Electrical Level 1

Front 1

Unintentional voltage drop formula

Back 1

Vd = (2×Lenth×Resistance×current)÷ 1000

Front 2

Synchronous speed formula

Back 2

Ns = 120 × (f÷p)

f = frequency (hz)

p = number of poles

Front 3

Slip % formula

Back 3

(Synchronous speed - full load speed) ÷ synchronous speed x 100

Front 4

Ohms law formula

Back 4

E(volts) = I(amperes) × R (ohms)

Front 5

Power formula (watts)

Back 5

Power(watts) = I (amperes) × E(volts)

Front 6

Effective voltage or rms voltage formula

Back 6

V rms = V max × .707

Front 7

Shaded pole motors are?

Back 7

Equipped with an additional winding in each corner called a shade winding. Used for low torque applications. Less then 1/10 HP

Front 8

Split phase motors are?

Back 8

Are used for fractional horse power duty with small loads. They have start windings which have smaller wire than run windings but have a greater number of turns.

Popular on systems that use capillary tube metering device due to easy starting load.

Front 9

Current relay are?

Back 9

-Activates on a high in rush of current.

-Normally open contacts

-Found on low torque, low horsepower motors.

-Wired in series with run windings of a single phase induction motor.

Front 10

Potential relays are?

Back 10

-normally closed contacts

-wired in parallel with start windings

-used with single phase, capacitor start / capacitor run motors.

- used when high torque is required.

Front 11

Contactor is?

Back 11

A heavy duty type of electromagnetic relay.

Front 12

Ture or false?

Higher the voltage, the lower will be the current for the same amount of the power.

Back 12

True

Front 13

True or false?

A transformer is a device that has no moving parts and that transfer energy from one circuit to another by mutual induction.

Back 13

True

Front 14

What is the emf generated in the second coil of a transformer called?

Back 14

Emf of mutual induction

Front 15

What is the primary winding in a transformer?

Back 15

The coil or winding which receives the source of energy.

Front 16

What is the secondary coil in a transformer?

Back 16

The coil or winding which receives energy from the primary winding by mural induction and delivers it to the load.

Front 17

Transformer ratio formula is?

Back 17

E1÷E2 = N1÷N2

Front 18

Why is iron desirable to use as a core material for electromagnets? (Transformers)

Back 18

Because of the high permeability or iron, meaning that magnetic lines force, or magnetic flux can pass through iron with relative ease.

Front 19

Transform losses are divided into two classifications. What are they?

Back 19

Copper losses and core losses.

Front 20

What is "copper loss"? And where does it occur?

Back 20

Copper losses occur in the windings which are usually made of copper wire.

Copper losses occur because of the resistance of the wire.

Front 21

What are "core losses"? And how is it caused? (Transformers)

Back 21

Core losses are due to "eddy-currents" and hysteresis loss.

It is caused by friction between molecules of the metals. Hysteresis loss is minimized by making the cores of silicon steel.

Front 22

Why do transformers work?

Back 22

Because of the expanding and collapsing magnetic field cuts across the conductors of the secondary winding.

Front 23

What is "eddy-current"? How does it flow?

Back 23

It is the electrical current in the core of a transformer. It flows against the electrical resistance of the core and appears as additional heat.

Front 24

What is the core in transformers made of? And why?

Back 24

The core is made of a number of thinner pieces of metal and they are electrically insulated from each other, current will flow in each piece.

The increased resistance of the electrical path in the thin piece reduces the magnitudes of eddy-currents and correspondingly reduces the losses.

The cores thus made are said to be laminated.

Front 25

What is counter electromotive force (cemf)?

Back 25

The rotors magnetic field induces a voltage with a polarity opposite of the voltage applied to the stator.

Counter electromotive force opposes the flow of current in the rotor.

Front 26

Power loss formula

Back 26

Power loss(p) = I² × R

Front 27

Voltage and current are in phase in what circuit?

Back 27

Resistive circuit.

Voltage and current are in phase when they both reach their peaks at the same time.

Front 28

In what circuit does the current lag behind the voltage?

Back 28

Inductive circuit

Front 29

In what circuit does the voltage lag behind the current?

Back 29

Capacitive circuit

Front 30

What is a thermistor?

Back 30

A thermistor regulates the flow of current by changing its resistance based on heat.

Used in low voltage electronic applications

Front 31

Ground fault circuit interrupter (gfci)

Back 31

Interrupter opens when the equipment connected to it is defective, misused or improperly grounded.

Opens when as little as 6 mA of current leaks out of the circuit and into the grounding system.

Front 32

Which conductors are grounded and ungrounded?

Back 32

Grounded conductors are connected to a grounded transformer. These are often called Neutral wires

Ungrounded conductors are connected to the phase lines of the transformer. These are often called hot wires.

Front 33

When does a short circuit occur?

Back 33

When the current is unintentionally routed around a component or electrical load, instead of through it.

Front 34

What is a ground fault.

Back 34

Ground fault is a condition in which a device or ungrounded metal part becomes electrically hot or live.

Front 35

What is overload?

Back 35

A condition in which too much current flows through a circuit.

Front 36

What is a stator?

Back 36

It is the stationary part of a motor that is attached to the inside of the motor housing

Front 37

Field poles and field windings are?

Back 37

Field poles are electromagnets whose polarities changed as the flow of current alternates in the field windings.

Field windings are the wires wrapped around the field poles of the stator.

Front 38

What is the rotor? What is it composed of?

Back 38

It is the axle-mounted unit that rotates as the polarities of the stator's field poles change.

Composed of coils or wire surrounding an iron core or metal bara mounted on an iron core.

Front 39

What causes the rotor to rotate?

Back 39

The interaction between the magnetic fields of the stator and the rotor cause the rotor to rotate.

Front 40

Run windings are?

Back 40

Run windings are stator windings that are energized during the entire operation of the motor.

They provide the bulk of the magnetic force for driving the rotor.

Front 41

Start windings are?

Back 41

Start windings are stator windings that are used for motor starting and additional torque.

Coil is made of smaller diameter wire and has more turns than a run coil.

Front 42

What is phase splitting?

Back 42

It is the means by which single-phase motors are started.

The current running through the start winding is out of phase with the current flowing through the run windings.

The split creates a rotating magnetic field in the stator causing the rotor to start turning.

Front 43

2 types of capacitors are?

Back 43

Start capacitor and run capacitor

Front 44

What is a centrifugal switch?

Back 44

An electrical device mounted on the end of a motor shaft that disconnects the start windings from the circuit.

Front 45

Capacitor start,Induction run (CSIR)

Back 45

-Is a single phase induction motor that has a start capacitor wired in series with the start windings.

- current passes through both start and run windings during start up.

- at about 75% of motors rated speed, a centrifugal switch or relay in series with the start winding opens.

Front 46

Capacitor start,capacitor run motor (CSCR)

Back 46

-Has a start capacitor and run capacitor wired in series with the start windings but the run capacitor is wired in parallel with the start capacitor.

-All capacitor are in the start winding circuit, but only the start capacitor is controlled by a centrifugal switch or relay.

- efficient motors

Front 47

Permanent split capacitor (PSC)

Back 47

Is a single phase induction motor that uses a single run capacitor in series with the start windings of the motors entire operation.

- easy start loads & low horsepower applications

Front 48

How does a variable frequency drive work?

Back 48

VFD uses a rectifier circuit to convert applied ac voltage to DC. It then uses an inverter with solid-state switching circuitry to convert the dc signal back into an ac sine wave that oscillates at the desired frequency.

Front 49

Electronically commutated motors ( ECMs)

Back 49

Is a programmable, brushless dc motor that uses an electronic control module to control voltage to the stator windings

- EMC's motor is made of permanent magnets instead of coils of wire or metal bars.

-EMC usually operate quietly.