We have Alternator 15 MW, 5500 Volt, with field Excitation 12 Volt and 30 Amp. are it possible and safe, we change field winding for 70 Volt? this time no load Voltage are 4.0 volt and 8 Amp. span is minimum.

 

Ali... are you sure about the parameters you presented? Excitation is only 0.0024 percent of the alternator's MW capacity!

Regards, Phil Corso

 

Yes I am Sure Field Voltage are 12 V and 30 Amp. and rotor Amp 900/1600 Amp

 

Ali...

1) Do you mean rotor values are 190V, 1600A?

2) Is the alternator a brushless machine?

Phil Corso

 

the specification as under,
Stator data
Volt 5500 +- 5%
Current 2000 Amp
speed 1500 rpm
Frequency 50 Hz
PF 0.8
capacity 19052 KVA

Rotor Data
type 86/12 no. 410017
Volt cc 70 / 125
current 900 / 1600 Amp
KW 63 / 200

field data
Excit volt CC 12 V
Current 30 Amp.

 

Ali... I should have asked the following question first:

Why do you want to change the voltage of the pilot-field, not the main-field, from 12V to 70V?

Phil Corso

 

we want to change pilot field voltage due to,

1. standard AVR in markeet are 70 Volt,

2. the span 70 volt is good instead of 12 volt narrow span,

3. low current of AVR also may be advantage

 

Ali... I don't believe that rewinding just the field-coil will work because the smaller wire-size will not fill-out the slot, thus affecting air-gap flux density!

Phil Corso

 

dear,

for fill air gape and reduced current and maintain (volt /turn), we will reduce the wire thickness.
are it ok?

 

Ali... unless the new conductor "area" is nearly equal to the original the solution proposed will not work! There are three reasons:

1) Current Flow
Current, not Volt Amperes, flowing through a conductor in a slot produces magneto-motive-force or mmf. Because your proposal produces less current, mmf will not be sufficient.

2) Flux Distribution
A rule for good design is that conductor-area should fill slot-area. Thus, flux distribution concentrates in the iron adjacent to the conductor. Unfortunately, in your proposal, this rule is negated. The smaller-size conductor will occupy about 17% of the original design. This causes flux-distribution to divide; one part in proximity to the conductor, the other in the slot space not occupied by the conductor. And, it does not matter whether the new conductor-area is located at the bottom of the slot or near the top!

3) Fill-in Material
What are you proposing? How will it be retained?

Regards, Phil Corso