System Design; Power Connections; Multiple Motoring Drives; Single Regen, Single Motoring Drive - Emerson SP1201 Installation Manual

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Introduction

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4

System design

4.1 Introduction
The sizing of a regen system must take into account the following
factors:
1. Line voltage variation
2. Motor rated current, rated voltage and power factor
3. Maximum required power and overload requirements
4. Heavy Duty / Normal Duty Regen drive ratings
In general, when designing a regen system, equal Regen and motoring
drive rated currents will work correctly. However, care must be taken to
ensure that under worst case supply conditions the Regen drive is able
to supply / absorb all the required power including total system losses.
If the Regen drive is unable to supply the full power required by the
motoring drive(s), the DC bus voltage will drop, and in severe cases may
lose synchronisation with the AC supply and trip. If the Regen drive is
unable to regenerate the full power from the motoring drive(s) into the
DC bus, then the Regen drive and motoring drive(s) will trip on over-
voltage.
4.1.1

Single Regen, single motoring drive

The following calculations can be carried out for either a single Regen
drive, motoring drive system or single Regen drive, multiple motoring
drive system.
Example
In the case of a 23A (Normal Duty), SP2403 operating in regen mode
from a 400V supply, and a SP2403 driving a 400V rated, 0.85 pf motor:
The rated power of the Regen drive is:
× ×
3 Rated current Supply voltage
= 1.73 x 23 x 400
= 15.9kW
The motoring drive can supply power:
× ×
3 Rated current Motor voltage
= 1.73 x 23 x 400 x 0.85
= 13.5kW
Drive losses
2 x Unidrive SP 2403 = 626W
When the motoring drive is supplying rated current to the motor, the
Regen drive needs to provide 13.5kW, plus drive losses = 14.126kW.
The Regen drive can supply 15.9kW at rated current, which is ample, in
this case.
Conversely, in some cases, a Regen drive of the same rating as the
motoring drive, may not be able to supply enough power, as the
following example shows:
Example
In the case of a 96A (Heavy Duty), SP4403 operating in regen mode,
and a SP4403 driving a 75kW, 400V, 0.95pf motor:
If the motoring drive is supplying 175% maximum current, and the
Regen drive has its 380V supply at the lower limits of -10% (342Vac),
then, with a regen current limit of 150%:
The Regen drive maximum available power is:
× ×
3 150% Rated current
= 1.73 x 1.5 x 96 x 342
= 85.1kW
The motoring drives maximum. power is:
× ×
3 175% Rated current
= 1.73 x 1.75 x 96 x 400 x 0.95
= 110.4kW
Drive losses
2 x Unidrive SP 4403 = 1.952kW
The Regen drive is also required to supply the Regen and motoring drive
losses in this example 1.952kW which brings the total power
30
System Mechanical Electrical
design installation installation
×
Power factor
×
Supply voltage
× ×
Motor voltage Power factor
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requirement to 112.352kW. However, this Regen drive is only capable of
supplying approximately 85.1kW and therefore a drive of a larger rating
is required.
4.1.2

Multiple motoring drives

In multi-drive configurations, the Regen drive must be of a sufficient size
to supply the net peak power demanded by the combined load of all
motoring drives plus the combined losses, including its own losses.
Due to the effects of increased DC bus capacitance, there is a limit to the
number of motoring drives that can be supplied from a Regen drive. This
is true irrespective of the balance of power between the motoring drives
and the Regen drive.
The previous calculations can be used for the sizing of multiple motoring
drives also.
4.2

Power connections

The following section covers the power connections required for
Unidrive SP regen systems.
• For single Regen, single motoring systems, AC supply connections
are made to L1, L2 and L3 drive terminals and the drive's internal
soft start circuit is used for power-up.
• The single Regen, multiple motoring and multiple regen, multiple
motoring systems require an external charging circuit due to the
extra capacitance from the additional drives. No AC connections are
made to the Regen drive's L1, L2 and L3 terminals. The external
charging circuit can consist of either the SPMC solution or an
external charging resistor as shown in the following.
• For the regen brake resistor replacement system, the motoring
drive's internal soft start is used for power-up with no AC
connections to L1, L2, L3 on the Regen drive.
For control circuit connections refer to section 6.6 Control
connections on page 83.
NOTE
If the regen system is not a standard configuration or changes are
required to the following systems and set ups, contact the supplier of the
drive.
Unidrive SP Regen Installation Guide
Technical Component
Diagnostics
data sizing
Issue Number: 2