Hvdc and Facts

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ABSTRACT
In this paper we look into the recent trends in power transmission engineering, FACTS and HVDC. The first part of our presentation starts with a quick idea of FACTS. FACTS is defined as a power electronic based system and other static equipment that provide control of one or more AC transmission system parameters to enhance controllability and increase the power transfer capability. This paper also deals with the basic concept involved in the usage of FACT controllers which are capable of controlling up to three system parameters; voltage magnitude, phase angle and transmission impedance. The simulation results for VAR compensation with and without one of the FACT controllers named THYRISTOR CONTROLLED SERIES CAPACITOR is also shown.

T he next part of our presentation begins with a brief historical perspective on the development of HVDC transmission systems. It also present the various types of HVDC transmission systems available and an overview of the status of HVDC system in the world today with specific regard to India. It then concludes with a brief set of guidelines for choosing HVDC systems in today’ s electricity system development INTRODUCTION:

In India, transmission planning has always been given a less priority when compared to generator planning. We experience wide band voltage variations in 33/11kv sub-transmission and LT system. One of the main problems is the RKVA management. The reactive power flows form generating stations and other devices to the load centers through 400kv, 220kv, 132kv sub transmission and distribution networks. This free flow of the reactive power results in undesirable volt levels in all parts of the network. Under maximum load conditions the lagging RKVA load is supplied by generating stations. On the other hand, under minimum load condition the leading reactive load, generated from transmission system is to be observed by generator. This RKA loading is limited by capability curve of sets and the deficiency is reflected in the system as low voltage under maximum load and as over voltage under minimum load conditions. The reactive power transmission over hundreds of KM’ s cause voltage gradient. Every voltage level should be self sufficient in VAR support even under heavily loaded conditions and reactive flows in the inter- connecting transformers should be minimum. The basic flaw in the Indian EHV network planning is one of the prime reasons for frequent grid collapses. Unless the syndrome of one voltage level expecting reactive support form other volt levels is broken, one of the main causes for grid collapses in India will not be addressed.

Large RKVA power demands on the system results in:
1. Higher MVAR support for given MW output, based on generator capability as per design parameters.
2. Transfer of more KVA power for lesser KW transmission there by over loading transmission lines and transformers.
3. Increased (I*I) Z losses and IZ drop, with poor power factor. 4. Reduced revenue and increasing operating cost.
For compensating this reactive power and for enhancing the capabilities of transmission networks FACT devices are being used. By FACTS technology transmission lines can be loaded up to their thermal limits.

CONCEPT OF FACTS:
The concept of Flexible ac Transmission Systems (FACTS)
has recently gained much attention in the Electrical Power world. FACTS technology is based on the use of high voltage, high current power electronic devices in association with communication links and local automatic controllers.

The power systems of today, by and large, are mechanically
controlled. But the problem with mechanical devices is that control cannot be initiated frequently, because these mechanical devices tend to wear out very quickly compared to static devices. In effect, from the point of view of both dynamic and steady state operation, the system is really uncontrolled. Thereby the FACTS technology is essential to alleviate some but not all of these...
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