Machines Flashcards
Motor starters, drawings, etc
The four basic types of drawings are _____.
1: Block
2: Wiring
3: Schematic
4: Interconnection
IEC schematics are drawn with the components on _____ lines.
Vertical
There is a single standard legend for electrical drawings, true or false.
False
A block diagram shows the _______.
Conceptual relationship between equipment or systems
Relationships on a block diagram may be _____ (3 items)
1: Physical,.ie elevation
2: Hierarchal, ie speed of response
3: Typical, ie relationship in installation
Wiring diagrams show the _____.
Detailed wiring or controls and equipment, related to the actual physical components.
Wiring diagrams show a _____ relationship between components.
Practical
A schematic diagram is also sometimes called an _____.
Elementary diagram.
Schematic diagrams show _____.
Circuit/devices, focused on functional relationship and sequence of operation.
OL contacts in a NEMA motor starter are usually connected between the coil and _____.
Line 2.
OL.contacts for IEC motor starters are connected to _____.and are located _____.
Terminals 95, 96.
Ahead of the coil
The rung numbers of a ladder style schematic are located on which side of the diagram?
Left
Interconnection diagrams show _____.
Specific connection details.
The concept of interconnection diagrams can be called the _____ approach.
“connect the red wire to terminal 2”
Termination schedules and pin-out diagrams can be _____ diagrams.
Interconnection.
Motors may also be required to react to additional perameters such as _____ (4 items).
1: Heat
2: Pressure
3: Motion limits
4: Fluid levels in tanks/vessels
Motor starters may require _____.
Timing sequences.
The three basic sections of a stop/start circuit are ______.
Stop, Start, Holding
Electrical interlocks can enable an operation or _____.
Prevent one from occuring.
Contacts connected in the start circuit affect the running of the motor, true or false?
False. Only affect starting.
To break a circuit from multiple locations, how must the control circuit be wired?
Stop buttons will be NC and in series.
To make a circuit from multiple locations, how does the control circuit need to be wired?
Start buttons NO and in parallel.
Overload heaters are placed in the control.circuit to protect the motor in case of an overload, true or false.
False
A drawing which shows only the electrical connection between equipment is called _____.
Interconnection diagram.
A magnetic motor starter should be used if the motor _____. What are two examples?
Has to be repeatedly reversed.
A planer, an elevator
What do the two contactors in a reversing motor starter do?
One operates the forward direction and the other operates the reverse.
What would happen if the forward and reverse contactor coils are energized at the same time?
It would create a short circuit condition
What will prevent a short circuit condition in a reversing motor starter? How does it work?
A mechanical interlocking device
By making it physically impossible for both sets of contacts to be closed at the same time
What happens if the forward and reverse buttons are pressed at the same time, with only mechanical interlocking?
One coil pulls in and the other has a current of 4 - 10 times it’s pulled in value.
What will prevent the excessive current in the contactor of a reversing motor starter?
Electrical interlocking
Which type of starter is normally already provided with mechanical and electrical interlocks (NEMA or IEC)?
NEMA
Seven sections of a control circuit for a reversing starter are:
1: General stop
2: Forward stop
3: Reverse stop
4: Forward start
5: Reverse start
6: Forward holding
7: Reverse holding
Electrical interlocks prevent _____.
Coil burnout
A standard push button is an example of _____.
Momentary contact
What are two examples of selector switches?
Standard on/off switch, selector switch
Switches and push buttons are examples of _____.
Manually operated pilot control devices
Three examples of automatic pilot devices are:
1: Float switches
2: Pressure switches
3: Limit of movement
8 items that can be monitored by automatically operated pilot devices are:
1: Movement
2: Pressure
3: Liquid level
4: Thickness
5: Light
6: Rotation
7: Temperature
8: Flow of liquid
What are four pieces of equipment which may require jogging?
1: Cranes
2: Hoists
3: Printing Processes
4: Large lathes
What is jogging?
When a motor is repeatedly energized in short bursts at rated voltage
What is inching?
Motor started at a reduced voltage to let machine creep to desired location
What is positive jogging?
When motor can jog regardless off time required
What devices could provide a jog control?
Limit switch, proximity switch, other selector switch
What does positive jogging prevent?
Prevents holding circuit from energizing if the button is released quickly
How much can the current be during the starting of a 3 phase induction motor?
2 - 8 times
A starter that requires jogging duty will normally be sized _____ compared to that for normal operations.
One size larger
Why is a starter sized up when a motor is to be jogged?
High inrush current that could cause overheating in the contacts
Timers are commonly used in _____ (3 items).
HVAC equipment, lighting and commercial fridge & freezers.
What are the three basic types of timing devices?
1: Spring wound internal timers
2: Mechanical/electronic time switches
3: Timing relays
Spring wound internal timers are _____ switches, and provide _____.
Wall, ‘timed on’
What are some typical uses for spring wound internal timers?
Lights, bathtub spa motors and sauna heaters.
What kind of timers use electrically driven clockwork motors? What do those motors control?
Mechanical timers. Control adjustable trip mechanisms or cams that operate contacts.
What are some applications for mechanical timers?
Security lighting, landscape irrigation, parking receptacle circuits.
Timing relays are sometimes preferred for _____ and _____ in motor control circuits.
Precision and versatility
What are three ways a timing relay can be controlled?
1: Pneumatic (by air)
2: Electronically
3: Fluid-filled dashpot
Pneumatic and fluid filled dashpots operate by controlling the rate of what?
A gas or fluid flowing through a hole between two chambers.
What are four ways that electronic timing relays are superior to pneumatic and dashpot relays?
Smaller, more accurate, versatile, cost-effective
What does TDOE mean and how does it work?
Time Delay On Energization. Contacts change position at a designated time after the moment the relay is energized.
The action of TDOE contacts closing after a set time is called _____ or _____
Delay on, delay on operate
TDOD means _____.
Time Delay On De-energization
How do TDOD contacts react when energized?
Contacts change immediately when energized, then change back after a set amount of time.
The action of TDOD contacts reacting to an energized circuit is called _____ or _____ or.
Off delay, delay on release.
Selectable time delay settings could be _____ to _____.
50 mS to 300 hrs
What is an example of TDOE use in a motor?
Switching on windings during the starting of part-winding motors.
The time delay of a TDOD begins when ______.
The coil is de energized
If a conveyor belt were run for a set time after the equipment running it has been stopped, this would be considered _____.
TDOD
What could interval timing be used for?
An exhaust fan to purge a combustion chamber before a gas valve opens
One shot timing is when power is applied to a relay and a start terminal, and the timing function begins whenever _____.
The start terminal receives a signal.
Repeat cycle timing provides regular on and off cycles for timed contacts. T or F
True
The cycle of repeat cycle timing can start when the contacts are in the _____ (normal, changed, or either) position.
Either
Two separately selectable on/off times may be something like:
5 min on, 2 min off, etc
Sequential ‘on delay’ starting capabilities may be part of timers with separately selectable times. T or F
True
Remote manual reset of a timing sequence can be possible using _____.
Multi function timing relay
Automatic-process-condotion control can be possible with a multi function timing relay by _____.
Automatic pilot device that provides feedback to the relay.
The electronic timing relay can change over a wye-delta starter in approx _____ mS after the Wye connection has timed out.
50
How many TDOE contacts are used in a wye-delta starter? Which ones are used?
- One NC and one NO
What is the purpose of the NC interlocks in a Wye-Delta starter?
Prevent line-to-line short circuits during start and transition.
When a TDOE is first energized what happens to the NO timed contact?
Stays open until the the relay times out.
What is the state of NC IC contacts in a TDOE when the relay is energized but hasn’t yet timed out?
They are open
3 additional functions of multi-function timing relays are:
1: Interval timing
2: One shot timing
3: Repeat cycle timing
When a multi function timing relay is set for one-shot timing, how is the timing period initiated?
Signal at the start terminal
Why is a timing relay used in a Wye-Delta starter?
To allow the motor to come up to speed before changing to Delta.
Four examples of applications for electrical motor braking are:
1: In an elevator when the brake tension is released when the power is on and applied when power is off
2: To stop a motor before an attempt is made to reverse it, and to prevent a de-energized motor from turning (cranes, hoists).
3: Accurate positioning, quick stops, direction changes in large machine tools
4: Prevent reverse rotation of a de-energized motor (ie ventilation fan)
Conveyors, door openers, centrifuges, wood chippers and speed reducers are examples of _____.
Motor braking
How is the solenoid coil of a friction brake connected with the motor power leads?
Parallel
Electromagnetic brake release will remove brake friction when the motor is _____.
De-energized
A solenoid coil for a mechanical friction brake would be connected to (L1 + L2, or T1 + T2).
T1 + T2
What is dynamic braking?
Operate the motor as a generator when the motor needs to be stopped quickly.
How is dynamic braking applied?
A braking resistor across the armature. Rotation in the motor as it slows generates emf, and current produced opposes the rotation.
Dynamic braking in AC motors is called _____.
DC injection braking
Is there inductive reactance when DC current is applied to the stator winding? What limits the current?
No. The resistance of the stator limits the current.
The stationary magnetic field created during DC injection braking changes polarity. T or F
False
In dynamic braking, current induced in the rotor of a SCIM by the stator’s DC magnetic field has what effect? What is the result of this effect?
Creates another magnetic field that is attracted to the stator field. This causes the motor to slow.
What controls the amount of braking force applied to an AC motor using dynamic braking?
DC current supplied to the stator field.
Interchanging the supply to two of the stator-phase windings of an induction motor is called _____.
Plugging
What is the purpose of plugging?
Stopping a motor immediately.
How does plugging stop a motor?
Reversed phase supply causes torque produced in the opposite direction.
Plugging is a good way to stop a motor frequently. T or F
False. The heat generated can cause overheating/melting in rotor bars.
What is anti-plugging?
Preventing a motor from reversing until it’s speed has decreased to a specific frequency.
What speed does anti-plugging slow a motor to?
Near zero
Anti-plugging switches are normally _____(open, closed).
Closed
Nominal line voltages for control transformers are: (4 items)
208, 240, 480, 600 AC
Typical secondary voltages in control transformers are: (4 items)
240, 208, 120, 24 AC
Does a control transformer electrically isolate the control circuit from the power circuit?
Yes
Does a control circuit carry power to the devices it controls?
No
What are four operating devices of a control circuit?
Relays, solenoids, contactor coils, pilot lights
What are four pilot devices of a control circuit?
Pushbuttons, limit switches, selector switches, proximity switches.
DC control circuits require what on the secondary side of the control transformer?
A rectifier.
Control transformer VA ratings range from _____ to _____.
25 VA to 5000 VA
Sealed VA is the _____ value.
Steady-state
Required capacity of a control transformer is calculated with the steady-state VA and the _____.
Total inrush VA
Low _____ helps reduce the amount of voltage drop in a control transformer.
Impedance
Outdoor control transformers are _____.
Enclosed
Open style control transformers must be mounted ______ for safety reasons.
Inside an electrical enclosure
Are control transformers usually mutual transformers?
Yes
Control transformers need to be grounded as a system per rule _____ but an exception is provided in subrule for systems less than _____ VA.
10-206, (2), 1000
What is an acceptable method of grounding a control transformer that is under 1000 VA?
To the metal enclosure of the supply, or to the bonding conductor within the enclosure.
A control transformer with a secondary voltage of 120 V would be grounded at terminal __.
X2
Control transformers have ____ inrush current, so _____ fuses should be used for overcurrent protection.
High, time-delay
Most control transformers are of the _____ type rated at ____ V or less.
Dry, 750
What is the overcurrent protection requirement for a Class 1 circuit used as a remote control circuit, using #18 AWG wire? And for #16 AWG?
5A, 10A.
When converting a wiring diagram to schematic, not all of the contactors and relays need to be identified. T or F
False. All must be identified
All contacts in a diagram conversion must be labelled with _____.
Associated relays/contactors
Must pilot devices be labelled in a diagram conversion?
Yes
What ways may conductors be labelled in a diagram conversion?
Letters, numbers, colours, other differentiating information
The label for a conductor only changes when the conductor is separated from the circuit by _____.
A device
Pilot lights and coils are examples of _____ devices and are placed on the _____ side of a drawing.
Load
Devices on the left side of a schematic diagram are called _____, such as contacts of switches.
Operating devices
In order to minimize the length of wire used overall, the conductor from a controller should first be run to _____.
The closest station
