Schweitzer Engineering Laboratories SEL-749M, Instruction Manual

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F.11
Date Code 20080918 Instruction Manual SEL-749M Relay
Motor Thermal Element
Thermal Element Trip-Time Equations
RTC
≠
Auto
Equation F.14
Curve Method
Equations
Equation F.15 and Equation F.16 apply to the starting element when
12
≥ Ι ≥
2.5 and SETMETH = Curve. To obtain the trip time (cold rotor),
substitute and in
Equation F.10 .
Equation F.15
To obtain the trip time (hot rotor), substitute
and in Equation F.10 .
Equation F.16
Equation F.17 applies to the running element when 2.5
> Ι >
SF and
SETMETH = Curve. To obtain the trip time (hot stator), substitute
and RTC in Equation F.11 .
Equation F.17
T
p
60 RTC
•
I
2
0.9 SF
• ( ) 2
–
I
2
SF
2
–
-------------------------------------
ln
•
=
U
0
0, = TD 1.0, = T
O
2.08 CURVE
• ( )
, = I
L
6.0 =
T
p
90 CURVE
•
I
2
-------------------------------- =
U
0
R, = TD 1.0, =
T
O
2.08 CURVE
• ( )
, = I
L
6.0 =
T
p
75 CURVE
•
I
2
-------------------------------- =
I
0
0.9 SF
• ( )
, =
T
p
2.5 CURVE
•
36 0.9 SF
• ( )
2
–
36 SF
2
–
---------------------------------------
ln
--------------------------------------------------
I
2
0.9 SF
• ( ) 2
–
I
2
SF
2
–
-------------------------------------
ln
•
=
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