GE 869 - Page 253

CHAPTER 4: SETPOINTS PROTECTION
869 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL 4–121
CURVE k FACTOR
Range: 1.00 to 1.50 in steps of 0.05
Default: 1.10
The setting applies only to the IEC motor curve and is applied as described below. Refer
to the IEC 255-8 standard for additional details on its application.
If “IEC” is selected as the Overload Curve, the 869 can apply the IEC 255-8 hot and cold
curve characteristics to the thermal model. In 869, appropriate selection of Hot/Cold
curve characteristic is based on the motor status and Thermal Capacity (TC) Used as per
the following table.
The IEC255-8 cold curve trip time is defined as follows:
Eq. 12
The IEC255-8 hot curve trip time is defined as follows:
Eq. 13
where:
•t
trip
= time to trip
• τ = IEC time constant defined by IEC Curve Time Constant setting
•I
motor
= measured motor load current
•I
p
= Motor load current before overload occurs
• k = k-factor (overload factor) defined by IEC Curve k Factor setting applied to FLA
• FLA = Motor rated current specified by the Motor Full Load Amps setting, can be found
in the
Setpoints > System > Motor menu
IEC CURVE TIME CONSTANT
Range: 0 to 1000 min in steps of 1
Default: 45 min
The setting specifies thermal time constant for IEC motor curves in the above equations
per the IEC 255-8 standard. When the IEC motor curves are selected, the 869 calculates
the time to trip using the IEC255-8 cold curve and IEC255-8 hot curve equations and
increases Thermal Capacity Used as defined by the Thermal Capacity Used equation
above. If the overload disappears or the motor is tripped (stopped), then the Thermal
Capacity Used decreases as per the equation (Eq. 8 in Cool Time Constant section) to
simulate motor cooling, depending on the motor status and the values programmed for
the Cool Time Constant Running and Cool Time Constant Stopped settings. If the IEC
curve is selected, then the following applies:
1. For two-speed motor applications, the IEC Curve k Factor and IEC Curve Time
Constant settings are used at both speeds.
Prior to overload condition Upon overload
condition
Selection of IEC curve
Characteristic by 869
Motor Status TC Used Motor Status
Stopped Less than 5% Starting Cold
Stopped Greater than or equal to 5% Starting Hot
Running Less than 5% Overload Hot
Running Greater than or equal to 5% Overload Hot