Pumping Station Desing - Second Edition by Robert L. Sanks, George Tchobahoglous, Garr M. Jones
Подождите немного. Документ загружается.
Figure
12-57.
Energy grade
line
and
velocities
at
pump-down.
d.
EGL at top of
ogee ramp
=
invert
+
E
s
=
1.200
+
0.214
=
1.414 above trench
floor
(see
Figure 12-57).
5.
Divide
the
ogee ramp
and the
trench into
four
sections.
Four
are
enough
for
preliminary
results.
For
more accuracy,
use six or
eight
and
limit
the
allowable discrepancy between
estimated
and
calculated values.
a. For any
section, state
the
velocity,
V
1
,
at the
beginning
of the
section.
b.
Compute depth,
J
1
,
at the
beginning
of the
section
=
2/Wv
1
=
0.063/0.8
V
1
=
0.07875/V
1
.
c.
Compute
EGL
1
at the
beginning
of the
section
=
invert
elevatio^
+
J
1
+
v
2
/2g,
where
2^
=
2x9.81
=
19.62.
d.
Estimate depth
of flow,
J
2
,
at the end of the
section.
e.
Compute velocity,
V
2
,
at the end of the
section
=
Q/wd
2
=
0.07875/J
2
.
f.
Compute
EGL
2
=
invert
elevation
2
+
J
2
+
v
2
/2g.
g.
Compute
v =
(V
1
+
v
2
)/2.
h.
Compute
J =
J
avg
=
0.063/0.8
v =
0.07875/v.
i.
Compute
R
m
.
The use of
R
m
in the
Manning equation
was
proposed
by
Escritt [28],
who
stated that
n
is
correct within
a few
percent
if the
perimeter includes half
the
width
of the
free
water surface. Here,
it is
equivalent
to
increasing
n
from
0.010
to
0.013.
See
Section 3-5.
i.
R
m
=
AI(P
+
w/2) where
A is 0.8 J, P is w + 2J =
(0.8
+
2J),
and w/2 is
half
the
width
of the
free
water surface, 0.40
m.
ii.
/J
1n
= 0.8
J/(2J+1.2)
j.
Compute
Ah
=
L(0.01
v
/?-
2/3
)
2
k.
Compute
EGL
2
=
EGL
1
- Ah.
1.
Compare
EGL
2
in
Step
k
with
EGL
2
in
Step
f.
m.
Repeat
as
necessary with
a
revised
J
2
.
6.
Flow
from
A to B: L = 1.1
m.
Invert
A
=
1.20
m.
Invert
B
=
0.59
m.
Steps correspond
to
those
of
Part
5
above.
Step
Trial
1
Trial
2
Trial
3
a.
V
A
,
m/s
1.59
b.
d
A
=
0.07875/v
A
,
m
0.050
c.
EGL
A
=
Invert
A
+d
A
+v^/19.6
1.379
d.
d
B
,
m
(estimate) 0.022 0.023 0.0225
e.
V
B
=
0.07875A/
B
3.580
3.42 3.50
f.
EGL
8
=
Invert
B
+
^
+
V
6
V
19.6
1.265 1.211 1.237
g
.
v
=
(v
A
+
v
B
)/2
2.585
2.510
2.545
h.
d
=
0.07875/v 0.0305 0.0314 0.0309
i.
R
m
=
Q.8d/(2d+l.2)
0.01935 0.01989 0.01959
j.
A/z
=
L(0.01
vR-^}
2
0.141
0.1286 0.1349
k.
EGL
B
=
EGL
A
-
A/z
1.238 1.250 1.244
1.
EGL
B
@£-EGL
B
@/
-0.027
+0.039 +0.007
O.K.
7.
Flow
from
B to C. L = 1.1 m.
Step
Trial
1
Trial
2
Trial
3
a.
V
B
,
m/s
3.50
b.
d
E
=
0.07875/v
B
,
m
0.0225
c.
EGL
B
=
Invert
B
+
d
E
+
v|/19.6
1.238
d.
d
c
,
m
(estimate)
0.020
0.021
0.0203
e.
v
c
=
0.07875/^
c
3.938
3.75
3.879
f.
EGL
c
=
d
c
+v£/19.6
0.810
0.7377 0.788
g. v =
(v
B
+
v
c
)/2
3.719
3.625 3.6895
h.
d
=
0.07875/v 0.0212 0.0217 0.0213
i.
R
m
=
0.8d/(2d+l.2)
0.01364 0.01396 0.01374
j.
A/z
=
L(0.01
v/?-
2/3
)
2
0.4669 0.4300 0.455
k.
EGL
c
=
EGL
B
-A/z
0.771
0.808 0.783
1.
EGL
c
@fc-EGL
c
@/
-0.039
+0.070
-0.005
O.K.
8.
Flow
from
C to D. L =
1.8
m.
Step
Trial
1
Trial
2
a.
v
c
,
m/s
3.879
b.
d
c
=
0.07875/v
c
,
m
0.0203
c.
EGL
C
0.7889
d.
d
D
,
m
(estimate) 0.030 0.032
e.
V
D
=
0.07875A/
D
2.625
2.461
f.
EGL
0
=
d
D
+v^/19.6
0.3812 0.3407
g
.
v
=
(v
c
+
v
D
)/2
3.252
3.170
h.
d
=
0.07875/v 0.0242 0.0248
i.
R
m
=
QAd/(2d+l.2)
0.01551 0.01588
j.
A/*
=
L(0.01
v/?-
2/3
)
2
0.4922 0.4532
k.
EGL
0
=
EGL
C
-
A/i
0.2966 0.3357
1.
EGL
0
@k-
EGL
0
@f
-0.085
-0.005
O.K.
9.
Flow
from
D to E. L = 1.8 m.
Step
Trial
1
Trial
2
a.
V
D
,
m/s
2.461
b.
J
D
=
0.07875/v
D
,m
0.032
c.
EGL
0
=
d
D
+
vg/19.6
0.341
d.
d
E
,
m
(estimate)
0.040 0.043
e.
V
E
=0.07875/4
1.969 1.832
f.
EGL
E
=
Invert
E
+
d
E
+
v^/19.6
0.2376 0.2139
g. v
=
(v
D
+
v
E
)/2
2.215 2.146
h.
d
=
0.07875/v 0.0356 0.0367
i.
R
m
=
O.Sd/(2d+l.2)
0.0224 0.02306
j. Ah =
L(0.01
v
#-
2/3
)
2
0.1401
0.1263
k.
EGL
E
=
EGL
0
-
M
0.201 0.215
1.
EGL
E
@£-EGL
E
<2)/
-0.037
+0.001
O.K.
10.
Froude numbers
a.
V
E
=
1.832
m/s
from
Part
9.e.
b.
d =
Q.Q63/(0.8
x
1.832)
=
0.043
m.
c. F =
1.832/79.81x0.043
=
2.82
d.
See
Froude numbers
on
Figure
12-57
11.
Comments
a.
It was
deemed desirable
to
carry some calculations
to a
greater number
of
significant
places.
b.
F can be
increased
in
several ways, such
as:
i.
Increase
the flowrate of
water during pump-down.
In
this example,
if the flow
were
increased
48%
(about
the
maximum),
the F
would increase about
32%.
However,
as
flow
increases,
it
takes longer
to
dewater
the
trench.
Of
course,
flow
cannot
exceed about
85% of the
last pump's capacity.
ii.
Improve
the
smoothness
of the floor. For
example, lining
the floor
with
PVC
reduces
n to
0.009
and
increases
F by
about 24%.
iii. Shorten
the
trench.
iv.
Slope
the
trench
floor to
match
the
slope
of the EGL
beginning
at the
point where
F
becomes less than about
3.0.
(It
does
no
good
to
slope
the floor
upstream
of
such
a
point, because,
as
shown
in
Figure 12-57,
the
slope would have
to be
very steep.)
v.
An
incidental advantage
of
sloping
the floor
between
the
last
two
pumps
is
that
the
last
pump intake
can be
lowered, thereby increasing
its
submergence during early
stages
of
pump-down
and
increasing
the
discharge capacity
of the
last pump,
because
the
surface
vortex would
not
form
so
soon.
The
safety
of the
entire clean-
ing
system
is
improved.
vi.
It is not
necessary
for F to be as
much
as 3 at the
last pump.
As
long
as the
velocity
is
above
1.4 m/s
(4.5
ft/s),
sludge
and
grit move reasonably rapidly
(see
Figure
12-36).
An
hydraulic jump
at an F of 3 or
more
is,
however,
an
extremely
effective
way
to
suspend solids
and
move them quickly.
Critique
of
Example
/2-5
It is
assumed that equilibrium prevails
for the
water
surface
shown
in
Figure 12-55.
But it is
doubtful
whether
equilibrium
is
reached when pumps
are
cycling rapidly. Furthermore,
the
S-shaped water
sur-
face
curve would never
be
confined
within
the
man-
hole. Instead, long backwater
and
tailwater curves
would
occur.
It is
likely that supercritical
flow
would
occur
first
near
the wet
well
and
progress slowly
up
the
approach
pipe
—
with
no
positive assurance
of
reaching
the
manhole before
the
pump
is
stopped.
Under
such circumstances, dropping
the
invert only
48 mm may be
risky.
If the
invert were dropped
92
mm
(0.30 ft),
the
available velocity head would
be
about
318
+ 92 =
0.41
m
(1.34 ft).
The
resulting veloc-
ity
would
be
2.84
m/s
(9.30
ft/s)—
only
14%
higher
than
the
value
in
Table 12-2.
As the
sequent depth
increases only one-third
as
much
as the
velocity
increases,
the
depth would increase
from
60% of the
pipe diameter
to 65%
(still
a
conservative amount)
with
greater assurance
of
critical velocity
in the
man-
hole.
If the
crowns
of the two
pipes were
at the
same
elevation,
the
velocity would approach about
3 m/s or
20%
more than
the
nominal value
in
Table 12-2
and
produce
a
sequent depth
of
about
67% of the
pipe
diameter. Such high velocities
are
quickly dissipated
by
friction.
In
conclusion,
it
seems wise
to
drop
the
invert
by at
least
100
mm
(0.3
ft) to
ensure supercriti-
cal flow at the
exit
from
the
manhole.
In
calculations
of the
velocity increase
in the
man-
hole between sewer
and
approach
pipe
(Part E.3),
the
A'-factor
in the
formula
h =
Kv
2
/2g
is
assumed
to be
0.25, whereas
in
Example 29-1,
K is
assumed
to be
0.10.
There
are no
known data
to
support either
assumption.
Probably
K
lies between
the two
values
and,
perhaps,
closer
to
0.
10.
It
should
be
noted
that
the
choice
of a
^-factor
is not of
great practical
signifi-
cance, because
the
initial velocity
in the
approach pipe
is
insensitive
to
headloss
(being
a
function
of the
square root
of
head)
and the
sequent depth
is
relatively
insensitive
to
velocity (increasing only one-third
as
much
as the
velocity increases
on a
percentage basis.
The
designer
of a
pumping station
for C/S
pumps
must
add the
following
to the
concerns listed
in
Example 12-5:
•
Storage volumes
in
both approach pipe
and
pump
sump
•
Setting elevations
for
starting
and
stopping pumps.
These tasks entail some tedious calculations, best
done with computers. Note that
the
allowable active
storage
in the
approach pipe depends
on the
influent
flowrate,
because
the
volume occupied
by the
influent
flowing
at
supercritical velocity
is not
available
for
storage.
The
trench might
be
made shallower,
but
consider
that
(1)
the top of the
trench must
be
positioned
so
that
the
cross-sectional waterway area above
it is
adequate
to
carry
all of the
inflow
(at the
water surface eleva-
tion, whatever
it is) at an
average velocity
of
less than
0.3 m/s
(1
ft/s);
(2) the
requirement
for
adequate sub-
mergence
of
pump intakes (Equation 12-1) must
not
be
compromised;
and (3)
there must
be
proper
floor
clearance
for the
pump intakes. These
are the
consid-
erations
that
establish
the
elevation
of the
trench
floor.
Nevertheless,
it is
unwise
to set the top of the
trench
at
much
less than
2 D
above
the
intakes unless model
studies indicate
a
shallower trench
can be
used.
The
sluice gate
in
this example
is
poor. Flow
through
a
circular segment results
in
large depths
in
the
middle
of the
ramp
and
shallow depths near
the
edges. This condition
is
only partially overcome
at the
toe of the
trench,
and it
results
in
excessive wave
action
("rooster
tails")
that
may
interfere with
the
hydraulic
jump. Discharge through
a
rectangular hori-
zontal
slot
the
full
width
of the
ramp
(as in
Example
12-4)
is
preferred.
The
radius
of the
ogee ramp curves
are (at
0.75
m)
rather small.
The
operators would
be
unable
to
start
the
cleaning routine with
a
higher water level than
the
mid-depth
of the
influent
pipe.
A
radius
of
1.25
m (as
in
Example 12-4) would improve
the flexibility of
operation
for an
increase
in
overall
wet
well length
of
only
0.4 m.
The
calculations
of
velocity
from
the
sluice gate
to
the
last pump
are
only rough approximations. Greater
accuracy
can be
obtained
by
dividing
the
sump into more
segments. Without
a
computer program, such calcula-
tions
are not
justified
unless Froude numbers obtained
by
the
rough approximation
are
close
to the
limit.
For
simplicity,
the
capacity
of a
single pump oper-
ating alone
was
taken
to be
110
L/s.
The
capacity
in a
real problem must
be the
"runout"
capacity
found
at
the
intersection
of the
pump
and
station
H-Q
curves,
and
the
solution
for
Equation 12-3 must
be
based
on
the q at
runout.
Round
Sumps
for
Small
Lift
Stations
Round
pump sumps
for
submersible pumps
or
self-
priming pumps
are
popular
for
small
flowrates and
duplex pumps with motors
of 3.7 to 15 kW (5 to 20
hp), although much larger pumps with motors
up to
110
kW
(150
hp) can be
used. Most manufacturers'
catalogs contain drawings
of
round sumps with
duplex pumps
in a flat-bottom
sump
—
occasionally
shown
with corner
fillets. The
advantage
of
these
sumps
is
their
low
cost. However,
one
overwhelming
disadvantage
is the
odor
from
the
deep, unstable
sludge bank that develops
and
surrounds
the
pumps.
A
second disadvantage
is the
thick blanket
of
scum that
develops,
and a
third
is the
free
fall
of
water that cas-
cades into
the
pool
and may
cause bubbles
of air to
enter
the
pumps. These disadvantages
are
eliminated
in
a
hopper-bottom sump with
a
sloping-
approach
pipe
discharging
at
LWL.
Hopper-Bottom
Pump
Sumps
Hopper bottoms
in
round sumps (see Figures
12-58
and
12-59) prevent
the
accumulation
of
settleable sol-
ids,
because
the
solids slide down
the
smooth, steep
sides
to the floor, and
every time
a
pump
is
activated,
the
sludge
is
pumped out. Scum
can be
eliminated
by
a
regular schedule
of
pumping until
the
pump
loses
prime (pump-down), thereby concentrating scum into
a
small area where
a
surface
vortex sucks
it
into
the
pump.
A PLC can be set for
pump-down
at
regular
intervals
—
say,
once
per day if the
pump
can
reprime
itself
reliably.
The
free
water surface area
at
pump-down must
be
small
if
scum
is to be
completely discharged.
As an
example,
the
Black Diamond pumping station
wet
well
(see Figure
17-11)
does
not hug the
suction inlets
closely enough
to
remove
all the
scum
on the first
pump-down.
Note that pumps suck
air and
begin
to
lose prime when
the
submergence
of the
intake
becomes much less than
the
intake diameter,
D.
Large
hopper bottoms with pumps that lose suction when
the
water level
falls
to the top of the
volute
of
submersible
pumps
are
unlikely
to be
fully
effective
in
removing
scum.
The
smallest
free
water surface area
at
pump-
down
(and consequently, better
and
quicker cleaning)
can
be
achieved
by
equipping submersible pumps
with
suction nozzles
(a
standard
feature
on
some sub-
mersible pumps)
set
within
a
vertical-sided trench,
as
shown
in
Figure
12-58c.
For
duplex
or
triplex pump installations, good
cleaning
can be
obtained without pump-down
(or
Figure
12-58.
Duplex
submersible
pumps
in
round
sump,
(a)
Section C-C;
(b)
Section B-B;
(c)
alternate Section
B-B;
(d)
Section A-A.
with
only partial pump-down)
by
operating
the
pump(s)
while mixing
the
contents with either
a
mechanical
mixer,
a
piping system such
as
shown
in
Figure 17-22,
or a
bypass
in the
pump that allows
some
of the
pumped
fluid to mix the
contents. Mixers
can be
programmed
to
operate only
a few
minutes
at
the
beginning
of
every pump start-stop cycle.
If
intakes
are set as
close together
as
shown
in
Figures
12-58
and
12-59, settleable solids cannot accumulate
in
significant
amounts
and
removal
of
scum
is the
only
reason
for
pump-down.
Sumps
for
Large
Pumps
The
most practical isolation valve
for
wastewater
pump
intakes
is the
eccentric plug type,
but
these
valves
become massive
and
expensive
for
pipes larger
than
400 mm (16
in.).
Solid-
wedge
gate valves have
been used
for
this service,
but
they
are
less satisfac-
tory
and are not
recommended. Furthermore,
the
larger
pipes make
the
pump elevation above
the dry
well
floor
inconveniently high
for the
maintenance
crew.
The
high pump pedestal exacerbates vibration
and
earthquake force resistance problems.
Draft
Tube Designs
The
foregoing considerations
on
size
of
pipe limits
the
size
of
pump
for the
configurations
in
Figures
12-19
through
12-22
to
about
14
m
3
/h
(6000
gal/min).
For
larger pumps, consider
draft
tube designs such
as
those used
for the
Duwamish
and
Interbay Pumping
Stations
(Figures 17-4
to
17-9)
for
which
an
inexpen-
sive
sluice gate
can be
used
for
isolation. Such
a
con-
figuration
permits mounting
the
pump
on a low
housekeeping
pad in the dry
pit.
The
Duwamish
Pumping Station has, incidentally, proven
to be the
best
of the
Seattle Metro stations
for
cleaning. Also
consider using
the FSI
design shown
in
Figure
12-30.
Vortices
are
likely
to
form
above
a
draft
tube inlet
unless
a
vertical vortex suppressor plate
is
installed
in
the
mouth
of the
draft
tube such
as
that shown
in
Fig-
ure
17-6.
The
forces acting
on the
plate
are
thought
to
be
substantial,
so use a
thick (12-
to
25-mm
or
V
2
-
to
1-in.)
plate strongly anchored
to the
wall. Round
the
outboard edge
so
that rags will
not be
caught
on it. For
side wall entrances,
the
vortex suppressor
can be
mounted
on the
sluice gate.
12-8. References
1.
Prosser,
M. J.
"The hydraulic design
of
pump sumps
and
intakes."
British Hydromechanics Research Association,
Cranfield,
Bedford,
England
MK43
OAJ
(July
1977).
2.
Hydraulic Institute Standards
for
Centrifugal, Rotary
&
Reciprocating Pumps, 14th ed., Hydraulic Institute,
Parsippany,
NJ
(1983).
3.
ANSI/HI
1.1-1,5-1994,
Centrifugal
Pumps
for
Nomenclature, Definitions, Application
and
Operation,
Hydraulic Institute, Parsippany,
NJ
(1994).
4.
ANSI/HI
2.1-2.5-1994,
Vertical
Pumps
for
Nomenclature, Definitions, Application
and
Operation,
Hydraulic
Institute,
Parsippany,
NJ
(1994).
5.
Sanks,
R.
L.,
G. M.
Jones,
and C. E.
Sweeney.
"Designing
self-cleaning
wet
wells
for
wastewater
pumping," Conference
Proceedings,
American Society
of
Civil
Engineers
National Conference
on
Hydraulic
Figure
12-59.
Sump
for
duplex,
self-priming
pumps,
(a)
Plan;
(b)
Section A-A.
Engineering, Part
1, San
Francisco,
CA
(1993),
pp.
180-185.
6.
Sanks,
R.
L.,
G. M.
Jones,
and C. E.
Sweeney. "Self-
cleaning
wet
wells: definitions
and
design
for
wastewater
pumping," Proceedings
of the
International
Conference
on
Pipeline Infrastructure
II, San
Antonio,
TX.
American Society
of
Civil Engineers,
New
York,
NY
(1993)
pp.
102-114.
7.
Sanks,
R.
L.,
G. M.
Jones,
and C. E.
Sweeney.
"Improvements
in
pump intake basin design."
EPA
600/R-95/041,
RREL-CI. Order
No.
PB95-
188090,
National
Technical Information Service, 5285 Port
Royal
Road, Springfield,
VA
22161.
8.
Sanks,
R.
L.,
G. M.
Jones,
and C. E.
Sweeney.
"Better
sumps
for
pumps," Engineering
and
Construction
Conference,
Proceedings, American Water Works
Assoc., Denver,
CO
(March 1996),
pp.
393-398.
9.
Dicmas,
J. L.
Vertical
Turbine, Mixed Flow,
&
Propeller
Pumps. McGraw-Hill,
New
York,
NY
(1987).
10.
Hecker,
G.
E.,
President,
Alden
Research Laboratory,
Inc.,Holden,MA(1996).
1 1
.
Kennon,
H. H.
"Design guidance
for
rectangular sumps
of
small pumping stations with vertical pumps
and
ponded approaches," Engineering Technical Letter
No.
1110-2-313,
Dept.
of the
Army, U.S. Army Corps
of
Engineers, Washington,
DC (29
April 1999).
12.
Triplett,
G.
R.,
B. P.
Fletcher,
and J. L.
Grace. "Pumping
station
inflow
—
discharge
hydraulics, generalized pump
sump
research study," Technical Report HL-88-2,
Department
of the
Army, Waterways Experiment Station,
Corps
of
Engineers, Vicksburg,
MS
(February 1988).
13.
Karassik,
I. J. , W. C.
Krutzsch,
W. H.
Fraser,
and J. P.
Messina. Pump
Handbook,
2nd
ed., McGraw-Hill,
New
York (1986).
14.
Fletcher,
B. P.
"Formed
suction intake approach
appurtenance geometry," Waterways Experiment
Station, Corps
of
Engineers,
3909
Halls Ferry Road,
Vicksburg,
MS
39180-6199.
15.
Fletcher,
B. P.
Private communication, July
21,
1995.
16.
Fletcher,
B. P.
"Cypress Avenue pumping station:
Hydraulic
model investigations," Technical Report
HL-
94-9, U.S. Army Corps
of
Engineers Waterways
Experiment Station,
3909
Halls Ferry Road, Vicksburg,
MS
39180-6199.
17.
Falvey,
H. T.
Air—
Water
Flow
in
Hydraulic Structures,
U.S. Dept.
of the
Interior, Bureau
of
Reclamation,
Engineering Monograph
41,
Superintendent
of
Documents, Washington,
DC
(1980).
18.
Beaty,
V. J.
Vice President
and
Chief Engineer (now
retired),
Fairbanks
Morse
Pump Corp., Kansas City,
KS.
19.
Linabond, Inc., 6922 Hollywood Boulevard, Ste. 303,
Los
Angeles,
CA
90028.
20.
Goldschmidt,
G.
"Mixing
fixed-speed
pumps
to
variable
flows,"
Journal
Water
Pollution Control
Federation,
50:1733-1741
(July 1978).
21.
Wheeler,
W.
Discussion
of
"Mixing
fixed-
speed
pumps
to
variable
flows,"
Journal
Water
Pollution Control
Federation,
51:2959-2960
(December 1979).
22.
ENSR. "City
of
Portland,
OR,
Columbia Boulevard
Wet
Weather
Treatment Facility
Influent
Pump Station
Project
Hydraulic Model
Study."
Prepared
for
Damon
S.
Williams Associates, L.L.C., Portland,
OR.
Document
2181-002-410,
ENSR, Redmond,
WA
(1997).
23.
Williams
D.
S.,
D. P.
Sowles,
S. P.
Reddy,
and T. C.
Demlow. "Computer
and
physical modeling
of a
large
hybrid
CSO
sanitary wastewater pump station,"
presented
at
WEFTEC
'97,
Chicago,
IL
(October 1997).
24.
Linabond, Inc., 12960 Bradley Ave., Sylman,
CA
91342. Phone (818)
362-7373;
Fax
(818)
362-5757;
Web
www.linkbond.com.
25.
Wheeler,
W.
PARTFULL®.
For a
free
copy
of
this
computer program with instructions, send
a
formatted
1.4
MB,
3-1/2-in
diskette
and a
stamped, self-
addressed
mailer
to 683
Limekiln
Road,
Doylestown,
PA
18906-2335.
26.
Design
of
Small Dams, Revised Reprint, U.S.
Department
of the
Interior, Bureau
of
Reclamation.
US.
Government Printing
Office,
Washington
DC
(1977).
27.
Chow,
V. T.
Open Channel
Hydraulics,
Classic
Textbook Reissue, McGraw-Hill,
New
York (1959).
28.
Escritt,
L. B.
Sewerage
and
Sewage Treatment:
International
Practice,
edited
and
revised
by W. D.
Haworth,
John Wiley
and
Sons,
New
York
(1984).
The
focus
of
this chapter
is the
practical selection
(from
the
myriad
of
special features
and
characteristics avail-
able)
of the
proper driver
in a
manner that will result
in
an
economical, dependable drive unit.
The
discussion
of
motors includes
an
elementary explanation
of the
sev-
eral types commonly used
as
pump drivers.
Refer
to
standard
texts
on
electrical fundamentals
and
alternating
current
machines
for an
in-depth theory
of
operation.
Before
designing
the
electrical system
for
driving
the
pumps,
it is
important
to be
aware
of
choices,
restrictions,
and
requirements, such
as (1) the
various
motor characteristics available both
as
standard
and as
specialty
or
custom products,
(2) the
costs
of the
vari-
ous
types
and
configurations
of
suitable motors,
and
(3)
the
restrictions resulting
from
station design crite-
ria or
earlier decisions.
For
example,
in
rebuilding
a
station, there
are
usually severe restrictions
on
space
—
sometimes
for the
motor
and
pump combina-
tion
and
usually
for
motor controls.
References
to a
code
or
standard
are
given
in
abbreviated
form
(such
as NEC for
National
Electrical
Chapter
1
3
Electric
Motors
PAULC.
LEACH
CONTRIBUTORS
Robert
S.
Benfell
Harrison
C.
Bicknell
Donald
R.
Bjork
Victor
G.
Gerez
Mayo
Gottliebson
Stanley
S.
Hong
Philip
A.
Huff
Richard
L.
Nailen
Stephen
H.
Palac
M.
Le
Roy
Patterson
Richard
N.
Skeehan
Patricia
A.
Trager
Frank
A.
Woodbury
Code).
See
Appendix
E for the
names
of the
abbrevia-
tions
and
Appendix
F for the
addresses
of
publishers.
13-1.
General
Some
of the
definitions (given here
for
convenience)
are
shortened, simplified versions
of the
definitions
in
ANSI/IEEE
Standard 100.
For
more definitions,
see
Chapter
2
(which also contains abbreviations), Chap-
ter
8,
and the
latest edition
of the
NEC.
Definitions
Adjustable-speed
drive:
A
drive designed
so
that
speed
can be
varied throughout
a
considerable
range
(1)
independently
of the
load
and (2) as
regu-
lated
by
some external signal (see variable speed).
Armature:
The
member
of an
electric machine
in
which
an
alternating voltage
is
generated
by
virtue
of
relative motion with respect
to a
magnetic
field.
The
armature
is the
stator
in a
squirrel-cage motor
and
the
rotor
in a dc
motor.
Brush:
A
conductor (usually made
of
carbon) that
maintains
an
electrical
connection between
the
sta-
tionary
and
moving parts
of a
machine.
Collector ring
(slip
ring):
A
metal ring mounted
on
an
electric machine that conducts current into
or out
of
the
rotating member through stationary brushes.
Commutator:
A
cylindrical ring
or
disc assembly
of
conductors, individually insulated
in a
supporting
structure
with
an
exposed surface
for
contact with
current-collecting brushes.
In
effect,
a
commutator
is
a
switching mechanism between
the dc of the
brushes
and the ac in the
armature
of a dc
machine.
Dripproof
enclosure:
An
open machine with venti-
lating
openings constructed
so
that drops
of
liquid
or
solid particles
falling
on the
machine
at any
angle
not
greater than
15°
from
the
vertical cannot
enter
the
machine.
Explosionproof
enclosure:
An
enclosure designed
to
withstand
an
explosion
of a
specified
gas
that
may
occur within
it and to
prevent
the
ignition
of the
same
gas
surrounding
the
enclosure.
It
must
operate
at
a
temperature that prevents
the
surrounding
flam-
mable atmosphere
from
being ignited.
Frame
mount:
A
supporting structure that
connects
the
motor
to the
pump
with
an
intervening
shaft
coupling.
Framework
(frame):
The
stationary supporting
structure
that contains
the
stator windings
and the
rotor.
Induction
motor:
An
alternating current motor
in
which
a
primary winding (usually
on the
stator)
is
connected
to the
power source
and a
polyphase sec-
ondary winding
or
squirrel-cage secondary winding
(usually
on the
rotor) carries induced current.
Inrush:
The
surge
of
electricity into
a
motor
at
rest
when
it is
energized.
The
surge, which diminishes
to the
running load current
at
full
speed
in
approxi-
mately
5 to 30 s, is
typically about
6
times
the
full-
load current,
but it may be as
much
as 10 in
some
motors
or it may be
reduced
in
"soft
starts"
to
1
.5
or
even
1.0
times
the
full-load
current.
Power
factor: True power divided
by
apparent power.
Lag of
current behind voltage
in
inductive
ac
cir-
cuits
reduces true power
from
VA to V x A x cos 6,
where
V is
volts,
A is
amperes,
and
0
is the lag
angle (see Equation 8-3).
Round
(cylindrical)
rotor:
A
cylindrical rotor
in
which
the
coil sides
of the
windings
are
contained
in
axial slots.
Salient
pole:
A field
pole that projects
from
the
yoke
or
hub
toward
the
primary winding
core.
Salient
pole
and
round (cylindrical) rotors ordinarily
are
used
to
describe
the
rotor design
of
synchronous
motors; i.e.,
a
salient-pole synchronous motor
or a
round-
(cylindrical-)
rotor synchronous motor.
Service factor
(SF):
A
multiplier (applied
to the
rated power) that indicates
the
built-in capability
of
carrying
a
continuous load greater than
the
name-
plate rating (but only
at the
rated voltage
and
fre-
quency). Standard service factors
are
1.0
and
1.15.
Slip:
The
difference
between
the
rotational speed
of
the
magnetic
field in an
induction machine
and the
rotor.
An
induction motor develops
its
ability
to
drive
a
load
by
virtue
of its
slip,
whereas
a
synchro-
nous
motor operates
at
zero slip.
Soft
start:
A
type
of
motor starting
in
which
the
inrush
is
greatly reduced.
Soft
start
is
generally
applied
to
solid-state starting
and
acceleration con-
trol systems.
Splashproof
enclosure:
An
open motor with
the
ven-
tilating openings constructed
so
that drops
or
parti-
cles
falling
or
coming toward
it at any
angle
not
greater than 100° downward
from
the
vertical can-
not
enter.
The
Splashproof enclosure
is no
longer
generally available. Weather-protected Type
I is an
alternative enclosure type.
Stator:
The
portion
of a
machine that includes
and
supports
the
stationary
portions
of the
magnetic
circuit
and the
associated windings
and
leads.
It
may
include
a
frame
or
shell, winding supports,
ventilation circuits,
coolers,
and
temperature detec-
tors.
A
base
is not
usually considered
to be
part
of
the
stator.
Submersible enclosure:
An
enclosure constructed
so
as to
operate
successfully when submerged
in
water
under specified conditions
of
pressure
and
time.
Synchronous motor:
A
motor that
has field
poles
excited
by
direct current
so
that
the
speed
of the
rotor equals that
of the
rotating magnetic
flux.
Synchronous speed:
The
rotational speed
of the
magnetic
field in an
electric
motor and,
in
synchro-
nous motors,
the
rotational speed
of the
shaft
and
rotor.
Torque,
accelerating:
The
difference
between
the
torque produced within
the
motor
and
that required
by
the
driven load
at any
particular
shaft
speed.
Torque,
full-load:
The
torque required
to
produce
the
rated motor horsepower
at the
rated speed.
Torque,
locked-rotor:
The
torque produced with
the
motor
at a
standstill
but
energized
at the
rated volt-
age. Locked-rotor torque
is
also called "starting
torque."
At the
instant power
is
applied
to an
induc-
tion motor
at
rest,
the
motor
is
analogous
to a
trans-
former
with
its
secondary short-circuited through
a
very
low
impedance.
Totally
enclosed (TE) motor:
An
integral enclosure
constructed
so
that, although
not
necessarily air-
tight,
the
enclosed
air has no
deliberate
connection
with
the
external
air
except
as
required
for
draining
and
breathing.
Totally
enclosed
Jan-cooled
(TEFC)
motor:
A
totally
enclosed motor equipped
for
exterior cooling
by
means
of
fans
integral with
the
motor
but
external
to
the
enclosing parts.
TotaUy
enclosed,
nonventilated
(TENV)
motor:
A
totally
enclosed motor that
is not
equipped
for
cooling
by
means external
to the
enclosing parts.
Totally
enclosed,
pipe-ventilated
motor:
A
totally
enclosed
motor except
for
openings arranged
so
that inlet
and
outlet
ducts
or
pipes
may be
connected
to
them
for the
admission
and
discharge
of the
ventilating air. This
air
may
be
circulated
by
means that
are (1)
integral with
the
machine
or (2)
external
to and not
part
of the
machine.
The
latter machines
are
called
"separately
ventilated"
or
"forced-
ventilated"
machines.
Variable-speed
drive:
A
drive designed
so
that
its
speed varies through
a
considerable range
as a
func-
tion
of
load (see adjustable-speed drive).
Weather-protected
(WP)
machine:
A
guarded machine
with
the
ventilating passages designed
to
minimize
the
entrance
of
rain, snow,
and
airborne particles
to
the
electrical parts. There
are two
types,
I and II.
Type
II is
designed
for
more severe applications.
Wound-rotor
motor:
An
induction motor with
the
rotor windings connected
to
collector rings.
The
brush
terminals
may be
either short-circuited
or
closed through adjustable circuits.
Standards
and
Codes
The
most authoritative information
on
standards relat-
ing
to
electric
motors
is
NEMA
MG-I.
The
Institute
of
Electrical
and
Electronics Engineers provides many
sources
of
reference material
in the
IEEE
Standards
and
in
various technical articles
in
IEEE
Transactions
on
Industry
Applications. These references
are
recom-
mended
for
in-depth information
on
motors,
new
developments
in
research,
and
motor manufacturing.
Many
manufacturers' catalogs
and
special brochures
provide
useful
information
on
motor characteristics
and
pricing.
If
motor characteristics
are
selected
from
a
partic-
ular
standard, there
is no
assurance that
any
manufac-
turer
will build
the
motor
as
specified because each
manufacturer
has its own
"standard"
models
and
modifications
(called
"adders").
During early stages
of
design, therefore, check with several manufactur-
ers
whose representatives
can
supply current infor-
mation.
13-2. Applications
of
Motors
Electric motors
are the
most frequently used drivers
in
pumping
stations, primarily
because
of
their versatility,
compactness,
and low
maintenance.
The
most com-
mon
machine
is the
polyphase squirrel-cage induction
motor; these motors range
in
size
from
less
than
one to
several thousand horsepower.
In
sizes larger than about
375 kW
(500 hp),
a
wound-rotor motor (for variable-
speed
pumping)
or a
synchronous motor
is
sometimes
more economical, although
the
controls
are
more com-
plex. Induction motors
up to
about
600 kW
(800
hp)
are
usually used
for
adjustable-speed drives,
but
larger
drives tend
to be
more economical with
a
wound-rotor
or
a
synchronous motor. Large squirrel-cage motors,
however, have high
efficiencies
and
power factors that
make
the
operating costs approach those
of
synchro-
nous
motors without
the
high capital cost.
Almost
all
pumping stations also require
electric
motors
to
drive auxiliary equipment.
These
auxiliaries
can
range
from
fractional kilowatt
or
horsepower rat-
ings
up to 30 or 40 kW (40 or 50 hp) in the
larger sta-
tions.
The
advantages
of
electric
motors
are
summarized
in
Table
13-1.
Ambient
Conditions
Electric motors
are
usually comparable
in
size
to the
pump
itself
—
particularly
in the
small-
to
medium-
sized stations. Therefore,
the use of
electric
motors
as
drivers
is not a
major problem
in
pumping station
space allotment. Enclosures
for
electric
motors
can be
selected
to
suit
a
wide range
of
environments:
(1)
totally
submerged,
(2)
humid,
(3)
explosive atmo-
sphere,
(4)
clean
and dry
areas indoors,
or (5)
out-of-
doors directly
in
intense heat, rain,
and
freezing tem-
peratures. Although
different
environments require
different
enclosures,
the
basic operating characteris-
tics
are the
same.
Mountings
Electric motors
may be
mounted
in
many ways.
The
motor
can be
close-coupled
to the
pump
in
either
a
horizontal
or a
vertical arrangement
in
which
the
pump
impeller
is
fastened directly
to the
shaft
of the
motor.
Wherever possible, however, avoid configurations that