Static vs Rotating Exciter

[rockman7892]

Are there advantages/disadvantages to using static vs rotating exciters for a given generator application?

Is it typically based on the particular generator application (size, type, etc...?). Is the rotating exciter more of an older technology with static becoming a more cost effective solution?

Is it based on cost to some degree? I would think static is more expensive for to power electronics and required PPT?

 

[FreddyNurk]

All the equipment I've ever seen is rotating exciter, within the range of tens of kilowatts up to megawatts.
Basler did an excellent presentation at one stage on the advantages of static excitation versus rotating excitation arrangements, which was targeted above the size range I'm familiar with.

From what I recall the advantages were much faster response times for larger plant with static excitation as compared to rotating excitation.

EDMS Australia

 

[edison123]

Rotating exciter
Pros
Cheaper.
No brushes or sliprings.
Control very small power to rotating exciter field to control the main rotor excitation.
Easier to troubleshoot since it is just a basic 3 phase bridge rectifier.
Easier maintenance since no brushes or wearing parts.

Cons
No direct measurement of main field current or voltage.
Rotating diodes more likely fail first.
Machine to be at rest to troubleshoot exciter issues.
Restricted range of power.

Static exciter
Pros
Direct measurement of main field current or voltage.
Machine need not be at rest to troubleshoot exciter problems.
No restriction on power range since it is external to the generator.

Cons
Definitely costlier.
Higher maintenance cost due to sliprings, brushes.
Troubleshooting might require supplier's inputs/services and hence a cost driver.
Big cables from generator to static exciter and from the static exciter to brushes. Another cost driver.
Field flashing from an external source needed at machine start. Another cost driver.

This is just from top of my head. Other experts might have more.

Muthu

http://www.edison.co.in

 

[davidbeach]

Negative field forcing is another advantage of a static exciter.

 

[edison123]

Good point by David. That's a big plus for static exciter.

Muthu

http://www.edison.co.in

 

[itsmoked]

You guys mean reversing the field or just driving it down to zero?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[edison123]

Keith - Upon load throw, though the AVR output is cut, the field will not collapse immediately due to its time constant. The field is then discharged through a series resistance (which IIRR is around 3 times the field resistance) to kill the generator voltage quickly. Of course, this can happen only through only sliprings.

Muthu

http://www.edison.co.in

 

[itsmoked]

Got it. Thanks Muthu.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[ScottyUK]

On a static exciter the rectifier is usually a fully-controlled bridge which is capable of regenerating into the source, so it can actively collapse the generator field by feeding the stored energy in the field back into the grid. The field discharge resistor is usually only in circuit when the AVR disconnects the rectifier from the field, and its purpose is to dissipate the stored energy in a controlled manner.