22 / 02 / 2022 5379 Views
  • Products

AT27- Compatible with all motor types!

The question of compatibility of frequency drives with electric motors used in industry and utilities has not often arisen today, and yet it is one of the key issues when the end user selects a frequency drive. Let's take a look at the main reasons that can influence the choice of a particular VFD for operation with different electric motors:

  1. Motor overheating;

  2. The breakdown of stator winding insulation;

  3. Wear of the electric motor bearing; and

  4. The technical condition of the electric motor.

1.Motor overheating

It is important to know that as the temperature of motor windings rises above the permissible values, the service life of the insulation becomes shortened rapidly. Therefore, the heat resistance of the insulation is the main requirement that determines the reliability of operation and the service life of the motor, which on average should be 15-20 years. The most commonly used motors in the industry are made with heat resistance class B and F, with allowable temperatures of active parts of the motor at 130 ° C and 155 ° C, accordingly. For harsh operating conditions, motors with heat resistance class H, with an allowable temperature of the active parts of the electric motor at 180 ° C, are produced. In general, these are motors for special purposes, designed for metallurgy, mining equipment and transport. Therefore, it is important not to create additional heating of the motor during its operation from the VFD.

This is possible if the stator and rotor windings are not influenced by harmonic currents or are within the limits specified in IEC 60034-17. Higher voltage and current harmonics in an Induction motor powered by a frequency drive cause additional losses in the steel, stator, and rotor windings. For motors powered by voltage inverters, the additional losses in the steel cannot be neglected. They depend on the amplitude of the harmonic components of the phase voltages and are almost independent of the frequency (see fig. below item 3).

While winding losses are strongly frequency-dependent and decrease with increasing frequency (see fig. below, item 2). The leakage inductances of these windings limit the harmonic currents determining the losses in the motor windings. Although the currents of these harmonics are small, their losses in the windings also cannot be neglected due to current displacement (surface effect and skin effect) at high frequencies. This circumstance applies to both coil and bulk windings. Rotors with a pronounced displacement effect are particularly sensitive to these losses. The dependence of steel and winding losses is shown in the figure below.

1 - total losses caused by harmonics; 2 - losses in windings; 3 - losses in steel

Numerous tests have shown that the total amount of additional losses caused by harmonics is independent of the load. It decreases with increasing switching frequency, as shown in the figure below, due to the reduction of winding losses at high switching frequencies.

Additional heating of the active parts of the electric motor leads to the fact that not all frequency drives are able to operate with electric motors made with heating class B. This is a fairly large group of electric motors, which were originally designed for a direct or soft start without frequency control. An example of how the insulation of the old windings of an electric motor with thermal class B, which has been operated under harsh conditions, is damaged, is shown in the figure below:

Corona discharges are shown in places of stator winding damage during an ultravision examination of stator insulation of an induction electric motor.

2.Breakdown of stator winding insulation

One of the most dangerous effects leading to the damage of stator windings is the effect of dV/dt of the output voltage of the frequency drive. There are many myths surrounding this phenomenon due to a lack of understanding of its effect and how it affects the insulation of stator windings.

Let's consider in detail the nature of this effect, as well as the physical processes in the motor windings caused by it.

1.

dV/dt- is the rate of the rise of the output voltage of the frequency drive, determined by the edge of the voltage generated by the power switch of the VFD inverter, e.g., an IGBT transistor.

According to IEC 60034-25, dV/dt is defined as:

where
V90% - voltage level corresponding to 90% of the pulse amplitude value, V; V10% - voltage level corresponding to 10% of the pulse amplitude value, V; and tr – pulse voltage rise time from the 10% level to the 90% level, µs.

2.

The pulse of the generated voltage is sent to the electric motor through the connected cable line. At the motor terminals the pulse is converted into a voltage whose shape resembles a damped oscillation, whose amplitude reaches twice the amplitude of the generated VFD pulse (see IEC 60034-17, IEC 60034-25). In some cases, the increase in peak voltage on the motor terminals exceeds the allowable values for long-term operation, which leads to rapid aging and breakdown of the stator winding insulation.

The figure below shows an equivalent diagram of the cable line between the VFD and the motor, and the response of the cable line to the applied voltage pulse.

Typical output voltage pulses in one phase of the VFD (graph C) and at the motor terminals at the end of the cable line (graph M).

3.

Depending on the quality and homogeneity of the impregnation, the material may contain voids (cavities) in which the process of destruction of the inter-strand insulation occurs. Deterioration of motor insulation due to voltage peaks occur by means of partial discharges. A complex effect occurs as a result of Corona. There is a relative voltage between neighboring charged conductors, which leads to an electric field. If the generated electric field is high enough (but lower than the breakdown voltage of the insulating material), the electrical strength of the air is broken. If enough energy is available, oxygen (O2) is ionized into ozone (O3). Ozone is extremely aggressive and damages the insulation. For this, the voltage on the conductors must exceed a critical threshold value, the so-called "Corona Start Voltage", i.e., the local breakdown strength in the air (in the void). The Corona Start Voltage depends on the winding design, insulation type, temperature, surface characteristics and humidity. The weakest insulation is the inter-twist insulation, especially in the area of the outermost turns (see IEC 60034-17).

Example of damage to the stator winding insulation of an induction motor.

Wear of the electric motor bearing

Accelerated wear of the bearing due to the frequency drive and motor operating together is one of the crucial criteria for selecting a frequency drive for operation with old, non-frequency-controlled motors. The essence of the problem is the presence of higher-order in-phase harmonics in the output form of the VFD voltage and the flow of currents through which the parasitic capacitance of the motor leads to the degradation of the reference bearing. IEC 60034-17 specifies that when a motor is operated from a sinusoidal mains voltage, the circular flux of the stator yoke induces an axial electromotive force (EMF) in the circuit formed by the shaft, bearings, flange and housing, as shown in the figure below.

The ring is defined as the axial EMF and parasitic current icirc

The ring flux is caused by inhomogeneities of the fair (dovetail for fair attachment, vent channels, and magnetic anisotropy of the plates). Usually the axial EMF is determined by the supply frequency and its threefold frequency caused by nonlinearity of the magnetization circuit. Experience has shown that if the axial EMF does not exceed 500 mV, there is no need for additional protective devices. Otherwise, currents pass through the bearings, which can destroy them within a short time. Bearing insulation, particularly at the rear end of the shaft, is generally sufficient to avoid currents flowing through both bearings and the mechanical parts of the drive that connect it to the load. This insulation is not necessary for motors manufactured to modern requirements and supplied with sinusoidal voltage.

However, when supplied by a frequency drive with a voltage inverter, interference occurs, and its maximum value is within 50% of the DC-link voltage value. Since interference in all windings is in-phase, it can be considered as a zero sequence in the voltage composition. An equivalent circuit for interference is shown in the figure below.

Parasitic current circuit diagram and bearing voltage

Where:

B- bearing;

C- cable;

Csr- stator-rotor capacity;

CB- bearing capacity;

Csf- stator- Enclosure capacity;

Crf- capacity rotor - Enclosure;

IB- bearing current;

IEDM- breakdown current;

L0- leakage inductance;

RB- bearing resistance;

R0- winding resistance;

Vsng- neutral stator- earth voltage;

Vbrg- bearing voltage;

Vcm- interference voltage.

When powering from an inverter as opposed to a mains supply with sinusoidal voltage, capacitive components of resistances play a large role at high frequencies. The amplitude of the interference depends on the resistance (mainly the reactive component) of the circuit through which it flows. This circuit is shorted at the zero point of the inverter. In general, parasitic currents flow through the motor bearings in three circuits. The practice of operating properly earthed drives with frequency drivers shows the following.

In motors with a shaft height of up to 280 mm, experience has shown that bearings rarely fail due to the inverter. Nevertheless, it can be argued that dielectric wear is highly dependent on the control method and switching frequency of the inverter. The use of inverters with switching frequencies above 10 kHz and voltages above 499 V requires attention to bearing isolation.

The effect of bearing wear can be eliminated by replacing it with an insulated bearing, but this is an additional cost that not all VFD users are willing to accept.

Technical condition of the electric motor

The technical condition of the motor largely determines whether it can work together with a frequency drive. This includes:

1.Operation with a reduced thermal class;

2.Operation with old weakened insulation;

3.Operating with uninsulated bearings;

4.Rapid passage of resonant frequencies.

This is a list of the most common problems of electric motors with poor technical conditions, which the AT27 series VFD copes with perfectly.

How does TRIOL solve this problem?

To solve the above-mentioned problems associated with the use of a frequency drive together with an electric motor, the TRIOL Corporation offers medium voltage frequency drives of the Triol AT27 series. They are built according to a multilevel topology using an input power phase-shifting transformer, the scheme of which is shown below:

Functional diagram of AT27 series frequency drive with 6 kV output operating voltage.

Such an architecture of the frequency drive allows the motor to form symmetrical quasi-sinusoidal output voltages with THDU ≤ 5%

Diagram of the quasi-sinusoidal output voltages of the AT27 frequency drive. PWM frequency in voltage form is 3...10 kHz depending on the number of cells in phase.

A specially developed algorithm of adding output voltages of each power cell to the total VFD output voltage allows TRIOL Corporation to reduce the level of dV/dt = 40...50 V/µs.

Oscillogram of the step component in the form of the AT27 VFD output voltage with dV/dt = 40 V/µs. The optional sine filter enables sinusoidal output voltages with THDU ≤ 2%, which removes any restrictions on the length of the cable line and the condition of the insulation of electric motors.

Review a summarization of how the above solutions allow the application of the Triol AT27 with any type of motor:

Conclusion

Understanding the physical processes that occur in electric motors at all life cycles and experience in studying the practices of operating users of operated electric motors has allowed TRIOL Corporation to develop a set of technical solutions that enables one to exclude any restrictions on the use of AT27 frequency drive with the existing number of general industrial and special electric motors. This has made the TRIOL AT27 VFD a valuable tool for the implementation of a wide range of tasks in industrial and municipal sectors.

close
АТ24 all regions 15.06
Triol Corporation
Triol AT24 Series: intellectual universal unique ultra-adaptive low-voltage drive (IUUU LV Drive).

Meet lines of Industrial Low Voltage VFDs AT24 Triol that are ready for order in Q3 2023!

Triol AT24 line UC

Upgrade your industrial processes with the intelligent Triol AT24 line UC Variable Frequency Drive (VFD). Experience high overload capability, precise frequency control, and increased control accuracy with the support of three encoder types. Enhance your system performance and efficiency today!

Learn more
Triol AT24 line UH

Optimize your operations in harsh environments with the Triol AT24 line UH Variable Frequency Drive (VFD). With its high-protective enclosure and separate airflow cooling channel, it's built to withstand extreme conditions. Experience reliable performance from -40 ºC to +50 ºC (-40...+122 F) and install it outdoors with confidence. Upgrade your system today for enhanced durability and efficiency!

Learn more
Frequency Drive AT24 line LE by Triol

Ensure the safe and reliable operation of elevator equipment with the Variable Frequency Drive AT24 line LE by Triol. Designed for synchronous and asynchronous, gear and gearless elevator winches, it offers advanced functionality and unique algorithms for modern elevators. Benefit from automatic measurements, easy configuration via Wi-Fi adapter and Triol Wizard, and reliable power supply with UPS operation. Upgrade your elevator system with Triol AT24 VFD line LE for enhanced performance and control.

Learn more

About Applications of LV AT24 VFD in different industries

Videos

Increase the profitability of rolled steel production with the specialized Triol AT24 VFD functions.

Learn in this video how to increase the profitability of rolled steel production with the specialized Triol AT24 VFD functions.

Learn more
Algorithm AT24 for controlling Sucker Rod Pump

Supercharge your Sucker Rod Pump operations with the cutting-edge AT24 algorithm.

Learn more
Improving the control efficiency of shipboard electric motors by implementing Triol VFD

Triol Corporation's AT24 and AT27 VFDs are cutting-edge solutions designed specifically for marine applications.

Learn more

Contacts

Dmitry Khachaturov

Dmitry Khachaturov Junior

Key Account Manager

Europe

dmitry.khachaturov.j@triolcorp.com

Nikita Poturoev

Nikita Poturoev

Head of Sales Department

Europe

n.r.poturoev@triolcorp.com

Discover new horizons with Triol equipment! 

close
Польша 30.05.23
Triol

Triol - Poland is gaining momentum!

We invite you to visit our new facilities in Poland!


Triol extends a warm welcome to our esteemed partners and new customers.

Dmitry Khachaturov
quote

Dmitry Khachaturov 

Junior

dmitry.khachaturov.j@triolcorp.com

PRODUCTION PROGRESS 

Availability of manufacturing:

  • Variable Speed Drive AK06 - 150 machines per month

  • Low Voltage VFDrive АТ24
    UC/UH line
    - 300 machines per month. 
    RT line - 100 machines per month. 
    MP line - 10 machines per month. 
    SD line - 30 machines per month

  • Downhole Measuring System TM01 - 50 machines per month

  • Medium Voltage Variable Frequency Drive AT27 - 10 machines per month

Poland
Video

Revolutionizing Offshore Electrical Equipment: E-Cabinet!

Available to order already!

Revolutionizing Offshore Electrical Equipment: E-Cabinet!
Learn more

Linear Electric Submersible Pump - EP01

To be available for order in August 2023

EP-01
Video

Triol TM01 Downhole Measuring System

Available to order already!

Triol TM01 Downhole Measuring System
Video

AT24 Triol Variable Frequency Drive 

Available to order already!

AT24 Triol Variable Frequency Drive
Video
close
email Eu 09.05
Triol Corporation

microsoftteams-image-4

Ver el vídeo

Triol AT27 línea ED tiene las dimensiones más pequeñas entre los VDFs de su clase.

Noticias

Revolutionizing Offshore Electrical Equipment: The Story of E-Cabinet.

Revolucionando el Equipo Eléctrico en Alta Mar: La Historia de E-Cabinet.

Aprende más
Construction material makes a difference!

El material de construcción hace la diferencia! Los intercambiadores de calor Triol están fabricados en acero inoxidable.

Aprende más
Reduce the risk of equipment damage and improve the energy efficiency of your equipment with Triol patented solutions!

Reduzca el riesgo de daños en los equipos y mejore la eficiencia energética de sus equipos con las soluciones patentadas de Triol!

Aprende más

Vídeos

Znimok_ekrana_2023-07-05_o_14

Soluciones Triol para aplicaciones HVAC.


Aprende más
Znimok_ekrana_2023-07-05_o_14

Variador confiable de voltaje medio (DD) VDF AT27 para operación en ambientes cálidos y húmedos

Aprende más
E-cab1

¡En septiembre de 2022, Triol lanzó el nuevo catálogo de productos E-Cabinet!

Aprende más

Contactos

22
Magdalena Maria Jarocka
 
Gestor de grandes cuentas

LATAM

m.m.jarocka@triolcorp.com

¡Abra nuevos horizontes con los equipos Triol!

close
Польша 13.02.23
Triol

TRIOL IS BACK TO BUSINESS!

Come to visit our new facility in Poland. More than 10 loyal partners have already audited Triol's new plant. We are ready to meet your needs and process your orders!

Mladen Spiric

MLADEN SPIRIC

Business Development Manager

mladen.spiric@triolcorp.com

RELOCATION IN POLAND

  • The plant construction has already started in June 2022

  • The first machine was launched
in July 2022

  • First electronics unit were produced in August 2022

  • First shipment made in October 2022

Poland
Video
Workers

PRODUCTION DYNAMICS

Production
 dynamics
Video
Catalog

Email us to find out more about our product line

View catalogs
close
email Eu 09.05
Triol Corporation
Open the door to more projects with Triol's smallest footprint VFD!

 News

Revolutionizing Offshore Electrical Equipment: The Story of E-Cabinet.

Revolutionizing Offshore Electrical Equipment: The Story of E-Cabinet.

Learn more
Construction material makes a difference!

Construction material makes a difference!

Learn more
Reduce the risk of equipment damage and improve the energy efficiency of your equipment with Triol patented solutions!

Reduce the risk of equipment damage and improve the energy efficiency of your equipment with Triol patented solutions!

Learn more

Videos

AT27 VFD Triol perfect operates with all types of motor windings

AT27 VFD Triol perfect operates with all types of motor windings!

Learn more
Perfect transfer of the motors to the distorted mains. And transfer from the mains.

Perfect transfer of the motors to the distorted mains. And transfer from the mains.

Learn more
Ventilation reservation as a tool to improve reliability

Ventilation reservation as a tool to improve reliability

Learn more

Contacts

Vasiliy Kravtsov

Mladen Spiric

Business development manager

Asia Pacific

mladen.spiric@triolcorp.com

Work with Triol — sell knowledge!

close
email 13.03
Triol Corporation
Сomplete Triol solution for offshore platforms

Solutions 

Triol SKID – Save time while commissioning and increase the personnel’s safety and comfort!

Triol SKID – Save time while commissioning and increase the personnel’s safety and comfort!

Triol Skid - a versatile and compact solution designed to simplify the commissioning process and enhance safety and comfort for personnel working in industrial environments

Learn more
Triol E-Cabinet – A specialized compact unit for oil production on offshore platforms

Triol E-Cabinet – A specialized compact unit for oil production on offshore platforms

Triol E-Cabinet - is a specialized compact solution combining in minimal dimensions a step-down phase-shift transformer, a variable frequency drive, and an output step-up transformer.

Learn more
Marine frequency drive systems based on the Triol AT24 and Triol AT27

Marine frequency drive systems based on the Triol AT24 and Triol AT27

The Triol AT24 and AT27 VFDs for marine applications meets challenges such as compliance with standards and certificates, installation in limited space, stable operation in shipboard mains, and other conditions.

Learn more

News

Triol SKID – Save time while commissioning and increase the personnel’s safety and comfort!

New production facilities in Poland are equipped with modern painting equipment!

Learn more
Great alternative for the transition of oil production on the low-flow well fund with a unique EP01

Great alternative for the transition of oil production on the low-flow well fund with a unique EP01

Learn more
Increase HPS performance with VSD AK06

Increase HPS performance with VSD AK06

Learn more

Contacts

Surmin_3

Nikolay Surmin

Business development manager

USA

n.surmin@triolcorp.com

Apply Triol equipment — work with professionals!