Energy conservation by addressing the resonance of a VFD driven condensate extraction pump at Dahanu Thermal Power Station (DTPS)

摘要

This paper shares a success story following the implementation of CM techniques at Dahanu Thermal Power Station (DTPS), wherein an imminent resonance problem of the variable-frequency drive (VFD) driven 650 kW HT auxiliary condensate extraction pump 2B was diagnosed. In 2007, a VFD was retrofitted for reducing pump speed in order to achieve energy conservation. Reducing the pump speed with the control valve in the fully open condition after VFD installation achieves deaerator level control as well as a reduction in power consumption. On 17 July 2014, the pump's mechanical seal was replaced to attend to a leakage and the pump was put back into service. On 22 July 2014, it was observed that in the motor drive-end (DE) bearing vertical vibrations deviated from 0.6 to 3.1 mm/s (RMS) between speed ranges of 1310 to 1335 r/min in VFD mode. From a vibration spectrum analysis, an electrical or mechanical resonance problem was suspected. A total harmonic distortion (THD) measurement of the VFD was carried out but all readings were found to be within limits, which eliminated the possibility of electrical resonance. To pinpoint mechanical resonance, a bump test was carried out. It showed the natural frequency of the system to be 1320 r/min, which is very close to the operating speed of the pump in VFD mode.