Pumping Station Desing - Second Edition by Robert L. Sanks, George Tchobahoglous, Garr M. Jones

to

accidental

flooding. Wet

wells

are

even more subject

to flooding,

and,

in

addition, they

are

generally classified

as

hazardous areas because

of the

high probability

of a

large

concentration

of

methane

or

other explosive gasses

resulting

from

accidental

or

illegal dumping

of

gasoline

and

solvents into

the

sewer system.

Avoid

placing junction boxes

in wet

wells

(or in

any

other other moisture-laden locations)

by

making

a

concerted

effort

to

feed

electrical systems

from

junc-

tion boxes

in dry

locations through conduit sealed

at

the

entry into

the

hazardous area.

But if

there

is no

alternative,

specify

nonwicking cable, watertight

motor

and

device terminations,

and

junction boxes

filled

with

a

waterproof sealant.

The box

itself must

be

rated

as

waterproof when properly installed.

One

example

of the

need

for a

junction

box in a

wet

well occurs

in

pumping stations with submersible

pumps

fed by

portable cables.

A

junction

box is

nec-

essary

to

transfer

from

the

normal branch circuit con-

ductors

to the

heavy-duty

flexible,

multiconductor

cable

to the

submerged motor.

One

solution

is to

mount

the

junction outside

the wet

well

and

feed

the

cable into

the wet

well through

a

sufficiently

large

conduit.

Switchgear

and

Switchboards

"Switchgear"

as

defined

in

ANSI

141 is a

general term

covering switching

and

interrupting

devices

alone

or

in

combination with other associated control, meter-

ing,

protective,

and

regulating equipment.

Metal-enclosed switchgear provides sheet metal

covering

on all

sides

and top

with access

via

doors

and/or removable panels. Other classifications

are

indoor, outdoor,

and

walk-in with

an

enclosed mainte-

nance aisle,

as

defined

in

ANSI

141.

Further

classifi-

cation

provides

for

metal-clad switchgear that meets

a

number

of

specific

safety

requirements

and is

usually

applied

to

systems operating

at

1000

V or

more.

Switchboards

are not

defined

in

ANSI

141

but,

although

of

open construction,

may be

provided with

equipment similar

to

that included

in

switchgear.

Modern switchboards

are of

dead-front construction

(no

live parts exposed)

for

operator

safety

and to

meet

NEC

requirements. Switchboards

are

usually

an

assembly

of

molded-case

circuit breakers, whereas

switchgear

is

ordinarily

a

grouping

of

power circuit

breakers

and may

include large motor starters. Incom-

ing

and

outgoing line-termination space must

be

pro-

vided,

with particular attention

to the

required

minimum

bending radius

of

large-diameter power

cables. Buswork must

be

braced

for the

calculated

maximum

fault

current

and the

structure must

be

rated

for

the

prevailing seismic conditions.

Service

Entrances

Every

building supplied with electricity directly

from

an

electric utility must have

a

UL-listed

service

entrance.

A

service entrance usually consists

of a

util-

ity-owned kilowatt-hour meter,

any

current

or

potential

transformers

(usually utility-owned),

and a

disconnect

consisting

of a

fused

switch

or a

circuit breaker.

The

neutral,

if

grounded,

is

grounded

on the

utility side

of

the

disconnect. Service entrance equipment, including

the

meter sockets

and

instrument transformer provi-

sions, must conform

to

utility requirements.

Meter

and

disconnect locations vary.

For

maximum

security,

both should

be

indoors,

but

utility

and

local

regulations

may

dictate otherwise

and

must

be

fol-

lowed. Sometimes other arrangements

can be

made.

A

second building

or

structure

on the

same pre-

mises

and

under

the

same management must also have

a

UL-listed service disconnect. Neutral grounding

can

be at

either

building.

Equipment

Installation

All

electrical equipment must

be

equipped

and

installed

per the

NEC.

Sufficient

access

and

working

space

is

required

for

ready

and

safe

access

for

mainte-

nance. Minimum working space

in

front

of

electrical

enclosures

not

requiring rear access

and

facing

metal

or

concrete

walls

is

shown

in

Table 8-5. Illumination

is

required

for all

working spaces.

At

least

one

adequate entrance must

be

provided

for

access

to the

working space

in

front

of

electrical

enclosures.

A

continuous passageway

is

usually

suffi-

cient.

For

equipment over

1.8 m (6 ft)

wide rated

1200

A

or

more

and 600 V or

less,

and for all

equipment

over

600 V and 1.8 m (6 ft)

wide,

two

entrances

at

least 0.61

m (2 ft)

wide

and

1.91

m

(6.25

ft)

high

are

required

—

one

at

each end.

If,

however,

the

depth

shown

in

Table

8-5 is

doubled, only

one

entrance

is

Table

8-5.

Minimum

Working

Space

in

Front

of

Electrical

Enclosures

Nominal

Dimensions,

m

Dimensions,

ft

voltage

to

ground

Depth

3

Width

Height

Depth

3

Width

Height

0-150

0.92 0.76 1.91

3.0 2.5

6.25

151-600

1.07 0.76 1.91

3.5 2.5

6.25

601-2500

1.22 0.92 1.98

4.0 3.0 6.5

2501-9000

1.53 0.92 1.98

5.0 3.0 6.5

a

Or

more

if

required

for the

access doors

to

swing

90°.

required,

but the

edge

of the

entrance nearest

the

enclosure must equal

the

depth shown

in the

table.

8-4.

Standby

Generators

and

Auxiliaries

Standby

generators

and

their auxiliary equipment

are

needed

in

many

pumping stations. Permanently installed

units

may be

required

by

state

or

local laws

or

regulations,

or

they

may be

included

in the

station design because

of

the

critical

nature

of the

station, probability

of

loss

of

util-

ity

power,

or the

owner's

or

engineer's standards.

Portable generators provided

with

cord

and

plug

connections

are

often

used

for

backup power

for

small

"package"

pumping stations,

and

trailer-mounted

engine-alternators

of up to

several hundred kilowatt rat-

ings

have

been cord-connected with suitably rated

cables

and

power plugs

to

serve medium-sized pumping

stations

during power outages. Bear

in

mind, however,

that

power outages occur

in

stormy weather that

may

make

it

difficult

to

reach

a

station,

and if the

power out-

age

covers

a

wide area,

many

portable units would

be

required. Distance

and

time

of

response must also

be

considered. Finally, consider that legislation

now

allows

competition between electric power

suppliers

—

a

policy

that

will inevitably lead

to

less reliable power because

of

the

need

to

reduce costs

to be

competitive. Thus,

the

need

for

standby generators

is

likely

to

increase.

Codes

and

Legal

Requirements

Generators

in

pumping stations

are

installed

in

accor-

dance

with

NEC

Article 701, Legally Required

Standby

Systems,

or

Article 702, Optional Standby

Systems.

If a

local code requirement seems

to

require

Article 700, Emergency Systems,

be

sure

to

negotiate

a

change

with

the

authorities,

and

never call

the

gener-

ator

an

"Emergency

Generator,"

because pumping sta-

tion

applications

in no way

involve

life

safety.

Use

Article 702,

if

possible,

due to its

minimal require-

ments

and flexibility of

operation.

Use

Article

701

only

in

case

of a

legal requirement

to do so. See

Arti-

cle

701-2 (FPN), which refers

to

sewerage disposal

and

fire fighting

applications,

but

take into account

the

wet

well

or

clear well storage capacity, including

any

available storage

in

upstream piping.

Ratings

Continuous

Rating

Two

nameplate ratings

are

offered:

prime

and

standby.

The

prime rating

is

that rating

at

which

the

engine-gen-

erator

set is

suitable

for

continuous operation

at

rated

conditions.

The

standby

(or

continuous standby) rating

is

defined

as

that rating

at

which

the

generator

set is

suitable

for

continuous operation

for

only

30

days

at

the

rated conditions. Continuous operation

at the

standby

rating causes relatively high temperatures that

age the

generator insulation

4 to 8

times

faster

than

at

the

prime rating. This aging

is not

considered serious

for

a

standby generator because

of its

limited use.

Refer

to

Chapter

14 for

engine ratings.

Motor-Starting Rating

Motor-

starting

ratings

are

limited

by

either

the

engine

or the

generator.

The

engine must supply

the

shaft

power required

by the

actual maximum load applied

to

the

generator.

The

generator size

is

normally cho-

sen to

match

the

engine output capability. Selecting

an

oversized generator where motor-starting

kVA

demands

are

high, however,

may be

advantageous.

The

running load

and the

motor-

starting

requirements

should

be

specified.

The

largest motor should

be

started

first, if

possible. Consult

the

manufacturer

for

selection

and

sizing

of the

engine-generator set.

A

30%

voltage

dip at

motor start

is

usually

tolerable,

but

20%

is a

more common design parameter

to

prevent

contactor opening.

When specifying

a

generator

for use

with AFDs,

require

the

generator supplier

to

work with

the

drive

supplier

to

ensure that

the

generator

is

suitable

for the

application. Loads with harmonic current content over

about

10% of the

generator rating cannot

be

supplied

by

standard generators.

Fault

Rating

With

a

brushless exciter whose

output

is

dependent

on

terminal voltage,

the

worst event

is a

three-phase

bolted

fault

(three-phase line-to-line short)

at the

gen-

erator terminals, because (with greatly reduced exci-

tation)

the

terminal voltage collapses

to a low

value

and

cannot supply

sufficient

fault

current

to

trip

the

breaker

on the

faulted

circuit. Field-forcing equip-

ment should

be

specified

to

sustain

the

rated excita-

tion

and

current

up to

three times

the

generator's

rated current

output

—

sufficient

fault

current

to

trip

the

generator

breaker.

Ensure that downstream

and

generator circuit breakers

are

coordinated

so

that

the

branch circuit breaker trips

first.

An

undervoltage

relay

is

recommended

for any

generator unit, large

or

small.

It is

actually

a

voltage-

restrained

overcurrent

relay that

has a

current setting

low

enough

to

trip breakers

and

shut down

the

engine

if

overcurrent

at

less than

full

voltage occurs

for a

pre-

determined length

of

time.

Derating

Refer

to

Section 14-6

for

derating engines

for

eleva-

tion

above

sea

level

and for

temperature. Derate

the

generator

1%

for

each

100 m

(3%/1000

ft)

above

900

m

(3000

ft).

Engine-Generator

Controls

The

engine instrument panel should never

be

mounted

on

the

engine

or on the

engine pad, because engine

vibration causes instruments

to

deteriorate.

The

instru-

ments

for the

engine should include:

• Oil

pressure

• Oil

temperature

•

Water temperature

•

Intake manifold pressure

and

vacuum

gauges

—

especially

for

large units.

A

battery-charging alternator

and

ammeter should

be

included. Require

safety

controls

for

engine shut-

down

to be

manually reset. Such controls should

include:

•

High water temperature

• Low oil

pressure

•

Overspeed.

The

following instruments

and

controls should

be

mounted

on the

generator control panel:

• An

ammeter with current transformers,

as

needed

• A

voltmeter with potential transformers,

as

needed

• An

ammeter/voltmeter phase selector switch

• A

frequency meter

(45 to 65 Hz)

• A

voltage-adjustment rheostat

• An

elapsed-time

meter

• An

annunciator

or

monitoring panel with

fault-

indicating

lights

for low oil

pressure, high water

temperature, overspeed, overcrank,

and

generator

undervoltage.

Standard annunciator panels

may be

specified

to

perform

all the

foregoing functions,

and

they usually constitute

a

much more economi-

cal

system than

a

hard-

wired

custom alarm system.

• A

fault

reset pushbutton

• A

generator output circuit breaker

• A

three-position

(manual-off-auto)

selector switch

• An

engine-start switch

• An

emergency stop pushbutton

• A

voltage regulator

• An

indicating-light test pushbutton.

Actuating

the

safety

devices must shut down

the

generator set, indicate

the

cause

of the

shut-down

by

lighting

the

appropriate indicating light,

and

provide

separate outputs

for the

remote alarm indication panel

and

the

computer.

Automatic

Transfer

Controls

Code

Requirements

Automatic transfer controls,

per NEC

701-7 (1981),

are

needed

for

legally required standby systems.

The

interconnection

of

normal

and

standby power sources

should

not be

possible

in any

mode

of

operation,

except where parallel operation

is

intended

and

suitable

automatic

or

manual synchronizing equipment

is

pro-

vided

per NEC

230-83.

In

pumping stations, automatic

transfer

control equipment

is

commonly installed,

except where portable generator sets

are to be

used.

Manual

Transfer

Switches

Manual

transfer switches

are

sometimes used with por-

table generating equipment.

Use

kVA-

(horsepower-)

rated, quick-make/quick-break, heavy-duty switches

or

mechanically interlocked circuit breakers.

If the

trans-

fer

switch

is

part

of the

station service equipment,

it

must

be

UL-listed

as

service equipment

or

better,

and it

must

have

a

separate UL-listed service disconnect (cir-

cuit

breaker) ahead

of it in a

separate enclosure.

Automatic

Transfer

Switches

(ATS)

Complete automatic transfer switches

are

available

in

suitable enclosures (e.g., NEMA

1) as

well

as in

open

style

for

installation

in

motor control centers. They

must conform

to all of the

requirements

of UL

1008

and

be so

listed

and

labeled. Bypass isolation switches

(that

allow

the ATS to be

removed

for

repairs)

are

desirable

for

avoiding shutdowns

for

repairs.

Automatic transfer switches include

a

switching

element, relays,

and

controls

and are

available

in

these

forms:

•

Molded-case

circuit breakers

•

Contactors

•

Double-throw switches.

Automatic

transfer switches should have

the

follow-

ing

ratings:

•

Continuous rating, which

is the

current rating

on a

24-hr basis.

•

Inrush rating, which

is the

ability

to

close

a

circuit

with

high inrush currents with minimum contact

bounce

and

welding.

•

Interrupting rating, which

is the

load- (not necessar-

ily

fault-)

interrupting ability under

the

worst condi-

tions, e.g., locked rotor currents that occur when

the

motor rotor

is

locked

in

place due, say,

to a

clogged

pump.

•

Withstand rating, which

is the

ability

to

withstand

the

thermal

and

magnetic

effects

of

downstream

faults.

Automatic

transfer

switches should include

a

pause-in-neutral

position (with

an

adjustable time

delay that should

be set for

several seconds) that

causes

the

motor

to be

disconnected

from

the

power

source during

transfer

and

allows

the

motor voltage

to

collapse

to a

safe

level prior

to

re-energization. Failure

to

allow

the field to

collapse

can

result

in the

motor

field

being

out of

phase with

the new

power source

(which

may

well occur when transferring

from

a

standby

generator

to the

power utility).

This

out-of-

phase condition

can

instantly destroy

the

motor

by

breaking

the

shaft

or

tearing

out the

windings.

Because

the

pause-in-neutral

feature

may be

unavail-

able (and adds complexity

and

reduces reliability),

consider other methods such

as

motor shut-down

before

transfer

and an

in-phase monitor relay.

Batteries

Starting

batteries

for a

standby generator

are

ordinarily

lead-acid type with heavy-duty ratings. Cranking bat-

teries

for

moderate-sized generators

are

usually size

4D or 8D

diesel starting types.

These

may be

series-

connected

for

voltages greater than their

12-volt

nominal rating. Cranking

batteries

should

be

located

as

close

to the

engine

as

possible

—

many

times

on a

rack that

is

engine-mounted. Cranking currents

up to

1000

A are not

uncommon.

It

is

recommended that

the

batteries

be

specified

as

part

of the

engine-generator package, with

the

specifi-

cations written

to

give

the

manufacturer some

free-

dom in

sizing, while making certain that cranking

capacity

is

adequate

for ten

attempts

at

starting

and

that

the

batteries

are of the

highest quality. Failure

of

an

engine

to

start

is

usually

a

simple problem (e.g.,

fuel

not

reaching

the

cylinders),

but one

that cannot

be

resolved

by

remote control. Three failures

to

start

should

shut

down

the

system

and

generate

an

alarm.

After

the

operator

has fixed the

problem, enough

cranking power must remain

for a

start with certainty.

Battery

Chargers

Battery

chargers vary widely,

from

simple

half-

wave

rectifiers

with

a

transformer

and

circuit

overcurrent

protection

to

precisely

controlled units with voltage

and

current regulated

and

with timed alternate high-

charging rate followed

by a

trickle-charging rate

after

initial recovery

from

a

cranking cycle. Batteries

are

well charged

by a few

hours

of

generator operation.

A

battery charger

may be

specified

with

the

engine-generator equipment,

but if the

engineer

wishes

to

include this item

as

part

of the

electrical

contract,

the

specifications

for the

battery charger

must

be

carefully

coordinated with those

for the

engine-generator.

8-5.

Grounding

is a

conducting connection, whether inten-

tional

or

accidental, made between

an

electrical

sys-

tem

and

earth

or to

some conducting body that serves

in

place

of

earth.

Two

types

of

grounding related

to

pumping station

design

are (1)

system neutral grounding

and (2)

equip-

ment grounding.

The

system neutral ground

is a

con-

nection

to

ground

from

the

neutral point

of a

circuit,

transformer,

rotating machine, service,

or

system.

System

Grounding

System grounding

offers

improved service reliability,

improved

fault

protection, greater

safety,

and a

reduc-

tion

of

transient

overvoltages.

The

present trend

is to

use

system neutral grounding

at all

voltage levels.

Solid grounding

of the

system

is

used

for

systems

operating

at 600 V or

lower, while

at

higher voltage

levels

a

neutral resistance grounding unit

is

used

between ground

and the

neutral

of a

power trans-

former

or

generator

to

limit

the

ground

fault

current

to

a low

value. Grounding principles

for ac

systems

are

shown

in

Figure 8-20.

The

following methods

can be

used

for

system grounding:

•

Solidly ground

the

system

by

connecting

the

neutral

conductor

to the

grounding

electrode

conductor

at

the

service.

•

Solidly ground

a

separately derived system, such

as

a

transformer,

by

connecting

the

neutral connector

to

the

grounding

electrode

conductor. When

the

source

is in the

same building

as the

service,

the

grounding electrode conductor

may be run

back

to

the

service.

•

When

the

service conductors originate outside

of

the

building

and the

neutral conductor

is

solidly

grounded

at the

service, ground

the

neutral conduc-

tor at the

transformer

as

well.

Figure

8-20. Grounding

of

low-voltage

ac

systems,

(a)

Grounding principles;

(b)

systems

that must

be

grounded;

150

V or

less

to

ground

or

bare

service

conductor used;

(c)

systems

recommended

to be

grounded:

not

over

300 V to

ground:

(d) a

system

that

may be

grounded: over

300 V to

ground.

Single-phase,

2- or

3-wire

120/240

V

3-phase,

4-wire

delta

240/120

V

3-phase, 3-wire delta

240

V

1

all

conductors

insulated

3-phase, 3-wire delta

480 V

Transformer

Main service

disconnect

Rigid steel conduit

Grounding

electrode

System

ground

3

phase, 4-wire

208Y/120

V

3-phase, 3-wire

delta

240 V

bare

grounded

service conductor

3-phase,

4-wire

480

V/277

V,

must

be

grounded

rf

neutral

is

bare.

•

When resistance grounding

a

medium-voltage (600

to

15,

000-

V)

wye

system, ground

the

system

at the

service

by

connecting

the

neutral conductor

to the

grounding

electrode conductor through

the

resistor.

For

low- (below

600-

V)

voltage systems, solidly

ground

to a

grounding

electrode.

Equipment

Grounding

Equipment

grounding

is

vital

to

protect people

as

well

as

the

equipment

by:

(1)

limiting

the

voltage between

equipment

and

earth

to a

safe

value

and (2)

providing

a

low-impedance return path

for

fault

current

to

oper-

ate the

protective devices quickly.

The

methods

of

equipment

grounding include

the

following:

• Run the

grounding conductor with

the

circuit con-

ductors.

• Use the

metal conduit

(if it is

electrically continu-

ous)

as a

ground conductor.

If it is not

continuous,

bond

each section

to the

grounding conductor.

Ground

Fault

Protection

System Protection

The NEC

requires ground

fault

protection

of

277/480

V

electrical

systems with

services

1000

A and

higher.

It is,

however, good engineering practice

to

examine

the

possible consequences

of

ground

faults

in any

polyphase system where

an

arcing ground

fault

may

burn

long enough

to

create

major

fire

damage.

Ground

Fault

Circuit Interrupter

A

ground

fault

circuit interrupter

(GFCI)

—

or

simply

a

ground

fault

interrupter

(GFI)

—

is

used

on 120 V

outlet

circuits

to

interrupt

the

circuits when

a

fault

current

to

ground exceeds

a

predetermined value

but

is

less

than that needed

to

operate

the

overcurrent

pro-

tective

device.

Class

A

GFCI units, designed

to

trip when line-to-

ground

current exceeds approximately

5

milliamperes

(mA),

protect personnel

from

electrical shocks.

The

average person can, without harm, withstand currents

of

5 mA or

more

for the

time needed

to

trip

the

unit.

Hand-held

power tools

and

their power cords

can be

hazardous

if

their insulation

is

defective, particularly

if

the

worker

is in

contact with

a

conducting

surface

such

as the

ground,

a

concrete

floor, or a

metal

pipe.

In

pumping stations,

GFI

units should always

be

required

in

outdoor

and

below-grade

receptacles,

in

hazardous (per

NEC

500) locations,

in all

areas with

bare concrete

floors

and/or metal work benches,

and

where specifically

called

for in the

NEC.

The

ground

fault

interrupter device

may be a

part

of

the

circuit breaker,

or it may be

inherent

in a

receptacle unit. Receptacles

are

cheaper

and

must

be

used

if the

circuit

run is

longer than about

30 m

(100

ft).

If

circuit breakers

are

used, each circuit must

have

its own

neutral because multiwire branch cir-

cuits

do not

work with

a

GFCI unit

in the

circuit

breaker.

The

receptacle unit

may be of the

type that

provides protection only

for

equipment plugged into

it, or it may be a

feed-through unit that protects

all

ordinary receptacles beyond

it in the

circuit.

Two

methods

of

ground

fault

protection

are

illustrated

in

Figure

8-21.

The NEC may

require ground

fault

protection

on

heat trace circuits

for

water pipe freeze protection

or

for

de-icing applications.

Use

Class

B

GFCI circuit

breakers (which trip

at 30 mA ) for

these applications,

or

ensure that

the

heat trace control package

has

this

protection.

Surge

and

Lightning

Protection

Lightning

arresters

and

surge capacitors

are

used

to

limit

the

peak voltage

of an

impulse

and to

reshape

the

impulse

to

absorb

the

energy. They

are a

necessity

in

lightning-prone areas

or if the

pumping station

is

equipped with

any

electronic gear such

as

AFDs,

and

they

are

highly recommended

in all

pumping stations

Figure

8-21.

Ground

fault

circuit interrupter.

because

of

their very

low

cost (relatively speaking)

and

the

excellent protection they

afford

motors. They

are

located

at the

service disconnect.

The

following sources produce sustained

overvolt-

ages (surges):

•

Intermittent ground faults: Intermittent arcing

ground

faults

on

480-V

ungrounded systems

can

alternately strike

and

clear, leaving

dc

charges

on

the

line-to-ground capacitance. Surges

or

overvolt-

ages

of five to six

times normal

may be

produced,

but

a

properly sized grounding resistor

can

elimi-

nate

the

overvoltages.

•

Series inductive capacitance faults:

The

inadvertent

connection

of an

inductance

from

line

to

ground

on

an

ungrounded system

can

cause surges

or

voltage

increases

by

resonance

effect.

•

Circuit switching: Circuit switching

by an air

con-

tactor

or

circuit breaker does

not

cause overvolt-

ages, because there

is no

trapped charge

on the

circuit when

the arc is

extinguished

at a

current

zero.

Vacuum

contactors

in

circuit breakers

or

start-

ers and

current-limiting

fuses

cause overvoltages.

Vacuum

contactors force

the

current

to

zero before

a

natural zero occurs. Current-limiting

fuses

have

built-in

overvoltage

surge suppressors.

•

Lightning: Lightning

is the

discharge

of a

highly

charged condenser.

The

clouds

are one

plate,

the

earth

is the

other.

Lightning

Protection

The

following

discussion

is

basic design

considerations

for

pumping station buildings

of

ordi-

nary

construction. Protection

of

high-

voltage

switch-

yards

is

usually

the

responsibility

of the

power

company.

The

details

of

lightning protection

are

quite

complex.

An art

rather than

a

science, they

are

best

left

to a

specialist.

The

role

of the

pumping station

designer

is

normally limited

to

specifying

the

quality

of

both

the

system

and the

materials.

Codes.

In

NFPA

78

(Lightning Protection Code)

a

distinction

is

made between

the

following building

classes:

•

Class

I: An

ordinary nonsteel building

less

than

23

m (75 ft)

high.

•

Class

II: An

ordinary building more than

23 m (75

ft)

high

or a

building

of any

height with structural

steel

framing

where

the

steel

framing

can be

used

for

the

down conductors.

All

steel

is

insulated

from

the

ground

by

concrete.

Design Objectives.

The

design objectives are:

(1)

to

provide

a

continuous low-impedance path

for the

discharge current

to

follow

in

preference

to

higher

impedance paths such

as

wood, brick,

or

concrete

and

(2)

to

provide

air

terminals

for

building parts most

likely

to be

struck, especially ventilators, gables,

and

roof edges.

Electrical Materials

and

Components. Electrical

materials must

be

resistant

to

corrosion under

the

anticipated environmental conditions

or

must

be

suit-

ably

protected.

The use of

aluminum

is

restricted

because

of the

problems

it

creates

in all

electrical

work,

and

furthermore,

it

must

not be

used

in

contact

with

the

earth

or

embedded

in

concrete

or

masonry.

Always

use

copper

or

bronze.

All

materials used must

be

protected

from

mechanical

injury.

Typical compo-

nents

of a

lightning protection system

are air

termi-

nals, down conductors, secondary conductors,

and

ground

electrodes

(see Figure 8-22).

8-6.

Lighting

and

Power

Outlets

Interior

Lighting

Equipment

Selection

Many

factors (including room size, ceiling height,

tasks performed,

frequency

and

length

of

room occu-

pancy,

and

special considerations such

as

damp, cor-

rosive,

or

hazardous areas)

determine

the

type

of

lighting

fixtures and

lamps

to be

used. Fixtures

are

varied

and

numerous,

but the

industrial type (ceiling

or

wall mounted)

is the

most suitable

for

pumping sta-

tions. Lamps

are

described

by

watts used

and

type

(e.g.,

100 W

incandescent),

but

they

are

rated

by

lumen output.

The

number

of

lumens

per

watt

is

called

the

"efficiency

of the

light

source."

There have been many changes

in

available lamps

since 1985.

High-efficiency

lamps with novel shapes

and

bases

and

unusual wattages have been produced.

Recent federal legislation

has

outlawed

the

production

of

a

number

of

low-priced incandescent

and fluorescent

lamps that once were almost engineering standards.

State energy conservation laws have proliferated.

The

net

result

is a

greater

choice

of

more expensive lamps

producing light

of

higher quality than ever before.

It is

still

possible,

however,

to

make recommendations

regarding pumping station lighting.

For new

installations,

32 W T-8 fluorescent

lamps

should

be

used

in

industrial

fixtures in

such non-haz-

ardous areas

as

control rooms, pump rooms,

and dry

wells. Hazardous-location

fixtures are

available

but

are

expensive.

Use

high-power factor ballasts. Con-

sider

electronic

ballasts where

fixtures

have high

usage.

These

ballasts

are now

reliable,

are

cost

effec-

tive,

but

still have

a

high

first

cost. Low-temperature

magnetic ballasts

are

available

for

areas

in

which

air

temperatures

can

fall

below

1O

0

C

(5O

0

F),

but

verify

that

lamps

can be

used with them. Fluorescent lamp

life

is

20,000

hours.

Use

the new

compact

fluorescent

lamps

in

sizes

7

to 26 W

single

or

dual

in

small rooms with

fairly

high

usage,

corridors,

and

outside

for

security where

the

brighter, high-pressure sodium lamps

are not

wanted.

Compact

fluorescent

lamps have excellent

color

and

10,000-h

lives. Wattages higher than

26 are

available.

Use

incandescent

or

metal halide lamps

in

waste-

water pumping station

wet

wells,

in

clear wells,

and in

small areas

not

often

used. Incandescent lamps have

low

efficiency

and

short lamp

life

(750

to

2000

h), and

several commonly used wattages have recently been

outlawed.

Use

guards where needed. Metal halide

lamps

should have back-up quartz lamps where

needed,

and

emergency lights require

an

off-delay

to

permit metal halide lamps

to

restrike.

Use

fixtures

suitable

for

damp

or wet

locations where needed.

In

wastewater

pumping station

wet

wells,

use fixtures

approved

and

labeled

for use in

Class

1,

Division

1,

Group

D

hazardous locations

per NEC

500.

As

alternatives

to fluorescent

lamps,

use

high-pres-

sure

sodium lamps outside

as

security lighting,

in

larger rooms

with

ceiling heights

of 3 m

(10

ft) or

more where

the

glare

and

color

is not

objectionable,

and

in

hazardous locations such

as

wastewater

wet

wells. Never

use

them where machinery

is in

motion,

because there

is a

dangerous stroboscopic

effect.

These lamps

are now

available

as

small

as 35 W. In

larger sizes they

are the

most

efficient

commonly used

lamps. Lamp

life

is

24,000

h, and

color

is

constantly

being improved.

Do not use

mercury vapor lamps

in

new

construction. They

are

relatively

inefficient

and

are now

considered obsolete. Metal halide lamps have

good color,

are

available

in 32 W,

100

W, and in

larger

sizes,

and

have

10,000

hours

of

life,

but

they

are

less

efficient

than high-pressure sodium. Color

is the

only

reason

to

choose them over high-pressure sodium.

Low-pressure sodium lamps emit objectionable color.

Fixtures suitable

for use in

damp and/or corrosive

areas

are

available with

all

types

of

lamps,

and the

selection depends

on

location

and

preference.

The fix-

tures

in

damp areas must

be

vapor tight

and

those

in

corrosive areas should

be

made corrosion resistant

with

a

coating

of PVC (or the

equivalent)

on all

metal

parts.

Energy

Conservation

Lighting energy conservation

is

mandatory

in

some

states

and may be

imposed throughout

the

country

by

the

federal government. Obtain requirements

and

Figure

8-22.

Lightning

protection

system

for a

building.

Ground

conductor

or

cable

Air

terminal

Service

Down

conductor

Ground

rod

forms

from

the

appropriate regulatory bodies,

and

consult

the

local building inspector. Some states (Cal-

ifornia,

for

example) require two-level switching

in

heated

or

air-conditioned rooms larger than

9 m

2

(100

ft

2

),

containing

two or

more

fixtures, and

draw-

ing

13

W/m

2

(1.2

W

'/ft

2

).

Such requirements might

be

waived

for

unattended pumping stations.

Fixture

Location

Space

fixtures

relatively evenly with

due

regard

for

motor control centers

and

pipe risers. Pumps, motors,

and

auxiliaries such

as

chemical feeders

and

motor

control centers need more light than piping areas.

Do

not

obstruct pump

and

motor

lift

space,

and do

allow

for

bridge cranes

and the

like.

In

high-bay rooms such

as

motor

and

engine rooms, make certain that lamps

in

the fixtures can be

replaced

from

the

crane working

platform.

Switching

Generally,

locate

a

switch

at

each entry

on the

door

latch side. Locate

wet

well

or

clear well switches inside

the

pump building (but

not in the wet

well

or

clear well)

and

include

a

labeled pilot light. Always provide

uns

witched

lights

at

stairways

and

along corridors,

especially

in

machine rooms

and

below-grade

rooms

where

hazards

may be

present. Sketch

a

wiring diagram

and

carefully

determine number

of

wires

from

the

dia-

gram.

If the fixture is

identified

by the

switch that con-

trols

it,

these diagrams need

not be

included

on

plans.

Exterior Lighting

Entry

or

Security Lights

The

following suggestions pertain

to

entry

or

security

lights:

•

Locate

the

lights

at

each principal entrance.

•

Lights should

be

able

to be

switched

or put on

pho-

tocell control.

• Use

vandal-resistant lenses

for

lights.

• Use 52- or

90-W incandescent lamps

in

smaller sta-

tions

where

fixtures are

manually switched.

Use

high-pressure sodium

fixtures in

stations with pho-

tocell control.

Roadway

and

Parking Lots

There

are

many types

of

roadway

and

parking

lot

light

fixtures

utilizing

both utilitarian

and

architectural

designs.

Use

only high-pressure sodium lamps. Photo-

cell

or

time-clock control

is

usual.

For

design informa-

tion

and

selections,

refer

to

manufacturers'

catalogs

and

the IES

handbook.

Emergency

Lighting

Codes

and

Legal

Requirements

Emergency lights

are

sometimes required

by

state

and/or local

law in

structures similar

to

pumping sta-

tions where

failure

of

power

to the

main lighting sys-

tem

would leave building exits

in

total

darkness.

Where required, they

are

subject

to NEC

Article

700

and

NFPA

Life

Safety

Code

No.

101, Section 5-10.

Se

I

f-Contained

Lighting Units

Approved lighting units

are

available complete with

battery,

charger, controls,

and

attached

or

separate

lamp

heads. Either unit-mounted

or

separate lamp

heads

are

available,

and the

types

of

lamp heads

include:

(1) 8- to

25-

W

sealed beam models,

(2)

non-

sealed beam models with automotive-type bulbs,

(3)

very

high

efficiency

halogen models,

(4)

decorator

models,

and (5)

explosion-proof (Class

1,

Division

1,

Group

D

from

NEC

Section

50)

models.

Exit

Signs

Incandescent

and fluorescent

exit signs

are

available

with

four

lamps

—

two

for

line voltage

and two for

bat-

tery

voltage. They

are

also available with

an

integral

battery, charger, transfer controls,

and

down light.

The

atomic

type

of

exit lights should

be

considered

if the

owners

are

made aware that there

is a

disposal prob-

lem for the

luminous tubes

at the end of

their lives.

They require

no

connections

to a

power source.

LED

(light

emitting diode) exit signs

are

more expensive,

and

they have

no

down light,

but

with lamp

life

exceeding

20

years,

and as

they draw

2 W per

face,

they

are

very cost

effective

over their lifetimes.

Transfer

Controls

Transfer

controls consist

of a

relay with

a

voltage sen-

sor

that transfers

to

battery power

and

energizes lamp

heads when line power

fails.

They

are

available with

battery low-voltage protection that shuts

off the

lights

to

prevent deep battery drawdown.

The

following

are

suggestions

and

recommenda-

tions

for

emergency lighting:

• If the

pumping station

is

underground,

use

battery

packs wired

to the

normal lighting circuit (but

ahead

of the

light switch)

to

illuminate

the

stairs

or

ladder.

• Use at

least

two

lamps

at

each lamp location

so

that

no

area

is

left

in

darkness

if a

lamp

fails.

•

Provide

at

least

10 lux

(1

foot-candle)

at floor

level

for

each exit.

•

Exit signs

are not

usually provided

in

pumping sta-

tions.

If

required, they

may not

have

to be

con-

nected

to the

emergency lighting system.

• Use a

sealed, maintenance-free battery rated

for 10-

yr

life.

• Use a

solid-state, automatic, two-rate trickle charger

with

trickle

and

high-charge indicators

and a

test

switch.

• Use an

automatic transfer relay with low-battery

protection.

Use

delayed retransfer when

the

normal

light

source

is

metal halide

or

high-pressure sodium

to

allow

for

restrike

time

(i.e.,

the

time required

for

lamp

to

relight).

• Use

NEMA

4x

enclosures

in

cold

or

damp areas.

•

Except

in

hazardous areas,

use

sealed beam

or

sealed halogen lamp heads.

• Do not

locate battery units

in

wet, corrosive,

or

haz-

ardous areas.

In

these hazardous areas install only

lamp

heads connected

to a

battery that

is

located

in

dry,

indoor, nonhazardous areas.

Convenience

Outlets

Low

Voltage

For 120 V

outlets,

use

NEMA 5-20 receptacles, speci-

fication

grade,

on 20 A,

single-pole circuits even

though

the NEC

allows NEMA

5-15

if two or

more

are

on a

circuit.

No

more than

five

should

be on a

cir-

cuit.

Locate them near pumps, electrical gear,

and

out-

side near pipe

or wet

well

or

clear well access.

Generally place them

so

that

any

location that might

require power

can be

reached with

a

15-m

(50-ft)

extension

cord.

Do not

locate them

in a wet

well

or

clear well. Install weatherproof covers

if

they

are

sub-

ject

to

weather

or

splashing, such

as

where equipment

is

hosed down.

Special

Outlets

The

following apply

to

special outlets:

•

Welding:

The

voltage

and

ampere rating must

be

compatible with welding machine requirements.

•

Telephone:

Use

NEMA

5-15

outlet

on

15-

A

circuits

where

more than

two

telephone lines will

be

brought

in.

•

Emergency lighting: Where permitted

by

codes,

use

single NEMA 5-15 outlets

on the

same circuit

as

the

room lighting. Permanent connection

to the

sup-

ply

circuit

is

required

for

legally required emer-

gency lighting.

•

Battery charger:

The

charger should

be

sized (and

specified)

according

to

battery requirements.

•

Light

fixtures: Use

twist-lock outlets near chain-

suspended

fixtures, and

consider

hard-

wiring

two

fixtures

together.

8-7.

Electrical

Circuit

Diagrams

Single-

Line

Diagrams

A

single-line diagram

is

used

to

show

the

electric

power system

from

source

to

load

in

symbolic form.

Conductors

and

their connections

are

omitted,

and

only

circuit elements, their relationships,

and the flow

of

energy through

the

system

are

shown.

The

diagram

should

be

simple, utilize standard symbols,

and

present

a

complete picture that enables

the

observer

to: (1)

assess

the

blocks

of

power required,

(2)

iden-

tify

the

major

feeders,

and (3)

ascertain

the

main pro-

tective devices responsible

for

plant outages.

An

example

of a

single-line diagram

of a

radial cir-

cuit

arrangement

of a

small pumping station

is

shown

in

Figure 8-23.

The

radial system

is the

simplest

and

most

economical type

of

circuit arrangement.

It

offers

good reliability

and

probably

is the

type most

often

used

in

small pumping stations.

The

drawback

of the

radial system

is

that

a

failure

in the

utility feeder, main

breaker,

or

motor control center

bus

shuts down

the

whole

station.

The flexibility of

being able

to

transfer

manually

or

automatically

to a

standby power source

is

illustrated

in

Figure 8-24.

Figure

8-23.

A

typical

single-line

diagram

for a

small

pumping

station.

Courtesy

of

Brown

and

Caldwell

Con-

sultants

Pumping Station Desing - Second Edition by Robert L. Sanks, George Tchobahoglous, Garr M. Jones

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