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Why the neutral voltage fluctuates?

Created by: PISCEAN 2010 at: 5/16/2011 11:46 AM (13 Replies)

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5/16/2011 11:46 AM	Rate (0)
PISCEAN 2010 Diamond Member Joined: 4/23/2010 Last visit: 11/23/2024 Posts: 8092 Rating: (884)	Hello Experts, Ours is a heavy general industrial unit with heavy machineries load of machine tool & fabrication shop. Total connected load is 2400 Kw with 325 KVA MD. Transformer capacity is 1500 KVA, Delta/Star with 33/0.433 KV voltage ratio. What I have observed is system neutral voltage with respect to ground varies from 0.6 volt to 2.3 volt. Why is it so? Connected machineries load is mix in nature like, conventional lathes, welding rectifiers, CNC machine tools etc. Is this neutral fluctuating voltage is dangerous? Will it affect in any way or may lead to malfunction the CNC controllers? I have checked the earth resistance & found less than 1 ohm. Is anything else needs to be check? How to overcome this problem? How much should be value between neutral & earth?

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5/16/2011 1:12 PM	Rate (0)
Ekalavya Posts: 2964 Rating: (485)	Hello Deep, Check this PDF document....its useful.... Regards, Ekalavya Attachment Earthing.pdf (1098 Downloads)
Ekalavya Posts: 2964 Rating: (485)
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This contribution was helpful to 1 thankful Users king_1985

5/16/2011 1:51 PM	Rate (0)
PISCEAN 2010 Diamond Member Joined: 4/23/2010 Last visit: 11/23/2024 Posts: 8092 Rating: (884)	Ekalavya Hello Deep, Check this PDF document....its useful.... Regards, Ekalavya Hello Ekalavya, I appreciate your helping nature & thanks for the same. Yes while installation of earthing every proper care has been taken. 2nos of 50 mm width * 6 mm thick electrolytic grade copper conductors & copper plates of adequate size are used for transformer main neutral earthing. Also we have ensured the joints of earthing conductors with proper hardware. As mentioned earlier, measured & found earthing resistance less than 1 ohm. Even then why this neutral voltage varies? Theoretically it should be zero (at least in mV) Secondly why it varies from 0.6 volt to 1.8 or 2.0 volt. What are its counter effects? Hope to receive the answer.

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5/16/2011 2:04 PM	Rate (0)
Ekalavya Posts: 2964 Rating: (485)	Hello Deep, Your right it should be less than a volt but in our country standard as you now you don't find it...... Normally voltageshouldn't be there but it is not right......!!!!!!! If this voltage exceeds by chance 20V for example it will affect theelectronic components on the module... and creates a problem.... Ensure your machine body is earthed properly and the COMMON ground inside it normallyle people fail to do this..... Axis motor power cable shiled to be grounded properly...... power and signal cable to be routed seprately.... Regards, Ekalavya
Ekalavya Posts: 2964 Rating: (485)	Last edited by: Ekalavya at: 5/16/2011 3:44 PM
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5/17/2011 7:21 AM	Rate (0)
PISCEAN 2010 Diamond Member Joined: 4/23/2010 Last visit: 11/23/2024 Posts: 8092 Rating: (884)	Hello Ekalavya, Thanks. We are taking care of axis motor power cable shield grounding as well as routing of power & control cables separately as suggested by you. Now the point is how or what steps should be followed so as this neutral voltage variation problem can be resolved? Suggestions/solutions to this problem are highly welcome.

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5/20/2011 8:19 AM	Rate (0)
Ekalavya Posts: 2964 Rating: (485)	Hello.... Check this document.....some what intersting.... Regards, Ekalavya Attachment TN TT.pdf (985 Downloads)
Ekalavya Posts: 2964 Rating: (485)
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5/20/2011 5:52 PM	Rate (0)
Vithani Platinum Member Joined: 7/8/2009 Last visit: 6/7/2025 Posts: 1977 Rating: (479)	Well I dont know much in detail but we faced same kind of problem in our Plant. At that time Plant was in comissioning state and so many welding works were going on. Now comissioning has been finished and No more or very less welding work is going and problem has been resolved.. Our conclusion was, it was due to improper earthing used during Welding. Normally people have bad habbit of Not to use proper Earthing during welding and believe me it has cost us a lot in terms of Damged electronic components Specially of Drives Regards, Devesh
	I dont Like people driving Fast, thats the reason I overtake them ;)
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5/22/2011 12:12 PM	Rate (0)
PISCEAN 2010 Diamond Member Joined: 4/23/2010 Last visit: 11/23/2024 Posts: 8092 Rating: (884)	Hello Ekalavya, Thanks for valuable information. Hello Mr. Vithani, Thank you very much for sharing your exprienece. Yes in our shop we have equipped with latest/modern welding rectifier/inverter based machines from reputed makes like Miller, Lincoln etc. These welding machine works on 3 phase 415 volt & no neutral is connected to machine. Out put of these welding machine i.e. +ve & -ve terminals are isolated & only connected to machine & job i.e. no connection to neutral & earth. Job like huge size M S Plates are also no way in connection with electrical neutral & earth. This welding application may pollute the supply line by the way of line surges & dips. But I don’t think it would affect the neutral voltage. This heavy fabrication shop is continuous production process & which is our key area, hence couldn’t stop the welding machines. But even if we assume that because of this, neutral voltage fluctuates, what would be the solution?

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5/31/2011 1:04 PM	Rate (0)
PISCEAN 2010 Diamond Member Joined: 4/23/2010 Last visit: 11/23/2024 Posts: 8092 Rating: (884)	Hello Experts, How to check the neutral resistance? How to ensure the neutral 100% earthing? Does any one has idea? Please share. Regards, DEEP.

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6/5/2011 12:37 PM	Rate (0)
PISCEAN 2010 Diamond Member Joined: 4/23/2010 Last visit: 11/23/2024 Posts: 8092 Rating: (884)	Hello Experts, Does anyone have measured the neutral & ground voltage. What values have been recorded? Practically how much is the acceptable limit? Please guide.

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