5-210 M60 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUALGROUPED ELEMENTS CHAPTER 5: SETTINGS5Figure 5-108: Voltage dependent overload curvesThis figure and the following procedure illustrate the construction of the voltage overload curves.1. Draw a curve for the running overload thermal limit. The curve is one that has been selected in the relay as a THERMALMODEL CURVE.2. Determine the point of intersection between the THERMAL MODEL CURVE and the vertical line corresponding to the per-unit current value of VD ACCEL. INTERESECT @ MIN V (see point 2).3. Determine the locked rotor thermal limit point for the minimum voltage motor start. The coordinates of this point arethe per-unit current value of VD STALL CURRENT @ MIN VOLTS and the time value of VD SAFE STALL TIME @ MIN V (see point1).4. The line connecting points 1 and 2 constructs the acceleration curve for the system voltage level defined by theVOLTAGE DEPENDENT MIN MOTOR VOLTS setting. The acceleration time-current curve for the minimum voltage starting
