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
Electronic – ‘load’ in percentage
generator
Related Solutions
It's worth remembering that a generator has an active control system that works to maintain a certain output voltage.
That is, the generator is responsive to changes in the load impedance. A step increase in load power requirement will cause a temporary voltage dip, as the output power of the generator at that instant is less than the amount of power required by the load.
However, within a period of five seconds, the generator's governor and automatic voltage regulator will act to increase the generator's power output (voltage, current) until it matches the amount of power (voltage, current) required by the loads.
Quick Summary: Check your reactive droop control setpoints on all three machines and make sure they match.
Forgive me; I don't know how much you've worked with this, so I'm going to write this for the uninitiated.
When machines are in parallel, they have to share load. If their controllers are set to maintain one, specific voltage, they don't share very well, shown in the next figure.
Here, the reactive load sharing pretty much depends on tiny little differences between the machines. In general, my experience has been that the machine that starts taking on the load will try to take all of it, and there isn't a great way to tell which one will do it.
The VR6 voltage regulator you mentioned has something called reactive droop control. The figure below shows how that cleans things up a bit.
The red line represents the total amount of reactive load in the system between the machines.
If both machines are set with the same droop percentage, then they will share the reactive loading in proportion to their KVAR ratings. The no-load set point can be adjusted up or down to increase or decrease the proportion of the reactive load taken - just imagine the red load lines sliding left or right when the black droop lines move up or down.
Looking at the VR6 manual that I googled, It doesn't seem to actually make you set the droop rheostat, so much as tell you that you can if you want to. Your three parallel machines all probably have slightly different droop characteristics. In this case, the one with the shortest droop compensation will eat up the most load, demonstrated below.
You can probably get pretty close to matched droop by just making sure all three machines droop rheostats have been turned by the same amount.
Best Answer
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 :-(