REGENERATIVE DC COMMON BUS SUPPLY 6
Unbalanced Distribution Systems
The
AC REGEN is designed to operate on three-phase
supply systems whose line voltages are symmetrical.
Surge suppression devices are included to protect the
AC REGEN from lightning induced over-voltages
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
AC
REGEN. Where this condition exists, an isolation
transformer is strongly recommended.
Ungrounded Distribution Systems
All AC Regen are equipped with MOVs that provides
voltage surge protection and phase-to-phase plus
phase-to-ground protection which is designed to meet
IEEE 587. Where the potential exists for abnormally
high phase-to-ground voltages (in excess of 125% of
nominal), an isolation transformer is strongly
recommended. 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.
If the AC source for the AC Regen does not have a
ground reference (neutral or phase ground), an
isolation transformer with the neutral of the secondary
grounded is highly recommended. These AC Regen’s
contain PE referenced MOV devices for input transient
voltage limiting. Transients occurring on a non-ground
referenced voltage source may generate excessive line
to ground voltages which could exceed the limits of
the insulation system of the AC Regen. Under these
conditions, it is highly recommended that a system
level transient voltage suppression device be
employed in order to limit the potential line to ground
voltage. Contact factory if the AC Regen must be
operated on an ungrounded voltage source.
Input Power Conditioning
The basic guidelines for determining if an isolation
transformer is required are as follows:
1.
If the AC input power system does not have a
neutral or one phase referenced to ground, an
isolation transformer with the neutral of the
secondary grounded is
highly recommended
.
If the line-to-ground voltages on any phase can
exceed 125% of the nominal line-to-line
voltage, an isolation transformer with the
neutral of the secondary grounded, is
always
required
.
2.
If the AC line supplying the
AC REGEN has
power factor correction capacitors that are
switched in and out, an isolation transformer is
recommended between the
AC REGEN and the
capacitors.
3.
If the AC line frequency experiences transient
power interruptions or significant voltage
spikes, an isolation transformer or a three
percent (3%) reactor is recommended.
Input Fusing
WARNING
AC REGEN does not provide input power short circuit
fusing. Maximum Recommended AC Line Fuses are
shown in tables 1, 2 and 3. Note that branch circuit
breakers or disconnect switches can not respond fast
enough to provide the level of protection that the
AC
REGEN components require.
Input Devices
WARNING
Hardwired Stop Circuit
The
AC REGEN “ENABLE” control input circuitry
includes solid-state components. If hazards
due
to
accidental
contact
with
moving
machinery or unintentional flow of liquid, gas
or solids exist, an additional hardwired stop
circuit is required to remove AC line power to
the
AC REGEN. When AC power is removed, the
motor will coast to a stop. Consequently, an
auxiliary braking method may be required.
ELECTRICAL INTERFERENCE (EMI/RFI)
AC REGEN
Immunity
The immunity of the
AC REGEN’S to externally
generated interference is outstanding. No special
precautions other than following the procedures
outlined in this manual are required.
It is recommended that the coils of AC and DC
energized contactors interfaced with the
AC REGEN be
suppressed with RC networks and diodes respectively
or with similar devices. This is because non-
suppressed coils (inductors) can generate high
electrical transients.
In areas prone to frequent lightning strikes, the
standard MOV’s (Metal Oxide Varistors) supplied with
the drive may need to be supplemented with
additional surge suppression MOV’s on the AC line
feeding the drive.