Pipeline Medium Voltage VFD Specifications overview


We’re seeing increased inquiries regarding Pipeline VFD specifications for pipeline VFD applications.  The following is a general overview that may prove helpful.  We cover Siemens, Allen Bradly, Yaskawa, Toshiba, and Nidec (Ansaldo). 

In the interest of full disclosure, we bid and sell medium voltage pipeline VFDs, and perform service on  all brands. However, I will attempt in this blog to provide an honest, unbiased comparison of the major specification advantages of each of the medium voltage VFDs and their specifications.  All of these are providers of medium voltage VFDs to the pipeline industry.   I trust and hope that it will prove useful.

Regardless of whose specifications a pipeline project engineer may use, there are more commonalities than differences between major brands.  That being the case, I’m going to concentrate on specific differences,  which are both advantageous and disadvantageous.

We can provide pipeline project engineers  a full suggested medium voltage VFD specification sheet if you wish.  EMAIL us, or hit any of the contact methods on the right of this page OR call 770-448-4644.  

We will cover the Siemens/Robicon Perfect Harmony, the Toshiba T300MVI, the Yaskawa MV1000, the Allen Bradly / Rockwell Powerflex 7000, and the Nidec / Ansaldo Silcovert S.

All of these are excellent VFDs, and can provide years of reliable service.  Here are some pipeline medium voltage VFD specification particulars by brand:

Siemens (formerly Robicon):  The Siemens Perfect Harmony medium voltage VFD has the largest installed base of any medium voltage VFD.  The newer generations have enhanced electronics, but the basic design has changed little in 17 years.  The inverter design topology is called Cascaded H Bridge topology. This is a voltage source VFD.

This design, in essence, uses single phase output VFDs, and cascades them to create the final output waveform.  This design was patented and Siemens/Robicon enjoyed a competitive advantage for years prior to the patent expiring.

This also allows the Siemens Perfect Harmony medium voltage VFD to incorporate a feature called “Cell Bypass.”  This allows the VFD to continue functioning with a failed cell.  Siemens influenced pipeline specifications always include this.  Frankly, it is a unique feature that is of interest to many pipeline operators.

There is a disadvantage to cell bypass in that it causes a neutral point shift at the motor. This can damage a motor if operation in this mode is prolonged.  Another disadvantage is the Siemens Perfect Harmony medium voltage VFD uses large numbers of electrolytic capacitors.  These have limited life, and should be replaced periodically.  (We have a blog on this if interested:  Click HERE)

Siemens Robicon Perfect Harmony:

Advantages:

  • Proven Market Performer
  • Cell Bypass

Disadvantages:

  • Old design
  • Cell Bypass causes common mode issues
  • Electrolytic Capacitor failures.
  • Difficult HMI/user interface

Toshiba t300MVI in stockThe Toshiba T300MVI:  The Toshiba T300MVI medium voltage VFD is the most popular voltage source medium voltage VFD after Siemens.  The T300MVI medium voltage VFD is a newer design, and exceeded Siemens sales in recent years.

The Toshiba T300MVI VFD uses a 5 level switching topology, which is an advantage over older 3 level designs. (See our blog on medium voltage VFD switching topologies for more information)

This gives the Toshiba medium voltage VFD an advantage in pipeline applications where the medium voltage VFD is being put on existing motors.  The 5 level topology is motor friendly.

Toshiba elected to include input switchgear as a standard feature within the T300MVI medium voltage VFD (including vacuum contactors.)  This can be a huge advantage if it allows a pipeline to avoid purchasing switchgear.  The Toshiba T300MVI also has a built in tertiary winding, which means it generates its own low voltage control power from the medium voltage input.  Advantage:  it does not require external control power.

Toshiba has a built in precharge circuit.  This is common in low voltage drives, but many (if not most) medium voltage VFDs use the input transformer impedance to limit bus capacitor inrush.  This has caused transformer failures in other brands.

Perhaps one of Toshiba’s biggest advantages is its use of oil filled bus capacitors in lieu of electrolytic.

Toshiba T300MVI :

Advantages:

  • 5 level topology
  • Built in switchgear with  vacuum contactors
  • Oil filled bus capacitors
  • Precharge Circuitry
  • Large installed base

Disadvantages:

  • No Cell Bypass
  • Cumbersome user interface

Yaskawa MV1000:  The Yaskawa MV1000 medium voltage VFD is a relative newcomer to the pipeline medium voltage VFD market.  Yaskawa is recognized worldwide as one of the highest quality VFD manufacturers in the world, and one would expect their MV offering to be no different.

For starters, the Yaskawa MV1000 has a 36 pulse input as compared to other voltage source medium voltage pipeline VFDs which normally have a 24 pulse input.  Yaskawa prides themselves on being the most powerline and motor friendly medium voltage VFD in the pipeline market, and the 36 pulse input is part of that.

The Yaskawa MV1000 medium voltage VFD uses what’s termed an enhanced H Bridge switching topology.  This uses 8 IGBTs in each cell in lieu of the standard 4 in other medium voltage VFDs (voltage source).

This allows Yaskawa to provide the cleanest output signal of any medium voltage VFD.  In fact, they boast that you can run up to 1 mile of cable between the drive and motor without a filter.

The Yaskawa MV1000 has the most user friendly customer interface of any medium voltage VFD presently used in pipeline applications.  Our experience with this is that if you can program a Yaskawa low voltage VFD, you can easily program the MV1000.

The Yaskawa MV1000

Advantages:

  • Enhanced H Bridge topology minimizes DVDT and noise issues to motor
  • 36 pulse input mitigates power line harmonics
  • Intuitive user interface
  • Considered one of the highest quality drive companies in the world

Disadvantages:

  • Uses electrolytic bus capacitors
  • no cell bypass

Nidec (Ansaldo) Silcovert TH:  Nidec Silcovert TH boasts the highest horsepower of any voltage source medium voltage VFD.   They go to 22,000 HP.  Above that they switch to current source.

The Nidec medium voltage pipeline VFD has historically been found in high horsepower applications, such as gas compressors.  Almost all other voltage source VFDs top out around 10,000 HP.

In fact, Nidec’s (Ansaldo) success in the very high horsepower ranges (Nidec lists up to 100,000 HP in their literature) has probably kept them from consideration at lower horsepowers since many pipeline specification engineers view them as high horsepower only. They are a first class medium voltage VFD and deserve consideration in medium voltage pipeline VFD specifications.

The Nidec output topology is the H Bridge, very similar to the Siemens.

Nidec (Ansaldo) Silcovert TH:

Advantages:

  • Available in very high horsepower
  • Nidec makes power semiconductors which gives some advantage over others that buy them from outside
  • Friendly user interface

Disadvantages:

  • Uses elctrolytic bus capacitors
  • No cell bypass

Rockwell (Allen Bradley) Power Flex 7000:   The Powerflex 7000 has been around a long time, and has a significant installed base.  Unlike the others mentioned so far, the Powerflex 7000 is a current source inverter.  Many engineers consider this old and dated technology, but it still appears in many medium voltage pipeline VFD specifications.

The first large horsepower VFDs were current source, and there is something to be said for a tried and proven design.  Current source VFDs tend to tolerate faults well, and have simpler switching circuitry than later designs.

Their primary disadvantages have to do with motors. Current Source VFDs use the motor as part of its switching circuitry.  Hence the pipeline user is limited to the motors he can use.

The other disadvantage most noted is that current source VFDs are normally disruptive to power lines, and have issues with DVDT, especially with long motor leads.   There are many IEEE and other documents to read regarding this.

All that aside, the Allen Bradley Rockwell Powerflex 7000 remains a popular and reliable pipeline VFD.

Rockwell (Allen Bradley) Powerflex 7000: 

Advantages:

  • Tolerant of faults
  • Large installed base

Disadvantages:

  • DVDT issues often require an output filter
  • Will not work with all motors
  • Disruptive to power line
  • Very old technology

 

I hope this has proven helpful.  If you’d like a standard medium voltage pipeline VFD specification to use, then contact us by EMAIL or any of the methods on the right of this page, or call 770-448-4644

No One, Anywhere, is Better at Drives than we are

 

 

 

 

 

 

Posted in: Newsletter on February 13th by Eddie Mayfield


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