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Backup Impedance protection against phase to ground faults in EHV systems seen through delta star grounded generator step up transformer

IP.com Disclosure Number: IPCOM000214849D
Publication Date: 2012-Feb-07

Publishing Venue

The IP.com Prior Art Database

Related People

IVAN BERNARD FULLER: ATTORNEY

Abstract

Distance element at the generator is used as back up protection for the transformer and connected transmission line network. Normally delta-Star transformer is used which causes the backup distance element under-reach for ground faults at HV side. In this document, the analysis using the symmetrical components is done to find the reason for under-reaching. Impedance measuring loop based on symmetrical components is proposed for the aforesaid problem. The proposed measuring loop is also tested thoroughly for the different fault conditions to check the dependability and the results are also provided in the document.

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Backup Impedance protection against phase to ground faults in EHV systems seen through delta star grounded generator step up transformer

Sachin Srivastava, A V Sai, Sethuraman Ganesan

Summary:

Distance element at the generator is used as back up protection for the transformer and connected transmission line network. Normally delta-Star transformer is used which causes the backup distance element under-reach for ground faults at HV side. In this document, the analysis using the symmetrical components is done to find the reason for under-reaching. Impedance measuring loop based on symmetrical components is proposed for the aforesaid problem. The proposed measuring loop is also tested thoroughly for the different fault conditions to check the dependability and the results are also provided in the document.

1.    Introduction

Help:  The introduction should provide an overview of the entire report. It should include the purpose, scope, definitions and structure of this report.

1.1    Purpose

Propose a measuring loop for detecting phase to ground faults through Delta Star Transformer in a generator back up impedance protection.

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1.2    Scope

This report describes the under reaching effect of the distance element due to delta /Star transformer and there by proposes an impedance measurement for a dYn1 transformer configuration. This report is based on mathematical derivations derived and also the simulation testing (Using MATLAB Simulink-simPower) of generator back up impedance protection. This report does not describe for all other transformer configuration except dYn1. These configurations can be handled by appropriate phase shift.

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1.3    Structure

This report has the following structure.

2- Problem Description

3- Requirement

4- Solution proposal

5- Results

6- Conclusions

7- Future Work

8- References

9- Enclosures:- APPENDIX A, APPENDIX B, APPENDIX C

2.    Problem Description

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2.1    Under Reaching Problem                      

Problem Statement: 

When the generator back-up distance protection function is tested with single phase to ground faults at different locations in the HV side of the system through Delta-Star transformer(Dy1) connection type, the function is under reaching.

Explanation:

The power system model considered for mathematical derivations and experimental testing and validation using Matlab is shown in Figure 1. The CTs and VTs are direct measurement points. The Generator rating is 300 MVA, 13.8 kV, 10%  and Transformer rating is 300 MVA, 13.8/400 kV, 15%. In transmission line system a line of 300 km has been simulated f...