Inverse Delay; More Stages (Definite Time Delay Only); Setting Groups - Allen-Bradley Rockwell Automation 857 User Manual

Inverse delay

The inverse delay is based on the following equation.
Equation 3.1
K
=
1
T , where
2
⎛ ⎞
I
⎜ ⎜ ⎟ ⎟
−
2
2
K
2
⎝ ⎠
I
MOT
T = Operation time
K = Delay multiplier
1
I = Measured and calculated negative sequence
2
phase current of fundamental frequency.
I = Nominal current of the motor
MOT
K = Pick-up setting I
2
allowed degree of unbalance.
Example:
K = 15 s
1
I = 22.9 % = 0.229 xI
2
K = 5 % = 0.05 xI
2
15
=
t
2
⎛ ⎞
. 0 229
−
⎜ ⎟
2
. 0 05
⎝ ⎠
1
The operation time in this example will be five minutes.

More stages (definite time delay only)

If more than one definite time delay stages are needed for current
unbalance protection, the freely programmable stages can be used
(see "Programmable Stages (99)").

Setting groups

There are two settings groups available. Switching between setting
groups can be controlled by digital inputs, virtual inputs (mimic
display, communication, logic) and manually.
Protection Functions
> in pu. The maximum
2
MOT
MOT
=
300 4 .
3-17
857-UM001A-EN-P – July 2009