1 Altivar 71 Output filters Selection Guide Producto y Versión:ATV61/71Primera versiónActualización diagrama de selección y contenidoSergio Núñez Núñez1/20113/20111.02.0ModificacionesAutorFechaRevisiónCentro de Competencia Técnica
2 ATV 71: Output filters Selection Guide Summary Selection DiagramCauses of motor overvoltagesMultiplication factorsSwitching frequency influencesMotors in parallelSelection TableOvervoltage and dv/dt limitation optionsSVL overvoltage limitation functionMotor Choke.Sinus Filter6. Adequation of the motor
5 Causes of motor overvoltages The switching of the output voltage on the output of a drive by the IGBT bridge generates rapid variations in voltage (dV/dt).+ VDC buse.g. 400 * 2 = 566V0 V- VDC busDrive output voltage (PWM)dV/dt 2 to 10kV/µSMotor currentnearly sinusoidal
6 Causes of motor overvoltages Overvoltages are generated by reflected waveforms due to dV/dt and to poor impedance matching between the motor and the motor cable.The amplitude and the dV/dt are principally functions of the cable length and the modulation technique.overvoltagedV/dtl cableOvervoltage at the motor terminalsTypically up to 2 x V bus DCex U main =400VacMotoring QuadrantÛ = 400xSQR2x2 = 1132VGenerating Quadrant (braking)Û = 790x2 = 1580VSometimes in certain cases the overvoltage can be greater than 2 Vdc ...+ Vdc- Vdc
7 Causes of motor overvoltages Overvoltages and dV/dt can degrade the insulation of motor windings and cables.This problem is generally above than 400V and for motors not having insulation compatible with variable speed drives (class F).Overvoltages can be destructive with cable lengths of 20 meters or above.The can be greater than 2Vdc in the case of PWM with short tmin (ex 2µS for 200m 4kW)Remarks :The dV/dt gradient is as bad for motor windings as the overvoltage itself (corona effect).And very short wires can also be a problem because of low inductance and parasitic capacitance.
8 Multiplication factors Factors to be taken into account:If parallel cables are used, the cable lenght to be considered must be multiplied by 2,If motors are in parallel, the cable lenght to be considered must be the sum of all motor cable lengthes.Note: a multiplication factor can be used if the swithching frequency used is greater than the default value, but in this case, the use of output filter is not allowed.
9 Switching frequency influences When using “SFR” parameter for example between 4 and 8 kHz the losses increase by 1,3 in tri-phase modulation so it is necessary to dicrease the length of motor cable.Recommendation for length of motor cable in function of switching frequency. (1) These factors are theorical values.Note: a multiplication factor can be used if the swithching frequency used is greater than the default value, but in this case, the use of output filter is not allowed.
10 Motors in parallelThe cable length to be considered for choosing an output filter is the sum of all the cable lengths (ex L1+L2+3L3).Minimize the cable length (drive as close as possible to the motors).L2L1L3
11 Selection table depending on cable length Output filter recommendation according to motor cable length and previous multiplication factors.
12 Software overvoltage limitation function The over voltage software function (SUL) permits the limitation of the over voltage in motor terminals to 2 times the DC bus voltage.To do this, the minimum time between two PWM voltage pulses is adjustable as a function of the cable length (from 6 to 10µS) by means of the optimization paramenter “SOP”. The value of the “SOP” parameter corresponds to the attenuation time of the cable used. It is defined to prevent the superimposition of voltage refections resulting from long cable lengths.The SUL function is useful by itself below certain wiring distances. For longer cable lengths it is necessary to add additional output filters.This function is based on the elimination of shorter pulses generated in the PWM output of the drive. On the other hand, the elimination of these pulses leads to a little loss of torque estimated about 3%, that leads in a lower dynamic performance.
13 Software overvoltage limitation function A PWM pulse too short with respect to the time constant of the cable can lead to the superposition of 2 oscillations and generate and overvoltage> 2*V bus DC
14 Software overvoltage limitation function Time [s]+ 2VdcFunction not activatedovervoltages greater than 2VdcSUL function activatedThe increase of « tmin » slightly degrades the performance but in a proportion that is acceptable with a long cable length.The switching frequency is automatically limited to the factory setting (2.5kHz to 4kHz)
15 Software overvoltage limitation function The tables in the programmation manuals gives examples of correspondence between “SOP” parameter and the length of cable between the drive and the motor.Unshielded "GORSE" cable type H07 RN-F 4Gxx:* These tables are not available for drives of power higher than 75kW.
16 Software overvoltage limitation function The tables in the programmation manuals gives examples of correspondence between “SOP” parameter and the length of cable between the drive and the motor.Shielded "BELDEN" cable Type 2950x:* These tables are not available for drives of power higher than 75kW.
17 Software overvoltage limitation function Summary:PrincipalA PWM voltage pulse time that is very short in comparison to the period can generate an overvoltage >2 times the DC bus voltage during a positive to negative transition.This function permits the limitation of the overvoltage to 2 times the DC bus voltage.To do this, the minimum time between two PWM voltage pulses is adjustable as a function of the cable length (from 6 to 10µS).This function is activated by the parameter SULApplicationsProtection of motors against overvoltages greater than 2 Vbus DCCable lengths up to 150m
18 Maximum cable length depending on motor choke selection See catalog in order to verify the maximum cable length depending on output filter selection.
19 Sinus FilterSinus filter is a low bandwidth filter with a cutoff frequency below the switching frequency (4 to 8kHz only).Sinus filter is the best solution with ATV71 to solve overvoltage at the motor terminal for long motor cable until 600m or 1000m depending on the drive power rate. Sinus filter is also the best way to reduce motor noise.For high power rates sinus filter only allows U/F motor control law and low dynamic.Vector control law in open loop is only posible until 75kW N4 or 45kW M3X voltage supply.See catalog in order to select the rigth reference.In next page you will find a table with maximum cable length depending on sinus filter reference.
20 Sinus Filter Maximum cable length depending on sinus filter reference: For motors in parallel, the sum of all the cable lengths must be taken into consideration. Due to capacitor between phases and ground at the output of the sinus filters, the maximum length of each cable must be divided:by 2,5 for two motorsby 4 for three motorsby 6 for four motors
21 VS. Output side of ATV61/71 Motor choke vs. Sinus filter Motor choke … is much cheaper than a sinus filterhas a smaller size, nearly no voltage drop, less lossesHas a better peak voltage limitation against earthAllows all motor control laws (Sinus filter in HHP only allows U/f and low dynamic)No drive derating necessary (Sinus filter operates at 4kHz!)Altivar 61/71M13VS.Motor choke21
22 Adequation of the motor Check is the selected motor is compatible with pre-selected drive and optionsPe-selected configuration: L < Lmax with no motor filterMotor insulation must be compatible for the use with the variable speed drive. Refer to the next slide.If not, it is required to add motor choke to protect the motor again dv/dt and over voltagesNote: activation of the SUL function and adjustment of the parameter SOP according to the type and length of cable suppress the over voltages exceeding 2 times the bus voltage.Pre-selected configuration: L > Lmax with motor choke and filterThe motor is protected against dV/dTMotor protection against over-voltages can be considered by SUL function activation.
23 Adequation of the motor Motor protection against dV/dT dV/dT protection : customer must be aware of the motor type intended to be used in its application,We consider here the dV/dT on motor terminals.Depending on this type, IEC defines a table for admissible dV/dT levels.A – motors up to 500V used with a variable speed driveB – motors up to 600V used with a variable speed driveC – motors not specified for use withvariable speed drives (IEC )Overvoltage kVRise time µS
24 Adequation of the motor Motor protection against dV/dT Independently of motor cable length, the limitation of dV/dT to 500V/µs or 1kV/µs (depending on supply voltage) is done by using a motor choke:dV/dT limitation values with motor chokes:< 400V < 500V < 690VThe motor choke also permits to reduce peak voltage (*).< 400V < 460V < 690V* (These values apply in motor mode operation).The use of a motor choke is mandatory in case of retrofit of an installation with an old motor.Supression of the dV/dT :The suppression of the dV/dT on motor terminals is done by using a sinus filter.
25 Adequation of the motor Motor protection against over-voltage A PWM voltage pulse time that is very short can generate an over-voltage >2 times the DC bus voltage during a positive to negative transition.The variable speed drives integrates the SVL function, that permits the limitation of the over-voltage to 2 times the DC bus voltage.In generative mode, the DC bus level will regulated at the DC bus braking level, that can be adapted via UBR parameter:ATV71oooM3p: factory setting 395 V.ATV71oooN4: factory setting 785 V.ATV71oooS6X: factory setting 980 V.ATV71oooY: factory setting 1127 V or 1080 V according to rating.The activation of SVL function will limit the setting range of the switching frequency of the variable speed drive.
26 IEC 60034-25 Find more information about Motor cabling Motor Isolation Reduction of voltage stressBearing problems and causesMotor filtersDrive principals