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d) Redundant Differential Current Protection (RDNT DP). The RDNT DP hardward circuitry is used as a back-up to the DP CPU. If the DP CPU is operative, the RDNT DP is inhibited.
e) The RDNT DP hardward circuitry is used as a back-up to the DP CPU. If the DP CPU is operative, the RDNT DP is inhibited.
2) Negative Sequence Voltage (NSV)
a) The negative sequence voltage protection is a back-up to the DP protection. The purpose is to detect an open phase condition or a line-to-neutral or a line-to-line of negative voltage on the adjacent synchronizing bus. An NSV condition exists when the negative sequence component of synchronizing bus voltage exceeds 18.5 |6.0 volts. When an NSV condition is detected, a timer function is implemented based on the amount of NSV. As the amount of NSV increases, the time between the fault occurrence and the protective trips listed above decreases.
3) If one of the above listed faults occurs on its half of the synchronizing bus, a fully operative BCU will perform the following: a) Send a command to the AGCU to trip the APB. b) Trip the XPC. c) Software will trip the SSB. d) Send a command to the opposite BCU to trip the SSB. e) Send a command to the adjacent GCUs to trip their
respective BTBs.
f) Hardware will trip the SSB.
4) If the BCUs CPU has failed and a DP condition exists, the BCU will perform the following: a) Send a command to the opposite BCU to trip the SSB. b) Send a command to the adjacent GCUs to trip their
respective BTBs.
c) Hardware will trip the SSB.
(p) APU Bearing Failure
1) The APU bearing failure is accomplished by monitoring a signal from the APU generator. An APU bearing failure exists if the signal is grounded. If the fault condition exists for 5 minutes continuously, the BCU outputs a command to the AGCU to trip its GCR.
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(q) Ground Power Plug Fault Protection
1) The ground power plug protection consists of the following protective functions: a) Overvoltage Detection
1. Ground power plug overvoltage fault circuitry
_ monitors pins E and F of the ground power plug. If an overvoltage condition exists, the +28 volt supply to pin F is latched open and a signal is sent to the CPU Indicating that the fault has occurred.
b) Overcurrent Detection
1. Ground power plug overcurrent fault circuitry
_ monitors Pin F of the ground power plug for an overcurrent condition caused by a short circuit. If an overcurrent condition exists on Pin F, the +28 volt supply to Pin F is latched open and a signal is sent to the CPU indicating that the fault has occurred.
(r) Sustained Unlike Source Parallel Protection (SUSP) 1) Sustained Unlike Source parallel Protection prevents sustained parallel operation of unlike power sources. The SUSP senses the position of the SSB, the adjacent and opposite XPCs and APBs, and all four GCBs and BTBs. If unlike sources remained parallel for 175 |25 milliseconds, the sources are isolated. Both BCUs perform SUSP protection.
2) If the unlike sources that are paralleled involves IDG channel power, the BCU sends a BTB SUSP signal to the adjacent GCUs or opposite GCUs, depending on whether the fault is associated with the adjacent or opposite synchronizing bus. If the fault involves both the adjacent and opposite synchronizing buses, the BCU will send a BTB SUSP signal to all four GCUs. In both cases, upon receiving the BTB SUSP signal, the GCU will sense if its GCB is closed. IF the GCB is closed, the GCU will command its BTB to trip.
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3) If the unlike sources that are paralleled involve an adjacent APU channel or adjacent electrical power (EP) source and no IDG channel, the BCU trips the associated APB or XPC. If the opposite APU channel or opposite EP source is associated with the fault, the BCU sends an APB trip or XPC trip signal to the opposite BCU. The opposite BCU then trips its associated APB or XPC.
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