Siemens 7SR105 Rho - Page 179

7SR105 Rho and 7SR17 Rho Applications Guide
©2018 Siemens Protection Devices Chapter 7 Page 6 of 31
Generally the relay thermal setting calculation is carried out in the following order:-
Motor Rating Plate or Data Sheet Information
Where available:
Rated output kW
Rated Voltage kV
Rated Frequency
Hz
Rated Power Factor
Rated Efficiency % (95% default
)
Service Factor
Stall Withstand Time Cold
/Hot
secs
Starting Method
Locked Rotor Current A primary
Permitted starts cold/
hot
Start Time
@ 100% Voltage
Max. Starts Per Hour
Min. Time Between Starts
Control Device
Calculate Thermal Protection Settings
Overload: OL protection settings, alarms and inhibits
Stall protection settings
Start protection settings
Current Unbalance protection settings
CT and VT Connection Details
CT turns ratio (T
)
VT Ratio and connection
Enable and Set Other Protections as Required
Nominate Basic Thermal Settings
NPS Weighting
Thermal Overload Setting (
49 Itheta)
Motor Start Current (x Itheta)
Motor Stop Current (
x Itheta)
Figure 2-2 Summary of Protection Settings Calculation Procedure