Multilin 469 Motor Management Relay ... - GE Digital Energy

CHAPTER 5: SETTINGS
Overload Curve feature is tailored to protect these types of motors. Voltage is continually
monitored during motor starting and the acceleration thermal limit curve is adjusted
accordingly.
The Voltage Dependent Overload Curve is comprised of the three characteristic shapes of
thermal limit curves as determined by the stall or locked rotor condition, acceleration, and
running overload. The curve is constructed by entering a custom curve shape for the
running overload protection curve. Next, a point must be entered for the acceleration
protection curve at the point of intersection with the custom curve, based on the minimum
allowable starting voltage as defined by the minimum allowable line voltage. The locked
rotor current and safe stall time must also be entered for that voltage. A second point of
intersection must be entered for 100% line voltage. Once again, the locked rotor current
and the safe stall time must be entered, this time for 100% line voltage. The protection
curve created from the safe stall time and intersection point will be dynamic based on the
measured line voltage between the minimum allowable line voltage and the 100% line
voltage. This method of protection inherently accounts for the change in motor speed as
an impedance relay would. The change in impedance is reflected by motor terminal
voltage and line current. For any given speed at any given line voltage, there is only one
value of line current.
5–48 469 MOTOR MANAGEMENT RELAY – INSTRUCTION MANUAL