TVA’s Transmission Voltage Unbalance Evaluation

tvas-transmission-voltage-unbalance-evaluation-2

GARY KOBET, THEO LAUGHNER, DAVID MARLER, ANTHONY MURPHY, JAMES ROSSMAN The paper presents transmission level voltage unbalance as measured by two primary methods across the Tennessee Valley Authority (TVA) Transmission system. It also discusses the recent focus on distribution voltage control. Three standards mentioning voltage unbalance (VUB) are discussed as well as TVA’s operations, limits, and limitations on voltage balancing. An example of equipment malfunction creating voltage unbalance is discussed. A team was formed to address voltage unbalance concerns and this team made a number of measurements across the TVA system. The team determined the average transmission system unbalance delivered to customer sites to be 0.59% (method 1) and 0.64% (method 2). In 2014, TVA transmission adopted a 161-kV-level VUB maximum limit for distributor service delivery of 1.4% (IEC 61000-3-13 methodology). One area in NE Tennessee experienced levels above this new delivery limit of 1.4% VUB during high system loading. To reduce this VUB in NE Tennessee, TVA initiated a capital project to transpose critical 500-kV lines which are known to operate above their surge impedance loading level creating VUB between phases.

GARY KOBET, THEO LAUGHNER, DAVID MARLER, ANTHONY MURPHY, JAMES ROSSMAN The paper presents transmission level voltage unbalance as measured by two primary methods across the Tennessee Valley Authority (TVA) Transmission system. It also discusses the recent focus on distribution voltage control. Three standards mentioning voltage unbalance (VUB) are discussed as well as TVA’s operations, limits, and limitations on voltage balancing. An example of equipment malfunction creating voltage unbalance is discussed. A team was formed to address voltage unbalance concerns and this team made a number of measurements across the TVA system. The team determined the average transmission system unbalance delivered to customer sites to be 0.59% (method 1) and 0.64% (method 2). In 2014, TVA transmission adopted a 161-kV-level VUB maximum limit for distributor service delivery of 1.4% (IEC 61000-3-13 methodology). One area in NE Tennessee experienced levels above this new delivery limit of 1.4% VUB during high system loading. To reduce this VUB in NE Tennessee, TVA initiated a capital project to transpose critical 500-kV lines which are known to operate above their surge impedance loading level creating VUB between phases.

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