One of the most important safety steps to prevent an overloaded motor, motor dam

Question

One of the most important safety steps to prevent an overloaded motor, motor damage, and a fire hazard is un- derstanding when a drive will remove power from the motor when a fault occurs. Electric motor drives must be programmed (using a parameter setting) to trip if the drive detects the motor is overheated. The time it takes before the electric motor drive trips the overloads and turns the motor OFF depends on the extent of the overload and the motor operating frequency. Electric motor drive manufacturers use graphs to explain the approximate overload trip time based on the amount of overload and the electric motor drive's output frequency (motor operating frequency). The percent of motor overload is found by applying the formula: % OL = 'RUN x 100 IFL where % OL = percent motor overload IRUN = motor current draw (in A) IF = motor nameplate listed current (in A) 1. Using the manufacturer supplied graph, determine the approximate amount of trip time, in seconds, before the electric motor drive would automatically stop the overloaded motor. 230 V/30 - MOTOR NAMEPLATE MANUFACTURER GRAPH TRIP TIME 60 S 90 S 180 S TYPE AC PHASEL 3 HP G CYCLE 60 vours 230 Amps [1.7 RPM 1725 TEMP RISE 40°C SF 1.15 CODE [L] TIME RITE CONT 300 S PERCENT MOTOR OVERLOADED (90% OL) * * & ? ? 3° 600 S BAN 0.2 0.4 0.6 0.8 MAXIMUM OPERATING FREQUENCY (IN Hz) - MAXIMUM MOTOR FREQUENCY ELECTRICAL MOTOR DRIVE- - MEASURED MOTOR CURRENT IS 2.55 A

Explanation / Answer

I_run= 2.55A

I_fL= 1.7A (given in nameplate)

OL = I_run/I_fL = 2.55/1.7 = 1.5  

from manufacturer graph

at OL= 1.5 , trip time is 300sec

Answer-300sec

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