Over the past fifty years, three major breakthroughs have taken place in capacitor technology:

• Elimination of paper dielectrics with the development of the all-film capacitor
• Development of non-PCB dielectric fluids
• Development of extended foil, mechanically crimped capacitor pack construction

All were the proud result of Cooper Power Systems' drive to "do it better" through research and development. Now, with the McGraw-Edison Type EX-7L capacitor, we bring you a major technological breakthrough - laser-cut foil that controls the electric field in the capacitor dielectric system.

Laser Cut Foil
The Manufacturing Edge
Applying laser technology, we have literally reshaped the foil edge in the EX-7L capacitor, and thereby reduced foil edge electrical stress levels, substantially enhancing capacitor performance.

The new EX-7L dielectric system uses foil that is slit by a laser beam, replacing the mechanically slit foil used in conventional power capacitors.

Figure 1 is a micrograph of the foil edge produced by conventional mechanical slitting procedures. Note the rough, non-uniform surface of the foil edge, which is where corona occurs.

Figure 2 illustrates the consistent rounded edge achieved through the laser-cutting process. The round edge significantly reduces dielectric stress at the foil edge, the critical point in the capacitor's dielectric system.

Figure 3 shows the advanced laser equipment used to slit the foil. This foil manufacturing breakthrough melts the foil, instead of tearing it, during the slitting process, resulting in consistently rounded edges. The use of this foil significantly increases the Discharge Inception Voltage (DIV) levels of the capacitor and endows the EX-7L with unprecedented performance capabilities.

Reduced Electric Field Stress
The Technological Edge
Corona, often referred to as discharge, occurs in a capacitor when the electrical field stress exceeds the dielectric strength of the fluid at the foil edge. Discharge conditions are the primary cause of premature capacitor wearout.

Figure 4 plots the electrical field at the edge of mechanically slit foil. The closer the field lines, the higher the edge stress.

Figure 5 shows how the laser cut foil edge reshapes the electrical field, thereby reducing stress. The lowered edge stress levels result in a substantial increase in the voltage at which a capacitor begins to go into corona. This is what gives the Type EX-7L its outstanding performance.

Figure 6 illustrates the dramatic improvement in the DIV performance of the Type EX-7L capacitor over that of a similar design using mechanically slit foil.

Figure 6 (67K)

The EX-7L Edge
Matching Product Innovation with Manufacturing Technology
The McGraw-Edison Type EX-7L capacitor combines all four material advancements introduced to the power capacitor industry by Cooper Power Systems:

• All film dielectrics
• Non-PCB dielectric fluids
• Mechanically crimped extended-foil high-energy construction (No Solder!)
• Laser-cut aluminum foil

Again, Cooper Power Systems matches product innovation with high-technology manufacturing. The result is a capacitor that's unsurpassed in the world for performance - performance you can count on down the line.

• Extended Foil
• Solderless Construction
• All Film Solid Dielectric
• 10 kA Fault Current Handling Capability
• 93000 kvar Parallel Energy Capability
• Low 0.07 Watts per kvar* Losses
• 
  * at 60 Hz