Hello every body;

Our power plant:
3 gas turbo generators, frame5, GE, single shaft, 5100 rpm, Gear Box 5100/1500 RPM,

Our Plant:
approx. consumption 15 Megawatt.
the large motors in plant are two 4 Mega Watt elector motors with soft starter(Gas Comp. driver)

Problem:
when our power plant (normally one GT generator) feeds the plant and parallel with Grid,every thing is OK.

In Island mode, where we are disconnect from grid, and our plant supplied by one or two GT generator, exactly when we start the 4 MW elector motors, the in GT generators gear box occurred vibration and will trip the generators.

4 MW motors have one harmonic filters to compensate the 5, 7, 11 harmonics.

any help will be appreciated
Ali Shakarami

 

Ali Shakarami... please answer the following questions:

1) Does tripping alway occur when operating in island-mode + 2 genr's, or is it random?

2) Capacity of the three generators?

3) Rated-speed of motor (2-pole, 4-pole?)

4) Plant-load at tiime of starting motor?

5) The expected acceleration-time of the motor?

6) The pre- & post-trip MW, MVAr, kV, kA, values?

7) The protective relay that tripped the plant?

8) The protective relay that tripped the motor?

Regards,
Phil Corso

 

Hello Corso;

thank you for your consideration, here are answer of your questions.

1:we just operate our power plant in Island mode three times, 2 of them with one generators and 3ed operation with two generators. for all three test we have all gearbox radial vibration high and trip.

2: capacity of each generator is 26.5MVA total 79.5MVA

3: Rated-speed of motor are 2-pole

4: Plant-load at time of starting motor is about 5MW.

5: The expected acceleration-time of the motor? from zero to 60% less than 10 second

6: >MW, MVAr, kV,kA, are constant at pre-& post trip

7: The protective relay that tripped the plant is bently nevada vibration protection radial because of reach to radial vibration trip on gearbox.

8: i do not the idea about that but, we have the total shut down because of lack of power.

best regards.
Ali Shakarami

 

Ali Shakarami...

the information submitted is indicative of a severe starting-current unbalance, resulting in uneven heating of the generator’s rotor! This effect is caused by the negative-sequence component in starting-current, thus causing misalignment between the generator and gearbox! Negative-sequence can be quite debilitating even for 10-second duration!

However, the lack of recorded electrical-parameters associated with the “event’ precludes further analysis. One very important concern is your observation that, for the 2-gen case, both are tripped by vibration of just one gear-box!

Phil