Online Learning Center

Introduction
Summary
Quiz
Glossary

Online Learning Center
Beckwith Electric Home

Impact of Voltage Transformer Connection and Grounding on Generator Protection Security and Selectivity

Example Six: Delta primary / delta secondary, corner grounded

Figure 8, Delta Primary / Delta Secondary, Corner Grounded

Pros:

• This arrangement will prevent the 24, 27, and 59 elements from operating for phase to ground faults in the generator zone. The phase-to-phase primary windings correctly transform the line-to-line voltage to the secondary windings in the presence of a ground fault on the primary side in the generator zone, and a voltage change to the relay does not occur.
• This arrangement will prevent the ground overvoltage protection (59N) from operating on VT secondary side ground faults. This is because a phase-to-ground fault on the secondary side appears as a phase-to-phase fault on the primary side.
• This arrangement is typically the least expensive (versus wye-wye), as two VTs are required.

Cons:

• This arrangement does not offer the ability to use single-phase power elements.
• This arrangement does not offer the ability to zero-sequence directionalize ground elements from phase to neutral voltages or use the 59D element.
• This arrangement does not offer the ability to view discrete phase voltages on oscillography (phase-to-phase composites are available).

Page 7 of 9

© 2002 Beckwith Electric Co, Inc. All rights reserved.