IMM 8001/8002 – Digital Motor Protection Relay
ICE / CEE
____________________________________________________________________________________________
IMU307-1 GB Ind. B
52
5.6. TOO LONG START PROTECTION [48]
Function
The IMM 8000 relays have a too long start and operating rotor stalling unit. Each start is individually
monitored to check that the heating characteristics defined by the start variables
Ist
: starting current and
tst
: starting time are not significantly reached.
To do so, an extremely inverse response time unit provides an efficient protection against abnormally
long starts, irrespective of the network voltage.
Main characteristics
Operating logic :
Parameters can be set by the user for handling a start in two ways :
- Motor switching device closing detection (closing of a contact
EL1
input).
- Positive phase sequence current automatic detection by analysing its changes on start
(
Ipos
detection).
This function is active during the relay reference start period, i.e. during a time equal to
twice the parameterised starting time, i.e.
2 tst>,
or during the actually measured starting
time
td
with current analysis when configured in
Ipos
current automatic detection.
Note
:
- time-delay 2 tst> is reinitialised under re-acceleration conditions.
- the relay considers that start occurred when the Ipos current, less than 12 % of In
during at least 0.1s, becomes greater than 70 % of In in less than 0.1 s.
- the end of the actually measured starting time (end of td) occurs when the Ipos
current becomes less than 107 % of In after a starting cycle again.
Settings
Starting current
48-Ist>
2 to 10 In (steps of 0.5 In)
Starting time
48-tIst>
1 to 240 s (steps of 0.1 s)
Operating curves
see figure below
Time/current characteristic
t (s) = 1.1
)²
In
/
Ipos
(
xtst
²
Ist
>
>
Note :
To ensure selectivity with fuse protection,
the minimum response time automatically becomes 250ms
when function [50] is disabled.
The recorded actual starting current (I last start) is the value of Ipos 0.5s after the start conditions
are detected.
The recorded actual starting time (T last start) is the value of the time which elapses between start
condition detection and the time when the Ipos current becomes less than 107 % In again.