Page 898 - Motor protection and control Manual motor starters, contactors and overload relays
P. 898

12/64            ABB  MOTOR PROTECTION AND CONTROL

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          Star-delta starters protected by overload relays
          With AF contactors - Open type version in kit form
          Switching frequency diagrams



          General
          Switching frequency/hour, according to acceleration time and load factor. Respect of the following conditions enables
          utilization of the starter without excessive overheating of the connections or nuisance tripping of the thermal overload relay.





          Thermal overload relay
          Intermittent periodic duty                 Example:

           70
          Switching frequency (ops/h)  60  ta = 8 s  Starting time of the motor: 7 second (use 8s curve) - Duty ratio: 63 %
                  ta = 5 s
                                                     means a permitted switching frequency of max. 15 operating cycles
           50
                                                     per hour.
           40
           30
                 ta = 10 s
           20
                                                     7 seconds acceleration, 2.5 minutes operation and 1.5 minutes rest.
                        ta = 20 s
           10      ta = 12 s  ta = 15 s              This corresponds to a 4 minute operating cycle (15 starts/hr) with
            0
             0  10  20  30  40  50  60  70  80  90  100
                                              Duty ratio (%)
           ta: motor starting time



          Electronic overload relay : please consult us

























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