KSEBEA FORUM

I had been asked about the constraints of changing Static to Brushless excitation at Idukki station!!
Heard once that we will use brushless only on small machines!! But i was searching for answers and found the following:)


1. The rotating AC field and diodes were overhung on the end of the generator shaft, extending out past the main generator bearing(UGB) with no support bearing on the outside end of the exciter.

2. A large generator required a large (heavy) field winding and diode assembly( Heat sink and etc) that created mechanical design problems. Adding another bearing support point raised other issues

Switching to a static exciter and collector rings( Not heavy as compared to brushless) avoided the mechanical issues.
3. Utilities required most large generators to have fast acting voltage regulation. The inherent delay of the brushless system and the inability to reverse the field voltage was not acceptable to many utilities.

I read that it's quite difficult to control the humidity of air in underground powerhouse and due to this reason we can't prefer Brushless system !!! I think its a valid point!! Isn't it????

brushless Excitation -- its not limited to Small machine now a days -- from my side, commissioned rotating diodes - excitation- for 80MW -GT -
The only drawback is limited control on dc voltage compared to Static, as static do have SCRs - and will have a fully controlled AVRs.
For example- IHEP units can be run on both sides of V curve..Please check the Var meters installed for the first stage units- its having both -ve and + ve , That is , both absorbing and Supplying of VAr ..Once , may be in 2005/2006 , the 1st stage units tested for reducing/increasing receiving end voltage by running as synchronous condenser.
The excitation panels in Sholayar (resistance cutting) may be kept as a demo piece, and even with simulation.
The panels in the Poringal PH , it seems , as scraped while renovation. The AVRs in IHEP is also versatile piece of technology - Mototrised AVRs with manual followup , and may be kept for future training purpose.
May need a detailed discussion ...