DC DRIVE BASICS

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DC DRIVE BASICS
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Purpose of a DC Drive
A DC drive converts AC power to DC voltage in
order to vary the speed and torque of the motor
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DC Motor Review

• Speed is primarily determined by Armature Voltage
• Torque is determined by Armature Current

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DC Motor Review

• Rotation is the result of two independent
  electromagnetic fields.
• Armature windings
• Field windings
• Extended motor speeds above base speed are
  achieved by reducing the field voltage (current)
• Field Weakening

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DC Drive
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DC Drive Components
DC DRIVE INPUT
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DC Drive Components
Silicon Control Rectifiers (SCR)

• Permits current to flow in 1 direction
• Gate signals when conduction occurs

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DC Drive Components
Field Supply

• Used to Control
• Field Voltage/Current

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DC Drive Components
Sends Instructions to Regulator
Operator Control Station
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DC Drive Components
Compares instructions feedback signals and send
appropriate signal to firing circuit Current
(Torque) Voltage (Speed)
Regulator
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DC Drive Components
Supplies the gate pulses that fire the SCRs
Firing Circuit
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Speed Power Curve
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Speed Torque Curve
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Forms of Stopping

• Coast to Rest
• Ramp Stop
• Dynamic Braking
• Regeneration

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Dynamic Braking

• Dynamic Braking
• - Dissipates rotating mechanical energy to
  heat
• - Faster than coasting to rest
• - Not Controllable (except by changing the
  resistor)

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Regeneration

• Regeneration
• - Occurs when load overhaul motor
• - Puts power back into drive through 2nd set
  of
• SCRs

• Benefits
• - Stop High Inertia Loads Faster
• - Return Energy to AC Power Line

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Stopping Time
Dynamic Braking
Ramp Stop
Coast Stop
Regenerative Braking
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Speed Regulation
How Much Will the Speed Change Between No Load
and Full Load? Expressed as a Percentage
of Base Speed
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Speed Regulation
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Feedback Options

• Speed Feedback Type Regulation
• Voltage - 2
• AC Tachometer RE O45 1
• DC Tachometer 5PY 1
• Encoder (pulse) RD-120-1 .01
• Encoder (pulse) RL - 1024 .01

Feedback device can determine speed regulation
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Types of Regulation

• Voltage
• Current (Torque)
• Speed
• Position

For discussion purpose, the regulation discussed
will be from 0 to base speed.
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Types of Regulation

• Voltage Regulator
• Drive Regulates Armature Voltage
• Feedback Voltage Current
• Speed Changes based on loading (5)
• IR Compensation
• Improves regulation
• Measures current feedback

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Types of Regulation

• Current (Torque) Regulation
• Adjusts armature voltage to change armature
  current
• Feedback Voltage Current
• Drive will provide only the current (torque) it
  is told

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Types of Regulation

• Speed Regulation
• Drive regulates speed of motor by changing
  armature voltage
• Feedback Speed Current

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Types of Regulation

• Position Regulation
• Drive regulates positioning device by changing
  the armature voltage
• Feedback Position Current

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Power Distribution Options
Isolation Transform
Circuit Breaker
Line Reactor
Inverting Fault Circuit Breaker
Contactor
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Power Distribution Options
Isolation Transform
Circuit Breaker

• Provides Impedance
• Reduce Electrical Noise
• Isolation from ground
• Protect from external
• transients
• Preferred for regenerative
• applications

• Provide power off switch
• Overload capability
• Thermal
• Instantaneous
• Current

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Power Distribution Options
Line Reactor

• Provides Impedance
• Reduces Electrical
• Noise

Inverting Fault Circuit Breaker
Contactor
Mechanical disconnect to Motor

• Provides power off switch
• Overload
• (Instantaneous Current)

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Power Distribution Options
Disconnect Switch

• Provides power off
• switch to drive
• Less expensive
• than circuit breaker

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DC Drive Modifications

• Blower Motor Starter
• 115 V Control Interface
• Enhanced Field Supply
• Electronic Field Trim (240 V Drives only)
• Field Economy
• Field Current Regulator

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DC Drive Modifications

• Blower Motor Starter
• AC motor starter
• Control of 3-phase blower motor
• Fused with adjustable overload interlocking

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DC Drive Modifications

• 115 V Control Interface
• Converts customer supplied 115 V to
• 24 VDC
• Inputs Outputs
• Run
• Stop
• Jog
• Fwd/Rev
• Auto/Man
• Coast Stop
• Customer Interlock

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DC Drive Modifications

• Enhanced Field Supply
• Adjust field voltage to control field flux
• Electronic Field Trim
• Changes Field Voltage/Current
• Field Economy
• Supply minimum voltage to keep motor warm

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DC Drive Modifications

• Field Current Regulator
• Actually regulates field current
• Improves regulation performance

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DC Drive Terms

• Constant Torque Variable Hp
• Cogging
• Full Wave / Half Wave
• Regulation ( of rated)
• M Contactor
• Contactor
• Turn down Ratio
• Enclosures (Page XIV)

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Questions ???