Thanks for watching, appreciated. Dave.