<p> HVDC TRANSMISSION Subject code: 10EE751</p><p>UNIT 1- LECTURE 05</p><p>Types of HVDC links:</p><p> Monopolar link</p><p> Bipolar link</p><p> Homopolar link</p><p>Monopolar link:</p><p>Having one conductor (-Ve Polarity) and ground is used as return path. </p><p>We can operated either in +Ve or –Ve polarity,but usually preferred -Ve polarity in order to reduce the Corona effect.</p><p>The major drawback in this system is power flow is interrupted due to either converter failure or DC link.</p><p>The ground return is objectionable only when buried metallic structures (Such as pipes) are present and are subject to corrosion with DC current flow.</p><p>Bipolar link:</p><p>There are two conductors , one is operates at positive and other is negative. During fault in one pole it will operate as monopolar link. This is very popular link in HVDC Homopolar link:</p><p>In this link, two or more conductors have same polarity.</p><p>Normally negative polarity are used(to less corona loss and radio interference).</p><p>Ground is always used as return path.</p><p>During fault in one pole it works as monopolar. Application of HVDC:</p><p> The main areas of application based on the economics and technical performances, are</p><p> Long distance bulk power transmission.</p><p> The underground of submarine cables.</p><p> Asynchronous connection of AC system with different frequencies.</p><p> Control and stabilize the power system with power flow control.</p><p>Based on the interconnection, three types of HVDC is possible.</p><p> Bulk Power transmission</p><p> Back to back connection</p><p> Modulation of AC system</p><p>Purpose of HVDC based on interconnection:</p><p> Bulk power transmission</p><p>(Transfer the power from one end to another end without tapping power in between).For this DC system is the best option. (Or) HVDC transmission where bulk power is transmitted from one point to another point over long distance.</p><p> Power flow control (Back to Back HVDC)</p><p>If two regions are very nearby, we can monitor the power flow from one region to another to control, emergency support as per our requirement.(Or)Back to Back link where rectification and inversion is carried out in the same converter station with very small or no DC lines </p><p> To provide stability to AC system</p><p>This is basically used to control the power and stabilize the system. It is also used to connect two different frequencies system.</p><p>(Modulation of AC) AC system is connected parallel with DC system.(or)Parallel connection of AC and DC links. Where both AC and DC run parallel. It is mainly used to modulate the power of AC lines.</p><p>HVDC is the better option for above cited purposes while compare with its AC system.</p>