Standard 13.8kV Generator BIL levels??

[AJ2002]

I need some help finding the standard BIL levels for synchronous generators. Does any one have a link or reference?

The application I am designing has a 50kV BIL (4.5MW) and the Utility is stating this is not hign enough for connection to their system, so they are requesting an isolation transformer.

Standard switchgear at this voltage range is 95kV Bil. Is there a way to increase this BIL level or minimize this weak point in the system with lightning/surge arrestors or something else?

Thank you.

 

[dpc]

The BIL of rotating equipment is generally always going to be lower than switchgear - that's why surge protection is necessary at the generator terminals.

 

[davidbeach]

Placing a transformer between the generator and the utility will also make the generator happy, particularly if you also high resistance ground the generator at the same time.

 

[AJ2002]

Is there a way to avoid the additional cost and operation expense of losses from adding a transformer? The system that it is connected to is a WYE connected 13.8KV, 4 wire.

I agree with David that the transformer is ideal but my client wants to avoid if possible.

I can not find typical Basic Impulse Levels for generators. What are typical #'s?

 

[edison123]

No generator winding (either new or old or rewound) is subjected to impulse voltage tests unlike transformers, which use vast quantities of oil as insulation. There is a type test for two stator coils /bars during manufacture at 2*(2U+1)which I follow in my shop. All Individual coils/bars are routine tested at 1.3*(2U+1) (BS 4999/5000, ESI 44-7)upon manufacture before installation.

A surge diverter is invariably used with generators connected to grid. Almost all generators have a transformer in between.





* Basically, I would like a full-time job on part-time basis *

 

[cuky2000]

The impulse test 1.2/50 (BIL) does not apply to rotating machines. Generators are tested based on an impulse withstand envelope similar to the figure shown below.

Surge mitigation could be achieved with a combination of different techniques such as generator grounding, surge arrester, surge capacitor, etc. However, this may not be enough to convince the power utility about their requirement. An insulation coordination study may be another alternative. Beware this study may delay the project and adding cost without guaranty to eliminate the transformer required by the utility.

 

[powerjunx]

cuky2000, as AJ2002 query could you give me a link to your post? That's quite pretty good presentation.

 

[electricpete]

The closest thing for rotating electrical machines would be a surge test per IEEE522.

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