CaptRawData
Topic Author
Posts: 15
Joined: Fri Apr 25, 2014 7:47 am

727 Electrical Question

Tue Oct 10, 2017 11:08 am

With regard to the Residual Voltage switch on the FEs electrical panel. Under what circumstances would the FE need to check the residual voltage of the Generator? A failure that could not be diagnosed from other lights or indicators?


I’m obviously not rated on the 727 but I am just trying to get an understanding of the various systems. The FE has lights indicating if the Gen breaker has tripped. My guess for the reason the FE would have to check the residual Voltage is if there was no output Voltage and no indicating lights that the breaker has tripped. If the FE sees that the Residual voltage is reading 10 – 18 Volts for example then that means that the Gen is rotating (residual voltage) but not getting any power in order to provide the necessary 115 V output voltage?


On a technical video I recently watched on You Tube, it was mentioned that both the Freq and Voltage indicator could be used to indicate the Phase B of an individual Gen in collaboration with the AC Meters Selectors and synchronizing lights (Phase A and C)
Am I completely off the target on that assessment? Anyone able to provide further info?
 
FlyHossD
Posts: 1495
Joined: Mon Nov 02, 2009 3:45 pm

Re: 727 Electrical Question

Tue Oct 10, 2017 1:48 pm

It's been such a long time and I don't have 727 manuals any longer...

I was a FE on the 727 for less than a year. It was an interesting job, but I wanted a pilot's seat.

IIRC (big IF), if a checklist called for a generator disconnect, the residual volts switch could be used to ascertain that the generator was in fact disconnected - 0 volts would be proof of that. One of my first flights after qualifying on the plane required just such a disconnect, but I really can't remember how it was done.
My statements do not represent my former employer or my current employer and are my opinions only.
 
User avatar
IFixPlanes
Posts: 258
Joined: Sun Feb 20, 2005 11:34 pm

Re: 727 Electrical Question

Tue Oct 10, 2017 3:12 pm

Out of the Operations Manual (Supplementary Procedures):
If a generator system in parallel
has a KW indication of zero or below
with no generator lights illuminated:

Generator Field Switch ..................TRIP
Observe GENERATOR BREAKER CIRCUIT
OPEN light and FIELD OFF lights illuminated.

Residual Volts Switch ..................PRESS

With the AC meter selector on affected
generator, a near zero or zero residual
voltage indication confirms a
generator sheared shaft. If residual
voltage normal, restore generator
system.
never tell an engineer he is wrong ;-)
 
113312
Posts: 648
Joined: Sat Apr 16, 2005 9:09 am

Re: 727 Electrical Question

Tue Oct 10, 2017 4:35 pm

Residual voltage is produced by a small permanent magnet generator, within the generator itself, that is used to excite the generator field. As stated before, zero voltage would indicate no rotation of the generator shaft either through successful generator drive disconnect or sheared shaft.
 
User avatar
tb727
Posts: 1909
Joined: Thu Jun 30, 2005 1:40 pm

Re: 727 Electrical Question

Tue Oct 10, 2017 5:33 pm

Never thought I'd ever see that button get pressed but had to disconnect a generator about 3 times during my time on them and sure enough, it was pressed!
Too lazy to work, too scared to steal!
 
Max Q
Posts: 5963
Joined: Wed May 09, 2001 12:40 pm

Re: 727 Electrical Question

Wed Oct 11, 2017 1:41 am

Great to see such an in depth question
about the mighty 727

Despite ‘serving’ four years on the panel
and three in the right seat I’ve forgotten
where the residual volts switch and indicator are

Can someone remind me ?
The best contribution to safety is a competent Pilot.
 
RetiredWeasel
Posts: 517
Joined: Sat Jul 05, 2014 8:16 pm

Re: 727 Electrical Question

Wed Oct 11, 2017 3:55 am

Max Q wrote:
Great to see such an in depth question
about the mighty 727

Despite ‘serving’ four years on the panel
and three in the right seat I’ve forgotten
where the residual volts switch and indicator are

Can someone remind me ?


As I recall you just selected the appropriate generator with the rotary meter switch, pressed the residual voltage button, then read the voltage right off the AC Voltage meter. But that was a longg time ago.
Here's a link to a photo of the panel: Image.
 
Max Q
Posts: 5963
Joined: Wed May 09, 2001 12:40 pm

Re: 727 Electrical Question

Wed Oct 11, 2017 6:45 am

That’s it, and thanks for the picture, all
coming back now

That panel looks exactly like the one I
worked except it appears to have some
auxiliary fuel gauges
The best contribution to safety is a competent Pilot.
 
User avatar
747classic
Posts: 2274
Joined: Sat Aug 15, 2009 9:13 am

Re: 727 Electrical Question

Wed Oct 11, 2017 7:41 am

On the 747 classic series the CSD disconnect procedure is exactly the same :
- PMG (Permanent Magnet Generator) voltage and also CSD RPM must be monitored by pressing the Gen Test button during CSD disconnect to verify an actual disconnect.

Note : when pressing the Gen Test button (most left hand button at the lower row) :
- CSD RPM is indicated i.s.o Frequency at the LH .Indicator
- PMG voltage is indicated i.s.o. Ac Voltage at the RH Indicator

Image
Operating a twin over the ocean, you're always one engine failure from a total emergency.

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