Unbalanced or Ungrounded Distribution Systems 2-169
Unbalanced or
Ungrounded
Distribution Systems
Unbalanced Distribution Systems
This drive is designed to operate on three-phase supply systems whose line
voltages are symmetrical. Surge suppression devices are included to protect
the drive from lightning induced overvoltages between line and ground.
Where the potential exists for abnormally high phase-to-ground voltages (in
excess of 125% of nominal), or where the supply ground is tied to another
system or equipment that could cause the ground potential to vary with
operation, suitable isolation is required for the drive. Where this potential
exists, an isolation transformer is strongly recommended.
Ungrounded Distribution Systems
All drives are equipped with an MOV (Metal Oxide Varistor) that provides
voltage surge protection and phase-to-phase plus phase-to-ground
protection which is designed to meet IEEE 587. The MOV circuit is
designed for surge suppression only (transient line protection), not
continuous operation.
With ungrounded distribution systems, the phase-to-ground MOV
connection could become a continuous current path to ground. Energy
ratings are listed below. Exceeding the published phase-to-phase or
phase-to-ground energy ratings may cause physical damage to the MOV.
1234
Joules (J)
Ground
Three-Phase
AC Input
T
S
R
Joules (J)
Joules (J)
Joules (J)
Device Rating (V
AC)
Phase-Phase Total
Phase-Ground Total
240/480 600
280J 320J
360J 410J
240 480/600
160J 320J
220J 380J
240/480 600
280J 300J
360J 370J
Phase-to-Phase MOV Rating
Includes 2 Phase-Phase MOVs
Phase-to-Ground MOV Rating
Includes Phase-Phase & Phase-Ground MOVs
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