Parallel Transformers With Common Neutral Grounding Resistor

ETAP Knowledge Base

Parallel Transformers with Common Neutral Grounding Resistor Description: How to model two parallel transformers with a common neutral resistor Category:

Transformer Editor, Common Neutral Resistance Grounding

Type:

Modeling, Workaround

Keywords:

Transformer, Common Grounding Resistor

ETAP does not currently support the option to ground two transformers through the same grounding resistor. If the transformers are operated in parallel with matched impedances and identical voltage ratings, then for an unbalanced fault involving ground it possible to model this configuration using a separate grounding resistor at each transformer. The separate grounding resistances each should be twice the value of the common grounding resistor. The following shows an example for two delta/wye transformers:

Actual Grounding

Equivalent Grounding

2xRn

Rn

2xRn

This document is confidential and proprietary to Operation Technology, Inc. and may not be reproduced, published or disclosed to others without the written authorization of Operation Technology, Inc., 17 Goodyear, Suite 100, Irvine, CA 92618, USA. © 2011 by Operation Technology, Inc. All Rights Reserved.

© Operation Technology, Inc.

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ETAP Knowledge Base

Parallel Transformers with Common Neutral Grounding Resistor The technique also applies when both primaries are wye connected and grounded through a common resistor. In general, if the separate grounding resistances can be chosen such that the zero-sequence network seen at the point of fault is identical to that of the system with a common grounding resistor, then it is permissible to model the system with separate grounding resistors. The following system, where the grounding resistor is tied to both transformer neutrals, cannot be modeled as described since the transformers are not in parallel:

This document is confidential and proprietary to Operation Technology, Inc. and may not be reproduced, published or disclosed to others without the written authorization of Operation Technology, Inc., 17 Goodyear, Suite 100, Irvine, CA 92618, USA. © 2011 by Operation Technology, Inc. All Rights Reserved.

© Operation Technology, Inc.

Page 2 of 2

ETAPKB