Motor Starting Protection (48); Description Of Motor Starting Protection - Siemens SIPROTEC 7SJ62 Instruction Manual
Multi-functional protective relay with bay controller
Hide thumbs
Also See for SIPROTEC 7SJ62:
- Manual (704 pages) ,
- Technical data manual (58 pages) ,
- Manual (94 pages)
Table of Contents
Advertisement
Functions
6.8
Motor Starting Protection (48)
6.8.1
Description of Motor Starting Protection
General
Inverse Time
Time-Overcurrent
Tripping Character-
istic
6-94
When the 7SJ62 relay is used to protect a motor, the starting time monitoring feature
supplements the overload protection described in Section 6.9 by protecting the motor
against the potential damage that might result from frequent starting or extended start-
ing durations. In particular, rotor-critical high-voltage motors can quickly be heated
above their thermal limits when multiple starting attempts occur in a short period of
time. If the durations of these starting attempts are lengthened by excessive voltage
surges during motor starting, by excessive load moments, or by blocked rotor condi-
tions, a tripping signal will be initiated by the device.
Motor starting protection consists of two time-overcurrent tripping characteristics initi-
ated by the motor starting recognition setting entered at address , 02725
67$57
.
One characteristic is definite time while the other one is inverse time. When
the motor phase currents exceed the setting entered at address , time delayed
tripping will be initiated. To gain a better understanding of how to set the motor starting
recognition setting at address
The inverse time time-overcurrent characteristic is designed to operate only when the
rotor is not blocked. When the phase currents exceed the motor starting recognition
setting entered at address , time delayed tripping via the inverse time character-
istic is initiated. The inverse time characteristic allows motor starting protection to ad-
just for those situations where high starting voltages result in decreased starting cur-
rents. The tripping time is calculated based on the following formula:
t
=
TRIP
where t
– Actual tripping time for flowing current I
TRIP
t
– Tripping time for nominal start-up current I
A max
I
– Current actually flowing (measurement value)
– Nominal starting current of the motor (set at address 4102)
I
A
I
– Pickup value for recognition of motor starting (set at address 1107)
MOT START
,
refer to Subsection 6.1.3.
2
I
⋅
A
t
---- -
where I> I
Amax
I
MOT START
(set at address 4103)
A
7SJ62 Manual
C53000-G1140-C121-1
Advertisement
Table of Contents
