Hysterisis Heating from single phase parallel conductors

[Karthik_venna]

Hello All,

I have read a lot of discussions regarding eddy currents and hysteresis heating when the conductors are entering into an enclosure made of ferrous elements like steel.

however my question is what would be the effect when a two parallel conductors of same phase entering separately in to a steel enclosure. For eg: In the below drawing, imagine Conductor 1 (Phase A) & conductor 2 (Also Phase A) are entering but with out a narrow slot cut between the entries. The entering cable glands are fixed with plastic lock nuts.

My question is Should I be worried of any induced heating issues. I do not think so as the both conductors belong to the same phase. Kindly correct me if i am wrong

Best regards
Karthik

 

[winnie]

The question is 'where are the other phases', or 'where is the complete circuit path'.

If you only feed a load with phase A, and have 'supply' through one hole and 'return' through another hole, then you need a slot or you will have problems.

-Jon

 

[kwired]

Hello All,

I have read a lot of discussions regarding eddy currents and hysteresis heating when the conductors are entering into an enclosure made of ferrous elements like steel.

however my question is what would be the effect when a two parallel conductors of same phase entering separately in to a steel enclosure. For eg: In the below drawing, imagine Conductor 1 (Phase A) & conductor 2 (Also Phase A) are entering but with out a narrow slot cut between the entries. The entering cable glands are fixed with plastic lock nuts.

My question is Should I be worried of any induced heating issues. I do not think so as the both conductors belong to the same phase. Kindly correct me if i am wrong

Best regards
Karthik

You typically parallel conductors because of need for increased ampacity. Therefore you have maybe double the current for two conductors then you may have for one conductor of same size. So if you have 2-200 amp conductors carrying same phase vs one 400 amp conductor your magnetic field effects should be about the same either case. Only when all conductors of a circuit pass through the same opening do the fields cancel one another and leave you with a zero net effect on surrounding ferrous material.

 

[Karthik_venna]

The question is 'where are the other phases', or 'where is the complete circuit path'.

If you only feed a load with phase A, and have 'supply' through one hole and 'return' through another hole, then you need a slot or you will have problems.

-Jon

Thank Jon. The application is phase segregated and each phase has its own housing. To give a better perspective, the below is the enclosure i am talking about. The three cables belong to the same phase. This is the entry side of the enclosure.



The exit of the enclosure how ever have only one opening when a single busbar is coming out to the load. One more Information is that this enclosure is earthed. Should i be worried about the induced heat in the enclosure due to the currents flowing through the cables and coming out through the busbar.



Looking forward for the responses. And thank you very much in advance.

Best regards
Karthik

 

[Karthik_venna]

You typically parallel conductors because of need for increased ampacity. Therefore you have maybe double the current for two conductors then you may have for one conductor of same size. So if you have 2-200 amp conductors carrying same phase vs one 400 amp conductor your magnetic field effects should be about the same either case. Only when all conductors of a circuit pass through the same opening do the fields cancel one another and leave you with a zero net effect on surrounding ferrous material.

Thank you for the input Kwired. kindly refer to the newly attached drawings. As you see all the conductors are not passing through the same opening. But the based on the enclosure design and it being earthed does the heating effect can be negligible?.

Best regards
Karthik

 

[GoldDigger]

Thank you for the input Kwired. kindly refer to the newly attached drawings. As you see all the conductors are not passing through the same opening. But the based on the enclosure design and it being earthed does the heating effect can be negligible?.

Best regards
Karthik

Earthing the enclosure has no effect on the hysteresis heating of the walls of the enclosure when an unbalanced current passes through them.
When you have a set maximum single phase current, the hysteresis heating will be roughly proportional to the magnitude of the current in a given hole. That means that the heating resulting from splitting a given phase line into two wires and two holes will have roughly the same heating effect as the same current through one wire in one hole.

 

[Karthik_venna]

Earthing the enclosure has no effect on the hysteresis heating of the walls of the enclosure when an unbalanced current passes through them.
When you have a set maximum single phase current, the hysteresis heating will be roughly proportional to the magnitude of the current in a given hole. That means that the heating resulting from splitting a given phase line into two wires and two holes will have roughly the same heating effect as the same current through one wire in one hole.

Thank you for the response. Can you elaborate what the unbalanced currents means? did you mean that the three cables do not carry identical currents which i believe is very common with atleast 5% deviation in current distribution in three cables.

Now i understand that the enclosure i have showed does have the hysteresis heating.
To get more in to details, the cables that are shown here are tested to carry up to 1800 A continuous but the test was done without this enclosure. Now the requirement is with the enclosure with 800 A for 11 hours duration with 1100 A in between for some 30 mins. After that no more current will be passed through for some days. The cables can handle these currents without any issue. But i am unable to estimate how critical this would be for the enclosure main with respect to heating.

Just seeing the amount of current i do not actually see any issue here. but with less expertise on hysteresis heating, experts opinion like you guys would be really helpful.

Thank you

 

[beanland]

Uncancelled Magnetic Field

Uncancelled Magnetic Field

Any time you have a conductor with current flowing there is a magnetic field created. If you have multiple phases, these magnetic fields can cancel. Anytime you have a magnetic material and a magnetic field, you will have induced current and the resulting heating. It is common to use a non-magnetic stainless steel plate when separate phases need to enter into a steel enclosure. For example, the bushings on a transformer.

So, if you have one phase or even two phases (assuming they are not 180-degrees apart) you will have a magnetic field that can cause heating. That is why the rule to install all three phases in each conduit. If you need to use segregated phases, then non-magnetic conduits are essential.

 

[kwired]

Thank you for the response. Can you elaborate what the unbalanced currents means? did you mean that the three cables do not carry identical currents which i believe is very common with atleast 5% deviation in current distribution in three cables.

Now i understand that the enclosure i have showed does have the hysteresis heating.
To get more in to details, the cables that are shown here are tested to carry up to 1800 A continuous but the test was done without this enclosure. Now the requirement is with the enclosure with 800 A for 11 hours duration with 1100 A in between for some 30 mins. After that no more current will be passed through for some days. The cables can handle these currents without any issue. But i am unable to estimate how critical this would be for the enclosure main with respect to heating.

Just seeing the amount of current i do not actually see any issue here. but with less expertise on hysteresis heating, experts opinion like you guys would be really helpful.

Thank you

With a simple two wire circuit - what goes one direction on one conductor must simultaneously go the other direction on the other conductor. With a three phase three wire circuit you could have different currents on each conductor but the vector sum of all those currents needs to be zero. Basically any current that comes in on one conductor must leave on either or combination of both the other conductors or else you will have a magnetic field that isn't totally cancelled by the conductors within the hole. (If you can clamp an ammeter around all the conductors it must read zero or else whatever current is read has to be going someplace besides the conductors being measured.)

Non ferrous enclosure won't have this issue, or at least not nearly as severe, cutting slot(s) between each entry effectively creates "one hole".

 

[winnie]

Okay, you have a big assembly with 3 separate conductors (all from a single phase) going in, and a large bus bar (for that single phase) going out, and the 'other phases' are in entirely separate assemblies.

As others have already noted, you have unbalanced currents, meaning current flowing one way through the holes not balanced by current flowing the other way. Unfortunately you won't be able to easily eliminate these unbalanced currents; to do so you would need a slot that somehow connects the 3 holes that the cables enter and the hole where the bus bar exits.

As to this being a problem, there is no simple calculation. The unbalanced current will induce a magnetic field which will induce current in the enclosure which will heat the enclosure. If the enclosure is magnetic (steel) then the field will be stronger and there will be more induced current. But even non-magnetic conductors will experience some heating.

The grounding may or may not be an issue, not because of the connection to earth, but because all three enclosures are connected to each other, and the grounding connections may provide a path for induced current to circulate. You need to think of the enclosures as unintended transformer secondaries and ask where will induced currents flow.

In any case, you will see induced currents in the enclosures, and they will cause heating...but there is no easy way to know if the heating is tolerable (makes the enclosure a little warmer but does not impact performance) or dangerous (causes enough heating to damage insulation or cause other failures).

-Jon

 

[Karthik_venna]

Thank you all for providing your valuable inputs . Doubts are cleared

 

[WarrMann]

Thank you all for providing your valuable inputs . Doubts are cleared

Im curious about your conclusion because you've gotten some good advice here.

Do you think that induced currents will not be in issue in your situation?

Or

Will you be taking measures to protect your enclosure from the heat caused by induced currents?

Sent from my SM-G950U using Tapatalk

 

[retirede]

Im curious about your conclusion because you've gotten some good advice here.

Do you think that induced currents will not be in issue in your situation?

Or

Will you be taking measures to protect your enclosure from the heat caused by induced currents?

Sent from my SM-G950U using Tapatalk

Or

Did you learn that the enclosure is non-ferrous?

 

[LarryFine]

Did you learn that the enclosure is non-ferrous?

Even non-ferrous metal has the same concerns.

 

[kwired]

Even non-ferrous metal has the same concerns.

But not the same level of heating will occur as for ferrous metals.

 

[GoldDigger]

Even non-ferrous metal has the same concerns.

Any resistive heating resulting from eddy currents will be minimal since the "secondary" surrounds the "primary" wire and is only loosely coupled via an air core.
This will be small compared to the heating from magnetic hysteresis losses in the "core" of the accidental inductance of an unbalanced current going through a ferrous plate.