Figure 4-14 Typical Protection Circuit For A Braking Resistor; Table 4-12 Minimum Resistance Values And Peak Power Rating For The Braking Resistor At 40°C (104°F) - Emerson unidrive sp User Manual

Safety Product Mechanical
Information Information Installation
Table 4-12 Minimum resistance values and peak power rating
for the braking resistor at 40°C (104°F)
Minimum
Model resistance*
Ω
SP5401**
7
SP5402**
SP6401**
5
SP6402**
SP3501
SP3502
SP3503
SP3504 18
SP3505
SP3506
SP3507
SP4601**
SP4602**
SP4603**
13
SP4604**
SP4605**
SP4606**
SP5601**
10
SP5602**
SP6601**
10
SP6602**
* Resistor tolerance: ±10%
** The power ratings specified are for a stand-alone drive only. If the
drive is part of a common DC bus system different ratings must be used.
Contact the supplier of the drive for more information.
For high-inertia loads or under continuous braking, the continuous power
dissipated in the braking resistor may be as high as the power rating of
the drive. The total energy dissipated in the braking resistor is dependent
on the amount of energy to be extracted from the load.
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.
Optimization 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. Braking capability will then be reduced, which could
cause the drive to trip during braking if the value chosen is too large.
80
Electrical Getting Basic
installation Started parameters
Instantaneous Average power
power rating for 60s
kW kW
82.5
86.9
86.9
122 122
4.4
6.0
8.0
50.7 9.6
13.1
19.3
22.5
19.3
22.5
27.8
95.0
33.0
45.0
55.5
67.5
125
82.5
113
125
125
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Running SMARTCARD
Optimization
the motor operation
Thermal protection circuit for the braking resistor
The thermal protection circuit must disconnect the AC supply from the
drive if the resistor becomes overloaded due to a fault. Figure 4-14
shows a typical circuit arrangement.

Figure 4-14 Typical protection circuit for a braking resistor

Main contactor
power supply
See Figure 4-2 on page 68, Figure 4-3 and Figure 4-4 on page 69, and
Figure 4-5 on page 69 for the location of the +DC and braking resistor
connections.
4.9.3 Braking resistor software overload protection
The drive software contains an overload protection function for a braking
resistor. In order to enable and set-up this function, it is necessary to
enter two values into the drive:
• Resistor short-time overload time (Pr 10.30)
• Resistor minimum time between repeated short-time overloads
(Pr 10.31)
This data should be obtained from the manufacturer of the braking
resistors.
Pr 10.39 gives an indication of braking resistor temperature based on a
simple thermal model. Zero indicates the resistor is close to ambient and
100% is the maximum temperature the resistor can withstand. A br.rS
alarm is given if this parameter is above 75% and the braking IGBT is
active. An It.br trip will occur if Pr 10.39 reaches 100%, when Pr 10.37 is
set to 0 (default value) or 1.
If Pr 10.37 is equal to 2 or 3 an It.br trip will not occur when Pr 10.39
reaches 100%, but instead the braking IGBT will be disabled until
Pr 10.39 falls below 95%. This option is intended for applications with
parallel connected DC buses where there are several braking resistors,
each of which cannot withstand full DC bus voltage continuously. With
this type of application it is unlikely the braking energy will be shared
equally between the resistors because of voltage measurement
tolerances within the individual drives. Therefore with Pr 10.37 set to 2 or
3, then as soon as a resistor has reached its maximum temperature the
drive will disable the braking IGBT, and another resistor on another drive
will take up the braking energy. Once Pr 10.39 has fallen below 95% the
drive will allow the braking IGBT to operate again.
See the Advanced User Guide for more information on Pr 10.30, Pr
10.31, Pr 10.37 and Pr 10.39.
This software overload protection should be used in addition to an
external overload protection device.
Onboard Advanced Technical
PLC parameters Data
Optional
EMC
filter
Stop
Start / Thermal
Reset protection
device
Braking resistor
Unidrive SP User Guide
UL Listing
Diagnostics
Information
Drive
+DC
BR
Issue Number: 13