HVDC in Bangladesh
Khalilur Rahman, Chair, IEEE RUET IAS Student Branch Chapter
Why HVDC in Bangladesh:
Bangladesh has huge demand in the electric power sector. There is always a gap between installed capacity and demand capacity. The demand is very high compared to its generation. In 2009, the peak demand was about 5,500 MW compared to its power-generating capacity was only 3,800 MW, implying a peak deficit of 1,700 MW. So to supply the demand, Bangladesh was looking to buy electric power from outside of Bangladesh. So, they began to plan on how to improve the installed capacity. The HVDC technology helped Bangladesh to improve its installed capacity.
[For now, the Total Installed Capacity (Including Captive Power & Renewable Energy) of Bangladesh is 22,727 MW as of 2nd December 2019. The demand forecast for Bangladesh is 17,304 MW in 2020 and 33,708 MW in 2030.]
Every country uses different utility standards of electrical power as there grid voltage is different. If synchronous interconnection is used between two countries, then a grid of both countries would operate at the same nominal frequency and voltage. As a result, faults in one grid will affect other country's grid. But in an asynchronous interconnection will allow independent operation for both the country's grid and it would facilitate complete control of the power exchange. Asynchronous interconnection has also additional equipment to protect one system against damaging faults and it would negate the need for and surges from the other system. Therefore, for the safety of both countries, an asynchronous High Voltage Direct Current (HVDC) link was selected. To meet the required power demands of Bangladesh, HVDC technology was introduced.
The first HVDC power station in Bangladesh:
A new chapter was opened between Bangladesh and India in October 2013. The first-ever HVDC transmission line in the region is HVDC Back to Back Station, Bheramara, Kushtia situated in the western border of Bangladesh. The HVDC Back to Back Station, Bheramara, Kushtia is operated by the state-owned Power Grid Company of Bangladesh Ltd (PGCB). It is the first-ever interconnection between the two countries in South Asia. The HVDC Back to Back Station in Bheramara, Kushtia began flowing 500 MW power from India to Bangladesh on 5th October 2013 after completion of the interconnection infrastructure. As of now, the power station has two Blocks. Both blocks have the capacity up to 500 MW each. Both work in parallel, so the total capacity of the station is up to 1000 MW power. Block 1 has been in operation since 2013 and Block 2 in commercial operation since 2nd July 2018. The 230-kV grid voltage of Bangladesh is connected via this substation and overhead lines to India's 400-kV grid.
Bangladesh is set to build another 500MW back-to-back High Voltage Direct Current (HVDC) station in Cumilla District. This station will import electricity from India as well.
Why HVDC Back to Back Station is used:
There are three general types of the asynchronous interconnection of HVDC transmission: Point to point transmission, Back to Back station, Multiterminal systems. Based on technical, operational, and economic considerations, the HVDC back to back interconnection was set up. HVDC back to back connected two alternating current systems on either side, without intervening transmission. A 400 kV switching station in Baharampur, India has two ends. One end of a 400 kV direct current (DC) transmission line is connected and the other end of the line was connected to a 400 kV transmission line at the India Bangladesh border and ends at the 1000 MW HVDC Back to Back Station. The station converts the power in DC then again change it to AC of 230 kV switching station in Bheramara, Bangladesh.
The benefits of using HVDC in Bangladesh:
The benefits of using HVDC stations are many. The main one, the control of the flow of power rapidly and securing the safety of both national grids from each other faults. The asynchronous interconnection is allowed adequate operational flexibility for connecting the power systems of both national grids. Also, the grid frequency is not the same as the countries. Bangladesh's grid frequency is 49.5 to 51 Hz. Where India's grid frequency is constant at 50 Hz. As a result, no direct connection is possible. So, HVDC helps in connecting incompatible electrical frequencies. It also helps in exceeding short-circuit power levels. Also, the interconnection costs of HVDC are less than that bought from the rental plants.
Bangladesh reduced its energy deficiency by importing electric power from India. India gained revenue by selling its available energy to Bangladesh as well. For emerging countries like Bangladesh, the availability of reliable power transmission is very crucial.
Contribution of Siemens:
This HVDC Back to Back Station, Bheramara, Kushtia was established with the help of a world-famous company Siemens. The company is responsible for the complete construction of the HVDC system in Bheramara. All the electrical components including the protection, control and monitoring systems for the HVDC system, the converter transformers, thyristor valves, and the AC filters are supplied by Siemens.
The significant challenge was choosing the mode of cross border grid interconnection in Bheramara, Kushtia it was the first time in South Asia. Bangladesh and India's cooperation helped in overcoming the barriers to reaching a purchase power agreement