It is an earth fault. Let us understand the above expiation with some numeric data. This will result in no zero sequence current component in I’, But mind that for relay to filter out zero sequence current, we need to enable this feature provided in the, Line Loadability – Universal Line Loadability Curve, What is IGBT? -Working & Types of UPS Explained. on the 33kV side from CT secondary (Star connection) until the Winding 1 (Star connection) of the Interposing CT, will the addition of a grounding (either on the CT star connection or ICT Winding 1 Star) defeat the zero sequence filtering? Awesome article Bro…. Hi,Interesting article. As zero sequence current cannot flow in Delta side, therefore line current IA – IB will not have any zero sequence current components and hence line CTs secondary currents I1, I2 and I3 won’t also have no zero sequence current component. This will create an imbalance in the differential current and may lead to actuation of Differential Relay even in through fault condition. zu��a}�3���(2 _�L��n�"aH��M�N��i�u�-�L��@�8��u�z�7��F�F�wB|2]��c�&�ː���`8�Wܙ4w:�*���R68�]�tn�����J�]]aU�+���c�tb��"Þ��
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�îH�&ߪa���ګs.ʚP:�w1NS�����p��l�M��N)�/���ޏ�������!��S����ez�����bd�J�3w. This fault current will flow through ground and winding PN for star side of Transformer. For additional info … CTs in Delta side of Transformer are connected in STAR while that in STAR side, it is connected in Delta. on the measurement point to the earth between the size of the impedance. For better understanding, consider a DELTA STAR Transformer as shown in figure below. If-0 = zero sequence current; X2 = zero sequence reactance; By principle, the single line to ground fault will develop and equivalent network where all sequence networks are connected in series. )=7hA�(E�ɪ�y�j�)Dmd`��`�@]rR����f���B��{A����l�כ���>�T!�/��O���Vvaڕ�m+�-ɺ�1�Q�h�n�9��f�U�vD�v���>P�C?� ��R�.B�ڷ�߬���|��Ԍx^����y��Q�qמ�GgP�9j(�SC��aRjd���u�V�=�T�[G���+�ȟ�EЂT.���w��x���r��jܘ�����(��Q���m"��Y�b�b;�����X}�~��[e�0%p|����}�'�z�@Ǡ�IS/N�5Qֈ�(te��9����Fv�[��iJ�Yg\KD�n#��?�������:���oi����ԡ You will come to know the reason. clear the limitations of the zero sequence directional polarizing method and clearly show the importance of the detailed modelling of protective devices in network protection studies. Therefore if filtering is enabled, then relay input for differential calculation will be (100 – x) A in Star side of Transformer and that in Delta side is (100 – x) A. !��`
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%c>Fǜn�6��A�3����+K�{n]�/����D����̛gibRz����9�H�����~�u�:�N��]�����e0ʳ��ȸN�P�u�3O�vk`��!8)~ *�]�y�g��R��,�:�aB����r��Ƀ�D2k����v H��Wmo�6����rhV�$~��=�A�p@q_���V��6�֮��;�)Rk'9\p0�\r^�yf8���F��U�.c�l8s�
�\\rV�m�7[^�Z����p���Oo^�����S\\H�4B��}�mSJwyk��Kv��0���x�����������m+�ư�K��Nm��D ��Pʇۖ�����̆=��v�~:���e^�� Thus a differential current of x A will be sensed by the relay and will cause the relay to operate though the fault is not in the zone protected. Therefore in line current of delta side of Transformer, there will not be any zero sequence current. Similarly in star side of Transformer, CTs are connected in DELTA to have phase correction. )ϭ{!$&��A�[2��E�� I. Where from its come or hows generated in delta? Let us have a detailed discussion on this topic. Similarly in star side of Transformer, CTs are connected in DELTA to have phase correction. During fault condition in Star side on transformer zero sequence current in delta side?? we respect your privacy and take protecting it seriously, Zero sequence filtering is a concept used to eliminate zero sequence current component from the secondary current of Current Transformer used in. Let us understand the above expiation with some numeric data. You can use a very low ratio (e.g. On the high side it is Star-Delta while the low side is Star-Star. Check for any fault in the protected zone. If there is a high zero-sequence current, earth fault will pick up in the phase CTs and clear the fault. �H�*�Zf��x�p�Q��lp7�� ��'O2���(&]`3v��|� �%`��ԉ*>��ꎇG���nƗ���U9pI9��]�`p��,�%��{����{���sB�hV%@W�ZZ9�̂��2��(K�+V���pj_��o���K�^��U�[�j��!3��ߺ}Ѻ� sequence impedance source such as a grounding transformer providing only zero sequence current for ground faults. Let the fault current be 100 A. When the system fails, the three phases become asymmetrical, then the decomposition of the amplitude of the negative sequenc. In modern Numerical Relays, this elimination of zero sequence current do not need such connection of line CT secondary. We have Ynd1 Power Transformer and we have a tripping of Biased Differential Protection during a downstream fault. This current of magnitude x A will circulate around the delta loop. Thank you so much… I am an engineer working in 400kV substation. o������Јv>d=;�* 9��9�k};�U,��;����7F-�/?0�����;t�[� �Ɓm�`_X���! This also have one more advantage. For better understanding, let us consider a Delta Star Transformer of voltage ratio 1:1 as shown in figure below. This concept is useful in Transformer having earthed Star winding. As zero sequence current cannot flow in Delta side, therefore line current I, Next you might ask why we didn’t connect these CTs in delta? Zero sequence voltage is a three-phase line in a phase or two-phase ground generated, the size depends on the degree of grounding, metal grounding, non-metallic grounding, is the grounding resistance. This is how zero sequence current is eliminated in differential protection of Transformer. Zero sequence voltage is a three-phase line in a phase or two-phase ground generated, the size depends on the degree of grounding, metal grounding, non-metallic grounding, is the grounding resistance. It’s quite easy. �Q��j�N�[�8�7>P]����0�����Cx\��;�#đ�Y��n�x{́aZV5�"�oN�y*RPY;�~`�a����Y��4��L�{ճ����x@D �WU��̷c�n���DЙʑ$�g��;&Sה%���h����an2� �=�t�w! ?��������O����69"���= 뵙c͗jAaX�͓q���ET But the current in the star side of phase PN = 100 A. From the Winding 2 of ICT until the Biased Differential relay, should there be grounding also or no, in order for the zero sequence filtering to work? We connect both Delta and Star side CTs in star and fed to relay. What is the Need for Zero Sequence Filtering? But mind that for relay to filter out zero sequence current, we need to enable this feature provided in the numerical relay. In earlier design, zero sequence filtering was achieved by proper selection of line CTs connection. What the numerical relay does is that it calculates the zero sequence current as. Remember, our Earth fault relays are set at 20% of Full Rated Load current to avoid tripping due to unbalance load current. '"�Ud�.9�?�u�)�UM�K��� pr��Cw8`�.! I��k� ��� �ۖ��PY��0���1�}�q�e�~�m�v;ۛq8Ax.�3Ë+��oئtMGY��\[�0�������㛍�;~qIm�~�P�W�_#�2�r�E���>KU��^�^\��AY����eEu�r��0��Z�^y+��D�?8u���%��:}���Kyu��;�t��y���#�X{Wu�C�榰��[+�q�6��Q�J��G�S�_�xV�ZǻV&w�:;i���EU%� ��b��J�T*�E�7�7�Z���!ׇ�,����s�����R"�2Uֈp���|#�n�f7�]qB�9>��$�ņ'���݈���X��V�0v�oW�8����: 4*K#��ДzE�2��6��rE��^��gq�+?�7�'��4ت�w�z��S՚�z�ZĀj��W���ë���,�L�3���IM@3Q�Z(3����f��`�, �Kr�6i#�*��-��Y���JW&\��s�@ē�����y�X�5.x� �9>�T���q�x[[D�nZ���NͲe��i
�̴�0��*i|�/����"�H�7��-](�N�����sZW. This fault current will flow through ground and winding PN for star side of Transformer. You can obtain a much lower setting with a sensitive ground fault protection (zero sequence ground fault protection) than with residual ground fault protection. If the CT input to relay is Ia, then the input from differential calculation of relay will be (Ia – I0). Thank you! �hEU���A�@ʏ��m��г���_�7�47N�Om3�����g/��M%�Q��9���7�l�y
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��h�*1�N�ֻ�uYN/���t4��;��M4����Z Voltage ratio of 1:1 has been considered for the sake of simplicity. Prev: Basic working principle of longitudinal differential protection of generator, Next: Zero sequence current protection principle, Copyright 2014, following Paul Business Network Shanghai ICP 11009447-2, Basic working principle of longitudinal differential protection of generator, Zero sequence current protection principle. Zero sequence filtering is a concept used to eliminate zero sequence current component from the secondary current of Current Transformer used in Differential Protection of Transformer. Actually in differential protection of Transformer we need to correct the phase as there is a phase change of 30 °in currents from Delta to Star, therefore to match the phase, we connected CTs in STAR fashion. �oZh~Ţ�e).���. In Star Star transformer we may or may not need this filtering but it is recommended to enable this. qչ0�.Ȏ�=�)d��i��V�f
��x�9o_2��w����$CJ���["{s}�M���-�������u=�'�rt8���KI0s�O�O��o�n(b:��E�,DۣQ�:$�4v]�� -� �dz���[���UU�M^�&(��ޭ��r�+�;Hc��½H[� Take IR of tranaformer and bus bar. In case of a line to ground fault, system draws an unbalance current and Earth fault relay trips after detecting zero sequence current above 20% Full Rated current. Why? Index Terms—Cross Country faults, Petersen Coil grounding, Ground fault directional protection, Negative Sequence directional protection.
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[V� Uj��kN�3�ϡo����hl Twhl�#kf��4�w�/�L ��%B:T*�CiDaNR5��2�}l燶���j��є�Tt�&����� ��r_�2V��K�� Since 100 A of current is flowing in winding PN of star side, therefore, the current in corresponding delta side of winding AB will also be 100 A as voltage ratio is assumed unity. A setting of 1%-2% Full Load Current is obtainable with sensitive ground fault protection while a setting of lower than 10% Full Load Current (residual ground fault protection) normally result in nuisance trips. Let us discuss this aspect in detail. An example is a three-phase wye-grounded-delta transformer connected to the line on thewye side. This means no differential current and hence relay is stable under through fault. In case of single line to ground fault in STAR side, fault current in line will contain zero sequence current component but due to DELTA connection of CTs, this zero sequence current will circulate around the DELTA loop. May I know for the zero sequence filtering to work, how should my ICT connection be? Zero sequence power at the point of failure, the fault point of the zero sequence voltage is highest, the distance from the fault point in the system the lower the zero sequence voltage, dependinge and zero sequence of the degree of measurement (sometimes only one of them), so by detecting the two should not be normal The weight of the system, you can know the system out of the problem (especially when the single-phase ground zero sequence component). Zero sequence current was x A. Commentdocument.getElementById("comment").setAttribute( "id", "a2eb1d8cb21fcd791d32636a1d75bb1a" );document.getElementById("dc65a5f484").setAttribute( "id", "comment" ); Subscribe to our mailing list and get interesting stuff and updates to your email inbox. I have some question which I faced during my work. Thus a differential current of x A will be sensed by the relay and will cause the relay to operate though the fault is not in the zone protected. But if you have anything to ask, please write in comment. Actually in differential protection of Transformer we need to correct the phase as there is a phase change of 30. in currents from Delta to Star, therefore to match the phase, we connected CTs in STAR fashion.
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