Pumping Station Desing - Second Edition by Robert L. Sanks, George Tchobahoglous, Garr M. Jones
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Table
9-1.
Coefficient
of
Utilization
(CU)*
Manufacturer's
Data
for a
Selected
Two-Lamp,
40-W
Industrial
Fluorescent
Fixture"
3
'
0
(Spacing/Mounting
height
=
1.5)
Room
R
w
(%)
with
R
cc
= 80%
R
w
(%)
with
R
cc
= 50%
R
w
(%)
with
R
cc
=
10%
cavity
ratio
50%
30%
U)%50%
30%
10%
50%
30%
10%
1
0.68 0.65 0.62 0.62 0.60 0.58 0.55 0.54 0.52
2
0.59 0.54 0.50 0.54 0.50 0.47 0.48 0.46 0.43
3
0.52 0.46 0.41 0.48 0.44 0.39 0.43 0.39 0.37
4
0.46 0.40 0.35 0.43 0.37 0.33 0.38 0.34 0.31
5
0.40 0.34 0.30 0.37 0.32 0.28 0.34 0.30 0.27
6
0.36 0.30 0.25 0.33 0.28 0.25 0.30 0.26 0.23
7
0.33 0.27 0.22 0.30 0.25 0.22 0.27 0.23 0.20
8
0.30 0.23 0.19
0.27
0.22 0.19 0.25 0.21 0.18
9
0.27 0.20 0.17 0.25 0.20 0.17 0.22 0.18 0.15
10
0.24 0.18 0.15 0.23 0.18 0.15 0.20 0.16 0.13
a
CU is for a 20% floor
cavity reflectance
(#
fc
).
b
R
cc
=
Effective
ceiling cavity reflectance;
/?
w
=
wall reflectance.
c
Coefficient
of
utilization varies depending
on
type
of fixture,
type
of
lamp,
and
manufacturer. Refer
to
manufacturer's data.
Example
9-7
Lighting
a
Small
Pumping
Station
Problem: Assume
a
pumping station control room
is 21 x 42 ft
with
a
15-ft
ceiling.
Mount
lamps
12
ft
above
the floor.
Assume
the
work plane
is 3 ft
above
the floor.
Design lighting
to
provide
40 ft • cd of
illumination
on the
work area.
Solution: Select
4-ft-long,
two-lamp industrial
fluorescent fixtures
with
32
WT-8 lamps
and
an
electronic ballast.
The
precalculation procedure outlined
in the IES
handbook
[2]
provides
a
detailed explanation
of
these parameters:
• LLD
(lamp lumen depreciation):
Use
0.90
for fluorescent
lights.
• LDD
(luminaire dirt depreciation):
Use IES
Category
III and
assume
fixtures are
cleaned
annually:
therefore
use
"medium"
(0.87).
• RCR
(room cavity ratio)
from
Equation
9-1:
RCR
=
H(L
+
W)IA
=
5X
0
V
x
^
2
1+42)
= 3.2
• RSD
(room surface depreciation):
use
0.95.
Find
the
coefficient
of
utilization
(CU)
from
the IES
handbook
[2],
or use the
manufacturer's
data
as
shown
in
Table
9-1.
For
two-lamp industrial
fluorescent fixtures,
2850 lumens
per
lamp,
and
typical room reflectance values
of
50/50/20,
CU =
0.46
by
interpolation.
From Equation
9-2:
XT
u
er
+
(40)(21X42)
Number
of
fixtures
=
2
x
285Q
x
0
.
4
^
x
Q
.
9Q
^
87
x
0.95
=
18
'°
Use
18
fixtures (2
rows
of 9 fixtures).
Fixture spacing must
not
exceed
the fixture's
desig-
nated spacing/mounting height ratio multiplied
by the
mounting height above
the
work plane
in
either direction.
The
illumination
on the
work area
is
found
from
Equation
9-2:
A
,.
,r
,
A^
18x2x2850xO.46xO.90xO.87xO.95
^
0
Actual foot-candles
=
———
=
39.8
Similar calculations
can be
made
for the
other
rooms
in the
pumping station. More than
one
light fix-
ture
and
lamp combination
may
often
appear appropri-
ate for an
area
or
space.
The final
selection
may
require:
(1)
calculations
for
each light
fixture/lamp
combination
proposed,
(2)
trial layouts with consideration
for
room
geometry
and
contents,
and (3)
consideration, per-
haps,
of
state lighting limitations.
For
even lighting
at
the
work plane, conform
to the fixture
manufac-
turer's designated spacing/mounting height limita-
tions
in
locating
fixtures.
Ensure that
fixtures are
accessible
for
cleaning
and
lamp changing.
9-8.
Power
Factor
Capacitors
are
used
to
correct
the
power factor,
as
computed
by
Equation 9-3.
Pf-
ac
tual
power (kW)
apparent power
(kVA)
active current
Q
=
=
cos0
total current
The
relationship between power, current,
and
power
factor
in
Example
9-8 is
shown
in
Figure 9-4.
Example
9-8
Power Factor
Relationship
Problem: Calculate
the
power, current,
and
power factor relationship
for
Pump
No. 1
(see
Example
9-1).
The
motor characteristics given
by the
manufacturer
are 25 hp, 460 V,
three
phase,
34 A, and
0.75
Pf.
Solution:
Use
Equations
8-4 and 6 to
calculate current
and
power values.
Active (true) power
=
P
3
^
=
j3V
L
I
L
Pf
=
73
x 460 x 34 x
0.75
=
20,300
W =
20.3
kW
Apparent power
=
«/3V
L
I
L
=
^3x460x34
=
27,100
VA =
27.1
kVA
Reactive power (see Figure 9-4a)
=
V27.1
2
-20.3
2
=
17.9
kV
AR
Correction
of
Power
Factor
Power company penalties
for low
power factor
can be
severe.
It is
often
economical
to
raise
the
power factor
to
meet
the
power company's minimum limit.
It is
nei-
ther economical
nor
necessary
to
correct
the
power
factor
to
1
.0,
but
raising
the
power factor
to
about 0.95
is
likely
to be
economical.
Example
9-9
Capacitor
Sizing
Problem: Calculate
the
capacitor sizes needed
to
raise
the
power factor
of the
pumping station
from
0.75
to
0.95.
Solution: From Example 9-1,
the
design amperage
is
187.5,
so the
normal operating station
load
is
V3(460)(
187.5
A)/1000
=
149.4
kVA . At the
present power
factor
of
0.75,
the
kilo-
watts
(kW) used
are
149.4
x
0.75
=
112.0
and the
reactive kilovolt-amperes
(kVAR)
are
V
(149.4)
-(112.0)
=
98.9
. The
vector diagram
of
power
is
shown
in
Figure 9-4b.
To
increase
the
system power
factor
to
0.95,
draw
the
vector diagram
of
Figure
9-4c.
The kVA
must
remain
constant. Therefore,
kW =
(cos9)(kVA)
=
(0.95)(
149.4)
=
141.9
and
kVAR
=
Locating
fixtures is
best done
by
drawing
the
room
to
scale,
making paper cut-outs
of the fix-
tures
to
scale,
and
moving
the fixtures
around until
the
best
effect
is
obtained. Assume
the
lamps
line
up
with
the
long dimension
of the
room. Then:
Transverse spacing
=
(2V
2
V(12
- 3) = 1.2 < 1.5 OK
Longitudinal spacing
=
[42
- (9 -
1)4]/(12
- 3) = 1.1 < 1.5
OK
Capacitors
Obtaining
satisfactory power factors
by
using capaci-
tors
is
preferable
to
using more expensive synchro-
nous
motors unless synchronous motors
are
otherwise
required. Switch
capacitors
with motors; that
is,
con-
nect
the
capacitors
to the
motor terminals
so
that both
units
are
switched
on at the
same time. Select capaci-
tors
to
supply approximately (without exceeding)
motor
no-load magnetizing current
or
nearly no-load
current.
If the
motor characteristics
are not
accurately
known
during design, check
the
shop drawings
or
confer
with
the
manufacturer
and
resize
the
capacitor
if
necessary.
Conductors
The
conductor ampacity should
not be
less than
135%
of
the
rated capacitor current,
nor
should
it be
less
than
one-third
of the
ampacity
of the
motor branch
circuit
conductors
(see
NEC
460-
8.
a).
9-9.
Engine-Generator
Sizing
Preliminary calculations
for
determining
the
engine-
generator size
are
shown
in
Example 9-10.
The final
size, however, should
be
determined
by the
manufac-
turer
based
on an
even more
careful
consideration
of
station
loading
and
starting requirements
and the
char-
acteristics
of the
generator
and
engine.
Figure 9-4. Vector diagrams
for
power
factor
correction,
(a)
vector diagram
symbols;
(b)
power
vector
diagram
with-
out
power
factor
correction;
(c)
power
factor
diagram
with
power
factor
correction.
V(
149.4)
-(141.9)
=
46.7
. The
rating
of the
capacitor must change
the
capacitance
from
98.9
to
46.7
kVAR,
so the
capacitor rating must
be
98.9
kVAR
-
46.7
kVAR
=
52.2
kVAR.
The
52.2
kVA is
based
on a
station load
of
187.5
A or
149.4 kVA. Because
it is not
econom-
ical
to
increase
the
power factor
to a
value greater than unity, less
kVAR
capacitor correction
should
be
connected
to the
system
at
reduced station load. Therefore,
it is
desirable
to
distribute
the
capacitors
to the
system loads
so
that,
as
system load
is
turned
on,
additional capacitance
is
also added.
The
pump motors
are
typically
the
largest loads
in a
pumping station,
so it is
often
advantageous
to
connect capacitors directly
to
each motor
so as to
switch them
on
with
the
motor. Calculations should
be
done
so
that
the
amount
of
capacitance
added
to
each motor does
not
correct
the
motor no-load power
factor
to
more than
unity.
Install
a
total
of 55
kVAR
capacitance distributed
as
follows:
Each motor:
15
kVAR,
Bus
capacitor:
10
kVAR
(but sized with care
to
make
up the
deficiency
after
motor capacitors
are
finally
chosen).
Example
9-10
Size
of the
Engine-Generator
Set
Problem:
Determine
the
generator
and the
engine power rating requirements
for the
entire
pumping
station described
in
Example
9-1.
Note that
as
more pumps come
on
line,
the
head
on
the
pumps increases,
but the
incremental
flowrate
decreases, with
the net
result that (for this
pumping
station)
one
pump operates
at
21.2
motor
hp, two
pumps operate
at
20.0
hp
each,
and
three pumps operate
at
18.4
hp
each.
Solution:
At
full
load,
the
power
factor
of a
720-rev/min
motor
is
about
0.75,
but
adding
capacitors
to the
circuit,
as
shown
in
Example
9-9,
increases
the
power factor
to
0.95.
The
locked-rotor
power factor
of a
standard
1800-rev/min,
25-hp motor
is
0.44,
and for a
720-rev/
min
motor,
the
power factor
is
estimated
to be
0.40.
The
addition
of a
15-kVAR
capacitor
(Example
9-9)
would have little
effect
on the
locked-rotor power factor. Starting
a
Code
F
motor
requires
5.3
kVA
for
each horsepower.
In
Example
9-1,
the
essential loads
on the
generator
for
heating
and
ventilating
are 5 A in
the
pump room
and 3.5 A in the wet
well. During
a
power outage, lighting
can be
restricted
to
11
A. The
sump pump
and
instrument
air
compressor consume
1 A
each,
but
these loads
can
be
ignored during motor start-up because they
are
small, intermittent,
and not
likely
to
exist
during
the
worst-case inrush, which persists only momentarily. Hence,
the
total load with
no
pumps
operating
is 5 + 3.5 +
11
=
19.5
A.
Because personnel discomfort during power
out-
ages
can be
acceptable,
but
freezing (even
of
small pipelines such
as for
seal water supply)
cannot,
it may be
necessary
in
very cold climates
to
include some
of the
heater loads
in the
sizing
calculations.
Starting
Running
Item
kVA
kW~
kVA
kW~
Ventilation
and
lighting (V&L)
loads
19.5
x
460^3/1000
15.5
15.5/0.95
Pf
16.3
Start
first
pump
25
hp x 5.3
kVA/hp
132.5
132.5kVAx0.40/>/
53.0
Add
V&L
loads
16.3 15.5 16.3 15.5
Total
148.8 68.5 16.3 15.5
Run
first
pump
at
21.2
motor
hp
21.2
hp x
0.746
kW/hp
(1/0.88
efficiency
a
)
18.0
18
kW
at
0.95
Pf
18.9
Add
V&L
loads
16.3 15.5
Total load
35.2 33.5
Start second pump
25
hp x 5.3
kVA/hp
132.5 53.0
Run
1st
pump
and
V&L
35.2 33.5 35.2 33.5
Total
167.7 86.5 35.2 33.5
Run
2
pumps
at 20
motor
hp
each
20
hp x 2 x
0.746
kW/hp
(1/0.88
efficiency
3
)
33.9
33.9
kW at
0.95
Pf
35.7
Add
V&L
loads
16.3 15.5
Total load
52.0 49.4
Start third pump
25
hp
x
5.3
kVA/hp
132.5 53.0
Run
2
pumps
and V&L
52.0 49.4 52.0 49.4
Total
184.5 102.4 52.0 49.4
The
calculations
for
Example
9-10
are
typical,
but
maximum
flow
might
be a
rare occurrence
of
short
duration,
and the
diversity
of
loads (the probability that
all
demands
may not
occur
at the
same time)
can
often
reduce
a
power requirement.
On the
other hand, some
heating
might
be
required.
A
more extensive analysis
might
result
in a
different
engine-generator unit.
A
typ-
ical engine-generator
set is
shown
in
Figure 9-5.
9-10.
Short
Circuit
Current
Calculations
The
purpose
of
short circuit current calculations
is to
find the
maximum current available under short circuit
conditions
at
each required location
and to be
certain
that
the
circuit interrupting devices (circuit breakers
and
fuses)
have
the
ability
to
interrupt this level
of
current.
It is
also important
to be
certain that other
devices required
to
carry this high level
of
current
have
appropriate withstand ratings
so
that
the
device
will
not
fail
at the
current level. Except
in
some
medium-
voltage
circuits with
local
on-
site
generation,
the
maximum available short circuit current would
occur
if all
phases
or
lines were connected together.
A
preliminary calculation
is
needed during design
for
properly sizing, rating,
and
specifying equipment.
The
designer must
use the
best available data
in
mak-
ing
this calculation, although
the
equipment
manufac-
turer
and the
exact data
may be
unknown.
If
the
expected
fault
currents approach equipment
interrupting
and
withstand ratings (typically
22,000
A
at
480 V), a final
calculation
is
made during construc-
tion
to
verify
the
equipment ratings
and set
adjustable
overcurrent
protective devices. This work
is
often
done
by the
equipment supplier using
a
computer
for
speed
and
accuracy. Make sure that
the
specifications
detail this requirement properly. Spot check
the
calcu-
lations
to
ensure that
the
proper
field
data
are
used.
Fault
(Short
Circuit)
Current
Magnitude
The
magnitude
of a
fault
current depends primarily
on
the
capacity
of the
supply system,
but
on-site
Starting
Running
Item
kVA
kVV~
kVA
kw"
Run
3
pumps
at
18.4 motor
hp
18.4
hp x 3 x
0.746
kW/hp
(1/0.88
efficiency
3
)
49.3 46.8
Add
V&L
loads
16.3 15.5
Total load 65.6 62.3
a
Efficiency
for
high-efficiency
motors
is
about
92 to
94%.
The
critical generator loads
are the
kilovolt-amperes
and
kilowatts
for
starting
the
third
pump.
During
the
start,
the first two
running motors
can act
momentarily (for half
a
cycle)
as
generators and, hence, reduce
the
demand
on the
generator,
but the
effect
lasts much less than
a
second
and is
difficult
to
assess,
so the
effect
is
ignored, especially
as it may
take
up to 6 s to
start
the
third pump.
Because
the
calculated size
of the
generator
is
184.5 kVA,
specify
a 200 kVA
standby
duty
rating.
The
future
flow of
4500
gal/min
requires about
15%
more horsepower,
but
only about
5%
more generator output because
the
inrush current
for the
25-hp
motor does
not
change.
Therefore,
a
200-kVA generator would
be
adequate.
The
engine
can be
sized
on the
basis
of
running power, partly because
the
inertia
is so
great
that
the
engine will maintain
its
speed during
the few
seconds
of
high inrush current
and
partly
because
the
engine
can be
overloaded
for a few
seconds.
Size
of
engine
=
—
62
'
3
kW
ff
.
.
=
73.3
kW
=
98.2
hp
0.85 generator
efficiency
Use an
engine
of not
less than
100 hp
(continuous duty rating).
This approximate analysis
may be
refined
by
methods explained
in
manufacturer's literature
[3],
but
always
confirm
engine-generator
size calculations
with
the
manufacturer.
Manufacturers
may
calculate required engine
and
generator size somewhat
differently,
so
supply
all of the
worst-case
figures.
Also supply generator site, altitude,
and
ambient temperature because these
affect
the
generator rating.
motors
and
generators
can
contribute
to the
fault
cur-
rent.
In
Figure
9-1,
the
characteristics
of
each con-
tributor
are:
•
Utility.
The
fault
current magnitude
is
assumed con-
stant
during
the
fault
period.
•
Local generators
are not
usually
on
line
in
pumping
stations.
If
they are,
the
magnitude
of the
fault
cur-
rent decreases during
the
fault
period. Practically,
the
fault
current
may be
assumed
to be
constant
in
low-voltage systems.
•
Synchronous motors
act as
synchronous generators
driven
by
load
and
rotor inertias.
The
fault
current
magnitude
decreases substantially during
the
fault
period.
•
Induction motors. Current
is
generated while
the
magnetic
field is
present.
The
induction
motor's
field
decreases rapidly when
the
driving voltage
drops
to a
small value
(as in a
fault
or
when
the
con-
tactor
or
circuit breaker opens).
The
fault
current
magnitude
is
initially about that
of the
locked rotor
current,
but it
decreases
rapidly, usually over
a few
cycles.
If the
running power factor
is
corrected
to
near unity,
the
magnitude
may not
decrease
as
expected
due to
self-excitation.
The
total
or
asymmetrical
fault
current
is
com-
posed
of an ac
component plus
a
decaying
dc
compo-
nent.
The
initial magnitude
of the dc
component
depends
on the
circuit reactance/resistance
(X/R)
and
on the
instantaneous voltage
of the
faulted phase
at
the
instant
the
fault
occurs.
To
allow
for the dc
com-
ponent, multiply
the
symmetrical value
by 1.6
(for
high-
voltage
fused
starters, current-limiting
fuses,
and
circuit breakers)
or by
1.25 (for low-voltage
fuses).
It
is the
asymmetrical current that must
be
inter-
rupted
by
low-voltage breakers
and
fuses
due to
short
(e.g.,
1.5
cycles) interrupting times. Low-voltage
breakers, however,
are now
rated
in
symmetrical cur-
rent,
so the
asymmetrical current need
be
computed
only
for
fuses.
Medium-
voltage
breakers
and
fused
switches
have both withstand
and
interrupting ratings
(which
are
lower
due to
their longer interrupting
times),
so the dc
decay must
be
taken into account.
For
sample calculations, consult
the
literature
[4, 5,
6].
Figure
9-5.
Atypical
engine-generator set. Courtesy
of
Waukesha Engine Div.,
Dresser
Industries,
Inc.
Coordination
A
coordinated system
is one in
which
the
overcurrent
devices
are
rated
and
adjusted
so
that
the
device just
ahead
of a
fault
will
safely
clear
the
fault,
dropping
only
the
downstream part
of the
circuit.
If
that device
should
fail
to
clear
a
fault,
the
next upstream device
will
clear
after
a
suitable time delay
to
give
the
proper
device
a
chance
to
operate.
In a
coordinated system,
the
withstand ratings
of
equipment
and
cable
are
suit-
able
for
withstanding
fault
currents
for the
time
needed
to
clear
the
fault
without damage
to the
insula-
tion
(see
the UBC for a
detailed discussion).
9-11.
Harmonics
In
pumping stations with adjustable frequency drives,
excessive harmonic contribution
to the
electrical
power
system must
be
prevented. Where
the
adjust-
able
frequency
drive load exceeds
25% of the
station
load
or
where adjustable
frequency
drives must
be
powered
by an
engine-generator,
a
harmonic calcula-
tion
should
be
made
and
suitable
filtering
specified.
IEEE
519
explains
how to
make harmonic calcula-
tions
and
specifies
harmonic current limits
for
systems
connected
to
electric power utilities. Where adjustable
frequency
drives
are to be
powered
by an
engine-gen-
erator, consult
the
manufacturer regarding
limits
for
that
specific
equipment.
Power
factor
correction capacitors must
not be
connected
to
power systems with
a
harmonic voltage
distortion
in
excess
of 5%
without suitable
filters
that
exclude harmonic currents
from
the
capacitors.
Past practice
in the
industry
has
been
to
make
the
drive vendors responsible
for
harmonic calculations.
As
with short circuit calculations discussed
in
Section
9-10,
harmonic calculations
are
best performed using
suitable
computer software.
9-12. Construction Service
A
thorough review
of all
submitted material
is a
time-consuming, unpopular,
and
unrewarding task,
but it is
vital.
Shop
Drawing
Review
The
shop drawing review
is the
last chance
to
make
a
design change
at a
reasonable cost. Once construction
has
begun, changes
are
very expensive.
Allow
no
deviations without good reason
and
with-
out
a
reduction
in the
contract
price.
Document
all
revisions,
and
keep
the
project manager
and
contrac-
tor
fully
aware
of all
conversations with suppliers that
result
in any
revisions.
Obtain
and
review
the
electrical
portions
of
sub-
mittals under other specification sections such
as
mechanical, process,
or
instrumentation.
Submittal
Checklist
Check submittals
for
conformance
to the
drawings,
specifications,
applicable codes, addenda,
and
change
orders. Checks
of the
following elements
are a
mini-
mum:
•
Voltage, phases,
and
other nameplate data
•
Control (schematic) diagrams
•
Wiring
and
interconnection wiring diagrams
•
Control
and
alarm interfaces with other equipment
•
Components
•
Wiring details
•
Inclusion
and
acceptability
of
required factory test
reports.
Release
the
generator shop drawings
to the
general
contractor only
after
including
the
following warning:
"Accepted
pending verification that
you
have coordi-
nated
the
generator sizing with your pump
and
motor
suppliers."
If the
warning
is not
included,
the
station's
generator will
be
inadequate
if the
motor size
is
increased.
Inspection
Adequate inspection
is
required
to
assure
the
owner
and
authorities that
the
construction meets code, spec-
ification,
and
drawing requirements,
so
several inspec-
tors, including city/county personnel
in
addition
to the
resident inspector
or
engineer,
are
likely
to
visit
the
job
site.
The
designer should make spot checks,
and
there should
be a final,
detailed inspection.
The
fol-
lowing
are
suggestions
for the
resident
inspector:
• Be as
thorough
as
time allows. Have
the
contractor
make
the
interiors accessible
for
inspection
and
observe
the
interior
of as
much equipment
as
possi-
ble. Note
the
condition
of
workmanship
as
well
as
conformance
to
drawings.
•
Check
all
work against drawings, specifications,
addenda, change orders, shop drawings,
and
codes.
•
Make
a
written record
of
each deviation, whether
it
is
to be
corrected
or
left
as is, and
give
the
record
to
the
project manager
for
transmittal
to the
contractor.
Tests
This
section
is
limited
to
electrical
system
tests.
Factory
Tests
Require
the
following
factory
tests:
•
Switchboard: Test
per
NEMA Standard PB2.
•
Motor control center: Test
per
NEMA Standard
ICS.
•
Transformer,
oil
filled: Test
per
ANSI
C57.
12.90.
•
Standby generator:
Run the
unit
at the
rated load
and
power
factor
for at
least
2 hr to
demonstrate
set
performance;
require
the
contractor
to
provide
a
load bank suitable
for
continuous duty, full-load
operation
of the
engine-generator,
and
require com-
plete mechanical
and
electrical records
and
fully
describe witnessed testing.
•
Automatic
transfer
switch: Test
for
proper operation
in
all
modes.
Field
Tests
The
following
tests
are
required:
•
480
-V
wiring: With contactors closed, measure
and
record
the
insulation resistance
to
ground. Motors
may
be
connected.
Do not
record
or
accept
"infin-
ity."
Use a
500-V
"megger"
(megohm meter).
•
480-V
motors
and
230-V
main pump motors:
Sepa-
rately measure
and
record
the
insulation resistance
to
ground.
Do not
record
infinity.
Reject
any
mea-
surements
below
1
MQ
.
Use a
500-V
megger.
•
Circuit breaker solid-state
trip
units: Have
an
inde-
pendent,
factory-certified
testing organization
field
test
and
certify
accuracy, operation,
and
adjustment.
•
Power sources: Check
the
voltage
at the
service,
at
the
lighting transformer,
and at the
generator termi-
nals
for
amplitude
and
balance (loaded
and
unloaded).
If the
voltage
is not
within
5% of
nomi-
nal or if the
unbalance exceeds
1%,
notify
the
power
company,
adjust
generator voltage regulator,
or
reconnect taps
as
applicable.
•
Tighten
all
electrical connections: Note that circuit
breakers inherently protect against single phasing
except
in the
case
of a
loose connection.
•
Motor phase currents: Measure these currents
for
each pump motor
at
full
load
and
check
for
over-
loading
and
imbalance. Note that
a 1%
voltage
imbalance will cause
an
approximately
8%
current
imbalance. Excessive current imbalance will cause
motor overheating. Consult with
the
equipment
supplier when
in
doubt.
•
Motor
and
generator rotation: Correct rotation,
if
necessary,
by
interchanging
any
two-line conduc-
tors
on
three-phase units.
•
Operational test: Take nothing
for
granted. Check
and
test everything
for
proper operation: prevention
of
single phasing, lights, GFCI outlet circuit protec-
tion, each mode
of the
automatic transfer switch,
standby
generator alarms
and
shut-downs, motor
space heaters, etc.
•
Motor protection list: Record
the
following data
and
verify
correctness
to
ensure proper motor pro-
tection
for
each motor
on the
job:
(1)
Unit name
or
designation
(2)
Motor nameplate data (horsepower, voltage,
service
factor,
current,
and
temperature rating)
(3)
Circuit breaker
or
fuse
rating
(4)
Circuit breaker setting,
if any
(5)
Starter size
(6)
Overload relay manufacturer
and
heater catalog
number
(7)
Capacitor size,
if
any.
Obtain
a
copy
of the
overload relay manufacturer's
heater table with instructions
for
selecting heaters.
Check each motor branch circuit
for
proper protection
and
adjustments.
9-13.
References
1.
CSI
Documents
MP
-2-1,
Master Format, Master List
of
Section
Titles
and
Numbers (1983 ed.)
andMP-2-2
Section
Format (1981
ed.),
The
Construction Specifications
Institute, Alexandria,
VA.
2.
Kaufman,
J.
E.,
and H.
Haynes
(Eds.),
IES
Lighting
Handbook, Illuminating
Engineering
Society
of
North
America,
New
York
(1981).
3.
Generator
Set
Sizing Guide, Bulletin
LE BX
6220.
Caterpillar
Inc.,
Peoria,
IL.
4.
Short-Circuit Current Calculation,
General
Electric
Co.,
Schenectady,
NY.
5.
IEEE
Standard
242-1975,
Recommended Practice
for
Protection
and
Coordination
of
Industrial
and
Commercial Power Systems,
The
Institute
of
Electrical
and
Electronic
Engineers,
Inc.,
Wiley-lnterscience,
Piscataway,
NJ
(1976).
6.
IEEE
Standard
141-1976,
Recommended Practice
for
Electric
Power
Distribution
for
Industrial
Plants,
The
Institute
of
Electrical
and
Electronics
Engineers,
Inc.,
Wiley-lnterscience,
Piscataway,
NJ
(1976).
The
purpose
of
this chapter
is to
introduce those fun-
damentals
of
centrifugal pump theory that
are
useful
for
background
and
sometimes necessary
for
selecting
and
specifying centrifugal pumps
in
water
and
waste-
water
pumping applications.
A
corresponding body
of
theory
for
positive-displacement pumps
can be
found
in
the
literature
[1,2,3].
This introduction includes
(1) the
general
classifi-
cations
of
centrifugal pumps,
(2)
pump application
terminology
and
usage,
(3)
pump operating character-
istics,
(4)
cavitation
and net
positive suction head,
(5)
pump characteristic curves
and
operating
ranges,
and
(6)
an
introduction
to
pumping system analysis.
1
0-1
.
Classification
of
Centrifugal Pumps
In
colloquial usage
in the
United States,
a
"centrifugal
pump"
is any
pump
in
which
the fluid is
energized
by
a
rotating impeller, whether
the flow is
radial, axial,
or
a
combination
of
both (mixed). Strictly
defined
(as in
European practice),
a
centrifugal pump
is a
radial-flow
pump only.
But
colloquial usage
is
followed here,
and
thus
centrifugal pumps
are
divided into three groups:
•
Radial-flow pumps
•
Mixed-flow pumps
•
Axial-flow
or
propeller pumps.
Chapter
1
0
Performance
of
Centrifugal Pumps
GEORGE
TCHOBANOGLOUS
CONTRIBUTORS
Richard
O.
Garbus
Robert].
Hart
Carl
W. Reh
Lowell
G.
Sloan
Earle
C.
Smith
These
classifications
are
derived
from
the
manner
in
which
the fluid
moves through
the
pump (see Figure
10-1).
Thus,
the fluid is
displaced radially
in a
radial-
flow
pump, axially
in an
axial-flow pump,
and
both
radially
and
axially
in a
mixed-flow pump.
The
physi-
cal
features
of
centrifugal pumps
are
described
in
detail
in
Chapter
1
1
.
10-2.
Pump Application Terminology,
Equations,
and
Performance Curves
The
basic terminology, equations,
and
curves
for
defining
pump performance
and
solving pump prob-
lems
are
given
in
this section.
The
development
of the
pump performance curves, which
are
used
to
define
the
operating characteristics
of a
given pump,
is
reviewed
briefly
at the end of
this section (this subject
is
covered
in
more detail
in
Chapter
12).
Capacity
The
capacity
(flowrate,
discharge,
or Q) of a
pump
is
the
volume
of
liquid pumped
per
unit
of
time, usually
measured
in SI
units
in
cubic meters
per
second
for
large pumps
or
liters
per
second
and
cubic meters
per
hour
for
small pumps.
In
U.S. customary units,
the
capacity
of a
pump
is
expressed
in
gallons
per
minute,
million gallons
per
day,
or
cubic
feet
per
second.
Equivalent
units
of
measurement
are
given
on the
inside back cover
and in
Appendix
A.
Head
The
term head
(h or H) is the
elevation
of a
free
sur-
face
of
water above
(or
below)
a
reference datum (see
Figures 10-2
and
10-3).
For
centrifugal pumps,
the
reference
datum varies with
the
type
of
pump,
as
shown
in
Figure
10-1.
In
accordance with
the
standards
of the
Hydraulic
Institute [1], distances (heads) above
the
datum
are
considered positive
and
distances below
the
datum
are
considered negative. Each term,
defined
graphically
in
Figures
10-2
and
10-3,
is
expressed
as the
height
of a
water
column
in
meters (feet)
of
water.
H is
used
for
total head, whereas
h is
used
for
head
from
the
datum
or for
headloss.
The
subscripts
s and d
denote
the
pump
suction
and
discharge, respectively. Other sub-
scripts
are
defined
as
follows:
Total
static head
(#
stat
):
The
total static head
is the
difference
in
elevation
in
meters (feet) between
the
water
level
in the wet
well
and the
water level
at
dis-
charge
(h
d
-
h
s
).
Static
suction
head
(h
s
):
The
static suction head
is
the
difference
in
elevation between
the wet
well liquid
level
and the
datum elevation
of the
pump impeller.
If
the wet
well liquid level
is
below
the
pump datum,
as in
Figure 10-3,
it is a
static suction
lift,
so
/i
s
is
negative.
Static discharge head
(h
d
):
The
static discharge
head
is the
difference
in
elevation between
the
dis-
charge liquid level
and the
pump datum elevation.
Manometric
suction head
(h
gs
):
The
suction gauge
reading
is
expressed
in
meters
(feet)
measured
at the
Figure 10-1. Typical
flow
paths
in
centrifugal
pumps,
(a)
Radial
flow,
vertical;
(b)
mixed
flow;
(c)
radial
flow,
hori-
zontal;
(d)
axial
flow.