Osram HQI-E 150 W/NDL CL Technical Information download pdf (Page 21)

21

4.6

C

able ca

p

acitanc

e

The capacitance o

f

the suppl

y

cables between lamp

an

d

i

gn

i

t

i

on un

i

t

d

epen

d

s on var

i

ous genera

l

con

di

-

ti

o

n

s

. Th

ese

in

c

l

ude

th

e

s

iz

e

a

n

d

s

tr

uc

t

u

r

e

of

th

e

cable

(

diameter, distances and insulation to

g

ether with

n

umber o

f

individual cables

,

dielectric coe

ff

icients o

f

the materials

)

. The capacitance also depends on the

g

roundin

g

and shieldin

g

o

f

the cable and where it is

fastened, e.

g

. close to

g

rounded surfaces.

C

ommonly

u

sed

p

ower cables are not suitable

f

or this

p

ur

p

ose,

because of their relativel

y

thin PV

C

-isolation, where

t

h

e w

i

res

li

e compara

bl

y c

l

ose toget

h

er.

Th

e capac

i

-

tance here is about 100 pF/m. Because of the hi

g

h

i

g

nition volta

g

e

f

or dischar

g

e lamps the lead wires

h

ave t

hi

c

k

er

i

nsu

l

at

i

ons an

d

t

h

e

y

are norma

lly

not

placed close to each other. The capacitance o

f

the

lead wires will there

f

ore be lower than

f

or the

p

owe

r

cable.

C

apacitances onl

y

form limited resistance to

h

i

g

h-

f

requency volta

g

e components o

f

the i

g

nition

pu

l

se.

Th

e capac

i

tance attenuates t

h

e

ig

n

i

t

i

on pu

l

se,

w

i

t

h

resu

l

t

i

n

g

ig

n

i

t

i

on pu

l

ses poss

ibl

y not reac

hi

n

g

t

h

e

amplitudes required to i

g

nite the lamp.

C

ertain load

capacitances must there

f

ore not be exceeded, de

-

pendin

g

on the speci

f

ications o

f

the i

g

nition unit

.

4.7

S

tart-u

p

behavior of metal halide lam

p

s

Af

ter i

g

nitin

g

the lamp and heatin

g

the dischar

g

e, the

di

sc

h

arge runs

i

n

i

t

i

a

ll

y on

l

y

i

n t

h

e start gas.

Th

e mer-

cur

y

an

d

t

h

e meta

l

h

a

lid

es are st

ill

i

n

li

qu

id

or so

lid

f

orm on the arc tube wall. The volta

g

e across the

dischar

g

e is initially still very low. The start

g

as ar

g

on

radiates a little in the visible ran

g

e

(

weak violet li

g

ht

)

,

which is wh

y

the luminous

f

lux in the initial phase is

st

ill

ver

y

l

ow

.

Throu

g

h power consumption in the lamp,

f

irst the mer

-

cury an

d

t

h

en a

l

so t

h

e meta

l

h

a

lid

es

b

e

gi

n to evapo-

rate. The individual

f

illin

g

particles evaporate at di

ff

er-

ent rates, resultin

g

in di

ff

erin

g

ratios o

f

the particles

durin

g

runup. The dominance o

f

individual particles

i

n t

h

e start-up p

h

ase resu

l

ts

i

n t

h

e co

l

our p

h

enomena

during this period shown in Fig. 22.

O

nly after a few

mi

nutes,

h

av

i

n

g

reac

h

e

d

t

h

e stea

d

y state,

i

s t

h

e re

-

quired composition achieved, producin

g

the

f

ull lumi-

n

ous

f

lux and the required li

g

ht colour.

after 20s

after 40s

after 60s

after 120s

after 100s

after 80s

CRI=66

CRI=29

CRI=36

CRI=70

CRI=85

CRI=92

Fi

g

. 22:

C

ourse of li

g

ht parameters of a H

CI

®

-T 150 W

/

NDL durin

g

start-up

1 2 ... 16 17 18 19 20 21 22 23 24 25 26 ... 55 56

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