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
Summary of Contents for 7SR105 Rho
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