Etap Knowledge Base: Impact Of Source Impedance On Ansi 2w Transformer Damage Curve

ETAP Knowledge Base

Impact of Source Impedance on ANSI 2W Transformer Damage Curve Description: 2-Winding Transformer thermal and mechanical damage/protection curve can be dependent on source impedance in addition to transformer impedance Category:

STAR, STAR View, Protection and Coordination, STAR Auto-Evaluation, Transformer

Type:

Information

Keywords:

2-Winding Transformer, Transformer damage curve, Tranformer protection curve, secondary fault, source impedance

Q: Does the source impedance have any impact on 2-Winding liquid immersed transformer damage or protection curve per ANSI/IEEE standard? A: Yes. 1. The 2W transformer through fault damage or protection curves are defined and displayed in ANSI/IEEE C57.109 standard and IEEE C37.91, 2000 standard, for 4 categories of transformers representing the Min Nameplate kVA.

2. The reference through fault current for the above-mentioned curves is the ANSI/IEEE C57.12.00 standard. Section 7.1.4 Short-circuit Current Magnitude of this standard (year 2000 edition) requires the following for calculation of the symmetrical fault current on secondary.

Page 1 of 4 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, Irvine, CA 92618, USA. © 2016 by Operation Technology, Inc. All Rights Reserved.

ETAP Knowledge Base

Impact of Source Impedance on ANSI 2W Transformer Damage Curve

Page 2 of 4 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, Irvine, CA 92618, USA. © 2016 by Operation Technology, Inc. All Rights Reserved.

ETAP Knowledge Base

Impact of Source Impedance on ANSI 2W Transformer Damage Curve

3. In addition, article 7.1.5.1 of the IEEE C37.91 (year 2000 edition), states that the symmetrical currents for 2 winding transformers are calculated based on consideration of source and transformer impedance. 4. The transformer category IV damage curve shown below refers to the IEEE C57.12.00 standard for Base Current. This was also according to the IEEE C37.91 standard (year 2000 edition).

Page 3 of 4 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, Irvine, CA 92618, USA. © 2016 by Operation Technology, Inc. All Rights Reserved.

ETAP Knowledge Base

Impact of Source Impedance on ANSI 2W Transformer Damage Curve 5. As seen above, article 7.1.4.3 requires the inclusion of source impedance in transformer categories III and IV, but not in categories I and II. 6. Therefore, ETAP is following the suggested guidelines by the standards leading to more conservative damage or protection curves for category III and IV. 7. If the user does not wish to incorporate the source impedance and prefers to follow less conservative damage or protection curve, then the Short-Circuit Contribution on Protection page of 2-Winding Transformer Editor can be set to User-Defined with zero kA or Zs on the source side.

Page 4 of 4 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, Irvine, CA 92618, USA. © 2016 by Operation Technology, Inc. All Rights Reserved.