Variable Frequency Drives
methods to control the stator and rotor flux angles
What else does a Flux Vector Control VFD use?
VFD voltages into shaft
High carrier frequency from the ______________ can induce ________________ into the ________________ of the motor
standard motor winding insulation.
High voltages spikes from a VFD can damage what?
often by microprocessors like the type used in computers.
How are VFD's controled?
converts DC from the dc link filter to AC for the load
Inverter
Shaft encoders
Inverter Duty motors can have what installed on them at a later date?
IGBT
Rectifier may also have _________ _________ _________ _____________
a special rectifier section in the VFD
Regenerative Braking requires what?
18 pulse
The _______- pulse rectifier is good at reducing problem harmonics, but is more expensive
Special cables
Due to the nature of the electrical output of a VFD __________ __________ may be needed when connecting a VFD to a motor
deceleration
Dynamic braking offers braking for ___________________
to prevent build up of induced voltage between the shaft and bearing
Explain the below feature of an Inverter Duty Motor: shaft bonding rings
Voided warranty and cause damage
For all installation issues. refer to the manufacturer's installation manual. Failure to do so May result in what?
compatible
For any motor and VFD combination, it is critical that the motor and VFD are
Proportional Integral Derivative control
PID
PID
Proportional Integral Derivative Control
microprocessor
what does the control circuit consist of?
Closed-Loop
A VFD is used to control a pump motor, if the pump is required to maintain a specific pressure under any condition of use, which VFD control would be the best choice?
direct
Closed loop VFD Speed control uses __________________ feedback from the motor to tell the VFD its exact speed and shaft position
False
Using pulse width modulation the output frequency of the inverter is reduced if the number of pulses generated per cycle is also reduced True or False
is the most common and lowest cost configuration of the three techniques.
V/Hz PWM control techniques
Electrical noise and is defined as a sinusoidal component of periodic wave having a frequency that is an integral multiple of the fundamental frequency.
What is Harmonic distortion best described as?
Variable Frequency AC power frequency
The _____________ _________________ drive uses an _____(AC,DC) power supply(single phase or three phase) and converts it to a 3 phase output at a selected __________________.
True, Each has their own way of telling the inverter how to create and control the output voltage
Both the microprocessor in the control logic board and the method of programming produce the required output may be different between manufacturers. True or False
Total harmonic distortion
THD
-the input AC voltage. 1) Vpeak=Vrms x 1.141 or Vpeak = Vrms/.707 2)Calculate the rectifier output Vdc = Vpeak x .955 example: (480/707)x.955 =648 Vdc
The output from the 6 pulse bridge rectifier can be calculated based on what? Each diode conducts when it is forward biased and allows the full positive alternation to pass. what is the calculation
inverter
The output section of the VFD is the what?
Pulse width Modulation (PWM)
The process of the Microprocessor telling the IGBT what to do is called what?
the amount of controller output until the sensor measurement matches the set-point
I controls what? the amount of controller output until the sensor measurement matches the set-point
Regenerative Braking
Line Regenerative Braking is also called what?
usually accomplished by keypad settings or locally or remotely by a potentiometer connected to the VFD. or input from a programmable logic controller, or a binary coded decimal signal from a thumb wheel or sensors monitoring process variables.
Manual speed control of a motor is:
A)Fans B)Pumps
Name two types of equipment that can achieve cost saving benefits by being operated by a motor connected to a VFD
Permanent magnet motors, wound field brush-less excited synch motors reluctance motors
Non induction motors that can be used with specific types of VFDs are:
is at minimum a Class 1 wiring method and the control panels to switches, pilot devices and analog signals are self-powered.
One of the factors that is Important when installing a VFD is Control Wiring- Please Elaborate
Voltages induced into the case and shaft of the motor can cause arcing in the bearings of a motor and result in premature bearing failure.
One of the factors that is Important when installing a VFD is Bonding
an incoming ac power supply with a fixed frequency and turns into a pulsating DC
VFD rectifies what?
a fixed bridge rectifier
what is a rectifier most commonly?
Vdc=Vpeak =480/.707 =678 Vdc
what is the maximum voltage of a 480 V VFD?
dynamic braking
what type of braking uses a resistor to dissapate the regenerative voltage as heat
two delta wye
A 12 pulse rectifier uses the output of a transformer with__________ secondary windings. one secondary is ________ (delta, wye)connected, the other is connected __________ (the same, wye, delta). to provide the 30 degree
voltage
Capacitors oppose a change in what?
to prevent build-up of induced voltage between the shaft and bearing
why are bonding rings sometimes installed on the motor shafts ?
460/60=7.67 ratio 60/2= 30 30 x 7.67 =230 Answer is 230.1 Volts
A 460 V, 60 Hz motor is operated by a VFD, If the motor speed is reduced to 50% of the name plate value, what is the required voltage
0-60
A VFD can be programed to deliver an output between ___-____ Hz or higher, depending upon the limitations of the motor and drive
rectifier
A fixed bridge rectifier is commonly used for what? a) inverter, b) rectifier
a keypad
A programmer enters values into the program using what?
Totally enclosed fan cooled
TEFC
Dynamic braking, line regenerative braking Dc injection braking
What 3 types of motor braking is there from a VFD
high temperatures and humidity
What are cooling towers sized for?
Fans Pumps industry Phase conversion
What are some applications of a VFD
Inverter ready Inverter duty vector duty
What are three ratings of induction motors used for VFD Use
Permanent magnet motors Wound field synchronous motors reluctance motors
What are three types of non induction motors suitable for VFD use?
Harmonics distort the voltage and current waveforms.
What do Harmonics do.
IGBT
What is the most common semi conductor switching device to produce PWM Output?
10-40 degrees Celsius
What is the temp operating range for a VFD
575/60 V/Hz
What is the volts per Hz ratio for a 575 V motor with a 60 Hz frequency rating?
closed loop
What kind of control does a system have if a heater is energized by a contactor controlled by a thermostat?
6 pulse, 12 pulse 18 pulse
What kind of pulse can a rectifier be.
Power wiring and control wiring
What wiring should never be run together?
dissipates Waste
Dynamic braking ____________ the energy as _________ heat.
Insulated gate bipolar transistors
IGBT
DC Injection braking
Injecting a dc voltage onto the motor stator windings, producing a steady flux is what type of braking?
Frequency
When controlling the speed of an ac motor, what factors does a VFD change to achieve different speeds
capacitors and/or reactors to
what does the filtering section contain to smooth the DC voltage.
to store the dc voltage and to filter out any surges or transients on the line power coming into the VFD
what is the function of the dc link?
480/.707 = 678.92 x .955 =648.37
6 pulse rectifier is used in a VFD. What is the DC average output voltage if this rectifier has 480 Vac Input?
PID, Proportional Intergral derivative control
Accurate closed loop control is provided by _________________ ________________ ________________ settings in some VFD control logics?
False, most days the cooling requirements never reach full load , and full horsepower capability of the motor is not required.
Most days cooling requirements of a cooling tower reach full load True or False
False they are required to be marked for VFD use.
Motors operated with a VFD are not required to be marked for VFD use. True or False
induction motors non induction motors
Motors that can be used with VFD's may be of what two kind?
it is filtered to a smooth dc voltage
Once a AC voltage is rectified what happens?
False, once the pulsating DC reaches the DC link, it is filtered to provide a steady state dc voltage
Once the pulsating DC reaches the DC Link, it is not filtered and does not provide a steady state dc voltage True or False
VFD's operate best between 10 degrees-40 degrees Celsius. should be in a relatively dust free location and must not be mounted in the following conditions: directly in sunlight, hazardous or corrosive locations high vibration areas
One of the factors that is Important when installing a VFD is Location: please elaborate
Line voltage to the drive input should not vary more than +/- 10%. - greater variation causes most drives to trip. Voltage stability, Install control signal cables independently of eachother and separate from any power wiring- to avoid inducing more electrical noise electrical noise can produce erratic drive behavior that is difficult to troubleshoot
One of the factors that is Important when installing a VFD is Supply Line Power Quality, please elaborate
does not have feedback from the system about its status
Open loop
the controller output to stop the change and bring it back to a steady state
P changes what?
carefully
PID settings have to be ______________ tuned to achieve the desired effect without overshooting, then undershooting in a hunting or oscillating pattern
not induction motors, no voltage is induced in the rotor they do not have a squirrel cage rotor that carries the current to create the necessary rotor magnet fields.
Permanent are only meant for operation with a VFD. These are:
permanent synchronous stator
Permanent magnet rotor , the magnet fields are from _________________ magnets on the rotor and operate with no slip of the rotor to the rotating magnet field of the stator. they can be thought of as a ________________________ motor which requires virtually no speed difference between the rotor and the rotating magnetic field of the ______________ to start the motor
true
Permanent magnet rotor motors may be though as a synchronous motor which requires virtually no speed difference (slip) between the rotor and the rotating magnetic field of the stator in order to start the motor True or False
are only meant for operation with a VFD
Permanent magnet rotor motors:
True
Regeneration may occur in elevators where the motor is used to break an elevators descent from upper floors. True or False
True
Regenerative braking recycles the energy True or False?
this motor has no squirrel cage, no permanent magnets and no wound field winding's. It operates on the principle of magnetic reluctance
Reluctance Motor
error.
The difference between the measured value of the process variable sensor and the set point in the controller is called the __________.
circulating currents rotor core
The high frequencies can also cause __________ currents in the _____________ core causing overheating
V/Hz Flux Vector
The most common PWM output techniques that provide effective motor control are:
Inverter or Vector Magnetizing
The motor is marked as _______________ or ______________ duty rated with the marked allowable speed range of the motor. In addition, they be marked with no-load or _______________ current or other information that may be important when programming the VFD
a magnetic pulse generator an optical encorder
Sensors can be
SCR
Some VFDs use a controlled _________ rectifier to aid soft starts and reduce inrush currents, due to the capacitor charging. but operates like a fixed bridge while running
VFD operation, Minimum speed rated speed to minimum
Some motors may be approved for ________ operation, but only to a ______________________ (Minimum,Maximum) speed as specified for that motor. This may be represented by a ration of ________________ speed to ____________________speed
THD Total harmonic distoration
Supply utility companies specify the _______________ that they allow back into their supply lines
True
The rectifier may also have a IGBT to offer regenerative breaking energy recover. True or False?
puts an electrical load on the motor when it is regenerating or acting like a generator. this causes the motor to slow down
The resistor of Dynamic braking does what?
pulses pulses
To change the frequency to the motor, the number of ___________ and the width of the ________ are either increased or decreased for each half cycle
squirrel cage induction or Synchronous motors
VFD's control the speed of _________________ _________ induction or ___________________________ motors
True.
VFD's must be properly bonded to ground. Effective bonding paths are important in VFD operator motor installations. True or False?
high frequency solid state switching in the drive
VFDs produce Harmonic distortion as a result of:
Vector type
Vector Duty motors are used with _______________ type VFDs for closed loop operation
changing the frequency by adjusting the VFD for the desired speed, input from a PLC program to the VFD or by feedback sensors from monitoring a process
What is done by the operator to control the speed of the motor?
Dynamic braking resistor
What is often included in a DC link to help dissipate the energy from dc voltage regenerated by a motor decelerating of overhauling.
Inverter duty
Which induction motor rated for VFD use provides the greatest operation speed ratio for constant torque loads?
2 pole
Which squirrel cage induction motor will run fastest when connected to a 60 hz supply. 2 pole, 4 pole, 6 pole,8 pole
DC injection braking
Which type of motor braking is employed at a low rotor speeds?
to protect the motor
Why are Harmonic filters used on the Load side of the VFD
to prevent the build-up of induced voltage between the shaft and bearings.
Why are bonding rings installed on the shafts of some motors that are operated by a VFD?
To avoid any issues, you want stability and ensure you calculated for the appropriate voltage drops for long runs.
Why do you want to select to consider voltage stability when installing a VFD?
It requires no feedback from the motor and offers basic drive adjustments
does V/Hz require feedback from the motor?
Induced voltages
Arcing across the bearings in a motor operated by a VFD is most likely caused from
open loop and closed loop
Basic types of control are
VFD
Capacitors oppose a change in voltage, and the expected dc value on the dc link rises to and stays close to peak voltage value for a __________ that is not under load
adds a factor to the calculation to determine a rate or how quickly the controler brings the process variable back to the set-point
D controls what?
final stopping
DC injection braking is used for the __________________
sometimes it may require one, to learn more about the motor it is operating.
Do Flux Vector control Drives require an auto tune?
Yes, they are more complex to program and usually require most of the name plate data on the motor
Do Flux vector controls' need most of the nameplate date on the motor to be entered into the drive?
connecting the motor to a resistor to dissipate the energy as heat
Dynamic braking
is often included in the DC link section to dissipate the energy from dc voltage regenerated by a motor decelerating or overhauling.
Dynamic braking resistor in regards of the dc link
the current through the resistor is controlled by a transistor.
Dynamic braking, to control the amount of braking, what needs to be done?
control
Electrical noise from power wiring ________ control wiring signals
to provide cooling (TEBC) totally enclosed blower cooled)
Explain the below feature of an Inverter Duty Motor: separately fed blower motor
End
Feedback from a closed loop VFD is provided on the _________ of the shaft.
an Improvement over the Basic V/Hz design. the core of this type of control is still V/Hz. also uses methods to control the stator and rotor flux angles to optimize motor control
Flux Vector control is what?
Independently adjusted to produce optimum torque from maximum speed, down to and including zero speed. These components are control the flux vector
Flux vector control logic does what with the motor current (out of phase producing component) and torque (in phase producing component) ?
mathematical algorithms in control software programs to: -adjust the frequency and magnitude of the voltage as in basic V/Hz - Control the phase angle of the voltage and current applied to a three phase induction motor
Flux vector technology is a control scheme that uses:
3% Any distortion above that requires remedial action.
Generally, a limit of ______% THD is allowed
Positive or negative switching of the dc voltage generates an alternating voltage to the motor
How do you generate an alternating voltage from a dc voltage?
the Positive voltage is removed
How do you turn the IGBT off?
based on how effectively the system was set up initially
How effective is a Open loop control on doing its job?
Regenerative energy proced b the motor is dissipated as waste heat by the resistor Heat sinks and fans dissipate the hat
How is heat dissipated in a dynamic braking system?
by switching an IGBT connected to the negative rail of the rectified dc voltage from the dc link.
How is the negative half of the sine wave generated by the IGBT?
semiconductor -emitter, -gate, -collector
IGBT is a _____________ consisting of 3 things what are they
False They can switch on and off several thousand times per second and are very reliable.
IGBT's can not switch on and off several thousand times per second and are not very reliable True or False
400 500
IGBT's can turn on in less than ________ nanoseconds and turn off in less than ___________ nanoseconds
it provides a constant torque produced by the motor although the speed changes
If the V/Hz is to maintain control, the current remains relatively as the motor speed is controlled up and down. what does this provide?
No, Dynamic braking may not work as required
If the motor speed is low, is dynamic braking required?
Full Flux vector Drive. .01%
In a closed loop, the feedback allows the drive, typically a ________ _________ _______________ _________ , to control the percent speed regulation to approx _______% from no load to full load conditions
feedback from the back emfs, stator fluxes and an encoder on the motor shaft that reports rotor position and speed to the drive.
In an closed loop operation the flux drive gets what?
feedback from the motor using the back emfs and stator fluxes
In an open loop operation the flux drive gets what?
the bearings can become pitted and may premeturely wear out.
Induced high voltages from a VFD can cause what in the bearings?
inverter ready inverter duty vector duty rated
Induction motors for use with VFD's may be
inductor
Input line of reactor A large __________in series with the drive on the line side . Inductors oppose change in current and suppress harmonic frequencies before they reach the supply line.
IGBT
Insulated Gate bipolar transistors
are specifically designed for VFD operation
Inverter duty Motors :
Motors have better insulation and thermal capacity standard motors.
Inverter ready motors have:
it tells the IGBT when to turn on how long to stay on when turn off how long to stay off
what does a microprocessor do in regards of a IGBT"?
Field oriented control
what else is Flux vector Technology sometimes called?
Full wave three phase rectifier, 60 degrees out of phase 360/6=60 degrees
what is a 6 pulse?
an inductor and a capacitor the inductor is in series with the output the capacitor is in parallel with the output
what is the DC link section made up of? are they in series or parallel, answer for each device
IGBT - insulated gate bipolar transistor
what is the most common switching device used to provide the high switching speed that is required for PWM inverter operation ?
line regenerative braking
what type of braking recycles the energy produced by decelerating motor back to the electrical system
the control logic circuit
where does the IGBT receive its gate pulse from?
Yes, it can produce higher voltage spikes than the voltage of the supply system.
Can VFD outputs produce voltage spikes higher than the peak of the supply line voltage of the system?
in the rotor core that reduce the otherwise increased iron losses produced by the high carrier frequency
Explain the below feature of an Inverter Duty Motor: Thinner steel laminations:
True
Manufacturers recommend the maximum cable lengths and type of cable True or False
Yes, atmospheres at higher elevations are thinner and more cooling effort is required
Must altitude must be considered where a VFD is to be installed?
Location, supply line power quality Bonding Control wiring
To correctly install VFD, you must pay attention to important factors what are they?
the frequency of the three phase stator currents
To provide a continuous range of synchronous speeds, a VFD drive varies what?
Oil wells Large mining trucks Forestry the pulp and paper industries steel mills
VFD's are used extensively to control the operation of motors in various applications and industries such as:
10 -40 degrees Celsius
VFD's operate best between __________ - ________ degrees Celsius
False, they should not be installed in direct sunlight
VFD's should be installed in Direct Sunlight True or False?
inverter motors
Vector Duty Motor are like _____________ motors
False, they are like Inverter Duty Motors
Vector Duty Motors are like inverter ready motors, but they come complete with shaft encoders that give feedback to the drive about rotor speed and position. True or False
A local operating keypad other control devices connected to a terminal strip through a network where the vd is controlled by a computer or PLC at a location a great distance from the drive
What are three control modes available to the User on a VFD
Harmonic filter techniques are often used on both the load side of the VFD to protect the motor, and on the line side
What can be used to reduce Harmonics?
A motor operating with a VFD runs slower and is subject to voltages higher than the peak of the line and at varying frequencies... which can cause problems for standard 3 phase induction motors
What can cause problems for standard three phase induction motors?
destructive conditions to the Motors insulation, such as pitting. The Result is motor failure,
What can high voltage spikes at the motor's terminal produce?
Produce peak voltage spikes and flow back into the Utility supply lines.
What do the harmonic frequencies do when they combine with the fundamental frequency.
The supply frequency and the number of pools, both of which determine synchronous speed: nsynch=(120xfrequency)/Number of poles Insert PICTURE HERE
What does the Speed of on induction motor depend upon?
Overheating of the motor
What is the major concern if a standard motor is operated by a VFD at slow speeds?
Inverter Duty
What motor is specifically designed for VFD operation?
motors that operate loads that require changes in speed or for loads that vary by amount.
What motors may benefit from a VFD?
to prtect the Utility's supply equipment
Why are Harmonic Filters used on the line side
The fan of a TEFC (Totally enclosed fan cooled) motor.
What cools the motor motor at rated speed?
to withstand voltage spikes
Explain the below feature of an Inverter Duty Motor: Better winding insulation
on the non drive end in addition to the shaft bonding ring to prevent circulating currents
Explain the below feature of an Inverter Duty Motor: insulated bearings
the use of equipment that draws current from the line in a non linear manner
Harmonic distortion results from what?
Are frequencies that are superimposed on a power system as a result of non linear electronic loads such as VFDs
Harmonics
by operating a load at no greater speed than what is required by the load.
How are Energy savings achieved?
Input line reactor
If the THD is too high, __________ on the line side of the VFD can be accomplished with an _____________ ______ ___________
VFD's
______ are sensitive to harmonic distortion and can also be a source of harmonic distortion
Load reactors
___________ __________ can be used between the drive and the motor to help the reduce with reflected wave.
because harmonics can distort the voltage and current wave forms Extra heat in distribution transformers Torque losses in motors, Disruptive noise in communication systems
Can Harmonics cause problems?
a low impedance path for stray currents
What does the Bonding provide?
Changes AC to DC
What does the Rectifier do?
the frequency of the output voltage of the VFD
What does this section control with control logics?
Flux Vector
Which VFD control technique may require an autotune?
V/Hz VFD
Which VFD controls technique reflects the least amount of harmonics back into the power source?
Vdc=Vpeak
The maximum voltage on a dc link is calculated how?
Impedance
The cable run between the motor and drive is seen as ___________ to the VFD
False, it does not necessarily require a three phase input. Most accept a single phase input and can recreate a three phase output
A VFD does only need 3 phase input
induction
A VFD enables an _______________ motor to run at any speed within range of speeds from near standstill to the maximum running speed
PID P I D
A _________ controller can be tuned by adjusting the amounts of the ______ the _______ the _________ has on the algorithms of the control software to achieve ideal control .
VFD Lower
A ______________ on air handling unitis can supply the optimum amoun of air (cool or hot) to meet daily requirements. Operating a fan at _______________(Lower,Higher) speeds requires less power
Yes
A flux vector VFD with open loop control is used to control a SCIM. If the motor load increases and greater motor slip results, could this VFD automatically adjust the voltage, independently from the frequency, to increase the motor torque and speed? No or Yes?
True
A flux vector control has more exact speed control under changing load conditions True or False
False it usually requires more information to function as a true flux vector drive. the number of parameters can be in the 100's.
A flux vector drive usually requires less information than a V/Hz to operate
True
A motor may have a 4:1 rated ration when operating constant torques loads, but a 20:1 ratio when operating variable torque load. Some motors are approved at rations of 1000:1 for very slow speeds. True or False
1/4 (a Quarter of )
A motor with an operation speed ratio of 4:1 may successfully operated at a minimum of __________ the rated speed of the motor
False
A pulse width Modulation VFD produces a true sinusoidal voltage True or False?
open-loop
A simple V/Hz control of the VFD can be used successfully for _________-______________control with the frequency of the VFD output set. and the motor runs accordingly
40
A standard V/Hz may have up to _____ parameters to enter into its program
True
An Induction motor always runs at a speed slightly less than synchronous speed, do to slip. True or False
A large inductor in series with the drive on the line side . Inductors oppose change in current and suppress harmonic frequencies before they reach the supply line.
An input line reactor is what?
Conductor insulation thickness Conductor Length
Cable inductance and capacitance are directly proportional to which two factors?
Inductance and capacitance Thickness
Cables contain significant values of ___________ and __________ that are directly proportional to the length of cable and the insulation __________ and type
Low
Cabling must provide a _________ impedance bonding path
has feedback from its system about its status , it has direct input from sensors that lets the system adjust for changing conditions.
Closed loop
has direct input from sensors that lets the system adjust for changing conditions.
Closed loop control
a Magnetic field, because it likes to concentrate in ferromagnetic material that is more permeable, rather than air.
Magnetic reluctance is the effect created by:
captures the energy produced by a decelerating motor and sends it back to the electrical system supplying the VFD.
Line regenerative braking,
VFD
Process operations at manufacturing plants or in refinery operations often used elaborate control valves and actuators to control the flow of process fluids within their operations. These systems were maintenance intensive and costly. Using ________, the operator need only to speed up or slow down the AC motor on his pump. This reduces the maintenance costs, reduces energy costs and increases equipment life expectancy.
IGBT IGBT IGBT
Pulse width modulation the ___________ is switched on for a short period of time to only allow a small amount of current to the motor and is then switched off. The _______ is switched on and left on for progressively longer lengths of time until the current in the motor reaches a peak. then the _________ is switched on for progressively shorter lengths of time. decreasing the current to the motor
False, The drive may not be suitable for all motors, and the motor may not be suitable for the use with all types of drives. Consult the VFD manufacturer and the Motor manufacture to ensure compatibility. Follow the manufacture or engineer recommendations for cabling types and installation locations.
The Drive may not be suitable for all motors, but the motor be suitable for all types of drives. True or False
True
The VFD with an open loop runs at a speed according to a set point or parameter programmed into the VFD by an operator either locally or remotely True or False?
Filtered AC
The _____________ DC voltage is then changed by an inverter to ________ at the desired frequency and magnitude under the direction of the control logic.
the required precision of the control for the system nature of the load cost versus benefit.
The type of control system chosen is determined by what?
Open
There is no feedback from the motor as to how much the slip is increasing or decreasing with changing load. What type of control loop is this?
Motor speed control
VFD are used for
Rated motor voltage Rated motor current rated Hz, max and min Hz rated Speed, Max and Min operational speeds Acceleration/deceleration rates Voltage boost local/remote operation dc braking requirements
VFD parameters
fractional thousands 120/208 600
VFD's are available in sizes from ___________________ horsepower to ______________________ of horsepower and accepts voltages from ___________/________ to _________ and higher
harmonics
What is a major undesirable issue associated with operating a VFD for the power system?
External fuses Circuit breakers contactors input isolation transformers output transformers line or load reactor or other active or passive harmonic filtering devices
What are some Auxiliary components
energy savings reduced noise reduced maintenance and cost control flexibility
What are some advantages of VFDs
torque limiting, voltage boost at low speed minimum and max speed control adjustable acceleration and deceleration rates
What are some basic drive adjustments which are offered by the V/Hz PWM control technique?
it is precise speed regulation and torque control
What are some benefits of Flux vector control?
Harmonics Special cabling requirements
What are some disadvantages of VFD's
thinner steel laminations better winding insulation shaft bonding rings insulated bearings or non conductive ceramic bearings separately fed blower motor
What are some features that an Inverter Duty Motor has:
values can be called parameters, macros Modes
What are some other names of the Values that are entered by the programmer for the PWM
Certain speed at peak line voltage of a specific frequency
What are standard 3 phase induction motors designed to operate at?
120Hz (2nd harmonic) 180 Hz (3rd harmonic) 300Hz(5th harmonic)
What are the harmonic frequencies associated with 60hz are what?
Rectifier Dc Link Inverter
What are the three main components or sections of a VFD
V/Hz control technique Flux vector control technique
What are two most common control techniques for producing a PWM output of a VFD
closed loop
What basic type of control requires feedback?
High voltages spikes at the motor's terminals
What can reflected waves can cause what?
motor current (out of phase producing component) and torque (in phase producing component) ?
What components control the flux vector
control logic that controls the switching of the IGBT in the inverter section for a full range of output frequencies
What does a micro processor provide?
PWM Pulse width modulation
What does an inverter use to convert dc to ac?
equalizes voltage differences between non-current carrying motor parts and non-current carrying parts of the wiring system.
What does proper bonding do?
wants to get rid of this error and makes adjustments to have the sensed value and the setpoint value the same.
What does the controller want to do the error(The difference between the measured value of the process variable sensor and the set point in the controller)?
little voltage (regenerative energy) is produced by the motor and little braking power is produced.
What happens at low rotor speeds?
the current rises to excessive values
What happens if the voltage is not reduces as the frequency is reduced?
it is changed by an inverter to AC at the desired frequency and magnitude under the direction of the control logic
What happens to the filtered DC voltage?
Some VFD can Judge how fast the motor is turning from the parameters that are programmed into the VFD. Sensor less flux vector control. FYI(Some open loop sensorless flux vector controlled VFD's can keep track of the speed of the motor to 1% of synchronous speed no matter how the load changes)
What happens when you need more exact control than can be offered with a simple V/Hz open loop control?
two Full wave three phase rectifiers is 30 degrees out of phase 360 degrees/12= 30 degrees
What is a 12 Pulse
3 full wave rectifiers. their supply voltages are 20 degrees out of phase. 360/18=20 degrees
What is a 18 pulse
V/Hz example: 460V/60 Hz = 7.61 V/Hz ratio for some clarification If you wanted the motor to run at 10%, you should supply 10 % frequency. 60Hz x 10%=6 Hz to achieve 6 Hz you'll need to apply a certain amount of voltage which you find by using the ratio that you calculated earlier 6 Hz x 7.61 (Ratio) = 45.66 Volts you will want to apply 45.66 volts to maintain the proper V/Hz ratio. refer to page 23 for more clarification if this shit is just more confusing
What is the Ratio calculation for V/Hz
480/60 = 8
What is the V/Hz ratio for a 480 V, 60 Hz Motor?
They synchronous speed increases Nsync = (120 x Hz)/Poles
What is the effect on synchronous speed if the VFD output frequency, increases above the rated nameplate frequency?
nsynch=(120xfrequency)/Number of poles Insert PICTURE HERE
What is the formula for synchronous speed
60 x 4 = 240
What is the fourth harmonic of a 60 hz system?
60 hz x 7=420 hz
What is the frequency of the 7th Harmonic on a 60 Hz system?
It must be able to invert the excess dc bus voltage to ac voltage at the supply frequency in order to regenerate back onto the system
What must the Special rectifier do? in regards of a Regenerative braking system
inverter section
What section of a VFD converts a dc bus voltage to pulse width modulated output?
Rectifier section
What section of the VD converts ac supply voltage to a dc voltage for the VFD
Dc link Section
What section of the VFD filters the Pulsating DC to smooth dc
shielded against transient voltages. Shield should only be bonded on one end to allow for draining.
What should the analog signals to and from the drive be
Never connect 120VAC to the control boards on VFD. can cause catastrophic results.
What should you never do with Control wiring or Control Boards?
dc injection braking
What type of braking is done by putting a dc voltage on the motor stator windings
open loop
What type of control does a system have if a heater is energized by a contactor controlled by a stop start station?
the IGBT turns on and current flows between the emitter and the collector.
When a positive voltage is applied to the gate of an IGBT of 15v dc, what happens?
dc link
When the pulsating DC voltage leaves the rectifier section it enters the _______ ________ section
an arc across the bearings
When the voltage exceeds the insulating value of the bearing lubricant what else can happen?
A reflected wave occurs
Whenever cable surge impedance does not match the surge impedance of the Motor what occurs?
control room. to enable an operator to view the status of VFDS.
Where are VFD's often networked to?
Flux Vector
Which VFD control technique controls the phase angle of the voltage and current applied to a three phase induction motor?
because it works well with motors ranging in size from fractional hp to over 1000hp Highly reliable affordable it is affordable reflects the least amount of harmonics available to 208 to 600 v, 3 phase provide output frequencies from 0hz to 400 hz in some units
Why is the V/Hz VFD the most commonly used VFD
Electrical noise it can cause erratic drive behavior that is difficult to troubleshoot
Why should you install control signal cables independently of each other and separate from any power wiring?
fewer of the low number harmonics that cause damage.
With the higher number of pulses what does it result in?
controllable power factor current
Wound field Synchronous motor: The speed of the synchronous motor is now _______________ and the wound field allows the _____________ _____________ to be changed for power factor correction by changing the ____________ flow in the field
Brushless
Wound field synchronous motors with _______________ excitation can also be used with VFD's
3 bonding Radio Frequency Interference.( RFI)
______________ bonding conductors are used in some VFD cables to provide this extra bonding conductor area and help with the reduction of _________ __________ ___________(RFI)
IGBT's this makes the rectifier bi-directional, ac to dc one way (normal operation) and dc to ac the other (Regenerative braking)
_______________ may be incorporated into the bridge rectifier of the VFD to do the required inversion as gated by the control logic for the regenerative braking. What does this make the rectifier?
