Why Grounding Transformers Used w/Delta Sec. Transformer?

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Grounding transformers are used with delta secondary transformers primarily to provide a neutral point for connecting single-phase ground loads and to enhance safety by ensuring proper grounding. Without a grounding transformer, connecting a phase to ground could lead to voltage surges and unsafe conditions, as the delta configuration does not allow for neutral current transfer. The grounding transformer helps minimize losses and maintains voltage stability by keeping potential differences within a known range. Additionally, it addresses phase shifts that may arise in doubly fed systems, ensuring compatibility with other sources. Overall, grounding transformers play a crucial role in industrial settings where large loads and safety requirements are present.
arnab ghosh
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Just curious about why grounding transformers are used with a delta secondary . What would happen if I connect a phase to ground load to the secondary of a star delta transformer without adding a grounding transformer?
 
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arnab ghosh said:
why grounding transformers are used with a delta secondary

A Δ/Y-coupled transformer cannot transfer a neutral current (no neutral on the Δ-side). In a power-line no power is transferred due to the neutral current as 0V*1000A = 0W, so the neutral current only results in ohmic losses (P=I2*R.Therefore we want to eliminate the neutral current so that the phasecurrents: Ia + Ib + Ic = 0 (KCL). Of course these phase-currents also result in ohmic losses, but they result in a power-transfer as well.

So Δ/Y-transformers are inserted to minimize losses. The grounding on the Y-side is used to keep the voltage potentials within some "known space".
 
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Hesch said:
A Δ/Y-coupled transformer cannot transfer a neutral current (no neutral on the Δ-side). In a power-line no power is transferred due to the neutral current as 0V*1000A = 0W, so the neutral current only results in ohmic losses (P=I2*R.Therefore we want to eliminate the neutral current so that the phasecurrents: Ia + Ib + Ic = 0 (KCL). Of course these phase-currents also result in ohmic losses, but they result in a power-transfer as well.

So Δ/Y-transformers are inserted to minimize losses. The grounding on the Y-side is used to keep the voltage potentials within some "known space".
Yes that is okay . That is the use of inserting Y-D transformers . But I wanted to know why Grounding Transformers(see the figure) are used with the secondary of a Y-D transformer when we need to connect single phase-ground loads. Is it because it completes the circuit and avoids voltage surges?
 

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There can be a couple reasons - but the one that comes to mind is that a Grounded circuit may be required for safety and code purposes (created by the grounding transformer), but the Delta secondary is needed due to phase shift. -- Each Y-D or D-Y transformer creates a phase shift, in doubly ( or more) fed systems it may be necessary to match the phase shift - in another source.
 
Oh -- In your diagram I do not feel this is for the connection of neutral loads. -If it is for connection of loads I do not like the naming of this a grounding transformer - we connect loads to neutrals, and not to ground in AC Systems. This if it is for a neutral load, I suspect for a relatively small percentage of the main transformers capacity. In an industrial setting the bulk of the load could be a large motor or system, yet the controller may need the neutral point connection.
There is also the issue of filtering the - transformer in this case would pass the 3rd ( and 3 multiple) harmonics. ( are there solid state loads ??)
 
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