Eaton 520 - Short Delay Settings; Instantaneous Settings

16
Operating Manual for Series NRX
Trip Units - Digitrip™ 520/520M
EATON www.eaton.com
Instruction Leaet IL01301051E
effective September 2013
Short delay settings
On Digitrip 520 LSI and 520M (R)LSI(G/A) trip units (IZMX...V and
...U) tripping due to the short-circuit current I
sd
can be delayed by the
time t
sd
. This provides selectivity for the short-circuit protection in
switchgear with several grading levels. Available setting values for the
short delay pickup I
sd
are:
I
sd
= (2/3/4/5/6/7/8/10) x I
r
Important: The short delay setting I
sd
is based on the long delay I
r
There are two different short delay response curve shapes: fixed time
(FLAT) and I
2
t. The shape selected depends on the type of selective
coordination chosen. The I
2
t response curve will provide a longer time
delay for current below 8 x I
R
than will the FLAT response curve.
Flat response: t
sd
= 0.1/0.2/0.3/0.4/0.5 s
I
2
T = 0.1/0.3/0.5
The I
2
t response is applicable to currents less than eight times the
ampere rating of the continuous current rating (I
R
). For currents greater
than 8 x (I
R
) the I
2
t response reverts to the FLAT response.
ote:N See section 2, zone interlocking.
Figure 10.
Turn rotary
switch to change
short delay time
setting t
sd
Turn rotary switch
to change short
delay current
setting I
sd
Applying Short Delay Settings
Figure 11.
I
SD
Available Settings
2, 3, 4, 5, 6, 7, 8, 10
In Multiples of Long
Delay Setting (I
R
)
Short Delay Current Settings
Figure 12.
t
sd
(s)
Available Settings
0.1, 0.2, 0.3, 0.4, 0.5
Seconds With
FLAT Response
0.1*, 0.3*, 0.5*
Seconds With
l
2
t Shape
l
2
t Shape Returns to FLAT
Response at Currents
Higher than 8 x I
R
* Indicates l
2
t Shape
8 x I
R
Short Delay Time Settings
Instantaneous settings
If the current setting I
i
is exceeded, the circuit breaker is tripped
instantaneously.
Available settings values for I
i
are:
I
i
= (2/3/4/5/6/8/10) x I
n
; OFF
Figure 13.
Turn rotary
switch to change
instantaneous
current setting I
i
Applying Instantaneous Settings
Figure 14.
I
i
Available Settings
2, 3, 4, 5, 6, 8, 10,
12, OFF
In Multiples
of Rating Plug
Amperes (I
n
)
Instantaneous Settings