- Circulates high purity water through each of the stator coil hollow conductors for removal of heat due to the stator coil losses.
- Dissipation of heat from the high purity water.
- Filtering of water to remove foreign material.
- Demineralization of the water to control its electrical conductivity.
- Instrumentation and alarms to continuously monitor conductivity, flow, pressure, and temperature of water.
- Piping and components made of corrosion resistant materials.
- Generator stator temperature limit is 96°C - cooled by stator cooling water.
- Rotor limit is 110°C - cooled by hydrogen cooling.
- Two manifolds connected to differential pressure switches and temperature switches to monitor abnormal conditions across the stator coils and trip the turbine if limits are exceeded. These limits are:
- U1 Trip 19.5 psid, normal is 24-34 psid (generally 12 psid less than normal)
- U2 Trip 15.5 psid, normal is 20-30 psid (generally 12 psid less than normal)
- Outlet water temperature ( ≥ ) 90°C
- 2/3 logic for both trips
- Interlocks for both the trips are generator >15% rated amps and 45 second time delay
- Local alarms:
- if the stator cooling water pressure drop increases “Stator Coil Water Pressure Drop High”
- Unit 1 is 35 psid
- Unit 2 is 31 psid
- ΔP drops “Stator Coil Water Flow Low”
- Unit 1 is 23.5 psid
- Unit 2 is 19.5 psid
- Provides for de-gasification of return water
- Water column level indicator. (Norm is mid sightglass)
- Alarms
- Low: 19 inches from top of tank
- M/U at 16 inches from top of tank (not automatic anymore)
- Norm: 14 inches from top of tank
- M/U off 12 inches from top of tank (not automatic anymore)
- High: 8 inches from top of tank
- H2 blanket kept on tank
- Keeps air from system to prevent corrosion of copper conductors.
- Normally 2 psig (Local pressure gauge on tank)
- Hi Pressure at 4 psig.
- Relief at 5 psig vents to TB roof.
- Supplied form H2 supply system via 2 psig regulator at H2 manifold El. 706
- This is NOT an automatic make-up. Must be manually made up.
- Turbine must not be allowed to operate with conductivity > 9.5 micromhos/cm
- There are 4 cells to measure this, give indication and record:
- Stator Coolant tank: .5 to 1.5 micromhos/cm at 25°C
- Demin return line to tank: 0 to 2.0 micromhos/cm at 25°C
- One on outlet of each HX: 0 to 20 micromhos/cm at 25°C
- There are three alarms on L-39 for this conductivity:
- Demin Outlet Cond High: 1.5
- HX Outlet Cond High: 5
- HX Outlet Cond Very Hi: 9.5
- Three vents back to coolant tank, each set at 10 gph adjusted manually
- Heat exchangers (with both in service 5 gph per HX for a total of 10 gph)
- Filters
- Demineralizers
- Provided to give H2 gas that may be released a path back to top of stator coolant tank.
- Two centrifugal pumps in parallel
- Normally operate one with other in standby (each rated at 100%)
- Powered from 480v Unit boards.
- Two heat exchangers normally operated in parallel
- Can be used individually to provide cooling for up to 75% rated stator current
- Gen. can carry up to 15% amps for 1 hour with both OOS as long as conductivity does not exceed .5 micromhos/cm.
- Cooled by RCV with a TCV on outlet set to maintain temp of Stator Cooling Water coming out of HXs. (Located on 662.5 and controlled by controller on the skid on 685)
- Establishes proper conductivity.
- Water comes from a recirc line between HXs and Filters and returns to tank.
- Normally flow set at 20gpm (50 gpm max)
- One normally in service, one in standby)
- Cartridge Type filters connected in parallel (1 normally in service)
- L-39 alarms at 10 psid (U1) and 9 psid (U2)
- Swap over to the spare filter at 3 psid. (Write WR to have filter replaced)
- Excludes air from system and prevents corrosion of the stator copper conductors which would be enhanced in the presence of atmospheric oxygen.
- Normal 2 psig.
- Relief relieves at 5 psig.
- Supplied from hydrogen supply system. Regulator set at 2 psig.
- Regulator located at hydrogen manifold elevation 706.
- Has Manual bypass. Used to manually adjust pressure and for feed and bleed process to increase hydrogen concentration.
- Set at 10 gph EACH
- Filters
- HX’s
- Demineralizers
- Start – Stop – Standby: on seal oil control panel TB El. 706
- Start – Stop – Test: at unit El. 685
- Reserve Selector Switch: on seal oil control panel TB El. 706
- Pumps will auto trip on Generator Differential (87GX)
- 20 psid decreasing across running pump closes PDS (Also alarms on l-39 “Pump Stopped”)
- Closes contact in reserve pump circuit (R-7), if non-running pump is in “reserve”
- OTS contact from breaker Amptector has contact to ensure the pump was not at low DP due to overload. Also alarms on L-39 at “Stator Cooling Water Pump Overload”
- Reserve pump will start as long as OTS was not picked up on running pump.
- One HX in service: 75% rated stator current
- No HX in service: 15% rated stator current for 1 hour as long as conductivity is ≤ .5
- Controller at the Skid (El. 685) or by using bypass around TCV (El. 662.5)
- Recirc line comes off HXs and filters with manual flow control valve.
- Set at 20 gpm normal with a 50 gpm maximum.
- Replace demineralizer bed when conductivity increases to 1.5 micromhos/cm at 25°C.
- 3 psid: Swap to spare filter and submit WR to replace filter.
- There is a PDS switch that assures machine gas pressure is greater that stator coolant pressure. This assures:
- Any stator bar leakage would be H2 to stator coolant
- No Liquid leakage into the generator
- Set point: 5 psig or less greater than inlet stator water pressure
- Alarms in MCR “Generator H2 Pressure Lo”
- Generator must be > 45 psig to run Stator Cooling Water system
- Generator must be > 45 psig to run stator cooling water system.
- Prevent moisture induction into casing
- ΔP switch, PDS-35-41 Assures machine gas pressure greater than stator coolant pressure.
- Any stator bar leakage would be hydrogen to stator coolant.
- No liquid leakage into generator.
- Setpoint: 5 psi Hydrogen pressure above stator inlet water pressure
- Alarm “Generator Hydrogen Pressure Low”.
- Prevents condensation on outer surface of stator bars.
- Unit 1 maintained according to a graph (normally 95 – 113°F {35°C – 45°C} when operating > 200 MW). Measured at generator inlet.
- Unit 2 maintained at 50°C measured at generator inlet.
- DCN on both units installed stainless steel wafer type butterfly valves on the Stator Cooling Water Pumps discharge piping downstream of the existing check valves to provide isolation capability for each pump for routine maintenance and repairs.
- Butterfly type valve operated by manipulating the valve handle through a 90° arc. Valve equipped with a latching mechanism to secure the valve in desired position. Latching mechanism operates by squeezing against spring pressure and releasing the latch into a set of toothed ridges.
- Stops were provided on the Unit-2 valve body and added to the Unit-1 valve body to prevent turning the handle the opposite way, such that the latch could be released into air, which would not keep the valve in position.
- Common discharge of pumps has recirculation line back to the tank, with a locked throttled valve.
- SQN unit 2 shut down for outage due to
excessive H2 leakage into SCW tank which indicated a H2 leak inside the generator.
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