HMI Flashcards by Feb Abuloc

AC Drives covert incoming DC to a AC bus? True or False?

False: AC drives convert incoming AC to a
DC bus

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What are parts 4 of an AC Drive?

Input 3 phase - Rectifier Circuit - DC bus - Inverter Circuit - Motor

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What does the DC bus use to filter current?

Large Electrolytic capacitors

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Do AC drives use pulse width modulation?

Yes

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What happens is the bleeder resistor blows up/not work?

The capacitors will not discharge? This can mean lethal voltages may be present hours after drive is locked out

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What do you need before servicing an AC Drive

-Wear correct PPE,

-Before locking out drive measure and actually see the DC bus voltage go to 0

-lock out at disconnect

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What does an AC drive use for its inverter circuit?

Transistors or IGBT devices are used to switch the DC bus on and off to the motor

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What is the term “Motoring”?

When a motor is controlling the speed of a load

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What is the term “Regeneration”?

When the load causes the rotor to rotate faster than the rotating field

The motor turns into an alternator and generates voltage back to the drive

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What are 2 ways to avoid “Regeneration”?

Oversize the motor/drive combination

Dynamic Braking

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What is does “Dynamic Brake” consist of?

A sensor to detect a rise in DC bus voltage. The sensor energizes a relay

One or more high wattage resistors that are connected across the DC bus by the relay contacts

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How does “Dynamic Brake” work in an AC drive?

If the voltage in a DC bus rises, a sensor picks it up. This energizes a relay that connects high wattage power resistors to limit the current (use excess energy into heat).

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Does “Dynamic Brake” only work is the load is slowed down?

No, if load is too fast it drags the rotor faster than the synchronous field rotation and causes regeneration

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What stop config is this: Typically used to slow down conveyor type loads

Ramp to stop

Ramp to 0 following the Decel curve

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What stop config is this: Used for fans and pumps

Coast to stop

turn off power
immediately

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What stop config is this: Drive applies a DC voltage and “locks” the rotor

DC Brake

applies a DC
voltage to the stator
-Can stop the load quickly but may
also overheat the motor

What stop config is this: Heavily loaded conveyors with high inertia

Ramp then DC Brake

Which mode is for safety?

Coast to stop with magnetic clutch

What is the equation for S-Curve time?

Scurve time = Accel or Decel time + S-Curve setting in percentage

What is the equation for total accel time if there is an S-Curve applied?

Total Accel Time = Accel time + Scurve time

What are parameters?

Storage Locations in the memory of an AC Drive

What can parameters be (Data type wise)?

Single bit, a byte, an integer value or a 32 bit value

What are parameters used for?

 They match the drive to the incoming
AC
 They match the drive to the motor
 They match the drive to the load
 They provide operating information
such as Load Current Being Drawn By
the Motor

What is accel time parameter?

The parameter that defines how long it will take the drive to ramp from 0 hz to maximum frequency

What is decel time?

how long it will take the drive to slow down to 0 frequency

True or false: The preset frequencies could be selected using hardwired controls or through network control

True

Some facts

- The Allen-Bradley 1305 AC drive had approximately 70 parameters - The AB PowerFlex70 has approximately 400 parameters

What are encoders?

Encoders are devices which are coupled to the shaft of a motor (DC or AC) and generate a series of square waves proportional to rotational speed Encoders typically offer some variation of a binary count – 512 square waves per 360 degrees rotation, 1024 and so on

How does an encoder detect direction?

They use "windows" which are mechanically offset by 90 degrees. If the motor is going CCW, light will pass through from LED A before LED B

How many wires does an encoder use? What are they?

5 wires A, ANOT - 180 degrees out of phase with A B, BNOT - 180 out of phase with B Z - homing shaft VDC DC COMMON

What speed references do most AC drives allow to be used?

-Built in potentiometer - External 0 to 10v DC - External 4-20 mA signal - Network Command (Ethernet) - Motor Operated Potentiometer - Pulse Train - Preset Frequencies

Analog References examples?

DC voltage or Current

What do majority of conveyor controlled by AC drives use for speed control?

Preset Frequencies

Where are Motor Operated Potentiometers used?

Common in industries where a film like substance (paper, steel, aluminum foil etc) is pulled through motor driven rollers Offers “Speed Up” and “Slow Down” buttons that change drive frequency

What can parameter P038 do?

Set which speed reference to use

What can parameter A051 do?

determines what function digital in 1 causes the drive to do  It can be set to the value shown to accomplish a different purpose:  1 Follow Accel 2 and Decel 2 curve  2 Use an external hardwired Jog  3 Cause an Aux fault (fault the drive on purpose)  4 Run at a preset frequency  6 Use Comm port data (Ethernet, DeviceNet, ControlNet)  7 Digital in 1 will clear a fault  8 Causes a Ramp to Stop  9 Causes a Coast to Stop  10 Causes a DC braking voltage to be applied to the motor

How does AC drives control speed of AC Motor?

Ac drives vary the frequency applied to a 3 phase AC Motor - Vary the frequency vary the speed Must also vary voltage or the motor will be destroyed