India's energy demand is expected to double by 2030. The Industry sector accounts
for 40% of the country's total energy consumption. Introducing energy efficient
processes and other energy saving measures can bring about considerable savings
for the country. With energy accounting for 35-40 % of production cost of energy-intensive
industries, the manufacturers stressing the need for energy efficiency, thus demand
for electrical drives is on the rise.
Drives are widely used in manufacturing industries to regulate and control rotating
equipment such as fans, conveyors, machine spindles, and pumps, which are used in
production processes. AC drives are widely used in process industries to increase
the efficiency of equipment. It controls the speed of electric motors according
to the process needs, typically reduces energy consumption by 35-40%.
However, the bulk of the load of an energy intensive industry is driven by High
Voltage / High Power AC motors. With the invent of High power transistor devices
the current trend is to use Medium Voltage (MV) AC drives for such applications
where the magnitude of savings in high.
Energy intensive industries such as Metal, Cement and Power have started using MV
Drives for controlling Medium Voltage Motors.
Some interesting applications.
Application : Long Conveyor in Material Handling
Long conveyors are extensively used in many industries like Mining, Cement, Ports
and Power. Traditionally, slip ring motors or fluid couplings have been used for
long conveyors Slip ring motors have high O&M cost due to which currently AC induction
motors are preferred. Drive system is used for controlled start-up and load sharing
in long conveyors.
New Approach
- Transport material over few Kms
- Reduce mechanical stress through controlled start-up and load sharing
- Control speed to match operation requirements
Benefits
- Longer mechanical life arising out of reduced mechanical stress through controlled
acceleration/deceleration and load sharing
- Significantly reduced losses when compared to Fluid Coupling
- High reliability with multiple co-ordinated motors driving Long Conveyor
Application: Twin Motor Kiln in Cement
Traditionally Kiln Motors are driven by DC Drives due to its high starting torque,
however DC Motors have high O&M cost and generate carbon dust. In addition DC Drives
also produce poor power factor and harmonics that are detrimental to the electrical
system.
With the advent of MV Drive technology, the traditional DC Drives are getting replaced
as AC MV drive to overcome all the above disadvantages of a DC system.
New Approach
- Reduce mechanical stress on Kiln system through twin motors instead of one.
- Replace the higher rating (>1000Hp) DC motors with two small AC motors which can
meet same or higher Toque Requirement
- Use MV Drive to achieve load sharing between twin motors and speed control
Benefits
- Lesser stress on Electrical system through reduced in-rush current, improved power
factor and lesser harmonics resulting in better asset utilization and longer life
- Reduced Power system components like Transformers, Breakers and HT Capacitors
- Reduced motor maintenance
The technology development has led to the networking features in drives, it is more
open to networking with the plant DCS on various networking protocols, configuration
and troubleshooting on network is possible.
Application: Pipeline in Oil & Gas
Cross country Pipelines are used to transport petroleum products from refineries
to demand areas and crude oil from sources to inland refineries.
To transport this product over long distance from source to destination and to maintain
desired flow, pumping stations are installed at strategic locations. Centrifugal
pumps used at these locations offer great potential for energy saving, as the application
always does not require 100% flow.
For better performance, VFD based solutions are being adopted because of their ability
to control flow efficiently and optimize energy use.
With the advent of MV Drive technology, the traditional DC Drives are getting replaced
as AC MV drive to overcome all the above disadvantages of a DC system.
New Approach
- Improve operational efficiency with MV VFD as compared to earlier LV VFD based solution
with Step-down & Step-up Transformers preceding & following the VFD popularly called
Hi-Lo-Hi solution
- Co-ordinated drive operation to control multiple pumps with Single VFD controlling
flow
- Ability to perform synchronous changeover to Mains and back to Inverter mode
Benefits
- Reduction in Source Transformer rating due to elimination of full voltage start
when compared to DOL star
- Reduction in number of Power components when compared to Hi-Lo-Hi solution
- Extended Equipment Life, Reduced Maintenance & Easy retrofit due to the near sinusoidal
waveform & soft-start
Application: Pipeline in Oil & Gas
Traditionally Fans and Pumps in a Steel plant were driven directly on mains voltage
and process fluid flow was controlled by Dampers.
These include different types of fans like Combustion Air fan, De-dusting fan and
a variety of pumps. Process efficiency is largely governed by the extent of speed
control of Fans and Pumps, which can better addressed by VFDs.
New Approach
- Variable Torque Load
- Eliminate Damper based flow control
- Precise flow control as per process requirement
Benefits
- Energy savings at reduced Fan/Pump speed
- Minimised vibration levels as compared to Damper control
- Enhanced Asset life by minimizing wear and tear on all drivetrain components
VFDs are now fully function driven, able to compensate for load changes, more intelligent
to understand the frequency conversion for speed with high precision, easy to form
a closed-loop control and component health monitoring . Also the power handling
capacity is changing from AC-DC-AC to AC-AC without storage device in between, this
improves the reliability and performance of drives.
Facing challenges from different application areas, the variable speed drive are
constantly upgrading and developing into application-specific algorithm, feature
rich , easy to operate, versatile, fully function driven software programs. High
torque and 4 quadrant applications are being handled by AC drives more intelligently
with the advent of software and built-in application algorithm. This gives flexibility
to user for easily configuring the drive for his application without much complexity.
Conclusion
Due to technological advancements in semiconductor devices such as insulated gate
bipolar transistors (IGBTs), MV drives are increasingly used in Petrochemical, Mining,
Steel and Metal, Transportation industries, among others, to conserve electrical
energy, increase productivity and improve product quality. Going forward, AC Drives
would replace the use of DC Drive system and contactors in motor control centres.
Also, the high power high voltage drives will replace the use of inefficient damper
and valve control system. This will give reliability of operation coupled with energy
saving.