Motor Control (Reduced voltage starters) Flashcards
List the 5 reduced voltage starters.
- Primary Resistance Starter
- Primary Reactance Starter
- AutoTX Starting (AKA: Compensator starter)
- Wye-Delta Starter
- Part Winding Starter (technically not a reduced voltage starter)
What are reduced voltage starters commonly employed for?
3 Phase SCIMS in the 5 - 200 HP range. Large motors
What are the advantages of a Primary Resistance Starter?
- Simple
- Reduces voltage and current
- Provides smooth acceleration
- OK for 3, 6, 9 & 12 lead motors
What are the disadvantages of a Primary Resistance Starter?
- Power consumption
- Inefficient (worse than pri. reactance)
- Limited in capability
What are the characteristics of a Primary Reactance motor?
Inductive characteristic:
limits current
keeps inrush low and line drops more tolerable
Advantages & disadvantages to a primary reactance motor?
Advantages:
- similar to pri. resistance
- more efficient
Disadvantages:
-Size of inductors needed
What are the 2 “Primary Impedance starters”?
- Primary Resistance starter
2. Primary Reactance starter
What are the advantages and disadvantages of an Auto TX starter?
Advantages:
- High torque to motor
- multiple taps permit on site selection
- Efficient
Disadvantages:
-More cost
What are the usual tap options on an Auto TX starter?
50%, 65%, 80%
Wye-Delta starter characteristics?
- Equally effective as an Auto TX
- Reduces inrush to 1/3
- Low starting current (33%)
- Low starting torque (33%)
What are Wye-Delta starters suitable for?
Suitable for inadequate power supply situations or where line drop exists
How many leads can you use for a Wye-Delta starter?
Must be 6 or 12 leads
Wye-Delta starter disadvantages?
- Weak starting torque limits applications
-Overloads must be set to I phase
(still only 3 required)
Part Winding starter characteristics?
- Must be a dual voltage motor
- limited torque (do not start under load)
- uses small size starters
- 6 wires to the motor
- inherently closed transition
- full voltage applied to half the windings
list 3 reasons why across the line starting in the most common method for starting AC motors
- High starting torque
- Inexpensive
- Simple
Why might across the line starting not always be suitable?
- High starting current
- High starting torque damaging to some loads
Is it permissible to short out the overload protection of 3 phase motors during starting? explain.
Yes, if the load is slow accelerating it may cause the overload device to open the circuit
How can you reverse control for 3 phase AC motors?
Interchange any two line leads supplying the motor
What is meant by the term open transition?
Motor momentarily disconnected from line leads during transition
what is meant by the term closed transition?
Motor continuously connected to lines
what advantage is offered by closed versus open transition starting methods?
Closed has less line disturbance
