GE N60 Instruction Manual page 328

CONTROL ELEMENTS
5
The thermal overload protection element estimates accumulated thermal energy E using the following equations
calculated each power cycle. When current is greater than the pickup level, I
thermal energy:
When current is less than the dropout level, I
where
∆t is the power cycle duration
n is the power cycle index
t is the trip time calculated at index n as per the IEC255-8 cold curve or hot curve equations
op(In)
t is the reset time calculated at index n as per the reset time equation
rst(In)
5-212
Figure 5-106: IEC 255-8 sample operate and reset curves
E = E + ------------- -
n n 1
– t
> 0.97 × k × I , the element starts decreasing the thermal energy:
n B
------------- -
E = E
–
n n 1
t
–
N60 NETWORK STABILITY AND SYNCHROPHASOR MEASUREMENT SYSTEM – INSTRUCTION MANUAL
> k × I , element starts increasing the
n B
t 
 
op In
t 
 
rst In
CHAPTER 5: SETTINGS
Eq. 5-16
Eq. 5-17