• Medium voltage Insulated Gate Bipolar Transistors (IGBTs)
  
• Oil-filled capacitors
  
• Heat pipe cooling technology
  
• Copper-wound transformer
  
• Lighting arrestors

This article provides some insight into these differentiating features.

Medium Voltage IGBTs
In mean time between failure (MTBF) analysis, minimizing part count is critical to long-term reliability. The use of medium voltage IGBTs in a neutral point clamp topology helps meet this criteria on two counts (neutral point clamp topology shown in Figure 1 below):

• Minimum number of power devices (IGBTs)
  
• Low part count in the associated gate driver circuits

Figure 1 - Neutral Point Clamp Inverter Topology

To fully appreciate the simplicity of this design, Table 1 below provides a side-by-side part count comparison between the Dura-Bilt5i MV and a typical 1000 HP, 4160 volt, Paice Multi-Level Voltage Source design (Robicon Perfect Harmony™) 12-module drive using LV IGBTs.

Table 1 - Part Count Comparison

The oil-filled medium voltage capacitors used in the Dura-Bilt5i MV design have a extremely long life compared to the low voltage electrolytic capacitors that have a published lifespan of 5-10 years, based on temperature and over-voltage conditions.

Heat Pipe Cooling Technology
A key element in IGBT life is controlling the device's temperature. Traditional drive design utilizes a cast aluminum heat sink with forced-air cooling. This technology is large and inefficient when compared to the heat pipe.

Heat pipe technology, frequently referred to as the super conductors of heat, uses the evaporation-condensation cycle to efficiently transfer the heat from the IGBTs to the air being pulled through the condenser portion of the assembly (refer to Figure 2 below). The heat pipe approach to cooling provides more efficient heat transfer and is more compact than the traditional aluminum heatsink method.

Figure 2 - Thermal cycle of heat pipe cooling assembly

Copper Wound Transformer
Both copper and aluminum are commonly used in the manufacturing of medium voltage dry transformers. The Dura-Bilt5i MV design incorporates a copper wound transformer as a standard (see Figure 3 below), providing customers these advantages:

• Copper expands/contracts less than aluminum in thermal cycling, which puts less stress on the insulation and welded joints where primary and secondary leads are attached
  
• Copper is more pliable than aluminum, which generates less stress on the insulation in thermal cycling
  
• Copper has lower resistance per mm of cross-section, allowing a copper wound transformer to be more compact than an equivalent aluminum transformer

Typical designs of medium voltage transformers are sized for 140° C rise throughout the range of operation. The Dura-Bilt5i MV copper wound transformer is sized for a 115° C rise, putting less stress on all associated components.

Incoming Power Lightning Arrestors
The Dura-Bilt5i MV also incorporates lightning arrestors in the incoming power compartment (see Figure 3). These distribution class lightning arrestors are provided as a standard to suppress any incoming power transients.

Figure 3- Copper-wound transformer and lightning arrestors

John Hamby is the General Industries Engineer Manager with GE Toshiba Automation Systems.

The above article is provided free of charge and without obligation to the reader or to GE Toshiba Automation Systems, LLC. By utilizing this article the reader expressly understands that GE Toshiba Automation Systems, LLC does not accept, nor imply, the acceptance of any of liability with regard to the use of the information provided. GE Toshiba Automation Systems, LLC provides the information included herein AS IS AND WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY IMPLIED STATUTORY WARRANTY OF MERCHANTABILITY OR FITNESS FOR PARTICULAR PURPOSE. The information is provided as a general reference to the potential benefits that may be attributable to the technology discussed. The reader is encouraged to perform independent analysis of the technical and commercial benefits described here in. If you have any questions regarding your project requirements please contact the GE Toshiba Application Center at 540-387-8070.

Dura-Bilt5i MV is a registered trademark of GE Toshiba Automation Systems, LLC
Perfect Harmony and Harmony are trademarks of Robicon