Power Line Disturbances, Electrical Grounding & Bonding, and Power Factor Correction

Flashcard review deck covering Power Line Disturbances, Electrical Grounding & Bonding, and Power Factor Correction / Ferroresonance for PEEE1-M.

How many times per second does standard AC power voltage alternate between positive and negative values in a standard $60\text{ Hz}$ supply?

$$60\text{ times per second}$$

What visual waveform represents standard AC power measured on an oscilloscope?

An AC sine wave

According to the transcript, what changes in a flowing AC wave shape indicate a power disturbance?

Changes in size, shape, symmetry, or frequency, or when it develops notches, impulses, ringing, or drops to zero.

How does starting an electric motor affect line voltage compared to stopping it?

Starting a motor causes a brief voltage drop (sag) due to high starting current, whereas stopping a motor causes a brief, sudden rise in voltage (swell).

What is the specific definition and duration threshold for a Voltage Sag?

A drop in voltage greater than $13\%$ within $2\frac{1}{2}\text{ seconds}$.

What are common causes of Voltage Sags?

Power line switching, motor starts, overload service panel, and office equipment.

How is electrical Noise defined in power line disturbance context?

Continuous distortion of line voltage.

What are common causes of electrical Noise?

Faulty wiring, office equipment, motor controllers, and fluorescent lighting.

How is a Spike defined in terms of voltage magnitude?

A sharp increase in voltage which may exceed normal voltage by $5\times$ to $10\times$.

What are common causes of voltage Spikes?

Lightning, power tools, elevators, and office equipment.

What is the duration range for a Momentary Interruption?

Breaks in applied voltage lasting half a second ($0.5\text{ s}$) to several seconds.

What causes a Momentary Interruption?

Utility recloser operation, faulty circuit breakers, and bad wiring connections.

How is a Voltage Swell defined?

A reverse form of a sag, characterized by an increase in voltage lasting from half cycles to $1\text{ minute}$'s time.

What causes a Voltage Swell?

Sudden load reductions or a single-phase fault on a 3-phase system.

What does an Uninterruptible Power Supply (UPS) system act as during normal operation?

It acts as a filter that removes noise and arrests any spikes while maintaining the battery at full capacity with an electrical charge.

When does the battery in a UPS unit come online during operation?

When the UPS monitors a surge, a sag, or a momentary interruption of power.

What is the typical power backup time provided by a standard UPS for a computer during an extended power interruption?

Approximately $10\text{ minutes}$.

How long can critical equipment like phone systems or security systems remain online with a higher-capacity UPS battery?

For an hour or more.

What are common internal sources of power disturbances in a commercial building or office?

Copy machines, elevators, air conditioners, electric motors, vending machines, electric furnaces, electric welders, telephone switching equipment, fluorescent lights, electronic equipment, and adjusting speed controls on rotating machines.

What are common external influences on a utility electric system that cause power line disturbances?

Lightning/wind, utility switching, vehicular accidents involving utility poles, dig-ins of underground lines, tree damage, animal contact with power lines, equipment malfunctions, and vandalism.

What clamping voltage is recommended at a minimum for point-of-use surge protectors protecting sensitive home electronics?

$330\text{-volt}$ clamping voltage.

What distinguishes a Power Outage from a Momentary Interruption?

A Power Outage is registered whenever electricity is completely interrupted for $1\text{ minute}$ or longer, whereas a Momentary Interruption lasts from a fraction of a second to a minute.

What are the seven categories of power quality disturbances defined by IEEE based on wave shape?

Transients, Interruptions, Sag/Undervoltage, Swell/Overvoltage, Waveform distortion, Voltage fluctuations, and Frequency variations.

What are the rise time and duration characteristics of very fast impulsive transients?

Rise time of $5\text{ nanoseconds (ns)}$ from steady state to peak impulse, with a duration of less than $50\text{ ns}$.

What transient phenomenon is illustrated in this waveform diagram?

Impulsive Transient caused by electrostatic discharge (ESD).

What causes impulsive transients?

Lightning, poor grounding, switching of inductive loads, utility fault clearing, and electrostatic discharge (ESD).

What relative humidity range should be maintained to help prevent impulsive transients caused by electrostatic discharge (ESD)?

Between $35\%$ and $50\%$.

What is an oscillatory transient?

A sudden change in the steady-state condition of a signal voltage or current oscillating at the natural system frequency, usually decaying to zero within a cycle.

What common utility action causes low-frequency oscillatory transients?

Utility automatically switching in capacitor banks.

According to IEEE classification, what are the duration thresholds for Instantaneous, Momentary, Temporary, and Sustained Interruptions?

Instantaneous ($0.5\text{ to } 30\text{ cycles}$), Momentary ($30\text{ cycles to } 2\text{ seconds}$), Temporary ($2\text{ seconds to } 2\text{ minutes}$), and Sustained ($> 2\text{ minutes}$).

How much current can a large electric motor draw during startup compared to its normal running current?

Six times ($6\times$) its normal running current, or more.

What solutions are used to mitigate voltage sags caused by starting large motors in industrial facilities?

Reduced voltage starters (autotransformer or star-delta configurations) and Adjustable Speed Drives (ASDs).

What term has traditionally been used to describe long-term voltage sag problems, now formally termed Undervoltage?

Brown-out.

What causes a Voltage Swell, and what are its potential solutions?

Causes: high-impedance neutral connections, sudden load reductions, single-phase faults on 3-phase systems. Solutions: power line conditioners, UPS systems, ferroresonant control transformers.

Why do Overvoltages commonly occur in seasonal regions during the off-season?

Supply transformer tap settings remain configured for high usage while actual community power consumption is significantly reduced.

What are the five primary types of waveform distortion?

DC offset, Harmonics, Interharmonics, Notching, and Noise.

What causes DC offset in AC distribution systems, and what problems does it create?

Caused by failure of rectifiers in AC to DC converters; causes overheating and saturation of transformers due to circulating DC currents.

What is the primary solution for resolving DC offset problems?

Replacing the faulty equipment using modular, user-replaceable equipment.

What is the frequency of the 3rd harmonic in a power system with a $60\text{ Hz}$ fundamental frequency?

$180\text{ Hz}$ ($3 \times 60\text{ Hz} = 180\text{ Hz}$).

What methods are used to mitigate harmonic waveform distortion?

Oversizing neutral conductors, installing K-rated transformers, and using harmonic filters.

What industrial devices create significant interharmonic power problems by converting supply voltage into a different frequency?

Cycloconverters controlling large linear motors used in rolling mill, cement, and mining equipment.

What is Notching in power quality?

A periodic voltage disturbance occurring every half cycle ($\frac{1}{2}\text{ cycle}$) caused by electronic devices like variable speed drives, light dimmers, and arc welders.

What are the primary solutions for Notching waveform distortion?

Moving the load away from offending equipment, installing UPS systems, or installing filtering equipment.

What effects can electrical Noise have on computer systems and electronic hardware?

Data corruption/errors, equipment malfunction, long-term component failure, hard disk failure, and distorted video displays.

What are five solutions to address electrical Noise on a power system?

Isolate load via UPS, install grounded shielded isolation transformer, relocate load away from interference source, install noise filters, and cable shielding.

What are the magnitude and frequency parameters that define Voltage Fluctuations?

Small voltage changes between $95\%$ and $105\%$ of nominal at low frequencies below $25\text{ Hz}$.

What is the most common cause of voltage fluctuations on transmission and distribution systems?

Arc furnaces.

What effect do power frequency variations have on connected electric motors?

Causes motors to run faster or slower to match the frequency of input power.

In electrical grounding terminology, what is a Grounded Conductor?

A system or circuit conductor that is intentionally grounded (designed to be a current-carrying conductor, such as a neutral).

In electrical grounding terminology, what is a Grounding Conductor?

A conductor used to connect equipment or the grounded circuit of a wiring system to a grounding electrode or electrodes.

What is a Grounding Electrode Conductor (GEC)?

The conductor used to connect the grounding electrode to the system grounded conductor or to the equipment grounding conductor at the service.

Does a grounding conductor carry current under normal operating conditions?

No, under normal conditions a grounding conductor does not carry current; it carries current only during a ground fault.

What is System Grounding?

Grounding one of the current-carrying wires of an electrical installation.

According to PEC/NEC 250.4(A)(1), how should grounding electrode conductors be installed to limit imposed voltage?

They should not be any longer than necessary, and unnecessary bends and loops should be avoided.

What is Equipment Grounding?

Grounding the non-current-carrying metal parts of an electrical installation.

Why are metal parts of electrical equipment grounded according to NEC 250.4(A)(2)?

To reduce arcing within buildings/structures from induced voltage caused by indirect lightning.

What is an Effective Ground-Fault Current Path?

An intentionally constructed, permanent, low-impedance, electrically conductive path designed to carry fault current from a ground fault to the electrical supply neutral terminal to trip the circuit overcurrent protective device.

What is defined as "Objectionable Current"?

Current regularly flowing over equipment grounding conductors when no ground fault exists.

How is Bonding defined in electrical installations?

The permanent joining of metallic parts together to form an electrically conductive, low-impedance path capable of safely conducting fault current.

What is a Bonding Jumper?

A reliable conductor used to ensure electrical conductivity between metal parts of an electrical installation.

In a 120/240V single-phase system, what are the required wire insulation colors for Phase A, Phase B, Neutral, and Equipment Grounding?

Phase A = Black, Phase B = Red, Neutral = White, Equipment Grounding = Green.

In a 208Y/120V three-phase system, what are the conductor insulation colors for Phases A, B, C, Neutral, and Ground?

Phase A = Black, Phase B = Red, Phase C = Blue, Neutral = White, Equipment Grounding = Green.

In a 480Y/277V three-phase system, what are the conductor insulation colors for Phases A, B, C, Neutral, and Ground?

Phase A = Brown, Phase B = Orange, Phase C = Yellow, Neutral = Gray, Equipment Grounding = Green.

What is Black electrical wire strictly used for, and what should it never be used for?

Used for hot/live power in all circuits; never used for a ground or neutral wire.

What do Red electrical wires indicate in residential and commercial wiring?

Secondary live wires in a $220\text{-volt}$ circuit, switch legs, and interconnections between hard-wired smoke detectors.

What are Yellow and Blue electrical wires primarily used for when pulled through conduit?

Yellow is used for switch legs to fans and structural lights; Blue is used as a traveler for 3-way or 4-way switches.

What colors indicate a neutral wire in electrical wiring, and to what component inside an electric panel does it connect?

White and Gray; connects to the neutral bus bar.

What does Green wire insulation signify, and where does it connect inside an electrical box?

Signifies grounding of an electric circuit; connects to the grounding terminal in an outlet box and the ground bus bar in the electric panel.

According to PEC Art. 250.5.17, what bonding is required between grounding electrodes?

Bonding is required between the system grounding electrode and the lightning rod grounding electrode.

What is the body effect of an AC electric shock at $1\text{ milliampere (mA)}$?

Threshold of sensation.

What is the body effect of an AC electric shock at $2\text{ mA}$?

Mild shock.

At what AC current level in milliamperes will a standard GFCI trip?

$5\text{ mA}$ ($\pm 1\text{ mA}$).

What is the body effect of an AC electric shock at $10\text{ mA}$?

Cannot let go.

What is the body effect of an AC electric shock at $20\text{ mA}$?

Muscle contraction.

What is the body effect of an AC electric shock at $30\text{ mA}$?

Suffocation possible.

What is the body effect of an AC electric shock at $100\text{ mA}$?

Heart stops beating.

What is the body effect of an AC electric shock at $200\text{ mA}$?

Breathing stops.

What is the body effect of an AC electric shock at $300\text{ mA}$?

Severe burns.

What is the body effect of an AC electric shock at $1000\text{ mA}$ ($1\text{ ampere}$)?

Will light a $100\text{-watt}$ bulb (and causes severe injury or death).

According to PEC-2.10.1.8(a), what are seven mandatory dwelling unit locations requiring GFCI protection for personnel?

1. Bathrooms, 2. Garages, 3. Outdoors, 4. Crawl spaces at or below grade level, 5. Unfinished basements, 6. Kitchens for countertop appliances, 7. Wet bar sinks.

How is Power Factor (P.F.) defined mathematically?

The ratio of Active Power ($\text{kW}$) to Apparent Power ($\text{kVA}$), expressed as $\text{P.F.} = \frac{\text{kW}}{\text{kVA}} = \cos(\theta)$.

What formula relates Apparent Power ($\text{kVA}$), Real Power ($\text{kW}$), and Reactive Power ($\text{kVAR}$)?

$$\text{kVA} = \sqrt{\text{kW}^2 + \text{kVAR}^2}$$

In the "beer mug" power factor analogy shown below, what do the Beer, Foam, and Mug Capacity represent?

Beer = Real Power ($\text{kW}$), Foam = Reactive Power ($\text{kVAR}$), and Mug Capacity = Apparent Power ($\text{kVA}$).

What are four major sources of reactive power (inductive loads) on an electrical power system?

Transformers, Induction Motors, Induction Generators (windmill generators), and High Intensity Discharge (HID) Lighting.

What power factor threshold is enforced by the Philippine Distribution Code (PDC), below which penalties apply?

Power factor less than $85\%$ ($\text{P.F.} < 85\%$).

What are five disadvantages of operating an electrical system with a low power factor?

Large line losses (copper loss), larger kVA rating/equipment size, greater conductor size and cost, poor voltage regulation, and electric utility penalties.

What are the three primary methods used for Power Factor Improvement?

Shunt Capacitors, Synchronous Condensers, and Phase Advancers.

What is a Synchronous Condenser?

A device identical to a synchronous motor whose shaft is not connected to any load and spins freely to improve power factor.

Where is a Phase Advancer connected to improve power factor?

In the secondary circuit of an induction motor.

According to IEEE C57.106-1991, what is the maximum suggested power factor percentage for new transformer oil received in new equipment rated $> 345\text{ kV}$ at $25^\circ\text{C}$ and $100^\circ\text{C}$?

Maximum $0.05\%$ at $25^\circ\text{C}$ and maximum $0.30\%$ at $100^\circ\text{C}$.

What is Ferroresonance?

An oscillatory non-linear resonance phenomenon caused by the interaction of system capacitance with the non-linear inductance of a transformer when subjected to a disturbance.

In what year did the term "Ferro-resonance" first appear in electrical engineering literature?

$$1920$$

What four basic components must be present in an electrical circuit for ferroresonance to occur?

A non-linear inductance (ferromagnetic and saturable), a capacitor, a voltage source (generally sinusoidal), and low circuit losses.

In a series RLC resonant circuit, what is the formula for calculating voltage across the inductor ($E_L$)?

$$E_L = \frac{E}{1 - \frac{X_C}{X_L}}$$

In a series RLC resonant circuit, what is the formula for calculating voltage across the capacitor ($E_C$)?

$$E_C = \frac{E}{1 - \frac{X_L}{X_C}}$$

Given $E = 7.621\text{ kV}$, $X_L = 2400\text{ }\Omega$, and $X_C = 1600\text{ }\Omega$, what is the total circuit impedance ($Z$) and circuit current ($I$)?

$Z = X_L - X_C = 2400 - 1600 = 800\text{ }\Omega$ and $I = \frac{E}{Z} = \frac{7621}{800} \approx 10\text{ A}$.

What are five observable phenomena associated with ferroresonance in power systems?

Overvoltages/overcurrents, sustained distortion, loud noise (magnetostriction), misoperation of protective devices, and transformer overheating.

What are five methods used to minimize or prevent ferroresonance in transformer installations?

Using grounded-wye-grounded-wye transformer connections, using switches rather than fuses at riser poles, keeping $X_C / X_m$ ratios high ($\ge 10$), installing neutral resistance, and using 3-phase switching devices.

In ferroresonance classification, what characterizes the Subharmonic Mode?

Signals are periodic with a period $n T$ (a multiple of source period $T$), resulting in subharmonic frequencies $1/n$ (normally of odd order).

What visual representation in the $v\text{-}i$ plane characterizes the Chaotic Mode of ferroresonance shown below?

A strange attractor formed by completely separate points occupying an area in the $v\text{-}i$ plane.