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44
Unidrive User Guide
www.controltechniques.com Issue Number: 9
The instantaneous power rating refers to the short-term maximum power
dissipated during the
on
intervals of the pulse width modulated braking
control cycle. The braking resistor must be able to withstand this
dissipation for short intervals (milliseconds). Higher resistance values
require proportionately lower instantaneous power ratings.
In most applications, braking occurs only occasionally. This allows the
continuous power rating of the braking resistor to be much lower than
the power rating of the drive. It is essential, though, that the
instantaneous power rating and energy rating of the braking resistor are
sufficient for the most extreme braking duty that is likely to be
encountered.
Optimisation of the braking resistor requires a careful consideration of
the braking duty.
Select a value of resistance for the braking resistor that is not less than
the specified minimum resistance. Larger resistance values may give a
cost saving, as well as a safety benefit in the event of a fault in the
braking system, however peak braking power is reduced. If the
resistance is too high this could cause the drive to trip during braking.
Thermal protection circuit for the braking resistor
The thermal protection circuit must disconnect the AC supply from the
drive if the resistor becomes overloaded. The thermal protection device
can be either an external thermal overload device or an integrated
temperature switch which is available from most braking resistor
suppliers. A suitable thermal overload device is the LR2D from
Telemecanique. Figure 4-7 shows a typical circuit arrangement.
Figure 4-7 Typical protection circuit for a braking resistor
4.7 Ground leakage
Unidrive sizes 1, 2 and 5 (including Unidrive REGEN size 3 and 4)
There is no direct connection with ground apart from the surge
protection on the input of the drive. Ground leakage is therefore
negligible.
Unidrive sizes 3 and 4 (400V product) except Unidrive REGEN
Ground leakage current is typically 9mA* (27mA with a Unidrive LFT
with date code K08 onwards).
*9mA at 380V to 415V 50Hz AC supply; up to 14mA at 480V 60Hz AC
supply. Measured by the method described in IEC950 Annex D.
Unidrive size 3 (200V product)
Ground leakage current is typically 5mA at 220V 50Hz.
4.7.1 Use of residual current device (RCD)
There are three common types of ELCB / RCD:
1. AC - detects AC fault currents
2. A - detects AC and pulsating DC fault currents (provided the DC
current reaches zero at least once every half cycle)
3. B - detects AC, pulsating DC and smooth DC fault currents
•
Type AC should never be used with drives.
•
Type A can only be used with single phase drives
•
Type B must be used with three phase drives
If an external RFI filter is used, a delay of at least 50ms should be
incorporated to ensure spurious trips are not seen. The leakage current
is likely to exceed the trip level if all of the phases are not energised
simultaneously.
4.8 EMC (Electromagnetic compatibility)
Compliance with EN61800-3 (standard for Power Drive Systems)
Meeting the requirements of this standard depends on the environment
that the drive is intended to operate in, as follows:
Operation in the first environment
Observe the guidelines given in section 4.8.2
page 48. An RFI filter will always be required. Some model sizes may
require additional filtering techniques to be applied.
Operation in the second environment
An RFI filter is required for all Unidrives with a rated current of less
than 100A. Where a filter is required follow the guidelines in section
4.8.2
on page 48. Where an RFI filter is not required
follow the guidelines given in section 4.8.1
.
Refer to Chapter 11
on page 190 for further information
on compliance with EMC standards and definitions of environments.
Detailed instructions and EMC information are given in the
Unidrive
EMC Data Sheet
which is available from the supplier of the drive.
N
The installer of the drive is responsible for ensuring compliance with the
EMC regulations that apply where the drive is to be used.
The drive will comply with the standards for emission, such as EN50081-
2, only when the instructions given in this chapter are followed closely.
When Unidrive sizes 3 and 4 are used the leakage current is
high. In this case a permanent fixed ground connection must
be provided, or other suitable measures taken to prevent a
safety hazard occurring if the connection is lost.
Optional
RFI filter
Stop
Start /
Reset
Thermal
protection
device
Braking resistor
Drive
Main contactor
power supply
+DC
BR
WARNING
Only type B ELCB / RCD are suitable for use with Unidrive.
This is a product of the restricted distribution class according
to IEC61800-3
In a domestic environment this product may cause radio
interference in which case the user may be required to take
adequate measures.
The second environment typically includes an industrial low-
voltage power supply network which does not supply
buildings used for domestic purposes. Operating the drive in
this environment without an RFI filter may cause
interference to nearby electronic equipment whose
sensitivity has not been appreciated. The user must take
remedial measures if this situation arises. If the
consequences of unexpected disturbances are severe, it is
recommended that the emission limits of EN50081-2 be
adhered to.
WARNING
WARNING
WARNING
NOTE
Summary of Contents for Unidrive 1 Series
Page 208: ......
