Autotransformer 220/115/38.5kV + compensation winding

[iskar2000]

Hi all,
Please somebody to say me, Is it posible Autotransformer with 3 work voltage + compensation winding (6kV)?
If it is posible, please say me What will be vector group of such autotr-r....YNynaO+d may be?

 

[tgott]

Yes you should be able to purchase a 4-winding transformer. We spec'ed one last year to serve as a start up transformer and received bids from Waukesha Electric and ABB Power T&D. Following is how we specified.

Primary Voltage: 161 kV RMS, wye connected to a 161 kV grounded wye system. The 161,000-volt winding shall have full capacity taps at:
173,075 Volts
169,050 Volts
165,025 Volts
156,975 Volts

Each transformer shall have an externally operated no-load tap changer.

Low Voltage: 4.16 kV RMS, wye for 3-phase units connected to a 4.16 kV grounded wye system.

Tertiary: 4.16 kV RMS, wye for 3-phase units connected to a 4.16 kV grounded wye system.

Medium Voltage “Stabilizing” Winding: 13.8 kV RMS, delta connected. This winding shall be provided for the circulation of third harmonic currents and stabilization of the neutral. This connection shall never be changed. No external load shall be taken from the MV winding.

 

[jwerthman]

tgott is correct that this is possible and has been done. However, my suggestion is to find another way. My experience is that these types of transformers are quite expensive and less reliable due to the complex short circuit forces between the four windings. Also, if the transformer ever fails, it will be nearly impossible to find a suitable replacement quickly.

 

[jbartos]

Suggestion: The four winding transformers are produced and installed. If properly protected, they will last as any other transformers. In the more remote past, GE Co. Catalog transformer section indicated percentage of additional cost for an additional transformer winding. It was a relatively small percentage, e.g. 15% or so for an extra winding. If an extra winding saves extra primary winding and extra transformer, the overall savings are big. Also, the larger transformer, more iron, is more likely to withstand short circuits on its secondary windings. However, there may be some voltage dip impacts of a short in one of those secondary windings on the other ones that do not experience any short. This may be viewed as an immediate drawback. However, the systems are supposed to be ready for voltage dips; therefore, this shortcoming can be somewhat downplayed.

 

[iskar2000]

YNao,yno+d?