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Loss of Essential AC Bus


apexlined
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Potentially - the rest of your life

While it has never happened in a herk (aside from the Dyess plane that was able to restart) You could probably get an hour out of a good battery. a little more if you don't use instruments or talk in the headset. But Without electrical power all your Karma is gone - Land Now!

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1- Losing the Essential AC Bus only will not put the battery under any load; Battery will remain charged by the main AC bus through the two main TR units.

2- Why to land as soon as possible? Well; check how many essential components using the effected bus then decide yourself if you want to continue or to land. I will give some of the lost:

a- Heading indications (C12 compass, INS heading)

b- No.2 fuel boost pump.

c- Both hyd. Suction boost pumps.

d- All trim tabs (the elevator trim will be shifted to emergency)

e- Both secondary ac buses (two invertors will be used to recover the power) =heavy load on generator.

f- Weather Radar, IFF/ATC, Auto-Pilot, INS, Radio Altimeter, Some of navigation/communication equipments.

g- ………….I think… enough to land as soon as possible.

3- How long the Battery will sustain if it is the only source of power? Depends on the load; but I think it will not sustained more than approximately 20 minutes.

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Yea, I never understood this whole ATM generator requirement. If you have one engine generator running, you have ESS AC. You'd only lose ESS AC if all 4 generators were out, and if all 4 were out, you probably wouldn't have any engines running, which means no bleed air for the ATM.

Not sure how long the battery would run the AC inverters, especially if you had both on. Maybe longer with soild state inverters, but an hour may be a decent guess. That depends on how old the battery is and how cold it is outside.

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Hi Tiny,

Losing the Ess Ac Bus during flight/ground can happened due to some malfunctions not necessarily due to generator failure.

Malfunction such as:

1- High load on the Ess Ac Bus caused by malfunction of component or wiring.

2- Bus Contactors failure.

May cause the Ess Ac Bus to be lost, in which no other generator can assume and takeover the Bus load.

Another possibility of losing the Bus in-flight is when flying crew are forced to isolate the Ess Bus due to electrical fire on a component or wiring belongs to the Bus.

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how long the battery can be sustain the load

Disregarding the "loss of Ess AC bus" part of it, the aircraft battery is rated as a 36 amp hour battery.

What that means is if you are relying on the battery it will last one hour with a 36 amp load (or 36 hours on a one amp load).

In real life you can expect to see 10 to 20 minutes on the battery, unless you severely disable lots and lots of stuff.

With the SCNS battery to use as well you can double the time but it still really really sucks to try and live just off the battery.

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tenten got it right no issue with your battery just all those ESSENTIAL systems...

Tiny, the (ATM or APU) gen is important to me because if I need to isloate a bus it is much easier to turn on the ATM/APU gen and turn off all engine driven gens....then only the ess AC/dc iso dc and batt buses are powered.

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Hi Tiny,

Losing the Ess Ac Bus during flight/ground can happened due to some malfunctions not necessarily due to generator failure.

Malfunction such as:

1- High load on the Ess Ac Bus caused by malfunction of component or wiring.

2- Bus Contactors failure.

May cause the Ess Ac Bus to be lost, in which no other generator can assume and takeover the Bus load.

Another possibility of losing the Bus in-flight is when flying crew are forced to isolate the Ess Bus due to electrical fire on a component or wiring belongs to the Bus.

I'm sure we could come up with scenario after scenario of what could happen, but I am still going to say that you should never see a total ESS AC fail. Circuit breakers and fuses are installed to protect the wiring from burning, not to protect the units/motors, bulbs, etc on the load side. It should be fairly easy to isolate a shorted phase on the bus.

But to answer the original question, you land because shit can get out of hand real quick. ESS AC will cause syncrophaser problems, causing power loss in all four, among other things.

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Tiny,

You know that engine generators output to feed the buses is going through a chain of 8 contactors, and the route to feed the Ess Ac Bus from any engine driven is requiring to go through two contactors only (K6 and K7), those two must be energizes if one failed you lose a 50% of your credit, if the two failed a lot of things will wake you up a side of “ESS AC BUS OFF†red light.

Have a look to this actual “scenario†in which I was lucky to lose only the 50% of my credit. (The culprit was K6 contactor, found burned).

On a short mission, on the way back to home station; Indication at the time of malfunction started with momentarily flickering of some engine instruments and heading indicators, generator no 2 checked nothing found abnormal, no 2 generator switched off to isolate the defect, load transferred as normal to No.1 gen; but after some time the momentarily flickering hit again.

No 2 gen returned to line and took over the load (I assumed not guilty and to avoid the high load on No 1 gen).

The last hit was a combined with disengaging of auto pilot and with some flx of engine RPM; We started switching off some “subsystems†in preparing our self to go through “Lose of Ess Ac Bus Proceduresâ€.

I was lucky during the last hit; I noticed that the load of Ess.AC was transferred from No 2 gen to No 3 gen and remained on No3 gen.

Why not to No1 gen??! Is it a “contactors†issue?!

At the moment the answer comes from the LM telling us that burning smell on the cargo comp……

APU started and APU gen was put on line, load of Ess Ac Bus was taken by APU.

Within the last 40 minutes to landing, defect never repeated burning smell gradually disappeared.

Two points on the issue; Bus contactors can malfunction, and using the APU generator will bypass the standard engine driven routing (K6 & K7) to a single route (K10).

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Of course, this isn't applicable to the H3s or AMP. We don't have a specific "Loss of ESS AC" procedure. BSUs will power the AV busses from the best source. On the E, getting the ATM online is important because it takes at least two contactor relays out of the picture, in case one of those is causing your problems.

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Can't the ESS and Main AC be tied on the E model? Just curious. That should be part of the checklist.

No idea about E models, our airplanes (H) having this function for ground operation only through fuel ground transfer switch on the SPR panel in which the APU gen. can also be connected to take the main Ac Bus through (K11).

Other civil registered (L100) which I have flown having the control switch (AC BUS TIE) on the over head control panel but also limited for ground use only when all engine generators are off the line.

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The E model doesn't have any capability to tie the ESS & MAIN AC busses, the ATM is only a 20kva, which we overload to 30 using cooling air.

I've never heard of the function on the H going through the SPR panel?? Educate me please! I know the K11 (K53K) and all, but never heard the SPR bit before.

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The main idea behind putting the control switch on the SPR panel (on some models) is to provide the ability for the operators with the APU gen alone (40KVA) to use the dump pumps during the defueling process ( As you know all fuel dump pumps powered by main ac bus).

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FM 382C-14E

Section 7 page 12.

Yes brother, AMPTestFE

This function is equipped on C-130H airplane configuration codes (382C-14E) and (382C-45E) Lockheed Serial No. 4879, 4882, 4983 and 4985. (Foreign direct sales Lockheed).

Edited by tenten
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From my FM 382C-57D section 7 page 7-1 state that on H1 and H2 airplanes, the APU generator will power the Main AC bus when single refueling GROUND TRANSFER SWITCH is placed in the OPEN position. This function for ground checks only. i already try use this function on H1 aircraft to defueling but can't and also check the loadmeter for Main AC bus.No indication. what the meaning for ground checks only?

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If you hav the K 11 installed you have the Ess to Main capability... Some aircraft have a AC bus tie switch on the Electrical control panel and some are activated with the SPR switch ON.

The SPR switch was used on the "older" aircraft and can only be used on the ground as the SPR is secured prior to flight (or you have a warning light and other indications).

Ground checks would be the transfer of fuel to empty out a tank or transfer feul into say the aux and ext tanks while you wait for the fuel truck...

The AC bus tie switch is for ground use only... how ever there is NO interlock (i see) preventing its use inflight. IF all generators are OFF you could use it but your load would have to be monitored!!!

I'm not telling you to use it; but if you ever end up with only the APU gen ON and need to say DUMP FUEL...

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An interesting note to the Refuel switch connecting the K11. All of Southern Air's L382's had the capability. On Aircraft 919SJ (4147) for some reason the switch for the light in the refueling panel had been modified so it would tie the K11 rather than the refuel switch

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