We will be discussing an example of the generator failure mechanism which can lead to a quick (months!) insulation breakdown. Do you wish to know that it is?

Please join us on Thursday 04 May 2023, 11am Brazil time (3pm UK time). We will go through details and RCA of 2 generator breakdowns, with hope that it will help you to prevent such situation in the future.

Please join the training using the link below:  
https://meet.zoho.eu/UDSxeI82x6

NOTE:
Please remember to register before the meeting, as number of participants is limited. Chrome and Firefox do not require downloading any other add-ons or apps, therefore these are preferable web browsers. Other web browsers may require downloading additional files. Please check with your IT Department.

O post FREE WEBINAR: Generator failure – Root Cause Analysis (RCA) of 2 generators with insulation breakdown apareceu primeiro em Nishi.

Voltage classification of generators/motors:

• Low Voltage: Round or Enameled Wire / Voltage Class: 127/220/380/440/760 V.
• Medium Voltage: Rectangular Wire / Coils or Bars / Voltage class: 2,3/3,4/4,16/6,6/6,9 kV.
• High Voltage: Rectangular Wire / Coils or Bars / Voltage Class: 13,8/16,5/18,0 kV or higher.

Standardized offline electrical testing:

• Insulation Resistance (IEEE-43);
• Polarization Index (IEEE-43);
• Ohmic Resistance (IEEE-118);
• HypotAC/DC (IEEE-4 / IEEE-95);
• Step VoltageDC (IEEE-95);
• Surge Test (IEEE-522);
• Off-line Partial Discharges (IEEE-1434 / IEC6034-27-1);
• Delta Tangent (IEEE-286);
• Capacitance (IEC 60034-27-30);
• Corona in darkroom) (IEEE-1799).

Turn on the subtitles in your language and watch below in Nishi’s Youtube channel the live recording and learn more about the definition and application of each electrical test according to voltage level and how it is essential for a good diagnosis of the condition of the motor/generator winding.

Take part in upcoming live opportunities to ask questions and make comments directly with an expert on rotating electrical machines.

Get in touch directly with engineer Fabio Toshio and get your questions answered: fabio.toshio@nishi.com.br

Request a commercial proposal: E-mail: nishi@nishi.com.br

O post Electrical Tests: Low Voltage Winding x Medium High Voltage apareceu primeiro em Nishi.

The brushless excitation system consists of an AC exciter and a rotary rectifier mounted on the same shaft as the generator. The exciter resembles a commutator less DC machine, with a field winding on the stator and an armature on the rotor. The output of the rotating armature of the three-phase AC exciter supplies a shaft-coupled rotary rectifier that supplies the generator field with direct current.

The great advantage of this excitation system is the non-use of brushes and collector rings that require special care, such as the cooling of the collector rings and the useful life of the brushes. The main precautions in this system are in the rotating plate that suffers centrifugal forces during operation. It is recommended that the semiconductor devices (diodes) and their fastening system be inspected at least once a year.

Watch the video demonstration of a maintenance of a turbogenerator rotor with Brushless excitation system:

Want to know more about turbogenerator maintenance tips? Contact our team for maintenance planning of your equipment.

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In the insulating system of the coils we have the deterioration of the main phase x internal ground wall and the contact surfaces between coil x core or between coils of different phases in the region we call. The internal discharges are monitored through specific equipment, mainly measuring partial discharges. Surface discharges, on the other hand, can be monitored by equipment or also through visual inspections.

The coils, when manufactured, with the objective of avoiding these surface discharges, have a corona suppressor system in the grooves and in their exit region. The material applied in the groove is conductive and in the output a semi-conductive with specific characteristics that soften the rapid rise of the electric field when there is a loss of reference to ground. These 2 materials (conductive and semi-conductive) are electrically connected, a region called the corona sleeve.

Over time of operation and during routine maintenance it is a practice, when visually observing the appearance of corona in these regions, to correct these points of the corona suppressor system.

The tip and warning we want to leave is that this action must be done with great care, because it seems that it is only a dark “paint job” and only its repainting does not guarantee the success of the operation, on the contrary, it may even make it worse. As we have already pointed out, its function is electrical, and the premises of smoothing the electric field must be maintained to achieve the goal of avoiding discharges in this region.

Contact our team and clarify your doubts about corona suppressor system and make an evaluation of your case with us.

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Endwinding vibrations is a failure mode that is becoming recurrent in large turbogenerators, especially those manufactured since the last two decades. This problem is not unique to one manufacturer and affects most of them, and may be related to market competitiveness and the need to reduce manufacturing costs. One of the parts affected by these cost reductions are the endwinding, which have suffered modifications in the old and consolidated fastening systems that did not present such problems.

Combining the problems in the design/manufacturing with the generator’s operating conditions, this problem can lead to major failures/losses, in the most severe cases, lead to short circuit of the winding and consequent need for rewinding of the stator. Besides the clear losses with the sending of the generator for maintenance, there is also the high loss in energy production due to the inability to operate the machine. Thus, the identification of problems related to vibration in the endwinding should be found as soon as possible.

By performing inspections, associated with periodic tests on the endwinding, failures and the most serious scenario can be avoided and as will be demonstrated in this article, by performing the bump test and the correct interpretation of its results, it is possible to identify the regions with endwinding vibration problem and perform the appropriate and timely corrections.

Watch the presentation below:

Read more Nishisan tips in our Blog and contact us to clarify your doubts about the solutions offered by Nishi in the maintenance of your equipment.

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