Beech 1900D Electrical System
All buss ties lit up
- Center buss has failed
Either generator exceeds 100 %
- Turn batt switch and monitor load meters -If continues turn off all non essential elect -Turn batt back on and monitor
Triple fed failed -what happens
-NO light will lite up -Answer- all engine gauges go to zero -Confirm by looking at the over head volt meter (normal volt is 27.25)
Hall effect device
-There are three on this plane- -Its a Instant high amp detection system
Whats the voltage on the triple fed bus?
1 volt less than where it was supplied from
The DC power is Triple fed...
1- 24 VDC 36 amp-hour nickel cadmium battery 2- 28 vdc starter / generators
What are the functions of the GCU's? (6) "VORPC"
1. Voltage regulation and line contactor control 2. Overvoltage and over-excitation control 3. Paralleling/load sharing 4. Reverse current protection 5. Line contactor control 6. Cross start current limiting
What is the output of the inverters?
115 VAC @ 400hz AND 26VAC @ 400hz (step down transformer)
Inverters out put
115 vac 26 vac
External power - How many volts on plane batt required
20 volts min to attempt GPU start
Nicad batt
24 volts
Normal acceptable range of voltage
27.5- 29 V
What is generator output ?
28.25 VDC, 300 Amp maximum continuous load
Over volt protection
32 +/- .05 volts
What is the maximum generator VDC output allowed by the GCU?
32 VDC
Hall effect
325 amps 275 amps
Gen tie pops at Battery tie pops at
325 amps 275 amps This causes them to open
The battery- am hours?
34 amp hours
What amperage output is a running generator regulated to when the opposite starter is selected "on"? Why?
400 AMP, to prevent transient surges from opening 250 current limiters
Starter comes off line
50%
Why is an Inverter needed
95 % of the plane is DC - The inverter makes the AC stuff work- Exotic instruments and engine torque gauges
If an AC bus fails its likely....
95% of the time its an inverter that failed not the bus. - Reset the inverter
Its a DC airplane that has
AC where you need it via the inverters
External power is on
All busses are powered
Triple bus fail
All engine gauges will go to zero- - Look at the colt meter- select triple fed bus- it will read zero
What does the AC Power?
Avionics mainly
Engine Starting voltage required
Batt start- 23 volts GPU start- 20 volts
AC Inverters are
Blower cooled inverters
Dual gen fail - Auto shedding- How is this done
Both Gen ties open this is how auto load shed works
Both generators have failed, what buses are going to be powered by the battery?
Center Bus, Battery Bus, and Triple Fed Bus
Gen tie manually closed
Connects gen bus to center bus and permits batt power to feed the entire system
What charges the battery?
DC generator power via Gen and Center Bus
Where are the CGU's located?
Directly behind the hump
White ring on Circuits ?
Fed by center or, triple buss Its always available to you as its fed from Batt buss
Important systems - Sourse of power
Flaps - Left gen buss Gear -Center bus engines- Center bus
How does the starter/generator receive power for engine start?
From the battery VIA the Center Bus and starter relay (controlled by the engine and ignition start switch)
External power off ?
GPU should be off before connecting to the plane
What feeds the Inverters?
Gen bus and center bus
External power generators
Generators should remain off until GPU is disconnected?
What does holding the Gen switch to the "reset" position do? What does releasing it to the "on" position do?
Holding up to "reset" brings it up to voltage, releasing it to "on" closes line contractor (connecting it to the rest of the system
External power Limit (airplane)
If above 32 volts it will kick off
Resetting circuits
If its essential- Only reset once
What is reverse current? How is our system protected from it?
If the generators can not supply 28.25 Volts - It will attempt to draw from the aircraft elect system- It will protect the Gen- by opening its line contactor
What does selecting the inverter switch to either position do?
It closes the power relay to the selected inverter, supplying it with DC power
How do we switch inverter power from the gen bus to the center bus?
It is an automatic function of the inverter power select relay
Center bus is the ....
Most critical of all the busses
External power must be grounded?
Negative ground
Is the electrical system positively or negatively ground?
Negatively ground
Type of battery
Ni cad 24 vdc- volts direct current 34 amp hour
Are the generator buses required to be powered for engine start?
No, but they can be VIA the Gen Tie switch
Dual gen fail - When to use Man buss ties close
Only on short final
Where are the inverters located?
Respective engine nacelle aft of firewall
Where is the battery located?
Right center wing, in an air cooled box
Current limiting devices
Slow blow fuse Hall effect Circuit breakers
How does a generator assisted cross-start work?
Start signal power is received by the GCU from the operating generator VIA its gen bus and the center bus, which in turn sends a signal back to the operating generator activating its voltage regulator. Voltage from the operative generator is regulated by its GCU, preventing the 250 amp current limiters from blowing by regulating the current whenever it gets close to 250 amps (usually providing 400 amps). If this system fails and the 250 AMP current limiters blow during start, the starter relay will open, stopping the start.
How does load shedding work?
The GCU's sense both gens failed, now have 2 functions; 1. They open their respective line contractors, removing their gens from their respective buses. 2. They close the circuit to bus tie PCBs, which de-powers their HED's, opening their Gen ties (gens are now isolated) and illuminates their annunciators.
What closes the batt tie and batt tie relay?
The HED's via the battery switch- (Hall effect device )
Center bus feeds the
The Landing gear
The center bus if fed by?
The battery The two generators
Why is the starter/generator not providing generator power during engine start cycle?
The field shunt has been disabled by the generator control relay.
L Gen bus feeds
The flaps
What buses receive power when the battery switch is turned on?
Triple Fed, Battery, and Center Bus
What is meant by generator load sharing?
When both generators are operating, generator control units should balance the electrical load to within 10% of each other when above 25% load.
If both generators have failed, how could you provide power to equipment on the gen buses? Why would you only want to do this for a short period of time?
You could close the gen ties manually (Gen Tie switch), but the battery would be discharging at a very high rate
What type of generators
a 300 amp Starter / generator with a 400 surge
What are on the hot wire buss Page 2-10
air step fire ext lights
Duel Gen fail -Effect on AC
if both gen fail- inverters will receive DC power from center bus and... the AC shed bus will be activated
Name all DC buses 6
two gen busses batt bus center fed bus tripe fed bus Hot batt bus
