Stator Water Cooling System - Stage-2
Stator Water Cooling System - Stage-2
Stator Water Cooling System - Stage-2
38
Mechanical filters 2 X 100 % duty
Magnetic filter 1 X 100 % duty
Other components employed in the system are gas trap device, expansion
tank, water jet ejector, valves and associated instrumentation. Together with the
connecting pipe work these components form the external circuit for the supply
of cooling water to generator windings. Refer stator water system diagram. The
cooling circuit makes use of either of the following water supplies, free from
oxygen.
(a) Distilled Water.
(b) Fully demineralised water from boiler feed water treatment plant.
(c) Condensate.
Fully demineralised water from the boiler feed water treatment plant and
condensate may only be used if no chemicals, such as ammonia, hydrazine,
phosphates etc. are present in the water or condensate. A part of water is
bypassed, and is treated in mixed bed ion exchanger, connected in parallel to the
stator winding, magnetic filter and expansion tank and returned into suction side
of the water pump, thus maintaining conductivity of closed loop circulating water
within permissible limit. The DM water pumps are of single stage type with spiral
casing and overhung impeller. The pump is connected to a three phase AC Motor.
Failure of the working pump due to fault or power supply failure results in an
automatic changeover to standby pump; the criterion for such a changeover is
the falling water pressures downstream the pumps. This falling pressure is sensed
by means of a pressure switch. The heat absorbed by the DM water in the
generator is dissipated to the secondary coolant in the primary water cooler. The
water treatment plant (polishing unit) provided across the stator winding,
essentially comprises an exchanger tank filled with anion and cation resins in the
form of a mixed bed ion exchanger.
The base substances of the exchanger resins are normally polymers
containing groups of diverse character featuring exchange activity. In this way
the synthetic resins are capable of cation and anion exchange. The cation
exchanger contains highly acidic groups, while the anion exchanger comprises
highly basic groups. The exchanger resins are thus capable of accepting ions
from the DM water, while releasing equivalent amounts of other ions (hydrogen
39
ions from the cation exchanger and hydroxyl ions from the anion exchanger) to
the DM water at the same time. This exchange can only take place between
equally charged ions. Therefore, cation exchanger exchange cation and anion
exchanger exchange anion. This process takes place within a very short time
while the DM water is passed through the ion exchanger. A combination of highly
acidic cation exchanger and highly basic anion exchanger constitutes a multitude
of small demineralization units, resulting in a high purity deionite.
The mechanical filter eliminates any foreign particles in the water, which
may choke, erode the hollow conductors. Difference of pressure at inlet and
outlet of the filter is indicative of the degree of choking. The choked filter may be
cleaned after using the standby without affecting the system corking. The
magnetic filter prevents any magnetic particles from entering the generator. Any
accidental leakage of hydrogen into the main distilled water stream is detected
by gas trap device (see description of gas trap device). The water from the outlet
of stator winding collects in an overhead expansion tank, which provides a
constant level of water during normal running of the system. The hot water
enters the tank through perforated pipe in the form of spray thus releasing any
entrapped gas. A water jet ejector is connected to expansion tank for creating
vacuum for the purpose of removing any traces of Oxygen/Hydrogen Gas which
may be present as a result of hydrogen leakage into the DM water stream. Level
signaling device provided in the expansion tank monitors the high and low level
of distilled water and initiates a tripping command for stator water pump at low
level in the expansion tank. Make up DM water to the system is provided at
expansion tank through a float operated level regulator.
The quantity of DM water flowing through the windings is measured by a
system of orifice plate, flow transducers, and flow indicator and recorder.
Signalling contacts are available in flow switch/the indicator/recorder, which are
set to annunciate at low flow through the windings, and initiates tripping of the
machine at emergency flow on the principle of two out of three. Conductivity cell
and suitable indicator and recorder do continuous monitoring of the conductivity
of water, which annunciate alarm at conductivity high set value. At very high
conductivity the unit is tripped automatically. In addition to above, the system
also provides for necessary instrumentation for indicating/Signalling of the
40
temperatures and pressures at various points of the system. Pressure interlocking
of the pumps is also provided.
41
(ii)
to the rated flow is of the order of 0.1 0.2 kg/Cm 2 (g). As the particles get
deposited on the wire meshes, the resistance to flow increases and consequently
pressure drop across the water filter increases. When the pressure drop increases
to 0.4 kg/Cm2 (gauge) cleaning is recommended.
2. Rated discharge
: 30 M3/hr.
: 12 kg/Cm2
: 0.224mm.
: Stainless Steel
: Brass
9. Weight (Kg)
10.Size of wire mesh (Aperture) mm
0.5
: 71.5
: 0.224 and
42
: 38 kg/Cm2 (G) for 15
minutes.
: Y 36
2.
Magnet type
: Permanent magnet
3.
: 4000 Gauss
4.
Capacity
: 36 M3/hr.
5.
Weight
: 113 kg
6.
7.
8.
9.
Pressure drop
: Negligible
43
which opens or closes depending on the level in the tank. The stator water pump
draws water from the bottom of the tank for recirculation. The tank is provided
with the following instruments/components.
(i)
(ii)
Two nos. of transducers for level signalling device to give high and
low level alarm signals.
(iii)
(iv)
(v)
PUMP CASING
SS316
SHAFT
IMPELLER
SS316
STATOR
SS316
CONTROL DISCS
INTERMEDIATE DISC
SS316
BEARING HOUSING
CAST IRON
SHAFT SEAL
SS
SS316
SS316
44
SERVICE LIQUID CONNECTION
COUPLING
:
:
BSP
FLEXIBLE
:
8 LPM AT 10 Psig
2T 30
VACUUM
DISPLACEMENT
51 M3/HR
R.P.M
SEALANT REQD.
:
:
8 LPM
BHARAT BIJLEE
TYPE
H.P.
R.P.M
VOLTAGE
:
:
2850
415 VOLTS
45
The polymer in the cation exchanger contains highly acid groups, while the
polymer in the anion exchanger is composed of highly basic groups. The
exchanger resins are thus capable of accepting ions from the primary water,
while simultaneously releasing equivalent amounts of other ions (hydrogen
ions from the cation exchanger and hydroxyl ions from the anion exchanger)
to the primary water. This process takes place within a very short time while
the primary water is passed through the ion exchanger. The combination of
highly acid cation exchangers and highly basic cation exchangers forms a
multitude of small demineralization units, resulting in a high-purity de-ionate.
The number of ions it can exchange limits the capacity of the mixed-bed of
the ion exchange. This capacity is primarily determined by the type of
exchanger used, but also depends on the quantity of reactivating agent, the
rate of flow and the water temperature. When the resins are exhausted, new
resins must replace them. After removal from the primary water treatment
system, the resins can be reactivated.
46
ii)
iii)
Annunciation cabinet.
47
Earthing point.
Flow indicator.
Alarm units.
Level switches.
D.O.L starter and control equipments for both working and standby
pump motors.
48
drainpipe consists of a plug (5), which has a central hole and a slot, which
connects the space at the upper chamber. The hole at the centre in the plug
faces a small hole in the drainpipe, which is having small loop at the bottom.
The loop remains filled with water during normal operation thus isolating the
atmospheric gases/air from the upper chamber. The cylinder is kept in
position by four bolts (7) between upper and lower covers. Two sampling
points are provided along with valves in the upper chamber of cylinder for
gas sampling.
*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
*-*-*-*-*-*-*-*-*-*-*-*-*