2 Functions
159
SIPROTEC 4, 7SJ62/63/64 Handbuch
C53000-G1140-C147-A, Edition 07.2015
2.8.2
Motor Restart Inhibit 66
The restart inhibit prevents restarting of the motor when this restart may cause the per-
missible thermal limits of the rotor to be exceeded.
2.8.2.1
Description
General
The rotor temperature of a motor generally remains well below its maximum admissi-
ble temperature during normal operation and also under increased load conditions.
However, high startup currents required during motor startup increase the risk of the
rotor being thermally damaged rather the stator, due to the short thermal constant of
the rotor. To avoid that multiple starting attempts provoke tripping, a restart of the
motor must be inhibited, if it is apparent that the thermal limit of the rotor will be ex-
ceeded during this startup attempt. Therefore, the 7SJ62/63/64 relays feature the
motor start inhibit which outputs a blocking command until a new motor startup is per-
mitted for the deactivated motor (restarting limit). The blocking signal must be config-
ured to a binary output relay of the device whose contact is inserted in the motor start-
ing circuit.
Determining the
Rotor
Overtemperature
Since the rotor current cannot be measured directly, the stator current must be used
to generate a thermal profile of the rotor. The r.m.s. values of the currents are utilized
for this. The rotor overtemperature
Θ
R
is calculated using the largest of these three
currents. Therefore, it is assumed that the thermal limit values for the rotor winding are
based on the manufacturer's data regarding the nominal starting current, maximum
permissible starting time, and the number of starts permitted from cold (n
cold
) and
warm (n
warm
) conditions. From this data, the device performs the necessary calcula-
tions to establish the thermal profile of rotor and issues a blocking signal until the
thermal profile of rotor decreases below the restarting limit at which point starting is
permitted anew.
Содержание siprotec SJ62
Страница 3: ...3 SIPROTEC 4 7SJ62 63 64 Handbuch C53000 G1140 C147 A Edition 07 2015 ...
Страница 9: ...Preface 9 SIPROTEC 4 7SJ62 63 64 Handbuch C53000 G1140 C147 A Edition 07 2015 ...
Страница 21: ...Contents 19 SIPROTEC 4 7SJ62 63 64 Handbuch C53000 G1140 C147 A Edition 07 2015 ...
Страница 35: ...1 Introduction 33 SIPROTEC 4 7SJ62 63 64 Handbuch C53000 G1140 C147 A Edition 07 2015 ...
Страница 365: ...2 Functions 363 SIPROTEC 4 7SJ62 63 64 Handbuch C53000 G1140 C147 A Edition 07 2015 ...
Страница 443: ...3 Mounting and Commissioning 441 SIPROTEC 4 7SJ62 63 64 Handbuch C53000 G1140 C147 A Edition 07 2015 ...
Страница 529: ...4 Technical Data 527 SIPROTEC 4 7SJ62 63 64 Handbuch C53000 G1140 C147 A Edition 07 2015 ...
Страница 699: ...A Appendix 697 SIPROTEC 4 7SJ62 63 64 Handbuch C53000 G1140 C147 A Edition 07 2015 ...
Страница 701: ...Literature 699 SIPROTEC 4 7SJ62 63 64 Handbuch C53000 G1140 C147 A Edition 07 2015 ...
Страница 714: ...Index 712 SIPROTEC 4 7SJ62 63 64 Handbuch C53000 G1140 C147 A Edition 07 2015 ...
Страница 715: ...Index 713 SIPROTEC 4 7SJ62 63 64 Handbuch C53000 G1140 C147 A Edition 07 2015 ...