Ac Supply Requirements; Table 4-1 Behavior Of The Drive In The Event Of A Motor Circuit Ground (Earth) Fault With An It Supply - Emerson unidrive sp User Manual

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4.2

AC supply requirements

Voltage:
SPx4xx 380V to 480V ±10%
SPx6xx 500V to 690V ±10%
Number of phases: 3
Maximum supply imbalance: 2% negative phase sequence (equivalent
to 3% voltage imbalance between phases).
Frequency range: 48 to 65 Hz
For UL compliance only, the maximum supply symmetrical fault current
must be limited to 100kA
4.2.1 Supply types
Drives rated for supply voltage up to 575V are suitable for use with any
supply type, i.e. TN-S, TN-C-S, TT, IT, with grounding at any potential,
i.e. neutral, centre or corner ("grounded-delta").
Grounded delta supplies >575V are not permitted.
Drives are suitable for use on supplies of installation category III and
lower, according to IEC60664-1. This means they may be connected
permanently to the supply at its origin in a building, but for outdoor
installation additional over-voltage suppression (transient voltage surge
suppression) must be provided to reduce category IV to category III.
Operation with IT (ungrounded) supplies:
Special attention is required when using internal or external
EMC filters with ungrounded supplies, because in the event
of a ground (earth) fault in the motor circuit the drive may not
WARNING
trip and the filter could be over-stressed. In this case, either
the filter must not be used (removed) or additional
independent motor ground fault protection must be provided.
Refer to Table 4-1.
For details of ground fault protection contact the supplier of
the drive.
A ground fault in the supply has no effect in any case. If the motor must
continue to run with a ground fault in its own circuit then an input
isolating transformer must be provided and if an EMC filter is required it
must be located in the primary circuit.
Unusual hazards can occur on ungrounded supplies with more than one
source, for example on ships. Contact the supplier of the drive for more
information.
Table 4-1 Behavior of the drive in the event of a motor circuit ground
(earth) fault with an IT supply
Drive size Internal filter only
May not trip – precautions
required
6 to 9
• Remove the EMC filter
• Use ground leakage
relay
4.2.2 Supplies requiring line reactors
Input line reactors reduce the risk of damage to the drive resulting from
poor phase balance or severe disturbances on the supply network.
Where line reactors are to be used, reactance values of approximately
2% are recommended. Higher values may be used if necessary, but may
result in a loss of drive output (reduced torque at high speed) because of
the voltage drop.
For all drive ratings, 2% line reactors permit drives to be used with a
supply unbalance of up to 3.5% negative phase sequence (equivalent to
5% voltage imbalance between phases).
Severe disturbances may be caused by the following factors, for example:
• Power factor correction equipment connected close to the drive.
50
Getting Basic Running
Electrical
Installation Started parameters the motor
External filter (in addition
to the internal filter)
May not trip – precautions
required
• Do not use EMC filter
• Use ground leakage
relay
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• Large DC drives having no or inadequate line reactors connected to
the supply.
• Direct-on-line started motor(s) connected to the supply such that
when any of these motors are started, the voltage dip exceeds 20%.
Such disturbances may cause excessive peak currents to flow in the
input power circuit of the drive. This may cause nuisance tripping, or in
extreme cases, failure of the drive.
Drives of low power rating may also be susceptible to disturbance when
connected to supplies with a high rated capacity.
All Free Standing drives have internal AC line chokes, so they do not
require additional AC line reactors except for cases of excessive phase
unbalance or extreme supply conditions.
When required, each drive must have its own reactor(s). Three individual
reactors or a single three-phase reactor should be used.
Reactor current ratings
The current rating of the line reactors should be as follows:
Continuous current rating:
Not less than the continuous input current rating of the drive
Repetitive peak current rating:
Not less than twice the continuous input current rating of the drive
4.2.3 Input inductor calculation.
To calculate the inductance required (at Y%), use the following equation:
Y V 1
× ×
L --------- - ------ - ----------- -
=
100 2πfI
3
Where:
I = drive rated input current (A)
L = inductance (H)
f = supply frequency (Hz)
V = voltage between lines
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