FINAL SEG 4 FUCK

What are types of overloads?

1. magnetic

2. electronic

3. thermal

what is a contactor?

an electrical solenoid that closes a set of contacts when the coil is energized

what is a relay?

a magnetically operated switch that contains small or auxiliary contacts

what is a motor starter?

a contactor that is equipped with an overload protection for the motor

what are the sections of an overload relay?

current sensing and control contact

what are the types of thermal overload relays?

solder pot and bimetalic strip

what are the benifits of using the bimetalic strip

permits trip current to be set between 85%-115% and it can be reset after tripped

why should someone never dissconnect the secondary leads of a current transformer while its on?

it will become a step up transformer and will have a high enough voltage to kill someone that comes in contact with it.

where is FLA (full load amperes) found?

on the motor nameplate

where is FLC found?

in the NEC

what artical of the NEC covers DC motors and where can u find it in the uglys?

430.247 pg.32 uglys

what artical of the NEC covers single phase AC motors and where can u find it in the uglys?

430.248 pg. 34 uglys

what artical of the NEC covers three phase AC motors and where can u find it in the uglys?

430.250 pg. 39 uglys

what should you do if u have a power factor of 90%?

multiply by 1.1

what should you do if u have a power factor of 80%?

multiply by 1.25

what is torque?

the rotational fource acting on the motor

The difference between the synchronous speed and the actual rotor speed is called ______.

slip

The speed of the rotating magnetic field is determined by the frequency and the number of ______ .

poles

the torque of an induction motor is ______ proportional to the square of the applied voltage.

directly

The ______ torque is the torque developed by the motor at the instant of starting

locked rotor

The speed of the rotating magnetic field in the stator of an induction motor is known as the ______ speed.

syncronous

The difference between the synchronous speed and the actual rotor speed, expressed as a percentage, is called ______.

slip

what is the syncronous speed formula?

120*frequency/number of poles per phase=RPM

what is the anatomy of a DC motor?

1. armature

2. startionary feild with magnets

3. commutator

what are the two types of DC motors

1. shunt (wired in parallell)

2. series (wired in seires)

what are types of compopund motors?

1. cumulative

2. seires

what are rectifiers?

convert AC to DC

what are rectifiers composed of?

diodes

what are diodes?

electrical check valve that allows current to flow in one direction.

what is another opposing force of current?

inductive reactance

assuming the reset button was pressed what will happen when the start button is pressed?

When the start button is pressed, power is connected to motor starter coil M1. All M1 contacts change position. The three load contacts connected to motor 1 close and supply power to motor 1. The M1 auxiliary contact in parallel with the start button maintains the circuit when the stop button is released. The M1 auxiliary contact connected in series with timer coil TR1 closes to supply power to the timer. Timer TR1 begins tim-ing. The M1 auxiliary contact connected in series with timer TR2 closes, but a circuit is not completed to coil TR2 because auxiliary contact M2 is open. After a delay of 10 seconds, TR1 contact closes and energizes the coil of M2 starter, causing all M2 contacts to change position. The three load contacts close and supply power to motor 2. The M2 auxiliary contact connected in series with timer coil TR2 closes and supplies power to timer TR2. Because TR2 is an off-delay timer, TR2 contact closes imme-diately, Figure 8-48. Both motors are now running. When the stop button is pressed, the circuit to M1 coil is open and all M1 contacts return to their normal position. The three M1 load contacts open and disconnect power to motor 1. The M1 auxiliary contact connected in series with timer coil TR1 opens and de-energizes the timer. Because TR1 is an on-delay timer, TR1 contact opens immediately. The circuit is maintained to motor starter coil M2 by the now closed TR2 contact. The Ml auxiliary contact connected in series with timer TR2 opens and de-energizes the timer. Because TR2 is an off-delay timer, the time delay begins when the timer is de-energized. After a delay of 5 seconds, contact TR2 returns to its normally open state causing starter coil M2 to de-energize and stop motor 2. The M2 auxiliary contact connected in series with timer TR2 opens and the circuit is back to its original de-energized state.

what are the charicotristics of a schematic?

1. dosent give you a specific location

2. read it from top to bottom left to right

3. the control coil activates a specific set of contacts that share the same identification number

4. all electrical components are shown in their de-energized position

5. when the circuits energize the contacts will change position

what is faradays law?

inducing voltage in a conductive material and the amout of induced voltage is proportional to the ratio of turns between two windings

what is lorentz law?

a charged partical moving in a magnetic feild will experience force

what is lenzs law?

speaks about inductive reactance induced voltage which moves in opposite polarity of our applied volatge limits current in the inductor itself its measured in ohms

what is eddy currents?

induced spirling currents that is induced within the material of the equipment

List the conditions that must be met for parallel conductors.

1. same lengh

2. same material

3. smae c/mills size

in a _____ connection, the phase voltage is less than the line voltage by a factor of the square root of 3

delta

the percent impedance is stamped on the name plate of transformers rated _____ KVA and larger.

25

when was the American Wire Gauge standardized?

1857

how many dies does a 12AWG drawn by?

12

what is an effect of bad power factor?

1. voltage drop across the electrical grid

2. overheating of equiptment and conductors

3. higher cost for installation of larger wires with thicker insulation

4. power loss

5. reduces electrical grid capacity

One of the secondary windings of the delta is often center tapped and grounded to produce a ______

neutral

______ are seldom employed because they can exhibit extremely unstable voltages between phases if the line current should become unbalanced. 

wye-wye

Special High voltage equipment is necessary to test the insulation on higher voltage units. A high voltage tester is refer to as a _____

hipot

______ transformers have a standard secondary current of 5 amperes under a short circuit condition. 

current

what is power factor?

the ratio of true power to apparent power

explain power factor according to the beer analogy.

beer is the true power (kw) what we need to work the foam is the reactive power (kvar) its usless and the glass holding everything is apparent power (kva) the sum of everything

Most dual-voltage single-phase motors will be of the _______ type, which contains both run and starting windings.

split phase

An induction motor is much like a(n) ________, except that the secondary winding and core are mounted on a shaft set in bearings.

transformer