Converting 220kV to 350kV DC with HVDC: Exploring the Theory

[AElcEng]

Hi,

Something is puzzling me with the HVDC work I'm currently working with. I'm working for contracting company here in NZ contracted to complete the new HVDC converter station.

We have 3 x single phase converter transformers on site converting the AC voltage. I was wondering why when having an input of 220kV you get 350kV DC. I believe the line windings is connected in Star and the Valve side connected in Delta.

Can someone direct me to a link or explain to me the theory behind getting 350kVDC output? It's very intriguing from a technical point of view. We don't usually get to work on DC links here in New Zealand.

Thank you in advance.

Regards

 

[jim hardy]

i don't know for sure but would bet it has to do with the smoothing reactor.
Reason i say that is 350/220 falls between √2 and √3 ,
and I remember from high school that a choke input filter has better regulation.

Here's a picture of a smoothing reactor

and a link to Siemens - perhaps there's a tutorial there.

http://www.energy.siemens.com/us/en/power-transmission/hvdc/

page 8 of this pdf looks like a start.
http://www.energy.siemens.com/us/pool/hq/power-transmission/HVDC/HVDC_Proven_Technology_.pdf

(if link doesn't work, i reached it by clicking on "HVDC Technical Compendium" here:
http://www.energy.siemens.com/us/en/power-transmission/hvdc/hvdc-ultra/dc-components.htm )

imteresting technology. I was never around it. Thank you Siemens for the introduction !

old jim

 

[davenn]

Hi,

We have 3 x single phase converter transformers on site converting the AC voltage. I was wondering why when having an input of 220kV you get 350kV DC. I believe the line windings is connected in Star and the Valve side connected in Delta.

Thank you in advance.

Regards

hi there

where in Kiwiland is that being constructed? I'm an ex-pat from the Dunedin area
350kVDC... FAR OUT! would love to see the rectifiers for that

very interesting... watched that video on developments in a China network
not my field, but enjoy learning :)cheers
Dave

 

[AElcEng]

Thanks for the replies.

Here is my understanding so far.

The input voltage to the converter transformer is 220kV AC, the transformer built in such a way with it's turns ratio to reduce the voltage to 143.7kV (RMS value). 143.7kVx(squar root 2) gives the voltage peak. Then you would multiple by square root 3 would give us 350kVDC output from the rectifer? Heres my question what is the meaning of square root 3? My understanding of a smoothing reactor is to reduce the harmonics in the DC output? Please correct me if I got any of the information wrong. I'm no expert just learning. Thank you for the link I'll try and comprehend what's being said. Thanks alot.

Dave, NZ always had a 350kV dc in the south island in Benmore since the early 1990s with pole 2 (ABB technology). We are currently replacing pole 1 (270kVDC) and replacing that with SIEMENS technology to up the capacity of the power flow. New pole will be 350kVDC. It's also being built in Benmore. The valve room in Benmore is a piece of ART! great technology!

 

[alphysicist]

,

I can provide some insight into the theory behind converting 220kV to 350kV DC using HVDC technology. HVDC stands for High Voltage Direct Current, which is a method of transmitting electricity over long distances using direct current instead of alternating current. This method is often used for long distance transmission because it has lower losses compared to AC transmission.

In order to convert the AC voltage of 220kV to a DC voltage of 350kV, a process called rectification is used. This involves converting the alternating current to direct current by using a device called a rectifier. The rectifier uses diodes to convert the AC voltage to a pulsating DC voltage, which is then smoothed out using capacitors.

In the case of HVDC, the input voltage of 220kV is first stepped up using transformers to a higher voltage, typically around 500kV. This higher voltage is then fed into the rectifier, which converts it to DC voltage. The reason for stepping up the voltage is to reduce losses during transmission, as higher voltages can carry more power with lower losses.

The output voltage of 350kV is achieved by adjusting the design of the rectifier and the number of transformer stages used. This is done to ensure that the output voltage is at the desired level for efficient transmission and distribution of electricity.

In terms of the connection of the line windings and valve side, the Star and Delta configurations refer to the way the windings are connected in the transformer. In Star connection, the windings are connected in a triangular shape and in Delta connection, they are connected in a star shape. The specific configuration used in the transformer depends on the design and requirements of the HVDC system.

I hope this helps to provide some understanding of the theory behind converting 220kV to 350kV DC using HVDC technology. If you would like more information or resources, I suggest researching HVDC systems and their components in more detail. Best of luck with your project in New Zealand!