Difference between revisions of "Transformer Impedance Correction Factor"

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IEC 60909 uses a simplifying assumption where the pre-fault voltage at the fault location is not calculated (e.g. by a load flow), but rather an equivalent voltage source is used (assumed to be the nominal voltage multiplied by some voltage factor c). Furthermore, the pre-fault load current is not known (i.e. not calculated) and transformers can operate at a wide range of off-nominal tap settings. Therefore, the simplified IEC calculations did not correspond to the calculations based on the more accurate superposition method. An impedance correction factor was thus introduced to improve the accuracy of the calculated fault currents.
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IEC 60909 uses a simplifying assumption where the pre-fault voltage at the fault location is not calculated (e.g. by a load flow), but rather an equivalent voltage source is used (assumed to be the nominal voltage multiplied by some voltage factor c). Moreover, two further issues complicate the matter: 1) the pre-fault load current is not known (i.e. not calculated in the IEC 60909 method) and 2) transformers can operate at a wide range of off-nominal tap settings. As a result, the simplified IEC calculations do not align with calculations based on the more accurate superposition method. An impedance correction factor was thus introduced in IEC 60909:2001 to improve the accuracy of the calculated fault currents.
  
 
In the older versions of IEC 60909 (pre-2001), there was no explicit impedance correction factor for transformers, instead just a suggestion that considerations need to be made. IEC found this unsatisfactory and introduced the correction factor in the 2001 edition. The correction factor was essentially defined empirically through a statistical analysis of a few hundred transformers. Most of this is described in some detail in IEC 60909-1.  
 
In the older versions of IEC 60909 (pre-2001), there was no explicit impedance correction factor for transformers, instead just a suggestion that considerations need to be made. IEC found this unsatisfactory and introduced the correction factor in the 2001 edition. The correction factor was essentially defined empirically through a statistical analysis of a few hundred transformers. Most of this is described in some detail in IEC 60909-1.  

Latest revision as of 05:24, 12 August 2018

IEC 60909 uses a simplifying assumption where the pre-fault voltage at the fault location is not calculated (e.g. by a load flow), but rather an equivalent voltage source is used (assumed to be the nominal voltage multiplied by some voltage factor c). Moreover, two further issues complicate the matter: 1) the pre-fault load current is not known (i.e. not calculated in the IEC 60909 method) and 2) transformers can operate at a wide range of off-nominal tap settings. As a result, the simplified IEC calculations do not align with calculations based on the more accurate superposition method. An impedance correction factor was thus introduced in IEC 60909:2001 to improve the accuracy of the calculated fault currents.

In the older versions of IEC 60909 (pre-2001), there was no explicit impedance correction factor for transformers, instead just a suggestion that considerations need to be made. IEC found this unsatisfactory and introduced the correction factor in the 2001 edition. The correction factor was essentially defined empirically through a statistical analysis of a few hundred transformers. Most of this is described in some detail in IEC 60909-1.