There are two types of transmission system; HVAC and HVDC system. In this article, we will make comparison between HVAC and HVDC system.

Comparison between HVAC and HVDC system

Sr No	Title	HVAC system	HVDC system
1	Effect of capacitance	Because of the effect of capacitance charging current produced in the line. The length of the line is limited due to the charging current.	There is no effect of capacitance in the case of DC. Hence, the charging current is not produced. So, there is no restriction on the length of a line.
2	Skin effect	In the HVAC system, the skin effect produced due to the non-uniform distribution of charge in a conductor. The power loss increases due to the skin effect.	There is no skin effect and power loss.
3	Supports	Heavy supports needed. So the cost is more.	The cost is less because of the use of lightweight support.
4	Corona effect	Corona effect is more in the HVAC system. Which results in the power loss and disturbance to the communication line.	Less effect of the corona. Power loss is less and no disturbance to the communication line.
5	Reactive loss	There is a net reactive loss.	There is no reactive loss.
6	Number of line wire	For bulk power transmission, six conductors used.	Only two conductors required.
7	Ferranti effect	In this system, the Ferranti effect produced.	In this system, the Ferranti effect is absent.
8	Power factor	The transmission line behaves as an inductor. Therefore, the power factor is lagging. Synchronous condenser or FACTS devices used to improve the power factor.	There is no question of the power factor in the case of DC.
9	Intermediate substation	Every 300km, one substation required.	No requirement of intermediate substation.
10	Use of earth return	It is not possible to use earth or marine as a return path.	It is possible to use earth or marine as a return path.
11	Line loss	Due to reactive power, line loss increases.	Line loss is less in this system.
12	Stability	The stability of this system is less. The length of a line is limited.	This system is more stable.
13	Voltage regulation	Poor	Good
14	Asynchronous tie	It is not possible to connect two tie line which has a different frequency.	There is no question for frequency.
15	Overload capacity	More	Less
16	Possibility of system failure	Less	More
17	Volume of conductor	More	less
18	Power transfer and control	Slightly difficult	Quick control of line
19	Short circuit level	Increases	Fault level remains the same
20	Complexity of system	Less	More
21	Cost	Less	More
22	Maintenance	Easy to maintain	Difficult to maintain and highly qualified staff need to maintain
23	Change the voltage level	Possible	Not possible

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