Q4 An industrial motor is to be protected against overload. Its nameplate details are three-phase 3.3 kV, 500 kW, 75 % efficiency and 0.85 power factor. The motor can withstand 15% overload continously. The time constant of heat withstand characteristic is 10 minutes. A thermal relay is connected across a C.T. of 120/1 ratio. The time constant of the relay is also 10 minutes. The range of settings is 70 % to 150 % of 1 A in steps of 5 %. Suggest the proper relay setting for this application

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An industrial motor is to be protected against overload. Its nameplate details are
three-phase 3.3 kV, 500 kW, 75 % efficiency and 0.85 power factor. The motor can
withstand 15% overload continuously. The time constant of heat withstand
characteristic is 10 minutes. A thermal relay is connected across a C.T. of 120/1
ratio. The time constant of the relay is also 10 minutes. The range of settings is 70
% to 150 % of 1 A in steps of 5 %. Suggest the proper relay setting for this
application.
Transcribed Image Text:Q4 An industrial motor is to be protected against overload. Its nameplate details are three-phase 3.3 kV, 500 kW, 75 % efficiency and 0.85 power factor. The motor can withstand 15% overload continuously. The time constant of heat withstand characteristic is 10 minutes. A thermal relay is connected across a C.T. of 120/1 ratio. The time constant of the relay is also 10 minutes. The range of settings is 70 % to 150 % of 1 A in steps of 5 %. Suggest the proper relay setting for this application.
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