For a reduced voltage, the starting current almost reduces linearly. At 80 % of the rated voltage, the maximum
starting current is 0.8 ⋅ I
starting
= 3.3 A.
The current threshold for detecting a motor starting must be bigger than the motor secondary rated current
and must be smaller than the maximum starting current. If no other influencing factors are present (peak
loads), the value for
Curr.thres.starting
, which is configured in the Motor-state detection function
block, can be an average value as follows:
Set the
Curr.thres.starting
= 2.1 A.
The
Tempr.thres. cold motor
parameter is used to set the threshold for the cold motor. If the rotor
temperature exceeds the
Tempr.thres. cold motor
, the motor is in
Warm
state. Otherwise, the motor is
in
Cold
state. The setting value of the
Tempr.thres. cold motor
parameter depends on the permissible
numbers of the cold and warm starts as follows:
Considering a safety tolerance, Siemens recommends setting the
Tempr.thres. cold motor
parameter to
40 %.
Step 5: Motor Restart Inhibit
Thermal Replica Rotor Function Block in the Motor Function Group
(_:104) Perm.no. of warm starts = 1
The permissible number of warm starts
(_:105) Perm.no. of cold starts = 2
The permissible number of cold starts
(_:106) Factor T-const. at oper. = 5.0
The extension factor for the cooling time constant
when the motor is running
(_:107) Factor T-const. standstill = 10.0
The extension factor for the cooling time constant
when the motor is stopped
(_:108) Starting time = 8.2 s
The maximum permissible starting time of the motor
(_:109) Equilibrium time = 1.0 min
The time of the standstill state for a motor
(_:112) Start.cur./mot.rated cur. = 5.2
The starting current which is a per-unit value with the
motor rated current as reference
Thermal Stage
(_:1) Mode = on
The mode of the stage
(_:11221:103) Min. restart inhibit time = 6.0 min
The minimum duration for the restart-inhibit time
Step 6: Determining the K-Factor
Take the maximum permissible current I
max, perm.
as 1.1 times motor rated current I
rated, motor
.
Thermal Overload Protection, 3-Phase - Advanced
(_:106) K-factor = 1.1
The parameter which is used to describe the limiting
value for the maximum permissible continuous load
Step 7: Selecting Overload Protection and Tripping Characteristics
Thermal Overload Protection, 3-Phase - Advanced
(_:101) Threshold current warning = 1.1 ⋅ I
rated,sec
=
0.88 A
The threshold to the maximum permissible contin-
uous current I
max, perm
(_:104) Threshold thermal warn. = 90 %
The threshold to indicate the thermal warning
(_:110) Thermal time constant = 150 s
The thermal time constant
Setting Example
SIPROTEC 5, Additional Information on the Protection of Explosion-Proof Motors with Type of Protection Increased Safety e,
Manual
27
C53000-H5050-C078-1, Edition 03.2019
