This e-learning video introduces the technology behind medium-voltage drives and their key features and benefits. Topics covered include LV vs. MV drives, MV drive advantages, drive topologies, reflected waves, input waveforms, synchronous transfer, and packaging.

---

---

Transcript

00:00:04 [Music] the Technical Training Department of yasawa America Incorporated presents medium voltage Drive Basics welcome to medium voltage Drive basics in this session we will explore the key technology and benefits of medium voltage drives now before we get started you may find it beneficial to view our related videos motor Basics and

00:00:37 drive Basics now motor Basics explores the construction operating principles and common applications of three-phase induction Motors Drive Basics introduces low voltage variable frequency drives their construction how they work and common motor applications that benefit from the use of drives well many industrial and Manufacturing Industries rely on the use of electric

00:01:07 motors including oil and gas water and wastewater tire and rubber mining power generation chemical and cement variable frequency drives are often utilized for precision control of motor speed and torque and play an important role in improving system reliability and efficiency now in this segment we will explore medium voltage drives a very specific

00:01:36 subset of variable frequency drives the majority of drives are low voltage drives or LV drives they typically operate on 240 volts 480 volts or 600v supplies and drive motors from fractional horsepowers up to 1,000 horsepower medium voltage drives or MV drives provide a robust solution for the largest of motor applications typical applications operate at 2400 volts

00:02:15 4,160 volts or 13.8 kilovolt supplies and operate Motors ranging from 500 horsepower up to 10,000 horsepower or more MV drives are used on similar applications as LV drives but on a much larger scale common applications include compressors pumps mixers and conveyors medium voltage drives function much like low voltage drives they may be programmed to provide volts per Hertz

00:02:51 open loop vector or closed loop Vector motor controls using the same keypad and software interface as their low voltage counterparts now you may be wondering why medium voltage what are the advantages of choosing an mvy topology how does a 1,000 horsepower medium voltage Drive differ from a 1,000 horsepower low voltage Drive well how

00:03:16 does it all work in high power applications MV drives have several advantageous characteristics now the primary Advantage is reduced current the electrical power that a motor requires to satisfy an application is determined by multiplying the motor voltage by the motor current power equals volts time

00:03:45 amps increasing the voltage allows the same amount of mechanical Power to be developed with fewer amps for example to deliver 1,000 watts of power with a 1vt supply the system would need to deliver 1 1,000 amps of current however if the voltage is increased from 1 volt to 1,000 volts the same 1,000 watts of power can be delivered with just one amp instead of a

00:04:14 th000 amps reducing amperage allows smaller conductors to be used reducing copper and installation costs and reducing transmission losses for a 1,000 horsepower application 20 24 4 o cables would be required to carry 1,200 amps on a 480 volt system medium voltage reduces the conductor requirement to three 1 a

00:04:43 cables to carry 125 amps at 4,160 volt the 24 low voltage conductors on the left deliver the same mechanical motor power as the three medium voltage cables on the right installation time and costs are reduced for both input and motor power wiring by using fewer and smaller

00:05:10 cables a second advantage of using MV drives is their ability to reduce motor inrush current at the start when started across the line with a mechanical starter starting motor current May exceed 6% of rated operating current when generator or utility Power Systems capacity is limited this starting current may result in severe voltage

00:05:34 drop on the supply impacting other connected equipment variable frequency drives avoid this problem by optimizing output frequency and voltage as the drive accelerates when a motor is started with a drive the current Demand on the supply is a small fraction of a cross the line in Rush current avoiding voltage drops and utility penalties

00:06:00 as an additional benefit drives provide nearly twice the starting torque when compared to starting across the line a third advantage of MV Drive multi-level topology is that it produces a nearly sinusoidal output waveform without additional output filtering using a drive with a sinusoidal output waveform reduces electrical and mechanical stress on the motor and

00:06:27 increases motor reliability and service life a clean sinusoidal output is also beneficial for applications that require long motor leads between the drive and the motor and prevents the damaging effects of reflected waves on the motor wiring system now this is especially important in applications like electric

00:06:50 submersible pumps where it is common to have a very long motor conductor between the drive on the surface and the downhole motor a fourth advantage of MV drives is their ability to minimize harmonic distortion on the power supply keeping the input waveform as clean as the output waveform with smart harmonics technology MV drives can achieve i e 519 compliance

00:07:19 without additional harmonic filtering or mitigation minimizing harmonic currents and resultant voltage distortions reduces thermal stress on the power distribution system and can improve the reliability of all equipment on the power system a final advantage of MV drives that we'll explore is their ability to synchronously transfer the motor from

00:07:44 the drive to the power grid and from the power grid back to the drive because the input and output waveforms of multi-level MV drives are so nearly sinusoidal like AC grid power loads can be bumpless trans erred without interruption to the application now before we dive into the details of how MV drives achieve these advantages let's take a moment to review

00:08:16 the basics of low voltage variable frequency drives covered in the esawa drive Basics video a drive is composed of three basic building blocks the DI Bridge converts AC line power to DC power the DC bus acts as a bucket of power bus capacitors store the energy that the diode Bridge pours in until it's needed the output section is comprised

00:08:47 of insulated gate bipolar transistors or igbts igbts are switches that turn on and off very quickly the output section igbts draw energy from the DC bus and through pulse width modulation construct a three-phase AC waveform of variable voltage and variable frequency pulse width modulation or pwm is a process in which a controller varies the average output voltage by

00:09:19 switching a higher voltage on and off at a high rate of speed the igbts switch the DC bus voltage on and off thousands of times per second the drive then arranges short pulses and long pulses such that the average voltage of the pulses approximates a sinusoidal waveform by alternating which igbts are switching power the drive can modulate a positive average voltage to motor leads

00:09:47 unv or a negative average voltage to motor leads unv by sequencing all six output igbts the drive can modulate an average sinusoidal signal to all three motor phases the pulse width modulation controls the average voltage of the output by varying the timing and sequencing of the output pulses the drive can mimic the 60 HZ frequency of

00:10:15 the line decrease the output frequency to make the motor turn more slowly or increase the output frequency to make the motor rotate more quickly using this method low voltage drives can approximate average sinusoid output waveforms of varying voltage and frequency to achieve optimal Motor Performance multi-level medium voltage drives build on the same fundamental

00:10:47 principles as low voltage drives medium voltage drives are constructed with the same three basic building blocks just more of them the diode Bridge converts AC DC the DC bus is the bucket of power that stores energy and the igbts switch on and off providing pulse width modulation modern MV drives utilize a cascaded h Bridge topology the cascaded bridge topology

00:11:20 allows for many modular power cells to be stacked creating higher voltages and smoother waveforms in the previous three-level low voltage example the drive can only switch three voltages to the output leads the positive DC bus voltage zero or the negative DC bus voltage a cascaded h Bridge connects multiple three-level igbt power sections

00:11:51 in series when two three-level bridges are connected in series or cascaded the result is a five level output bridge in the five level cascaded H Bridge topology shown the drive can switch five voltage levels to the output leads the full positive DC bus voltage half the positive DC bus voltage zero half the negative DC bus voltage or

00:12:24 the full negative DC bus voltage compared to the three-level drive five level drives create a waveform that more nearly approximates a sinusoid the smoother waveform has many advantages including less stress on motor windings and conductors improved motor control and reduced audible noise so how does this magic work a five level Drive uses two three

00:12:54 level power sections and this means that there are two independent Banks of DC bus capacitors and the output is Switched by two independent sets or bridges of igbts with two DC bus potentials and additional igbts the drive may choose the level closest to the desired average output voltage the drive can switch between zero and half voltage between

00:13:24 half and full Voltage between full and back down to half voltage from half voltage back to zero between 0o and negative half voltage negative half voltage and negative full Voltage negative full Voltage back to negative half voltage and then from negative half voltage back to zero voltage creating a stepped sinusoidal output

00:13:53 waveform now that we've seen how a five level cascaded H Bridge may be used to create a smoother output waveform let's build on that by connecting two five level cells in series The resultant output waveform now has nine levels each time we add more switching levels the output voltage steps get closer and closer to the ideal sinusoidal output

00:14:21 waveform let's take a closer look at how two cells can be coordinated to create nine voltage levels each five level cell can modulate positive or negative 1,000 volts or 2,000 volts connected in series nine voltage levels including zero can be achieved the drive can switch between zero and quarter voltage quarter and half

00:14:49 voltage half and 3/4 voltage 3/4 voltage and full Voltage half and 3/4 voltage quarter and half voltage zero and quarter voltage and continue the same steps with negative voltage we created this nine level singlephase waveform with two modular cascaded H Bridge Drive cells since the output of these two cells is singlephase

00:15:22 we're not quite ready to drive a three-phase motor yet the next step is to combine three sets of cascaded singlephase output sections to form a single three-phase cascaded output section connecting three sets of two cells in a y configuration we form a cascaded multi-level 3phase y output now if it's easier to visualize think of connecting the power cell

00:15:55 outputs in the same way you'd connect three y secondaries on a Transformer to form a three-phase y output with six cells connected in series y we can now create a 17 level three-phase output each additional output level brings the waveform closer to the ideal sine wave a smooth waveform reduces electrical stress on the conductors and

00:16:26 motor insulation system and because mechanical torque is created by current a smooth waveform also provides consistent motor torque reducing cogging vibrations that can cause mechanical wear and create audible noise three levels of switching is coarse five level switching is less coarse nine level switching is fairly smooth with 17 level switching the steps

00:16:58 are so small that the result is nearly sinusoidal now that's a fine looking waveform but you might be wondering how can the output waveform cause stress on the motor reflected wave phenomena can occur when the individual switched Pulses from the igbts are reflected back on the line from the motor impedance as the first pulse is reflected back the

00:17:32 potential can sum with the next incoming pulse exposing the insulation system to as much as twice the bus voltage repeated exposure to high voltages will break down conductor and motor insulation causing premature failure reflected wave still occurs with the multi-level output topology however because the voltage levels are a small fraction of the bus voltage the

00:18:01 potential Reflections are also a small percentage of the total bus voltage and are typically safely within the rated limits of the motor insulation system on a three-level drive reflected wave can increase the peak voltage seen by the motor to nearly three times the nominal RMS Supply voltage but with a 17 level output the maximum Peak voltage seen by the motor

00:18:28 is limited to about 160% of the nominal RMS Supply voltage well within the tolerance of standard motor insulation systems well we've explored how multi-level MV Drive topology can improve system performance and reliability by improving the motor output waveform so now let's look at how choosing an MV topology can improve system input power

00:19:00 quality MV smart Harmonic Technology can be utilized to nearly eliminate the concerns of total harmonic Distortion or THD present in three level Drive topologies what is harmonic current and where does it come from harmonic currents are created by the nonlinear switching of the diode bridge and occur at frequency multiples of the power supply frequency

00:19:29 the third harmonic of a 60 HZ system is 180 Hertz that's three times the fundamental frequency the fifth harmonic is five times the fundamental or 300 Hertz and harmonic currents don't contribute to beneficial mechanical work we need to be cautious of harmonic currents because they do contribute to conductor heating voltage drop and voltage Distortion that can adversely

00:19:58 impact other equipment on the power system in a typical low voltage six pulse Drive current is only conducted when the sinusoidal supply voltage is greater than the bus voltage this creates a rabit ear waveform on each phase one ear occurs when the L1 L2 voltage exceeds the bus voltage the second here occurs when the L1 L3 voltage exceeds the bus voltage

00:20:29 and the current waveform is nonlinear and does not resemble a sine wave in a three-phase system the diodes conduct at the top and bottom of each phase Peak creating six pulses per cycle multi-pulse Transformers provide multiple phase shifted three-phase outputs here is an example of a 12 pulse Transformers output voltages compared to a standard 3 three-phase

00:21:00 Supply as you can see two sets of three-phase voltages are provided in the same period of time essentially creating a six-phase power supply instead of being 120 electrical degrees apart the phases are separated by only 60° a 12 pulse Drive adds additional diodes to take advantage of the multipulse Transformer by rectifying a second set

00:21:30 of input waveforms a second set of phase shifted rabbit ears are also generated when summed on the line the two sets of rabbit ears overlap the resultant waveform is more smoothly sinusoidal and is comprised of less harmonic content the mv1000 medium voltage Drive is comprised of six power cells each connected to an ice is olated Phase

00:22:00 shifted secondary creating a 36 pulse Drive input six three-phase systems create 18 unique phase shifted sinusoids each sinusoid charges the DC bus at the top and the bottom of the waveform for a total of 36 pulses per cycle just as a 12 pulse Drive creates a smoother waveform than a six pulse P drive by summing two sets of rabit ear a

00:22:33 36 pulse Drive nearly approaches a sinusoidal waveform by summing six sets of phase shifted rabit ear the resulting current waveform contains negligible harmonic current content and exceeds industry guidelines for allowable harmonic distortion we've examined how multi-level MV topology can be used to create gridlike sinusoidal motor waveforms while

00:23:08 maintaining near linear sinusoidal load on the supply the power quality is so close to the 60 HZ grid that MV drives are able to smoothly transfer loads from Drive control to line power and from line power back to drive control without interrupting the application this is referred to as synchronous transfer for example a water utility may have periods of varying demand

00:23:38 throughout the day during periods of low demand one pump may be required at partial load during periods of high demand four pumps may be required each running at full load now this is an effective solution however it may not be cost effective to have a drive on each pump if they're only needed for Peak Demand with synchronous transfer a

00:24:04 single Drive can bring each pump online with a soft start ramp to limit the impact on the power system when each pump reaches full load the system seamlessly transfers the pump to line power and accelerates the next pump as each pump is needed the drive can provide speed regulation from zero to full speed to exact exactly match the demand of the system and conserve

00:24:33 energy in a typical synchronous transfer application an array of contactors is used to connect an MV Drive output to the first motor the drive is used to start the motor and can be used to regulate motor speed and torque operation when full speed operation is required the MV Drive accelerates the motor to 60 HZ and synchronizes the drive output frequency with the Utility

00:24:58 Supply frequency when the voltage is match the drive closes a contactor to bring the motor on the line for a few Cycles the motor is connected to both Drive power and line power with no disruption to motor current or Torque once synchronized the drive opens a contactor to isolate from the first motor leaving it running on line power the drive may now close a contactor to

00:25:26 connect to the second motor the drive accelerates the second motor and synchronizes its output with the AC line when the waveforms match the drive simultaneously connects to line power after transferring to the line the drive can disconnect from the second motor and connect to a third as load requirements are reduced the process is reversed and the drive seamlessly transfers the line

00:25:52 connected Motors back to drive control where they can be operated at variable speed or decelerated to a controlled stop unlike a contactor bypass application or open transition synchronous transfer maintains uninterrupted motor current and smooth torque transfer medium voltage drives can be packaged for indoor

00:26:22 use General outdoor use or to withstand the most EX extreme outdoor climatic conditions while each application has a different look and different construction each Drive is comprised of the same basic building blocks a multi-pulse Transformer ensures clean power quality modular power cells provide precise sinusoidal motor control

00:26:53 a low voltage control section provides an interface for control inputs and monitoring and units may also be provided with optional switch gear to provide an integral means of disconnecting the medium voltage Supply from the drive components well in this session we have introduced the basic construction of a multi-level medium voltage drive and

00:27:16 explored how multi-level topology benefits power quality both on the supply and at the motor and now it's time for everyone's favorite segment review questions review question number one when starting an MV motor what advantage does a drive have versus an across the line start the answer inrush can exceed 600%

00:27:44 of rated operating current when starting across the line using a drive allows us to increase the voltage and frequency over time to help reduce excessive current draw question number two how many voltage levels or steps does an mv1000 medium voltage Drive have when measuring phase to phase voltage on the output

00:28:11 17 17 levels or steps are achieved with six cells connected in series y to form a three-phase output at yasawa we do everything in our power to make each experience with us better than the last because to us it's personal to learn more about how medium voltage drives can benefit your application visit yasawa

00:28:39 docomo yasawa representative and thanks for watching