Tertiary Connected Reactors

Can you not obtain separate single phase oil filled reactors you could then connect in Delta?

Yes, but the manufacturers wont build us small single phase oil filled reactors. what they offered was 3 individual air coils and we can connect them in delta, but they are hesitant for us to connect them in vertical installation and in delta. they offer vertical but connect as star configuration.

Why is that, is there an issue with the clearance voltage or mechanical support that Star may not have over Delta, or do they just not offer a tested Delta connection solution?

_{Jack - More a Neutral Earth Resistor man.}

they wouldnt say, but i reackon its to do with the type testing.

i have asked, will see what thier response is. if we do go for a star config, will i need to re specify the reactance?

I am not sure (probably), you would need to check to see how the star configuration is going to affect your protection and the rest of the system.

5MVAR is a "small" reactor?

Avoiding a vertical stack may keep heat from the lower ones from affecting the upper ones; so that's understandable.

When you connect the 5MVAR, 11kV rated reactors in Star, the effective reactance in each limb and the net MVARs connected in the system will be lower (by 1/v3) than when connected in Delta. Hence, we need to connect in Star only (for wahetever reason), you will have to go for higher (by v3) rated reactors, keeping the voltage rating same.

Really, the overarching question is what purpose do the reactors on the tertiary serve? Whether they are oil-filled or air-core doesn't impact their electrical function. You need to determine if reactors in a Wye (star) configuration will provide the same function as in Delta, except possibly with some adjustment in value, as raghun has suggested. Does the tertiary feed something in your system (station service power?)? Does it perform a function in your protective relaying scheme? You need to figure that out first before you change the connection of the reactors.

Also, just because the manufacturer won't connect them in delta doesn't mean you cannot do it. You may need to add some bus bar or tubing, and some insulators and supports, but it is not impossible to connect them in delta. Put your engineering skills to work!

yeah....what raghun said. Remember that the current through the reactor connected in delta is lower than in the wye (star) configuration by a factor of 1/√(3) at the same voltage level. you can connect them in wye (star), but in order to maintain the same voltage level you might need to reevaluate your ratings.