6.2.2.2 Heat Exchanger and Filters
The lubricant oil heat exchangers (LOHX-1 and LOHX-2) connect to the parallel lubricant filters (LF3-1 and LF3-2). This design is provided so that filters not in service can be changed (or heat exchangers cleaned) without taking the turbine out of service. Filter housings and heat exchangers are self-venting. A sight glass is located in the vent line from the filter and heat exchanger.
When the heat exchanger and filter housing are full, oil will be visible in this sight glass. By means of the manually-operated three-way transfer valve, one filter can be put into service as the Second is taken out, without interrupting the oil flow to the main lube oil header. The transfer of operation from one filter to the other should be accomplished as follows:
1. Open the filler valve and fill the standby filter until a solid oil flow can be seen in the flow sight in the filter vent pipe. This will indicate a “filled” condition.
2. Operate the transfer valve to bring the standby filter into service.
3. Close the filler valve. This procedure simultaneously brings the reserve heat exchanger into service.
6.2.2.3 Pressure Protection Devices
Two pressure switches (63QA-1A and -1B) mounted on the main pump discharge header sense lube oil pressure. If either of these senses low lubricant oil pressure, an alarm is sounded and the lag pump is automatically started. Pressure switches 63QT-2A and -2B in combination with alarm switches 63QA-1A and 63QA-1B trip the unit and start the emergency DC motor-driven pump (88QE-1) when they sense low pressure.
This will occur if AC power is lost. For a trip, one of the two 63QT switches and one of the two 63QA switches must signal. This voting logic prevents a trip due to a false signal. The DC Emergency Pump is designed to provide adequate lube oil circulation for coast down following a trip. Once the unit is at rest, the DC pump should only operate a few minutes per hour, in order to remove heat, but conserve battery life. If the bearing metal temperature is above 250F, the DC pump is run.
Continuously, the emergency pump is sized to clear the trip pressure switches (63QT-2A, - 2B), but will not clear the alarm pressure level (63QA-1A, -1B). On dual fuel units with a single atomizing air compressor pressure switch (63QA-3) is provided at the oil supply to the air compressor gearbox. Two Pressure switches (63QA-3 and 4) are provided on dual fuel units with two atomizing air compressors. These pressure switches will alarm if low pressure is sensed at those points but they will not start the Lag pump.
The operation of the 63QA and 63QT switches can be verified by shutting off the normally open valve between the switch and the oil system. When the normally closed valve to the oil drain is opened, the Oil in the switch lines will drain, the proper warning signal will annunciate and proper lag/emergency pump start-up should occur.
The lubricant oil heat exchangers (LOHX-1 and LOHX-2) connect to the parallel lubricant filters (LF3-1 and LF3-2). This design is provided so that filters not in service can be changed (or heat exchangers cleaned) without taking the turbine out of service. Filter housings and heat exchangers are self-venting. A sight glass is located in the vent line from the filter and heat exchanger.
When the heat exchanger and filter housing are full, oil will be visible in this sight glass. By means of the manually-operated three-way transfer valve, one filter can be put into service as the Second is taken out, without interrupting the oil flow to the main lube oil header. The transfer of operation from one filter to the other should be accomplished as follows:
1. Open the filler valve and fill the standby filter until a solid oil flow can be seen in the flow sight in the filter vent pipe. This will indicate a “filled” condition.
2. Operate the transfer valve to bring the standby filter into service.
3. Close the filler valve. This procedure simultaneously brings the reserve heat exchanger into service.
6.2.2.3 Pressure Protection Devices
Two pressure switches (63QA-1A and -1B) mounted on the main pump discharge header sense lube oil pressure. If either of these senses low lubricant oil pressure, an alarm is sounded and the lag pump is automatically started. Pressure switches 63QT-2A and -2B in combination with alarm switches 63QA-1A and 63QA-1B trip the unit and start the emergency DC motor-driven pump (88QE-1) when they sense low pressure.
This will occur if AC power is lost. For a trip, one of the two 63QT switches and one of the two 63QA switches must signal. This voting logic prevents a trip due to a false signal. The DC Emergency Pump is designed to provide adequate lube oil circulation for coast down following a trip. Once the unit is at rest, the DC pump should only operate a few minutes per hour, in order to remove heat, but conserve battery life. If the bearing metal temperature is above 250F, the DC pump is run.
Continuously, the emergency pump is sized to clear the trip pressure switches (63QT-2A, - 2B), but will not clear the alarm pressure level (63QA-1A, -1B). On dual fuel units with a single atomizing air compressor pressure switch (63QA-3) is provided at the oil supply to the air compressor gearbox. Two Pressure switches (63QA-3 and 4) are provided on dual fuel units with two atomizing air compressors. These pressure switches will alarm if low pressure is sensed at those points but they will not start the Lag pump.
The operation of the 63QA and 63QT switches can be verified by shutting off the normally open valve between the switch and the oil system. When the normally closed valve to the oil drain is opened, the Oil in the switch lines will drain, the proper warning signal will annunciate and proper lag/emergency pump start-up should occur.
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