Bobby's final notes
What is a holding circuit also known as (3 other names)
1.)Seal in 2.)Memory logic 3.)Latching
Fault currents typically causes what kind of damages?
1.Melting/vaporizing conductors 2.arcing fires and explosions 3.severe insulation or electrical damage
What are 5 examples of motor failure
1.Single phasing 2.contaminants 3.old age 4.bearing failure 5.rotor failure
What is the benefit of using wye connected motors?
1.Used for dual voltage application 2.used for balancing load 3.less amperage on start up
Name 5 types of reduced voltage starters
1.wye/delta 2.auto transformer 3.primary resistor 4.VFD 5.solid state soft starter
Most motors are not designed to start more than ___ times per hour.
10
Force drying a motor is accomplished by applying ___% of the rated voltage to the motor for 2 to 4 hours to dry the coil.
10%
Overlords are sized to not exceed ______ of the rated FLA to the motor?
125%
Below what level of frequency will motors experience the highest motor losses?
15 HZ
A motor that has an insulation class testing A should not exceed ____°F
221°F
What are the voltage and amperage limits of SCR constructions
2500V and 3000A
The majority of industrial application normally use ________ motors.
3 ph induction
OCPDs must be sized to protect from fault currents they can range from _____ to _____
30KA to 200KA
A dual voltage wye connected motor has ____ separate circuits.
4
A motor started in wye configuration receives approximately ________% of the normal voltage and also approximately_______%
58% volts & 33% torque
A dual voltage wye connected motor (12 lead) has how many winding circuits?
6
A solenoid coil pulls how much times FLA on start up?
6 to 10 times
What is the approximate length of time it takes to transition from wye to delta in a closed transition starter
6-10 seconds
At what percent of RLA during wye delta closed transition starting does a motor transition from wye to delta?
85% of RLA
Which 3 ph motor starter mentioned in ch 15 is not considered an actual reduced voltage starter
Across the line
The NEC defines OL and overcurrent as what?
Any current in excess of the rated current of equipment or the ampacity of the conductor
What is the purpose and function of the 1M contactor
Applies line voltage to motor windings T1 T2 & T3 always pulled in
The _______ starting method provided the highest possible starting torque per ampere of the line current
Autotransformer
The amount of reduced torque is adjustable when using the ______ starting method which has taps
Autotransformer
________ starting is one of the most effective methods of reduced voltage starting
Autotransformer
Troubleshooting a solenoid coil NC 24V you measure 5 V at your solenoid what could be your diagnosis and why?
Bad common;bad supply voltage
What is not an example of a solid state switch?
Biacs
What is the purpose of the air gap in the armature
Break the magnetic field
Of all the OCPDs discussed which is the most sensitive to fault currents?
Circuit breakers
List 2 pros and cons each for water cooled starters
Con-terrible water quality & it requires more components Pro-water is an effective heat transfer medium & temp is easy to regulate
The _____ circuit determines when and how a motor starts
Control
An electric OL senses changes in
Current and temperature
What is the purpose and function of the 2M contactor
Delta or run contactor energizes T4 T5 & T6 of the motor to line voltage
_________ fuses are normally required for part winding starting
Dual element
What resistance should be read in the windings of a 3 ph motor?
Each windings resistance should be equal
What prevents S and 2M contractors from pulling in at the same time?
Electrical & mechanical interlocks
What is the benefit of the bypass contactor in a solid state starter
Eliminates need to cool starter
A IFM flow sensor trips because heat is pulled away from the sensor head, as the thermal conductive sensor is messing flow T or F
F
A three wire control circuit is not as safe as a two wire control circuit T or F?
False
Eddy current is the unwanted current generated in the metal structure of a device due to the rate of change in the DC magnetic field T or F
False
What are 2 separate ways motors are cooled in our industry?
Fans & fins
The maximum recommended acceleration time depends on the motor _____ size.
Frame
What is not a type of solenoid configuration 1.full port 2.plunger 3.horizontal action 4.Vertical action
Full port
________ starting is the least expensive and most efficient means of starting a motor for applications involving small HP motors.
Full voltage
What is the control point of the SCR?
Gate
What causes high temperatures in solid state starters?
Gates firing;SCR operation
What are 2 fault currents?
Ground fault & short circuit
What is used to remove heat from SCRs in these high temperature cabinets
Heat sinks
The longer a motor takes to accelerate the _______ the temp rise in the motor.
Higher
What is the definition of interrupting rating of a device?
Highest current at rated voltage that a device will interrupt the circuit.
Name the 3 most important motor nameplate information.
Hp RPM Frame
Explain the importance of of wiring both the low and high voltage contacts of an overlaod
If low voltage is not wired-single phases High voltage-will not open circuit no protection
Reduced voltage starting provides ______ current draw over a longer period of time
Incremental
What are the 3 main components of the VFD
Inverter Rectifier DC bus
How does wye delta reduced the voltage to the windings?
It reduces by connecting the windings in series or wye
What is the purpose and function of the line reactor used in the VFD starters?
It reduces harmonics
_______ is a type of motor control in which the motor may be bumped slightly
Jogging
What is the purpose and function of the capacitor in the DC capacitor bud bank?
Maintain voltage levels when voltage fluctuates
What type of starting method allows you to start or stop multiple motors independently of each other.
Multiple motor starter
What is the most common type of thermistor and the base temperature for standardizing all thermistors?
NTC; 77°F
What are 2 types of wye delta starters
Open transition Closed transition
How do you differentiate between the two types of wye/delta starters
Open transitions has 3 contractors and closed has 4
A _____ is a condition that occurs when the load connected to the motor exceeds the full load ampere rating of the motor.
Overload
An electrician can observe the even blackening of all motor windings that occurs when a motor has failed due to?
Overloading
Thirty percent of motors fail due to _____?
Overloading
List 3 ways a motor can overheat internally
Overloading Overcycling Poor air ventilation
When connecting a dual voltage 3 ph motor for low voltage are the windings connected in series or parallel
Parrallel
The motor stator windings must be divided into two separate electrical circuits of equal value when using ____________ starting method
Part winding
What is the difference from Ph to Ph short and Ph to ground short.
Ph to Ph short is when the motor windings insulation fails and the windings touch each other and Ph to ground is when the winding insulation fails and the winding touch the motor casing
Define plugging a motor
Plugging a motor forces a running motor in a reverse direction to rapidly stop the motor
List 2 pros and cons for refrigerant cooled starters
Pros-most efficient heat transfer method & uses the same refrigerant as the chiller Cons-repairs are more expensive & it requires sub cooled liquid
What is another name given to reproducing AC sine waves used in the DC circuit?
Pulse with modulation
How does a solid state starter start up and operate a motor?
Pulses to operate SCRs to slowly bring motor up to full speed; operate motor, mechanically loading and unloading
What is not a typical device used for a 2 wire control?
Pushbutton switch
Explain the proper procedure to troubleshoot a thermistor
Remove thermistor from the circuit, place in ice water 32°F, measure resistance, compare to manufacturers resistance.
A_______is the rotating part of the AC motor. The stationary part is the_______where the electromagnetic field is produced. This coil of wire allows electricity to pass through it without shorting wire to wire because it is__________.
Rotor Stator Enamel coated
Explain the procedure practiced to troubleshoot an SCR using a multimeter
Set your meter to the diode scale check for forward and reverse bias between the line voltage and the DC bus.
What is the purpose and function of the S contactor
Short or shunt contactor ties T4 T5 and T6 in wye configuration
___ is the operation of a motor designed to operate on 3ph but only operating on 2ph
Single phasing
What is the advantage of using VFD starting over solid state or other reduced voltage starting methods?
Speed can be reduced/RLA can be reduced electrically
On wye delta starters what contactors are energized in the following start to run sequence order?
Start-1M And 1S Transition-1M and 2S RUN-1M and 2M
______ voltage is any higher than normal voltage that temporarily exists on one or more of the power lines
Surge
Define thermistor
Temp sensitive resistor whose resistance changes with change in temperature
How is a motor rating affected when operating at altitude above 3300'?
The motor will derate or reduce capacity
What physically happens to a motor when it's running as the applied power's phase unbalance is increasing?
The motors temperature will proportionally increase as well.
Why do OL and fuses not trip or open on startup when the motor draws LRA (up to 6x FLA)
They have a time delay to overcome initial inrush current caused by high torque required to initially start the load.
What 2 methods are used to cause or start transition in closed transition wye-delta starters
Time delay or current
A _______ is provided in a primary resistor starting control circuit to short the resistors after the motor accelerates to a specified point.
Timer
Why does a soft starter use SCRs facing both directions per ph?
To allow positive and negative waves to be pulsed to motors
What is the reason for reduced voltage starters in general
To reduce inrush current
What is the main goal of using a reduced voltage starter with a 3 ph induction motor?
To reduce the large current draw or inrush current at start up
A motor will not start and the motor overloads will trip if the starting _______ is reduced too much.
Torque
Part winding starting usually classified as reduced voltage starting because of the resulting reduced current & _______
Torque
What is the purpose and function of the 1A contactor
Transition contactor energized transition resistors
A three ph motor can run on single ph power and go virtually undetected in some cases T or F?
True
Autotransformer starting may use its ________ advantage to provide more current on the load side of the transformer than in the line side
Turns ration
What are 3 ratings found on a fuse?
Voltage rating Interrupting rating Rating of the fuse (amps)
What are 3 ways solid state starters are cooled?
Water cooled (glycol) air cooled; refrigerant cooled
The _______ starting method is used when it is necessary to restrict inrush current to predetermined increments.
primary resistor