Three-Phase Motors and Starters Flashcards
What terminal numbers are expected at a dual voltage motor’s junction box?
Terminals 1 through 9.
What would be the designation of a 3 lead motor?
A single voltage, wye OR delta motor.
What would be the designation of a six lead motor?
A single voltage wye/delta motor, (3 groups of 2 leads); or
A split winding motor, (2 groups of 3 leads).
What is the best way to change a motor’s direction?
Interchange any two line conductors to the motor.
What is the most common voltage to run a dual voltage motor?
240/480 V.
How many windings does a dual voltage motor have?
Six.
Is high or low Voltage connection the same for wye and delta dual voltage motors?
The high voltage (series connection);
T4 - T7
T5 - T8
T6 - T9.
What are the two main types of starters?
Across the line (full voltage);
Reduced voltage.
Why might using a reduced voltage to start be an issue?
If the available torque is not enough to rotate the load.
Is a standard motor controller considered a disconnect by the CEC?
No, it uses magnetic (not manual) means to control the circuit.
What type of starter is a part winding?
Full voltage, reduced current/torque.
What is the typical inrush current of a part winding starter?
60 to 65 percent of full V starting current.
What would happen if the second winding contactor refused to engage, in a part winding starter?
The first winding would overheat under rated load.
What symbol signifies an on delay contact?
A single pole switch with an arrow tail (feather end).
What symbol signifies an off delay contact?
A single pole switch with an arrow head ( sharp end).
What ratio is the tap setting of an autotransformer starter?
Reduced voltage to full voltage.
Why is line current a product of tap2 in an autotransformer starter?
To satisfy VAIN = VAOUT.
Why is torque a product of tap2?
Because torque is based on the interaction of stator and rotor flux; and
Flux is directly proportional to voltage;
Transformer action says if we reduce VStator by a factor of X, V rotor also gets reduced by a factor of X and the combined field strength is reduced by X2.
What kind of autotransformer transition offers better performance?
Closed transition.
Does a wye delta starter require a six lead motor?
Yes.
What is the inrush deration factor when using a wye/delta starter?
One third for both current and torque.
What current do wye/delta overloads monitor?
Delta phase current.
Why is a wye delta starter always open transition?
Otherwise we would produce a line to line short.
Which two acceleration modes could be provided by an electronic soft starter?
Ramp starting;
Current limit starting.
What is a kick start?
Soft starters providing a slight inrush current surge for extra starting torque.
What kind of load would prove most challenging to start with reduced voltage?
How might we make this easier?
Constant torque loads;
A mechanical alteration which reduces starting torque (like a decompression valve).
What is the starter which produces high torque and low current at start?
WRIM and controller.
What is the purpose of a phase converter?
To change single phase voltage into roughly 3 phase.
Which is the less expensive type of phase converter and what are it’s main drawbacks?
Static;
It can only supply one motor, non ideal output.
In a rotary type phase converter, what is the main component?
An induction motor generator.
What is the high capacitance electrolytic capacitor used for?
Starting a motor or the motor generator.
Which two power ratings would be on a rotary phase converter?
Running hP;
Starting hP (biggest motor).
Why does a static phase converter rely on the motor to generate the third line?
Because, unlike a rotary converter, there is no generated induced voltages, the load simply draws current at 90 degrees lead by the cap.
When is a static phase converter most balanced?
At full load.
