DIFFERENT TYPES OF DC LINKS
How many types of dc links?
Direct-current links are classified as follows
- Mono polar dc-link
- Bipolar dc-link
- Homo polar dc link
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Monopolar dc-link
The monopolar link has one conductor usually of negative polarity, and ground or sea return.
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| Fig :Mono polar dc link |
Bipolar dc link
The bipolar link has two conductors one positive, the other is negative. Each terminal has two converters of equal-rated voltages in series on the dc side. The midpoint (junction between converter) is grounded at one or both ends. neutrals are grounded the two poles can operate independently. Normally they operate at equal current; then there is no ground current. In the event of a fault on one conductor, the other conductor with ground return can carry up to half of the rated load. The rated voltage of a bipolar link is expressed as 100kv or pronounced plus and minus 100 kV
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| Fig: Bipolar dc link |
The homopolar link
The homopolar link has two or more conductors all having the same polarity, usually negative, and always operating with the ground return.
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| Fig: homopolar link |
In the event of a fault on one conductor, the entire converter is available for connection to the remaining conductor or conductors, which, having some overload capability, can carry more than half of the rated power, and perhaps the whole rated power, at the expense of increased line loss. In a bipolar scheme reconnection of the whole converter to one pole of the line is more complicated and is usually not feasible because of graded insulation. In this respect, a homopolar of the line is preferable to a bipolar line in cases where the continual ground current is not deemed objectionable
