This is one of the largest thermal power plants in MENATI region with a capacity of 1500 MW with multiple Gas Turbines and Steam Turbines operating in combined cycle.
Challenge & Resolution
In March 2021, during the Covid-19 pandemic outbreak, the Original Equipment Manufacturer (OEM) had just completed a major outage on one of the critical steam turbine generators, including replacement of STG blades, replacement of the turning gear toothed wheel which is mounted close to ST Bearing-1, and removal and inspection of the generator rotor. The customer invited Bently Nevada’s Machinery Diagnostic Services to support the startup activities, including possible in-situ balancing of the unit.
The unit was started and loaded, but after thermal stabilization, while passing through 1st critical speed during shutdown, the unit tripped. During the subsequent startup, the customer observed that the vibration during transient and steady state operation were relatively high as compared with pre-outage levels.
Based on data collected by Bently Nevada’s ADRE data acquisition unit, a static weight of 400 gm was installed on both steam turbine balancing planes, resulting in significantly reduced vibration levels at the 1st critical speed during the following startup. Overall vibration amplitudes reduced from 260 µm pp to 158 µm pp at the 1st critical speed which was now just below the ISO Zone B Limit of 165 µm pp.
A coupled balance shot of 300 gm on each plane was installed to reduce the vibration at the 2nd critical speed, and the previously installed 400 gm weights at both ends were shifted. This significantly reduced the balance resonance response at both critical speeds. The 1st critical speed amplitude reduced from 260 µm pp to 118 µm pp, while the operational speed amplitude reduced from 130 µm pp to 60 µm pp.
Bently Nevada’s accurate diagnostic assessment and efficient balancing of Customer’s Steam Turbine Generator just in two shots resulted in a drastic reduction of vibration levels, enabling the plant to bring the unit online for production, avoiding additional startups, further OEM mobilization costs, and heavy government penalties associated with delays.
Fig. 2 - Bode plot of Steam Turbine Vrg-1X Before and after Balancing.
The OEM sent appreciation to Bently Nevada for the expertise and efficient support provided to the Customer which allowed them to bring unit online within very short time in following words:
This is to commend the support of the BH Team for the successful Steam Turbine Rotor Balancing job at customer’s site. This email also comes to communicate the customer satisfaction to Muhammad Akmal. The customer’s plant management team was very happy and said very good words for Akmal for his professionalism, expertise, and candor. Akmal took full ownership of the task and delivered beyond expectations to ensure timely conclusion of customer outage.