Motor Protection Principles.pdf

More documents

Recommendations

Info

Short Circuit <strong>Protection</strong> • The short circuit element provides protection for excessively high overcurrent faults • Phase-to-phase and phase-to-ground faults are common types of short circuits • When a motor starts, the starting current (which is typically 6 times the Full Load Current) has asymmetrical components . These asymmetrical currents may cause one phase to see as much as 1.7 times the RMS starting current. • To avoid nuisance tripping during starting, set the the short circuit protection pick up to a value at least 1.7 times the maximum expected symmetrical starting current of motor. • The breaker or contactor must have an interrupting capacity equal to or greater then the maximum available fault current or let an upstream protective device interrupt fault current. 32
Stator RTD <strong>Protection</strong> • A simple method to determine the heating within the motor is to monitor the stator with RTDs. • Stator RTD trip level should be set at or below the maximum temperature rating of the insulation. • For example, a motor with class F insulation that has a temperature rating of 155°C could have the Stator RTD Trip level be set between 140°C to 145°C, with 145° C being the maximum (155°C - 10°C hot spot) • The stator RTD alarm level could be set to a level to provide a warning that the motor temperature is rising 33
Page 1 and 2: Motor Protection Principles Craig W
Page 3 and 4: Various Industry Motor Applications
Page 5 and 6: Thermal Stress Causes Motor Failure
Page 7 and 8: Motor Electrical Protection • The
Page 9 and 10: Thermal Model - Motor States • Mo
Page 11 and 12: Thermal Overload Pickup • Set to
Page 13 and 14: Overload Curve Selection for Therma
Page 15 and 16: Hot/Cold Safe Stall Ratio HCR = LRT
Page 17 and 18: Overload Curve Selection A custom o
Page 19 and 20: Thermal Model - Current Unbalance B
Page 21 and 22: Thermal Model - RTD Bias • Accele
Page 23 and 24: Overvoltage Protection • The over
Page 25 and 26: Unbalance Protection • Indication
Page 27 and 28: Ground Fault Protection Zero Sequen
Page 29 and 30: Differential Protection • Differe
Page 31: Differential Protection Biased diff
Page 35: Conclusions • Induction & synchro

Motor Protection Principles.pdf

Create successful ePaper yourself

Delete template?

Save as template?