Danfoss VLT 2800, VLT 5000, VLT 5000 FLUX Installation guide
■ Contents
VLT®2800/5000/5000 FLUX/FCD 300
Introduction
Description of the brake system ............................................................................. 2
....................................................................................................... 2
Examples ............................................................................................................ 3
Example 1 - Conveyor belt ..................................................................................... 3
Example 2 - Centrifuge ........................................................................................... 5
Calculation of the brake resistor ............................................................ 6
Brake setup ........................................................................................................... 6
Calculation of brake resistor values ......................................................................... 6
Calculation of braking power .................................................................................. 7
Calculation of the brake resistor peak power .......................................................... 7
Calculation of the brake resistor average power ..................................................... 8
Braking ................................................................................................................. 9
Braking of inertia .................................................................................................... 9
Continuous braking ................................................................................................ 9
D.C. injection braking ............................................................................................. 9
AC-braking VLT 2800 and FCD 300 ....................................................................... 9
Optimum braking ................................................................................................... 9
Brake cable ............................................................................................................ 10
Protective functions during installation .................................................................... 10
Description of VLT 5000 brake ............................................................................... 11
Programming .................................................................................................... 12
VLT 5000 Process parameters ............................................................................... 12
VLT 5000 FLUX parameters .................................................................................... 12
VLT 2800 parameters ............................................................................................. 13
FCD 300 parameters .............................................................................................. 13
Brake resistor overview .............................................................................. 14
Brake resistor for VLT 5001-5500 10% duty-cycle data and codenumber .............. 14
Brake resistor for VLT 5001-5102 40% duty-cycle data and codenumber .............. 16
Brake resistor for VLT 2803-2882 duty-cycle 40% data and codenumber .............. 17
Brake resistor for VLT FCD 303-335 duty-cycle 40% data and codenumber .......... 17
Brake resistor for VLT 5001-5500 10% duty-cycle cablegland, weight and drawing
no. ......................................................................................................................... 19
Brake resistor for VLT 5001-5102 40% duty-cycle cablegland, weight and drawing
no. ......................................................................................................................... 20
Brake resistor for VLT 2803-2882 40% duty-cycle cablegland, weig
no. ......................................................................................................................... 21
Brake resistor for VLT FCD 303-335 40% duty-cycle cablegland, weight and drawing
no. ......................................................................................................................... 21
ht and drawing
Drawings 1 - 19 ................................................................................................ 22
MI.90.F1.02 - VLT is a registered Danfoss trademark
1
Danfoss offers a range of brake resistors for
frequency converters, types 2800, 5000, 5000
FLUX and FCD 300.
■Description of the brake system
When the speed reference of a frequency converter is
reduced, the motor acts as a generator and brakes.
When a motor acts as a generator, it supplies energy
to the frequency converter which is collected in
the intermediate circuit. The function of the brake
resistor is to provide a load on the intermediate circuit
during braking, thereby ensuring that the braking
power is absorbed by the brake resistor.
If a brake resistor was not used, the intermediate circuit
voltage of the frequency converter would continue to
increase, until it cuts out for protection. The advantage
of using a brake resistor is it enables braking of a
heavy load quickly, e.g. on a conveyor belt.
Danfoss has chosen a solution in which the
brake resistor does not form an integral part
of the frequency converter.
This offers the user the following advantages:
- The resistor time cycle can be selected as required
- The heat developed during braking can be
conveyed beyond the panel cabinet to allow
theenergytobeused
- There is no overheating of the electronic
components, even if the brake resistor is overloaded
VLT®2800/5000/5000 FLUX/FCD 300
■Knowledge of the system
If the right brake resistor is to be selected, it
is necessary to know how often and by how
much the motors are to brake.
In the following, some examples are given of
calculations of the required braking for a conveyor
belt and a centrifuge, respectively.
2
MI.90.F1.02 - VLT is a registered Danfoss trademark
■Example 1 - Conveyor belt
Fig. 1 shows the relation between the braking power
and the acceleration/braking of a conveyor belt. As can
be seen, the motor power during braking is negative,
since the torque on the motor shaft is negative. The
braking power, i.e. the power to be dissipated to the
brake resistor, corresponds almost to the negative
motor power, taking the losses in the motor and the
frequency converter into account. The example also
shows that the motor power is time-dependent.
Kinetic energy (E) in conveyor belt + motor:
m = mass with linear movement [kg]
v = speed of mass with linear movement [m/s]
2
j = inertia of motor and gear box (kgm
]
VLT®2800/5000/5000 FLUX/FCD 300
This formula may also be expressed as follows:
However, not all of the energy is to be dissipated to
the brake resistor. The friction of the conveyor belt
andthepowerlossofthemotoralsocontributetothe
braking function. Consequently, the formula for energy
dissipation (E
) to the brake resistor is as follows:
b
Mf= Friction torque [Nm]
= Motor efficiency
M
When:
Examples
is inserted, the result is as follows:
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3
■Fig. 1
The relation between braking power and
acceleration/braking of a conveyor belt.
VLT®2800/5000/5000 FLUX/FCD 300
4
MI.90.F1.02 - VLT is a registered Danfoss trademark
■Example 2 - Centrifuge
Another typical application in which braking
can be required on centrifuges. The weight of
the centrifuge content is m.
VLT®2800/5000/5000 FLUX/FCD 300
jC= centrifuge inertia =
2
2
+r
½xmx(r
j
= Gear motor inertia [kgm2]
M
= Gear motor efficiency
η
M
n
= max. motor speed [rpm]
1
= max. centrifuge speed [rpm]
n
2
1
)[kgm2]
2
Examples
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5
■Brake setup
Fig. 2 shows a brake set-up using a
frequency converter.
The following sections use expressions and
abbreviations with respect to a brake set-up
that can be seen from fig. 2.
Fig. 2
VLT®2800/5000/5000 FLUX/FCD 300
■Calculation of brake resistor values
To keep the VLT frequency converter from cutting out
for protection when the motor brakes, the resistor
values are to be selected on the basis of the peak
braking power and the intermediate circuit voltage:
As can be seen, the brake resistor depends on
the intermediate circuit voltage (Udc).
Udc is the voltage, where the brake is activated. For
values see further on in this instruction.
Another option is to use the brake resistor
recommended by Danfoss (Rrec). This guarantees
that the frequency converter is able to brake at the
highest braking torque (Mbr), i.e. 160% / 150% /
100%. See the tables further on in this instruction.
6
MI.90.F1.02 - VLT is a registered Danfoss trademark
NB!:
Remember to check whether your brake resistor
is able to handle the intermediate voltage (Udc
for your specific drive can be found in the table
below) if you do not use Danfoss brake resistors.
VLT®2800/5000/5000 FLUX/FCD 300
ηηηη
VLT type Udc
is typically 0,9, while ηηηη
motor
is typically 0,98. R
vlt
can be expressed as follows:
rec
Max. Braking
torque
5001-5027 Process and FLUX / 200-240 Volt 397 Volt 160 %
5032-5052 Process and FLUX / 200-240 Volt 390 Volt 150 %
5001-5062, 5072 and 5102 Process and FlLUX /
380-500 Volt
822 Volt 160 %
5075, 5100 and 5125-5500 Process / 380-500 Volt 795 Volt 150 %
5075, 5100 and 5125-5500 FLUX / 380-500 Volt 795 Volt 100 %
5001-5250 Process / 550-600 Volt 958 Volt 160 %
2803-2840 / 200-240 Volt 385 Volt 160 %
R
=
rec
2805-2882 and FCD 303-335 / 380-480 Volt 770 Volt 160%
NB!:
Choose a brake resistor which is max. 10%
below the value recommended by Danfoss.
If a bigger brake resistor is selected, 160% /
150% / 100% braking torque cannot be obtained,
and there is a risk that the frequency converter
will cut out for protection.
Ifbrakingisonlye.g. at80%torque,itispossibleto
install a bigger brake resistor, the size of which can
be calculated using the formula R
■Calculation of braking power
When calculating the braking power, it is to be ensured
that the brake resistor is able to handle the average
power as well as the peak power. The average power is
, no. 1.
rec
determined by the process period time, i.e. the length
of the braking time in relation to the process period time.
The peak power is determined by the braking torque,
which means that as braking progresses, the brake
resistor must be able to dissipate the energy input.
Fig. 3 shows the relation between the average
power and the peak power.
Fig. 3
brake resistor
Calculation of the
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7
VLT®2800/5000/5000 FLUX/FCD 300
■Calculation of the brake resistor peak power
P
peak, mec
is the peak power by which the motor brakes
on the motor shaft. It is calculated as follows:
P
is the name used for the braking power dissipated
peak
to the brake resistor when the motor brakes.
is lower than P
P
peak
peak,mec
since the power
is reduced by the efficiencies of the motor and
the VLT frequency converter.
The peak power is calculated as follows:
If the brake resistor recommended by Danfoss is
selected (R
) on the basis of the tables further
rec
on in this instruction, the brake resistor will be
certain to provide a braking torque of 160% /
150% / 100% on the motor shaft.
■Calculation of the brake resistor average power
The average power is determined by the process
period time, i.e. the length of the braking time in
relation to the process period time.
Danfoss offers brake resistors with a duty-cycle of
max. 10% and 40%, respectively (some drives are
only available with a duty-cycle of max. 10%). If
a 10% duty-cycle is applied, the brake resistors
are able to absorb Ppeak for 10% of the period
time. The remaining 90% of the period time will
be used on deflecting excess heat.
The average power with 10% duty-cycle can
be calculated as follows:
The average power with 40% duty-cycle can
be calculated as follows:
The calculations apply to intermittent braking using a
period time of 120/300 seconds (to define whether it is
120 or 300 seconds. Please see the tables further on).
NB!:
Longer time than the specified intermittent
braking period time may result in overheating
of the resistor.
If the amount of kinetic energy (Eb) transferred to
the resistor in each braking sequence (see examples
1 and 2) is known, the average power of the
resistor can be calculated as follows:
Tp= period time in seconds (see drawing on page 3).
If the amount of kinetic energy transferred to the
resistor in each braking sequence is not known, the
average power can be calculated on the basis of the
process period time and the braking time.
The duty-cycle for the braking sequence is
calculated as follows:
Tp= process period time in seconds.
T
= braking time in seconds.
b
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MI.90.F1.02 - VLT is a registered Danfoss trademark
VLT®2800/5000/5000 FLUX/FCD 300
■Braking of inertia
In the case of braking of high inertia values on the
motor shaft, the brake resistor values can be based
on the inertia,
ω, t. See fig. 4.
Fig. 4
t is determined by the ramp-down time
in parameter 208.
NB!:
The ramp-down time goes from the rated motor
frequency in parameter 104 to 0 Hz.
P
can be calculated as:
peak
Since the electrical resistance of the rotor cage is very
low, even small induced voltages can create a high
rotor current. This current will produce a strong braking
effect on the bars and hence on the rotor. As the speed
falls, the frequency of the induced voltage falls and with
it the inductive impedance. The ohmic resistance of the
rotor gradually becomes dominant and so increases
the braking effect as the speed comes down. The
braking torque generated falls away steeply just before
standstill and finally ceases when there is no further
movement. Direct current injection braking is therefore
not suitable for actually holding a load at rest.
■AC-braking VLT 2800 and FCD 300
WhenthemotoractsasabraketheDC-linkvoltagewill
increase because energy is fed back to the DC-link. The
principle in AC-brake is to increase the magnetisation
during the braking and thereby increase the thermal
losses of the motor. Using par. 144 in VLT 2800 and
FCD 300 it is possible to adjust the size of the generator
torque that can be applied to the motor without the
intermediate circuit voltage exceeding the warning level.
The braking torque depends on the speed. With
the AC-brake function enabled and parameter 144
= 1,3 (factory setting) it is possible to brake with
about 50 % of rated torque below 2/3 of rated speed
and with about 25 % at rated speed. The function
is not working at low speed (below 1/3 of nominal
motor speed). It is only possible to run for about 30
seconds with parameter 144 greater than 1.2.
jistheinertiaofthemotorshaft.
Calculate the value on the brake resistor as described
under the preceding paragraphs.
■Continuous braking
For continuous braking, select a brake resistor in
which the constant braking power does not exceed
the average power P
of the brake resistor.
avg
NB!:
Please contact your Danfoss distributor
for further information.
■D.C. injection braking
If the three-phase winding of the stator is fed with direct
current, a stationary magnetic field
will be set up in
the stator bore causing a voltage to be induced in the
bars of the cage rotor as long as the rotor is in motion.
NB!:
If the value in parameter 144 is increased,
the motor current will simultaneously increase
significantly when generator loa
ds are applied.
The parameter should therefore only be changed if
it is guaranteed during measurement that the motor
current in all operating situa
tions will never exceed the
maximum permitted current in the motor. Please note:
The current can not be read out from the display.
■Optimum braking
Dynamic braking is useful from max. speed down to a
certain frequency. Below this frequency DC braking
is to be applied as required. The most efficient way
of doing this is to use a combination of dynamic
and DC braking. See fig. 5. The parameters can
be found further on in this instruction.
Braking
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