Unidrive Regen Installation Guide
7
Issue Number: 2
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3.2
Non standard configurations
There are a number of possible options available when designing a Unidrive Regen system depending on the user requirements and the nature of the
AC supply. Non standard systems can be created where favourable supply conditions exist, allowing cost and space savings to be achieved by
reducing the number of components.
3.2.1
Switching frequency filter
If the supply to the Regen drive is shared with other equipment, then it is strongly recommended that a switching frequency filter be incorporated in
order to avoid the risk of interference or damage to the other equipment.
3.2.2
Supply assessment
The following guidelines should be used when assessing whether or not a switching frequency filter is required.
Symbols used are:
I
Drive
Nominal drive 100% current rating.
I
SC
Short circuit current of supply at point of coupling with other equipment.
I
Supply
Rated current of supply.
The switching frequency filter may be omitted if the following relation is true:
If the short-circuit current is not known, then a reasonable estimate can be made if it is assumed that the fault current of the supply is 20 times the
rated current. This is very commonly the case where the supply is derived through a distribution transformer from a higher voltage supply with a high
fault level.
Then:
This second relation is helpful but must be used with care. It is reliable where the Regen drive is supplied through its own cable run from a point close
to the distribution transformer terminals. If the Regen drive shares a long cable run with other equipment, then the effect of the cable impedance on
the fault level must be taken into account if a risk of disturbance to the other equipment is to be avoided.
This procedure will normally be applied when assessing a non-dedicated low-voltage supply. It may also be applied to the medium/high voltage
supply where the low-voltage supply is dedicated to the drive. In that case the currents used must be referred to the high voltage side of the
transformer.
3.2.3
RFI filter
Whether or not an RFI filter is required is dependent upon the user requirements and the AC supply network. For further details refer to Chapter
7 Unidrive Regen EMC information on page 19. An RFI filter must not be fitted without a switching frequency filter present in the system.
I
Drive
<
1
I
SC
140
I
Drive
<
1
I
Supply
7
