Converter Component Failures - What you don’t know can hurt your bottom line

15 Jul 2019

Make no mistake, the wind energy industry has experienced a serious boom.  In 2018, wind energy generated 6.5 percent of the nation’s electricity.  To put that into perspective, it’s enough energy to power 26 million homes.  Over the last decade, the US wind industry has invested over $142 billion in new wind projects - it is the largest source of renewable generating capacityin the country.

Despite growth of this industry, new wind turbines are expensive: up to $4 million per unit installed, which can last up to 20 years.  Many things factor into the overall reliability and performance of each unit, including wear-out related failures, temperatures, humidity, precipitation, as well as the age of turbine components. Older wind turbines will feed more into your operation and maintenance costs.  Understanding and finding ways to improve the reliability and performance of these turbines is paramount. The cost of new equipment (from the OEM) isn’t cheap, nor is upgrading obsolete technology. Ordering replacement parts from your OEM often keeps a unit down for weeks because the parts are coming from overseas. 

IRSP Partner

The key to improving wind turbine reliability is bridging the gap between the wind farm and the OEM. How do you do this? Partner with an Independent Repair Service Provider (IRSP). Wind farm managers should establish preventative maintenance strategies and preventative repair actions after the OEM’s warranty has expired.  The IRSP can help reduce operation and maintenance costs by identifying high failure components which, in turn, will help extend overall turbine life. If your IRSP isn’t experienced in servicing electronic components such as IGBTs, Pitch Controls, Printed Circuit Boards, PLCs, and can’t fully load-test your AC drives/Converters, you should look elsewhere.

Another advantage of a great IRSP is the service warranty that they can provide to your equipment on the back end - anywhere from 3 months to 2 years.  Equipment warranties vary from provider to provider, so dig in and really get to know what’s covered and what isn’t. 

The Power Converter Blues

One failure unit that comes to an IRSP from a wind farm is inarguably the Converter.  The best way to identify high failure components is to open the unit and inspect the electronics.  Not all Converters are created the same - high failure components will vary with each OEM.  Take this failure example:  

  • IGBTs
  • Flat ribbon cable that connect IGBTs to the control board
  • Clamp Capacitors
  • Gate driver boards that mount to the IGBTs

If there is an IGBT failure, the reasons could be excessive voltages, excessive current or excessive thermal stress, or even insufficient cooling.  Excessive currents can happen because of wrong limits set forth for currents, or even an external short circuit (i.e.: motor, cable).  Other failure factors could be temperatures, vibrations, humidity, and even age of components.  All of these factors should be considered in order to accurately diagnose any performance issues and repair actions.

Troubleshooting Converters

Here is an effective, 5-step process for troubleshooting and repairing Converters by an IRSP technician: 

  1. Remove the cover on the unit and perform a VOI (visual overall inspection); inspecting for any burnt, blown, loose connections, and bus caps that have swelled.
  2. Perform a static check with a digital multi-meter(DMM). The DMM checks the inputs and outputs of the rectifier section and the inverter section.
  3. Power up the control board and power supply board to verify all voltages are correct.
  4. Test the DC link for leakage, also known as Internal Resistance (IR).
  5. Test the blower.

The Repair Process

After initial inspection, the IRSP technician begins to remove, repair, clean, and rebuild any stressed parts and obsolete components.

  1. Remove the IGBTs, heater plates with control board, power supply, and blower.
  2. With all components removed, clean bus bars and heat sinks inside and out of unit.
  3. Verify which IGBTs are the correct ones for the unit; this is dependent upon the type of DC filter inside the unit.
  4. Install of IGBTs with the correct torque specifications.
  5. Build heater plates and install control and power supply boards, and make sure all connectors are securely fastened.

VFD Testing Phase

This is by far the most crucial step in the overall process, because the IRSP technician must make sure that all components are in working order before they are returned to the wind farm.  The repaired unit moves into a load testing center and fiber optics connect to the control board.  Proper voltage is applied to the DC link and control power is applied to an external controller.  The unit should power on with no faults.  After power up, initiate a run command and ramp the unit up to 50 Hz.  The final step is scoping the outputs to verify that each phase is properly turning on and off.  

If the unit passes all the above, the VFD connects to the load center and runs at a 200amp load for one hour to allow burn-in of the IGBTs.  It’s important to use an IRSP that can fully load-test drives up to 400 horsepower.  The testing process allow technicians to identify weak and faulty components, as well as any hotspots, while measuring and monitoring the voltage and currents coming out of the drive.  It’s important to send all test reports to the client.  It will give them peace of mind that their equipment will work as soon as it’s shipped back. 

Properly maintaining converter components is a big deal, particularly after hoisting a 100lb unit up a 300-foot wind turbine.  Partnering with the right IRSP who can fix and test your equipment is critical, and can help you avoid a big (and costly) headache down the road. 

 

Tommy Duckworth is Electronics Shop Manager and Colleen Voisin is Marketing Director for Industrial Repair Service. Industrial Repair Service technicians use state-of-the-art technology to test and repair wind power equipment, especially older and obsolete components.

Industrial Repair Service | www.industrialrepair.net  


Volume: 2019 July/August