# What is 'load' in percentage?

Aircraft Airbus 320 has two 110/220v 400 hz 90 kva generators, run by two engines. There is an electronic display in the aircraft that also shows the parameters of the electrical system. One of the parameters is 'load'. Shown in percentage for both the generators separately. It's value is about 26% most of the time. Can anyone please explain to me what this load is? Thanks in advance

• Presumably it means the load is 26% of 90kVA or about 23kVA, or do you mean what in particular would be using that power? – PeterJ Jun 21 '13 at 13:17
• @PeterJ I know 'load' means various equipments connected to the circuit. I was not sure how load can be mentioned in percentage. – KawaiKx Jun 22 '13 at 10:36
• @Saurabh Really? Suppose you can lift a maximum of 40 kg. If you lift 20 kg, then you're loaded 50%. – Kaz Jun 24 '13 at 17:58

There is an upper limit to the amount of power each generator can supply. That upper limit is 90 kVA.

At any given time, the amount of power needed to operate the aircraft systems will vary depending on which systems are active. For example, pumping fuel between tanks presumably uses electrical power and increases the load on the generators.

The amount being used can be expressed as a percentage which gives you an idea of how much reserve capacity the generator has available to power new loads.

If both generators are operating with a load of 26% and one fails, I imagine the remaining generator would take over the job of providing all power† and would then be operating with a load of 52%.

From Airbus STL 945.7136/97 1998 - A320 Flight Deck and Systems Briefing for Pilots

† Apparently, on the A320, a failed generator is replaced by the 90 kVA Auxilliary Power Unit (APU) if that is available. Only if the APU is not available is the load transferred to the remaining main generator. In the latter case there is automatic galley load shedding - I think that means the PAX get cold meals :-(

• What could be the reason for load shedding if a single generator is powerful enough to take up the entire load ? A single generator failure is not an emergency yet. Is it about reducing risk/chances of failure of the lone generator? Why this TR box (transformer-rectifier) shows the ampere value? – KawaiKx Jun 22 '13 at 10:34
• @Sourabh: Normally you have three generators, two main and one APU. Load shedding occurs when you are on your last remaining generator (apart from the RAT which is 5 kVA only). I guess it's about preserving reserve generator capacity for important tasks like lowering landing gear & extending flaps. The TR is rated to take everything the gens can deliver, you don't need to worry what % of TR capacity are in use. What you may need to know is how many DC amps are coming from each source (2xTR + 2xBattery). An A320 pilot should get better answers by asking the airline engineers. – RedGrittyBrick Jun 22 '13 at 15:23
• landing gear and flaps don't put any extra load on electrical system at all. they are operated hydraulically (hydraulic pumps driven by engine shaft directly). – KawaiKx Jun 24 '13 at 17:48
• @Saurabh: OK. I knew vaguely that the trend was to more electrically powered systems on newer designs but it seems they're limited to hybrid back-up systems (e.g. A380 Electrohydrostatic Actuators (EHA). Sorry for my error. – RedGrittyBrick Jun 24 '13 at 19:28