On September 27 at 11:30 a.m. in the Parque Barigui room, engineer Fabio Toshio Nakatani will give a presentation on: Hybrid analysis (man+technology) in predictive maintenance of rotating electrical machines. Discussing Industry 4.0 in the area of maintenance in relation to industrial automation and the integration of different technologies. Artificial intelligence, robotics, neural networks and big data with the aim of improving processes and increasing productivity and reliability. But where does this technological evolution leave the role of man (specialist)? How will integrated work between technology and specialists increase the degree of reliability of rotating electrical machines?

Register at https://cbmga.abramanoficial.org.br/ and visit the Nishi stand during your participation in the country’s main Maintenance and Asset Management event.

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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.

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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

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More contents of NISHISAN tips: https://nishi.com.br/novo/en/blog/

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What is corrective maintenance?

Still very present in companies, corrective maintenance is only used when some equipment breaks down or fails. This method does not use maintenance planning, which leads to the need for parts inventory and availability of professionals, since the failures are not foreseen and cause the idleness of machines and labor.

For example, a machine seems to be in perfect condition and in constant production, but at some point a part presented a failure and the production had to be stopped. Since there was no planning, the maintenance professional, before correcting it, needs to understand the problem, check if the part can be replaced and if there is in stock. This situation will cause the company to make the machine unavailable, which will generate costs per machine stopped, part that needs to be replaced, and labor costs.

When performed without planning, corrective maintenance generates huge inconveniences, compromising the fulfillment of deadlines and especially operational profitability.

What is preventive maintenance?

When we talk about maintenance planning, one of the best paths to follow is certainly the preventive maintenance. It is the maintenance that corrects problems and failures even before they happen, thus reducing costs, machine unavailability, and increasing maintenance efficiency. Its main characteristic is the possibility of scheduling maintenance, avoiding problems with parts inventory, idle machines, and lack of production.

The tip we leave in this maintenance is to focus on the expected result, to evaluate the condition and operational reliability of the equipment, and not to focus only on the execution of the tasks pre-established by the planning. In an electrical machine, the electrical and mechanical tests and visual inspection are conditions to analyze its results and from there make a critical analysis and conclude potential problems and the degree of reliability that it is, that is, for this the presence of an electrical machine specialist is essential.

In the market we also commonly hear the term “rejuvenation” for preventive maintenance, which can lead to a misinterpretation. There is no way to rejuvenate what is already aging. We can prevent accelerated aging.

What is predictive maintenance?

It is safe to say that predictive maintenance is a step ahead of preventive maintenance. It is the most accurate follow-up and planning maintenance, requires greater qualification of the professional and aims to prevent any failure of parts before they even present a defect. It is characterized by monitoring equipment parameters, such as partial discharges, vibration, temperature, etc.

Predictive maintenance uses the monitoring of the parameters of the parts so that their replacement can be done before the end of their useful life. By inspecting the machine, the maintenance professional – based on the monitoring parameters – identifies the need to change components and schedules the best moment for maintenance, which is done without intervention in production, facilitating maintenance and avoiding higher costs with machine idleness.

What company wants to stop its production because of a failure or defect? Very similar to preventive maintenance, predictive maintenance has as a positive point the possibility of programming its actions. Planning and follow-up of the parts are important factors, which working together, reduce costs with losses and increase the effectiveness in the production of the machines.

NISHI offers solutions for all types of maintenance. Contact us and request an evaluation of reliability and operational warranty of your electric machine.

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Induction motors have their stator winding divided into a number of poles (2; 4; 6; etc.) creating the rotating magnetic field and defining the synchronous speed in the stator. This rotating field induces voltages in the rotor generating currents in the rotor.

The field and current interacting with each other cause forces to arise that result in motor conjugate (torque), causing the rotor to rotate.

The rotor, if it turned at synchronous speed would have the same speed as the rotating field of the stator (inductor) and by the rules of induction there would be no induced voltage in the rotor and consequently no torque. The motor would stop spinning.

Normally it has a speed slightly lower than the synchronous speed and this difference, in percentage, is called slip. For small motors, the slip varies from 3 to 5% and less than 1% for medium and large motors.

Learn more about the services provided by Nishi and contact one of our experts for information about maintenance and characteristics of medium and high voltage induction motors.

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A common first question is what determines motor life? Is it determined by the lifetime of the insulation material? By the wear period of the bearings? By the deterioration of the steel? Others?

When we “explode” a motor and stratify its components we see in its composition basically steel, copper and insulating materials. When comparing the materials, we conclude that the insulating material is the most fragile in relation to the others. Is it correct to say that the life span of the motor is determined by the life span of the insulating material? What about the bearings that wear out over time, is it correct to say that the end of their life is the end of the motor’s life?

With good maintenance practices, ensuring the integrity of the insulation system can be a determining factor for long motor life. In medium and high voltage motors, predictive and preventive maintenance will prevent the acceleration of the aging of the insulation system. Statistics show that the stator winding alone accounts for almost 40% of failures.

Having knowledge of the failure mechanisms of a motor’s insulation system and intervening in them will ensure long-lasting uptime. We list below the main causes of failure or accelerated aging:

• high motor temperature;
• electrical stress;
• high contaminant environment.

It is common for all three phenomena to act simultaneously.

Learn more about the services provided by Nishi and contact one of our experts for information about failure modes of insulation systems.

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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 maintenance we have no way to make the machine “younger”. An insulating system, a bearing system, or others do not become younger after an intervention of this nature. Only in complete corrective maintenance can we rejuvenate it. By replacing the coils, the bearings and other items with new ones, we will be restoring the useful life of these components.

We consider preventive maintenance, which we prefer to call Overhaul (act or effect of reviewing or revising; inspection to correct or prevent failures). With the improvement of predictive techniques is increasingly common to preventive intervention as a complement to the indications and trends evaluated in predictive intervention.

In this work, the “keen eye” of the technical expert is fundamental to see, inspect, test, and systemically evaluate the components. To detect potential loss of life and also intervene at points that may be accelerating the aging process.

Inspections of the cooling system, insulation system, winding tie system, corona and partial discharges, wedges, bearings have avoided early and unexpected losses when detected and corrected. However, as we said, there is no way to “rejuvenate” if they are already aged.

Read more about the GAP-N electrical predictive analysis methodology for rotating electrical machines by clicking on the link:

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Moisture and dirt on stator or rotor windings decrease the insulation resistance by reducing surface resistivity. Operating a machine under these conditions can accelerate the aging of the insulator and even lead to equipment burnout.

A cleaning technique used in the market, besides the traditional one with electric solvent, is the application of CO2 in the insulation system. This cleaning consists of blasting CO2 in the solid state, by means of appropriate equipment, where kinetic energy, thermal shock, and thermo kinetic energy (sublimation effect) must be controlled to remove the dirt without affecting the insulating material. The knowledge of the insulating material is fundamental to determine the parameters of the application method and to avoid damage to the material to be cleaned.

The principle is based on throwing a jet of ice at high pressure and speed that, when it collides with the surface to be cleaned, causes two phenomena (a) cooling of the set dirt + substrate (base or surface to be cleaned), which by the temperature gradient, instantly causes cracks that become weak points in the mass of contaminants on the equipment to be cleaned; (b) in parallel, the ice molecules collide with the surface and their sublimation occurs (they pass from the solid state directly to the gaseous), with the molecules expanding their volume by approximately 800 times, instantly. In a colloquial way, we can say that millions of microbursts occur that cause the “dirty mass” to be pulled off the surface from the inside out, by detachment. Since the dirt or contaminant surface is not cohesive (it is “cracked” by instant cooling), the layer of material to be cleaned is removed with impressive efficiency.

This procedure should not be confused as a simple machine “washing” technique, but rather as a process of recovering the insulating system from dirt and moisture. The technician who operates the system is not a simple “washer”, but an electric machine specialist who knows the winding and the insulating system and evaluates its degradation stage, thus avoiding undesirable results. We also caution that the types of soiling are crucial to the effectiveness of the result and also to the choice of intervention method – traditional solvent or dry ice.

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