# How grounding of tertiary winding of Power Transformer helps in reducing the harmonic

If we use the tertiary winding of a Power Transformer as an Open Delta and ground it then how could that will be helpful in reducing the harmonics of system?

 Newton1Law Posts: 60, Reputation: 20 Junior Member #2 May 11, 2011, 08:45 AM
Power Transformers do not usually have a tertiary winding that allows you to use it as an open delta, however, if it did, just as with a full delta, all zero sequence currents are blocked effectively reducing these currents from loads on the tertiary. You could use the tertiary winding as a filter or trap for some harmonics also. This is not much help but I would need the full configuration of the transformer and connected circuits to better answer this question.
 pratikgrover Posts: 4, Reputation: 10 Junior Member #3 May 11, 2011, 10:15 AM
Comment on Newton1Law's post
Quote:
 Originally Posted by Newton1Law Power Transformers do not usually have a tertiary winding that allows you to use it as an open delta, however, if it did, just as with a full delta, all zero sequence currents are blocked effectively reducing these currents from loads on the tertiary. You could use the tertiary winding as a filter or trap for some harmonics also. This is not much help but I would need the full configuration of the transformer and connected circuits to better answer this question.
It's a 160MVA STAR-STAR POWER TRANSFORMER, 220KV/66KV/11KV.
11kv side is the tertiary and it is used as an Open Delta and is grounded for reducing the harmonic effect. But I don't have knowledge of how does it reduces the harmonic effect.

Does this information sufficient?
 Newton1Law Posts: 60, Reputation: 20 Junior Member #4 May 12, 2011, 11:54 AM
Your transformer has a full closed delta tertiary winding. This winding may be used for a number of applications. For instance by measuring the phase relationship of the circulating current you can determine if a line fault is beyond the secondary side of the transformer or the primary line side of the transformer. The tertiary winding is commonly used to supply station service tramsformers. The fact that the tertiary winding is a closed delta allows it to help balance voltgae during unbalanced fault conditions and provides a sink or trap for third harmonics which can cause considerable unbalalnce for a Wye Wye (Star-Star) transformer.

If the transformer is designed for operation as a variable speed drive transformer or a supply transformer to a 12, 24, 48, etc. pulse rectifier of some kind, it may be manufacturered with six terminals broought out for the tertiary windings allowing you to connect it however you want or it may have only two terminals of delta tertiary as an indeed open delta tertiary. (I've never seen one however). Is yours this type of unit? How many terminals are available to you from the tertiay winding?

In these cases one of the terminals is grounded. This allows for common mode third harmonic current to flow in the delta supporting the supply voltage by stabilizing the neutral. The tertiary winding connected in delta reduces the impedance offered to the zero sequence curretns so a larger earth fault current flows for proper operation of protective equipment. For unbalanced load it limits the imbalance in voltage.

One item I did not mention is the harmonics produced by the transformer itself. Harmonics are caused because of use of high flux densities in the core. If the core gets saturated during part of the sinusoidal wave, then secondary wave will be non-sinusoidal. This may be due to inadequate core area or characteristics of core material.

Harmonic currents result in higher copper loss, core loss, magnetic interference and interference with communication systems due to higher frequency common mode coupling on the ground system.

Often when a transformer is just energized without a load on the output, the harmonic inrush is so great that fault protection relays are blocked by harmonic restraint relays on the transformer.

 pratikgrover Posts: 4, Reputation: 10 Junior Member #5 May 13, 2011, 11:03 AM
Comment on Newton1Law's post
Quote:
 Originally Posted by Newton1Law Your transformer has a full closed delta tertiary winding. This winding may be used for a number of applications. For instance by measuring the phase relationship of the circulating current you can determine if a line fault is beyond the secondary side of the transformer or the primary line side of the transformer. The tertiary winding is commonly used to supply station service tramsformers. The fact that the tertiary winding is a closed delta allows it to help balance voltgae during unbalanced fault conditions and provides a sink or trap for third harmonics which can cause considerable unbalalnce for a Wye Wye (Star-Star) transformer. If the transformer is designed for operation as a variable speed drive transformer or a supply transformer to a 12, 24, 48, etc. pulse rectifier of some kind, it may be manufacturered with six terminals broought out for the tertiary windings allowing you to connect it however you want or it may have only two terminals of delta tertiary as an indeed open delta tertiary. (I've never seen one however). Is yours this type of unit? How many terminals are available to you from the tertiay winding? In these cases one of the terminals is grounded. This allows for common mode third harmonic current to flow in the delta supporting the supply voltage by stabilizing the neutral. The tertiary winding connected in delta reduces the impedance offered to the zero sequence curretns so a larger earth fault current flows for proper operation of protective equipment. For unbalanced load it limits the imbalance in voltage. One item I did not mention is the harmonics produced by the transformer itself. Harmonics are caused because of use of high flux densities in the core. If the core gets saturated during part of the sinusoidal wave, then secondary wave will be non-sinusoidal. This may be due to inadequate core area or characteristics of core material. Harmonic currents result in higher copper loss, core loss, magnetic interference and interference with communication systems due to higher frequency common mode coupling on the ground system. Often when a transformer is just energized without a load on the output, the harmonic inrush is so great that fault protection relays are blocked by harmonic restraint relays on the transformer.
Thank you for your reply. And you we here are having two terminals of delta tertiary and one of them is grounded.
 Adithya123srini Posts: 1, Reputation: 1 New Member #6 Apr 24, 2012, 11:50 AM
Newton1Law I have a doubt! Why is that the delta connected tertiary reduces 3rd harmonic alone? Could you just elaborate about the harmonics?
Thanks
 sinnadurai Posts: 124, Reputation: 9 Junior Member #7 Apr 24, 2012, 09:38 PM
Quote:
 Originally Posted by Newton1Law Your transformer has a full closed delta tertiary winding. This winding may be used for a number of applications. For instance by measuring the phase relationship of the circulating current you can determine if a line fault is beyond the secondary side of the transformer or the primary line side of the transformer. The tertiary winding is commonly used to supply station service tramsformers. The fact that the tertiary winding is a closed delta allows it to help balance voltgae during unbalanced fault conditions and provides a sink or trap for third harmonics which can cause considerable unbalalnce for a Wye Wye (Star-Star) transformer. If the transformer is designed for operation as a variable speed drive transformer or a supply transformer to a 12, 24, 48, etc. Pulse rectifier of some kind, it may be manufacturered with six terminals broought out for the tertiary windings allowing you to connect it however you want or it may have only two terminals of delta tertiary as an indeed open delta tertiary. (I've never seen one however). Is yours this type of unit? How many terminals are available to you from the tertiay winding? In these cases one of the terminals is grounded. This allows for common mode third harmonic current to flow in the delta supporting the supply voltage by stabilizing the neutral. The tertiary winding connected in delta reduces the impedance offered to the zero sequence curretns so a larger earth fault current flows for proper operation of protective equipment. For unbalanced load it limits the imbalance in voltage. One item I did not mention is the harmonics produced by the transformer itself. Harmonics are caused because of use of high flux densities in the core. If the core gets saturated during part of the sinusoidal wave, then secondary wave will be non-sinusoidal. This may be due to inadequate core area or characteristics of core material. Harmonic currents result in higher copper loss, core loss, magnetic interference and interference with communication systems due to higher frequency common mode coupling on the ground system. Often when a transformer is just energized without a load on the output, the harmonic inrush is so great that fault protection relays are blocked by harmonic restraint relays on the transformer.
If in both cases(open/closed delta) 3rd harmonics is cancelled or suppressed,why do they have two systems?
 Nazarpasha Posts: 1, Reputation: 1 New Member #8 Jun 26, 2012, 11:39 PM
Please explain how a tertiary winding is grounded.I request you to make a sketch of the groundinding.ofcourse without a NGR.in our system,the tertiary is directly grounded.

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