07-09-2013, 03:07 PM
MODERN TRENDS IN POWER TRANSMISSION SYSTEMS (6-PHASE)
MODERN TRENDS.doc (Size: 324 KB / Downloads: 56)
Introduction:
The concept of six phase transmission lines was introduced by Barns & Barthold during 1972. Six phase power system is a part of multiphase power system. Due to harmonics effect and various other reasons Six phase systems and six phase machines are not popular but six phase transmission lines are more popular due to its increased power transfer capability by times, maintaining the same conductor configuration, rights of way, better efficiency, better voltage regulation, greater stability and greater reliability
High Phase Order(HPO) transmission is the use of more than the conventional three phases to transmit power over a given transmission corridor. Table I illustrates the increased power that can be potentially be transmitted if an existing double circuit line is
converted to a 6-phase line.
Feasibility of an interconnected 3-phase / 6-phase transmission systems
Basic feasibility of interconnected 3 phase / 6 phase transmission system has been reported for normal steady state operation, over voltages, insulation requirements, power flow etc., in several studies.
The studies reveal several interesting features of six phase transmission system and found to posses better characteristics than those of its 3-phase counter parts. The important findings of these studies are consolidated here for ready reference.
(i) Power transfer capability :
Consider 3 practical cases as follows:
(A) : 138 KV, 3 phase double circuit line configuration
(B) : 230 KV, 3ph transmission line configuration
© : 138 KV, 6 phase transmission line configuration
To convert the existing 3phase double circuit line to 6phase transmission line with little modification of the terminal equipment in the substations to provide 3phase / 6phase transformer etc., without changing the transmission towers, without additional rights of way etc,. Then power transferred is given by
The three line diagram of the GOUDEY Substation is shown below:
The substation consists of the installation of two three phase transformers with the appropriate phasor displaced to achieve the desired 60 degrees phase displacement between adjacent phases. In addition, circuit breakers of the single pole, live tank design will be installed to demonstrate the substation compaction concept along with switches, surge protection and an extensive relaying and metering/monitoring system.
CONCLUSION:
Six phase transmission technology provides a technique for reducing physical space requirements for transmission lines while providing a means for increasing power transfer capacity of a new or existing transmission corridor. The cost for constructing a new six-phase line versus a three phase line of the same voltage level, is not excessive, particularly if physical constraints exist. In India, the 6-phase transmission system is not existing because there is no technical knowledge over the operation of the 6-phase systems.