ABB REM 610, Technical Reference Manual

Page: 133 / 158

133
6.1.2.3. Checking the set safe stall time for cold starts
By selecting the correct trip curve from the trip curves at no prior load according to
the previously selected or calculated safe stall time setting, the total start-up time of
the motor can be read from the curve. The total start-up time should permit as many
cold starts as stated by the motor manufacturer.
In applications where, for instance, three cold vs two hot starts are allowed, the total
start-up time of the motor may allow too many cold starts. In this case, the thermal
protection can be supplemented by using the cumulative start-up time counter for
limiting the number of cold starts. Alternatively, setting the weighting factor to 40
per cent, instead of to 50 per cent, has at times proved useful.
The operate time when no prior load with the selected safe stall time setting can also
be calculated as follows:
operate time
= × ×
⎛
⎝
⎜
⎞
⎠
⎟
⎛
32 15
6
2
. ln
int
int
t
I
FLA
I
FLA
x
start
start
⎝⎝
⎜
⎞
⎠
⎟ −
⎧
⎨
⎪
⎪
⎩
⎪
⎪
⎫
⎬
⎪
⎪
⎭
⎪
⎪
2
1 1025 .
(8)
6.1.2.4. Checking the set safe stall time for a single start
If the safe stall time of the motor is shorter than the operate time when no prior load,
a single motor start up should instead be protected by the start-up supervision.
6.1.2.5. Restart disable level, 49 RESTDIS
The restart disable level can be calculated as follows:
49 RESTDIS
start-up time of the motor
operate time whe
= −
100%
n n no prior load
margin
× +
⎛
⎝
⎜
⎞
⎠
⎟
⎛
⎝
⎜
⎞
⎠
⎟
100%
(9)
For instance, if the start-up time of the motor is 11 seconds and the calculated
operate time of the thermal protection element when no prior load 25 seconds, one
motor start up will use 11 s/25 s = 45% of the thermal capacity of the motor.
Therefore, the restart disable level must be set to below 100% - 45% = 55%, e.g. to
50%.
6.1.2.6. Prior alarm level, 49 ALARM
Tripping due to a beginning overload can be avoided by reducing the load of the
motor at a prior alarm.
The prior alarm level can be set to a level, which will allow the use of the motor
’
s
full thermal capacity without causing a trip due to long-time overload.
Motor Protection Relay
Technical Reference Manual - ANSI Version
REM 610 REM 610
1MRS755537