A NEW TECHNOLOGY IN A NEW WORLD HVDC LIGHT

ABSTRACT:
From past many decades of year we are using AC transmission where dealing with this ac transmission has many limitations .This limitations are overcome by HVDC.Even though HVDC having many limitations they are overcome by following system.
This paper describes the updated form of HVDC Light. The HVDC Light technology is well suited to meet the new markets and its demands and the reasons for this are explained. HVDC Light is the most interesting power transmission system using high voltage direct current. These may be installed in existing AC grids for their role in stabilizing power flow without the additional short-circuit current. This concept is called "HVDC Light" which uses pulse width modulation. It extends the economical power range of HVDC transmission down to just a few tens of megawatts (MW).
In this paper the usage of HVDC Light, application, their limitations, HVDC Light characteristics and how they are installed is described in detail manner
INTRODUCTION:
Nowadays there is a huge competition in the electrical industry as a means of achieving cost effective outcomes. So most of the long AC transmission lines in the world are replaced by HVDC transmission lines because of their economical properties. Though HVDC transmission line has many advantages there are some limitations too. So, some of the HVDC transmission lines are replaced by the HVDC Light to meet the limitations of HVDC.
HVDC LIGHT:
HVDC Light is the most interesting power transmission system using high voltage direct current. HVDC Light was introduced in 1997 by ABB Manufacturers. It is an electric power transmission technology which employs the latest in power semiconductor technology, the IGBT based on voltage source converters with pulse width modulation and modern HVDC cables. It has the potential of changing the way transmissions are built in the future. The HVDC Light system comprises two (or more) converter stations at the ends of the transmission, and an underground (or submarine) cable page link between them. This characteristic is well suited to meet the demands from the new markets.
What makes HVDC Light special?
• Underground polymer cables
• Easy permits
• Connection to passive loads
• Independent control of active and reactive power flow
• Short delivery times
• No special dc transformers
• No electrodes
• feeding of power in passive networks(network without any generation)
• power quality control
• modular compact design
• unmanned operation
• robust against grid alternators
PULSE WIDTH MODULATION:
The operation of the converter is achieved by Pulse Width Modulation (PWM). With PWM it is possible to create any phase angle and/or amplitude (up to a certain limit) by changing the PWM pattern, which can be done almost instantaneously. Thus, PWM offers the possibility to control both active and reactive power independently. This makes the PWM Voltage Source Converter a close to ideal component in the transmission network.
HVDC LIGHT CHARACTERISTICS:
An HVDC Light converter is easy to control. The power reversal without interruption is possible. It can be start up dead AC network. There is no increase in the short circuit currents and equal or longer service life than
XLPE AC cables. The Light converter has a switching frequency of 2 kHz that is 40 times faster compared to a phase commutated converter operator at 50Hz.
CONTROL OF ACTIVE AND REACTIVE POWER:
The control of active and reactive power makes it possible to create any phase angle or amplitude, which can be done almost instantly. This offers the possibility to control both active and reactive power independently. As a consequence, no reactive power compensation
Equipment is needed at the station, only an AC filter is installed. While the transmitted active power is kept constant the reactive power controller can automatically control the voltage in the AC-network
VSC converter –single phase circuit diagram Continuous control of Active and Reactive Power:
The combined active and reactive capabilities can most easily be seen in a P-Q Diagram