Frequently asked questions (FAQ)

Listed below are some of the most frequently asked questions we receive from our customers. Hopefully you will find the answers to these questions helpful if you have a similar enquiry. If you need further assistance do not hesitate to contact us.

FAQ – Generators

1      Q    The Rotor Ground Fault Alarm is activated on my generator. Can I continue to run and check it out sometime later?

         A    No, You should not operate the generator with a rotor ground fault. You need to stop the generator, ascertain the cause of the ground fault and rectify before returning the generator to service.

2       Q   I notice there is a earthing/grounding brush on the drive end of the generator shaft. What is the purpose of this brush?

          A  When the rotor is turning at full speed the film of oil between the rotor and bearing journal acts as an insulator.  Without a earthing/grounding brush, voltages could build up on the rotating shaft and discharge via the bearing Journal which would eventually damage the journal and Bearing Babbitt. Brushes should be renewed when their length has worn down to 14mm.

Special Offer!! - Click here for replacement earthing/grounding brushes

3       Q   The generator DE vibration alarm is activated can I continue to run in this mode?

          A   Yes, but only for investigative purposes. You should look for increase in vibration trends; determine if the vibration is time related or the result of a step change. You should advise BRUSH and the Turbine manufacture without delay.

4       Q   The Leak Detector Alarm on my TEWAC generator is activated.  Can I continue to run in this mode?

          A   You should remove the generator from service. Internally inspect the cooler nests for leakage and repair before returning the generator to service.

5       Q   I have a BRUSH Frame 7-290ERJT generator. During start up the turbine is unable to break away?

          A    The most likely cause is lack of generator shaft lift. Make sure the Generator Lift Oil pump is operating, check the shaft lift which should be at least  0.0015".

6    Q  What is meant by the term  Polarization Index?

         A    A Polarization Index (PI) is usually carried out on the generator stator winding using a 5000 Volt Insulation Tester.  The PI is the result obtained by dividing the 10 minute by 1 minute reading. This PI ratio can be a high as 8 but should not be less than 2.

FAQ – AVR’s

1    Q      My AVR has tripped to Standby. Can I continue to operate in this mode?

       A      Yes, But you should determine the cause of the trip, reset the monitor and transfer back to Main Control ASAP

2     Q     Why is the over-flux alarm activated on my AVR. This is prevented me from Exporting MVAR’s?

        A     This is because the over-flux limiter set point has been reached, usually 1.15 per unit, this value is set by design to prevent over-fluxing of the generator and possible damage to the core-pack.

3     Q      The Diode Failure Alarm is indicating on my AVR, Can I continue to operate the generator?

        A      Yes, But at the earliest opportunity you should shut the unit down and check the fuses and diodes on the Rotating Rectifier assembly.

4       Q   We have the old type MAVR voltage regulator at our site. How often should it be calibrated?

         A    At least every 3 years. Remember these analog units are no longer manufactured, you should consider upgrading to the BRUSH Digital Excitation controller.