MikeHolt_Section01_Electricial Basics

Unit 01: Basic Electrical Math and Formulas

Fractions

  • Adding:
    • Step 1: Denominators are the same
    • Step 2: Add the numerators
    • Step 3: Simplify
    • (I.E.  Want to add:  1/11 + 2/3?  The LCM of 3 and 11 is 33 . Multiply the numerator and denominator of 1/11 by 3 , and multiply the numerator and denominator of 2/3 by 11)
  • Convert to Decimal Number:
    • Numerator / Denominator

Percentages

  • Conversions
    • to Whole/Decimal numbers
      • Move decimal point two to left
    • Multiplier
    • Convert % to Whole number or decimal , then Multiply
    • Increase or decrease:
    • Convert % to Whole number or decimal , then add 1.0 to decimal, then multiply

Reciprocals

  • Convert number to a fraction with 1/ as the numerator
  • For percentages:
    • Convert percentage to decimal
    • Divide 1 by resultant decimal

Unit 02: Electrical Circuits

NEC Article

  • Current flow is Series, Parallel, Series-Parallel, or Multi-wire branch
  • Grounding wire is ╧
  • Grounded wire is Neutral
  • Ungrounded wire is Hot / Live
  • Basic electrical circuit is:

    • Power Source
    • Conductor
    • Load
    • Protection Device
    • Switch

  • Electrical circuit problem-solving is for:

    • Voltage
    • Current
    • Resistance
    • Power

3-wire, 1Ø Circuit_Determine Current in Neutral

  • In = L1 – L2
    • In = current neutral
    • Current in Neutral = Difference between current flow of L1 and L2
  • Balanced system in a 3-wire, 1Ø and all 3Ø circuits is when Neutral current equals zero.
    • In = L1 – L2 = 0
    • Hot wires all have equal current flowing

3 or 4-wire, 3Ø Circuit_Determine Current in Neutral

  • In = √(L12 + L22 + L32) – [(L1 x L2) + (L2 x L3) + (L1 x L3)]

Voltage Drop

Material Resistance DC Voltage AC Voltage
Inductive Reactance
Capacitive Reactance

Unit 03: Alternating Current

NEC Article 

Alternating Current (AC) is used to transmit electricity cheaply at high voltage and low current

  • less voltage drop
  • conductors and equipment can be smaller and cheaper
  •  Energy Storage means:
    • Inductor – Electro-Magnetic Field
    • Capacitor – Electrical Field

AC values of wave forms/Sine waves

  1. Instantaneous is any value in time measured on a sine wave.  Ranges from -peak to 0 to +peak
  2. Peak is maximum value of a voltage or current sine wave
  3. Effective Voltage / Effective Current is same amount of heat in resistors equivilent to VDC or DC current

RMS determines effective voltage or current value

  1. Square instantaneous values
    • Determine the Mean(average) of all instantaneous values
  2. convert negatives values to positve
  3. Calculate square root value of the Mean
    • reverses the numerical effect of squaring the values in step 1

Capacitance

  • Capacitance is the property the stores & releases electrical energy using an electrical field.
  • Capacitive Reactance is a

Capacitors

  • Direct current can not flow through a capacitor
  • Permits current to flow by the ability to store and discharge energy as alternating current flows in opposite directions
  • Resists changes in current
  • Introduces reactance to a circuit
  • Shifts Sine wave to current leading voltage by 90
    • Voltage lags current wave form by 90

A capacitor resists changes in voltage or changes in current

Capacitor capacitance factors:

  1. Plate Distance
    • Capacitance is inversely proportional to the distance between capacitor plates
  2. Surface Area
    • Capacitance is directly proportional to surface area
      • Capacitors in Parallel increases the capacitance by the sum of the capacitors
      • Capacitors in series increases the dielectric and decreases the capacitance
  3. Dielectric Strength
    • The maximum voltage that can be applied across the dielectric before it shorts out (fails)

Capacitor Uses:

  • Momentary current flow to a capacitors prevents arcing across a switch during opening/closing
  • Source AC-current waveform transforms through a full-wave bridge rectifier into pulsating direct-current waveform whereby a capacitor smooths out the direct-current waveform resulting in near-steady direct-current
  • Adding circuit capacitors
    • counteracts high inductance
    • increases power factor

Capacitive Reactance (XC) (Ω)

  • Capacitive Reactance is the opposition to alternating current flow by capacitors , expressed in Ω using Xc
  • Capacitive Reactance is when alternating current sine wave reached + peak & a capacitor fully charges to the same polarity.  As the sine wave decreases heading to – peak, the capacitor discharges which has the effect of resisting changes in alternating current circuit voltage.
  • Voltage Lags Current
  • XC = 1/(2 * π * f * C)
    • Xc is Ω
    • π is 3.14
    • f = frequency / hertz
    • C = capacitance / farads

Induction

  • Inductance is an electrical circuit property which stores and releases electrical energy using an electro-magnetic field
  • Induced Current is the movement of electrons caused by an external magnetic field
  • Induced Voltage is the associated potential of the movement of electrons caused by an external magnetic field
  • Induction uses:
    • Transformers
    • Motors
    • Generators

Counter-Electromotive Force (CEMF)

  • 90° out of phase with circuit current
  • 180° out of phase with applied voltage
  • CEMF either opposes or aids conductor current flow
  • AC current increases CEMF opposing conductor current preventing current increases
  • AC current decreases CEMF aiding conductor current preventing current decreases
  • CEMF created within a winding is directly proportional to:
    • current flow
    • The winding
      • Conductor length
      • number of turns
    • Frequency
    • Increasing winding current
      • increased alternating magnetic field
      • CEMF
    • Increasing the number of winding loops & the closer the winding loops are
      • increases CEMF
    • Increasing the frequency
      • increase CEMF
    • Soft, iron core within windings increases CEMF compared to air core
      • CEMF is directly proportional to winding core cross-sectional area
      • CEMF is inversely proportional to core’s length

Inductive Reactance

  • Inductive Reactance is self-induced voltage (aka CEMF) acting to oppose the change in current flowing in conductors
  • Measured in Ohms
  • Expressed using XL
  • XL = 2 * π * f * L
    • XL
    • π is 3.14
    • f = frequency / hertz
    • L = Inductance / henrys

Efficiency

Energy efficiency is the ratio of its useful power output to its total power input

Total amount of power loss in watts

Expressed in percentage (%)

How much input energy is used for the intended purpose

Ratio of output true power to input true power

Output power never greater then input power; Output always less than input

Efficiency factor always 1 or less (100% or less)

P= I2R = Power/heat losses

DC Circuit Conductor Resistance

  • Current and voltage affected only by resistance
  • Directly proportional to conductor length
    • If conductors length doubles, total resistance doubles
    • Smaller diameter = higher resistance
    • 1/2 diameter = 1/4 cross-sectional area = 4X resistance
  • Inversely proportional to conductor cross-sectional area
    • Larger diameter = lower resistance
    • 2X diameter = 4X cross-sectional area = 1/4 resistance

AC Circuit Conductor Resistance

  • Current and voltage affected by:
    1. resistance (same as DC Circuit Conductor Resistance)
    2. Eddy Currents
    3. Skin Effect
  • Eddy Currents
    • small, independent currents resulting from the expanding and collapsing magnetic field
    • Flows erratically
    • Consumes power
    • Increases opposition to current flow
    • Greatest at conductors center
  • Skin Effect
    • Expanding and collapsing magnetic field induced voltage in conductors which repels flowing electrons towards the conductor surface
    • Applied AC current flows towards conductor surface
    • Increases opposition to current flow
    • Stranded conductors reduce skin effect
  • Conductor Windings
    • CEMF created within a winding is directly proportional to:
      • current flow
      • The winding
        • Conductor length
        • number of turns
      • Frequency
    • Increasing winding current
      • increased alternating magnetic field
      • CEMF
    • Increasing the number of winding loops & the closer the winding loops are
      • increases CEMF
    • Increasing the frequency
      • increase CEMF
    • Soft, iron core within windings increases CEMF compared to air core
      • CEMF is directly proportional to winding core cross-sectional area
      • CEMF is inversely proportional to core’s length

Power Factor

  • Inductive Reactance
    • Voltage leads current
  • Capacitive Reactance
    • Current leads voltage
  • Unity Power Factor

    • ‘Perfect Power Factor’ of 1 (100%)
    • Voltage and current are in phase
      • both reach 0 and peak value at same time
      • no leading or lagging
      • PF = 1.00 = 100%
    • Achieved with power supplied to a pure resistive load
      • incandescent light bulb
      • heating element

Apparent Power (VA)

  • Power supplied to circuit by the source determined by measuring voltage and current in an inductive or capacitive circuit and then multiplying together
  • Measured in kVA
  • Apparent Power (VA) is greater then True Power (W)
    • Use VA to size circuits and equipment
    • Fewer loads can be supplied using VA than W
    • Larger circuits, panels, and transformers may be required
  • Inductive loads
    • Transformers, motors, generators, etc.
  • Power Factor / True Power (W) / Apparent Power (VA)

    1. Apparent Power (VA)
    2. True Power (W)
    3. Power Factor (PF)
    • Apparent Power (VA) = W / PF
      • also VA = kW / PF
      • also VA = E*I (Apparent Power  = Volts * Amps)
    • True Power (W) = VA * PF
    • Power Factor (PF) = W / VA
    • also PF = KW / kVA

True Power (W)

  • Measured in KW
  • Resistive loads
    • incandescent light bulbs, heating elements, etc.