WARNING: TGT limiting does not prevent over temperature during the following conditions:
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Engine start - ECU functions are not fully operational during engine start.
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ECU lockout - Pilot has locked-out the TGT limiting circuit, Np governing, and Load Share circuits.
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Compressor Stall - TGT limiting system can't react quick enough.
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Alternator Failure - TGT limiting, Np governing, and load share circuits have no electrical power.
(4)
Np governing circuit maintains Np and Nr at a constant speed, normally 100%. The Np governor compares actual Np speed from the Np sensor to the Np reference set by the pilot. Any time the actual Np speed differs from the reference, the Np governor sends an increase or decrease fuel flow signal to the HMU through the torque motor. The Np governor has authority to increase the fuel flow to maximum, or decrease fuel flow to idle. Np governing is disabled when the system is in ECU lockout.
(5)
Torque matching circuit (Load Share Comparator) maintains a 5% match between both engine torques. Load share is active when the engine torques are not within 5%, only the low torque engine load shares. The load share comparator in each ECU monitors Q1 and Q2, any time Q1 is more than 5% less than Q2 the load share circuit temporarily increases the Np reference in Np governor by 3%. The Np governing circuit increases fuel flow, causing Np and Nr to increase, the other engines Np governor reacts to the increasing Nr by reducing its fuel flow. So the low engine increases power as a function of load share, while the high engine reduces power as a function of Np governing. When both engine torques fall back into the 5% range, the load share allows the Np governor to revert to its original governing speed, which is normally 100%. TRQ matching is disabled when the system is in ECU lockout.
(6)
The Np Overspeed protection circuit protects the power turbine from overspeed conditions that might cause damage or destruction. Np O/S circuits obtain operating power from two independent sources, the engine driven alternator and the main AC generator (s). The Overspeed switch senses a separate Np signal from the torque and O/S sensor, and is independent from all of the other ECU circuits. The Np O/S protection activates when the Np speed exceeds 22,200 RPM (106 ±1%), the overspeed switch activates a solenoid in the POU, fuel flow to the engine is immediately reduced, Ng output decreases, and the power turbine speed decreases. The reduction in fuel flow will continue until the cause of the overspeed is removed or % RPM is reduced manually.
(7)
The history data recorder circuits include a TGT signal that is relayed directly to the history data recorder, and a Ng speed signal originating from the engine alternator which is relayed to the history data recorder as well. History data is used to track the life span of the GG rotors and the IPS blower.
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