sepam 20 user manual - Schneider Electric

Protection functions Thermal overload
ANSI code 49RMS
Setting examples
Example 1
The following data are available:
b time constants for on operation T1 and off operation
T2:
v T1 = 25 min
v T2 = 70 min
b maximum curve in steady state: Imax/Ib = 1.05.
Setting of tripping set point Es2
Es2 = (Imax/Ib) 2 = 110 %
Please note: if the motor absorbs a current of 1.05 Ib in
steady state, the heat rise calculated by the thermal
overload protection will reach 110 %.
Setting of alarm set point Es1
Es1 = 90 % (I/Ib = 0.95).
Knegative: 4.5 (usual value)
The other thermal overload parameters do not need to
be set. They are not taken into account by default.
Example 2
The following data are available:
b motor thermal resistance in the form of hot and cold
curves (see solid line curves in Figure 1)
b cooling time constant T2
b maximum steady state current: Imax/Ib = 1.05.
Setting of tripping set point Es2
Es2 = (Imax/Ib) 2 = 110 %
Setting of alarm set point Es1:
Es1 = 90 % (I/Ib = 0.95).
The manufacturer’s hot/cold curves (1) may be used to
determine the heating time constant T1.
The approach consists of placing the Sepam hot/cold
curves below the motor curves.
DE50368
Figure 1: motor thermal resistance and thermal
overload tripping curves
time before tripping / s
665
70
PCRED301005EN - 06/2008
2
1
1.05 2
motor cold curve
Sepam cold curve
motor hot curve
Sepam hot curve
I/Ib
For an overload of 2 Ib, the value t/T1 = 0.0339 (2) is obtained.
In order for Sepam to trip at the point 1 (t = 70 s), T1 is equal to 2065 sec ≈ 34 min.
With a setting of T1 = 34 min, the tripping time is obtained based on a cold state
(point 2). In this case, it is equal to t/T1 = 0.3216 ⇒ t ⇒ 665 sec, i.e. ≈ 11 min,
which is compatible with the thermal resistance of the motor when cold.
The negative sequence factor is calculated using the equation defined on page 3/13.
The parameters of the second thermal overload relay do not need to be set.
They are not taken into account by default.
Example 3
The following data are available:
b motor thermal resistance in the form of hot and cold curves (see solid line curves
in Figure 1),
b cooling time constant T2
b maximum steady state current: Imax/Ib = 1.1.
Setting of tripping set point Es2
Es2 = (Imax/Ib) 2 = 120 %
Setting of alarm set point Es1
Es1 = 90 % (I/Ib = 0.95).
The time constant T1 is calculated so that the thermal overload protection trips after
100 s (point 1).
With t/T1 = 0.069 (I/Ib = 2 and Es2 = 120 %):
⇒ T1 = 100 s / 0.069 = 1449 sec ≈ 24 min.
The tripping time starting from the cold state is equal to:
t/T1 = 0.3567 ⇒ t = 24 min 0.3567 = 513 s (point 2’).
This tripping time is too long since the limit for this overload current is 400 s (point 2).
If the time constant T1 is lowered, the thermal overload protection will trip earlier,
below point 2.
There risk that motor starting when hot will not be possible also exists in this case
(see Figure 2 in which a lower Sepam hot curve would intersect the starting curve
with U = 0.9 Un).
The Es0 parameter is a setting that is used to solve these differences by lowering
the Sepam cold curve without moving the hot curve.
In this example, the thermal overload protection should trip after 400 s starting from
the cold state.
The following equation is used to obtain the Es0 value:
Es0 =
lprocessed ------------------lb
tnecessary 2 ----------------------
T1 – e
. lprocessed ------------------lb
2
– Es2
with:
t necessary : tripping time necessary starting from a cold state.
I processed : equipment current.
(1) When the machine manufacturer provides both a time constant T1 and the machine hot/cold
curves, the use of the curves is recommended since they are more accurate.
(2) The charts containing the numerical values of the Sepam hot curve may be used, or else
the equation of the curve which is given on page 3/13.
3/15
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