What is Field Flashing

[UKEng]

Hi,

Could someone please explain the term 'field flashing' with reference to generators. What is it and how is it carried out.
Many thanks in advance

PaulUK

 

[peterb]

Field flashing is used on self-excited generators, where the residual magnetism is not high enough to build up the terminal voltage when starting. What is done is to connect an external DC source to the field winding to start the voltage build up; the flashing source is removed for normal operation.

 

[GOP]

for permanent pole pilot exciters also flushing can be done to strengthen the poles by connecting the poles to the dc source in proper polerity.
saraswat

 

[gpattu]

Dear PAULUK,
As you know every alternator requires residual magnetism so as to build up voltage on its own. You can check this by measuring voltage at Alternator terminals while running it with field connections open. Some times due to long period of idling or due to wrong connections, this magnetism may be lost. In such cases, alternator does not build up voltage even if connected with Automatic Voltage Regulator. Now you have to disconnect the field and connect it momentarily with a DC source keeping the polarities correct. If you connect Reverse polarity the flashing will not help. Thereafter run the alternator with field connected to voltage regulator. It shold build up voltage and magnetism should sustain for future operations.

 

[busbar]

From

http://www.basler.com/downloads/Design_exc.pdf

on commercial static exciters: “Prime power application specifications almost always specify the need for “black start” capability. This is the ability of the generator to build up voltage when there is no other power source available, except for the station batteries. To ensure positive voltage buildup, a field flashing circuit can be added. Most modern generators do not require flashing except in those rare occasions when residual is lost.”

On smaller units, flashing can be simple application of a 6-volt lantern battery with a pair of clip leads.

 

[jbartos]

Suggestion: Visit

http://www.utcpower.com/pwps/html/mobileswiftpac50.html

http://www.geindustrial.com/products/applications/GEZ-8087.pdf

http://avstop.com/AC/apgeneral/BRUSHLESS.html

http://members.shaw.ca/diesel-duck/library/tech_notes/flashing_generator.htm

(Caution not mentioned so far: The fiel leads to regulators may need to be removed during flashing to avoid the destruction of the regulator.)
etc. for more info.