1 3 8
M O T OR DRIV E ALARMS
A cont
i
nuous compar
i
son
i
s made by the contro
ll
er of the speed feedback and armature vo
l
tage feedback. If
the d
i
fference
i
s greater than the va
l
ue set by 8.1.2 M O T OR DRIV E AL ARMS / Speed feedback m
erance PIN 1 7 2, the a
l
arm
i
s operated. If armature vo
l
tage feedback
i
s se
l
ected, then the speed feedback
a
l
arm
i
s automat
i
ca
ll
y suppressed.
If 1 0 3)FLD W E A K EN A BLE
i
s enab
l
ed, then the contro
ll
er suspends the speed-to-vo
l
ts compar
i
son
i
n the
f
i
e
l
d-w eaken
i
ng reg
i
on w here the vo
l
ts are c
l
amped to a max
i
mum va
l
ue. Instead, w hen
i
n the f
i
e
l
d-
w eaken
i
ng reg
i
on
i
t checks w hether the speed feedback
i
s be
l
o w 1 0 % of fu
ll
speed. If so, the a
l
arm w
ill
operate. Th
i
s means that
i
t
i
s not pract
i
ca
l
to start f
i
e
l
d w eaken
i
ng be
l
o w 1 0 % of fu
ll
speed
i
.e. 1 0 : 1 range.
The automat
i
c s w
i
tch to A V F feature a
ll
o w s cont
i
nued runn
i
ng, a
l
though at the
l
o w er accuracy
l
eve
l
of
Armature V o
l
tage feedback. The A V F rema
i
ns the source of feedback unt
il
the next ST OP / ST ART
sequence. The or
i
g
i
na
l
feedback source
i
s then restored and the a
l
arm reset to a
ll
o w auto A V F protect
i
on
once aga
i
n. It may be necessary to reduce the 1 7 2)SPEED TRIP T OL to about 1 5 %
i
f a smooth transfer to
auto A V F
i
s requ
i
red. Ho w ever,
i
f the thresho
l
d
i
s too
l
o w then an un w arranted transfer may occur dur
i
ng
speed trans
i
ents.
There
i
s a f
l
ag on h
i
dden PIN 7 0 3 w h
i
ch w arns of a speed m
i
smatch after the norma
l
de
l
ay t
i
me. Th
i
s f
l
ag
i
s
reset by a ST OP command. It
i
s suggested that the f
l
ag
i
s conf
i
gured to a d
i
g
i
ta
l
output to prov
i
de a w arn
i
ng
that the auto A V F has occurred.
The speed feedback m
i
smatch a
l
arm
i
s norma
ll
y tr
i
ggered by fa
il
ure of the feedback mechan
i
sm
i
n one of the
fo
ll
o w
i
ng w ays:-
1) D
i
sconnect
i
on of w
i
r
i
ng.
2) Fa
il
ure of the tachogenerator or encoder.
3) Fa
il
ure of the tachogenerator or encoder mechan
i
ca
l
coup
li
ng.
Note. A
l
arm de
l
ay t
i
me: 0.4 secs to TRIP, 0.2 secs to automat
i
c A V F s w
i
tch.
W A
R
N
I
NG. Th
e
p
r
ot
ec
t
i
on
a
ffo
r
d
e
d
i
n f
i
e
l
d w
eake
n
i
ng mod
e
i
s
li
m
i
t
e
d to tot
a
l
f
ee
db
ack
l
oss on
l
y. Th
i
s
i
s
b
eca
us
e
th
e
sp
ee
d / AVF
r
e
l
a
t
i
onsh
i
p
i
s not m
a
i
nt
a
i
n
e
d
i
n f
i
e
l
d w
eake
n
i
ng mod
e
.
I
f
a
p
a
r
t
i
a
l
l
oss of f
ee
db
ack
o
cc
u
r
s th
e
moto
r
w
ill
r
un to
e
x
ce
ss
i
v
e
sp
ee
d. Wh
e
n th
e
f
i
e
l
d h
a
s b
ee
n
c
omp
l
e
t
e
l
y w
eake
n
e
d
a
nd
i
s
a
t
i
ts
m
i
n
i
mum
l
e
v
e
l
, th
e
a
r
m
a
tu
r
e
ov
e
r
vo
l
t
a
g
e
t
ri
p w
ill
c
om
e
i
nto op
e
r
a
t
i
on. Th
i
s m
a
y on
l
y o
cc
u
r
a
t
a
d
a
ng
e
r
ous
sp
ee
d.
I
t
i
s th
e
r
e
fo
r
e
r
ec
omm
e
nd
e
d th
a
t
a
m
ec
h
a
n
i
ca
l
d
e
v
i
ce
b
e
ut
ili
s
e
d to p
r
ot
ec
t
a
g
a
i
nst th
i
s poss
i
b
ili
ty.
Correct sett
i
ng of 1 1 0)MIN FIELD C URREN T shou
l
d ensure that the overvo
l
ts TRIP occurs
j
ust above the
max
i
mum operat
i
ng speed.
Summary of Contents for PLX
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