Electrical Power Equipment Maintenance, Harmonics, and Safety Flashcards

Flashcards covering electrical power equipment maintenance, mitigation of harmonics, grounding standards, and safety regulations including NFPA 70E, OSHA, and arc-flash hazard analysis.

What specific issue occurs in passive filters as their capacitors age?

Their effectiveness diminishes as they lose $\mu F$ and thus raise their notch frequency.

What is the primary function of active filters in harmonic current mitigation?

They are power electronic converters that inject equal-but-opposite distortion to yield more sinusoidal voltage waveforms throughout a network.

What specific capability do active filters have to prevent overload from new harmonic sources?

Current-limiting capability.

According to the transcript, what is the recommended recording duration for monitoring mitigation equipment after commissioning?

One week of measurements is needed to observe the entire weekly load cycle.

Which transformer configuration is used for phase relationship shifts through cancellation techniques?

Delta–delta and delta–wye transformers.

Why are isolation transformers considered a good solution for AC or DC drives using SCRs?

They provide voltage matching (stepping up or down) and provide a N–G reference for nuisance ground faults.

What are the standard impedance ranges for line reactors (inductors)?

$1.5\%$, $3\%$, $5\%$, and $7.5\%$.

Why is the use of three-light circuit testers not recommended for verifying wiring adequacy for critical loads?

They have limitations, can provide a correct indication even when problems exist, and are incapable of indicating the integrity of power conductors.

Why should phase, neutral, and equipment grounding conductors be routed through continuously grounded metallic conduit?

To provide a shield for radiated interference.

How can a technician determine if a neutral conductor is being shared with other loads?

Check the neutral current with the sensitive load turned off; if the current is not zero, a shared neutral is being used.

What is indicated by a zero voltage measurement between neutral and ground at outlets?

The presence of a nearby N–G bond.

What is the recommended practice for the impedance level of an equipment grounding conductor?

$0.25\,\Omega$ or less.

Under what condition can an accurate measurement of grounding electrode resistance be taken?

Only when the grounding electrode is disconnected from all other grounds.

What does a zero current flow in the grounding electrode conductor usually indicate?

An open connection.

To which first upstream point must the IG (Isolated Ground) and conduit ground terminate?

The first upstream N–G bonding point.

What are the five major areas covered by the National Electrical Safety Code (NESC)?

Grounding methods, installation/maintenance of supply stations, overhead lines, underground lines, and work practices for operation.

As of January 1, 2009, when must an employer require employees to wear arc-rated clothing?

When an assessment determines a potential employee exposure is greater than $2\,cal/cm^2$.

Which materials are strictly prohibited for clothing when an employee is exposed to an electric arc or flame?

Acetate, nylon, polyester, or polypropylene.

What is the principle objective of the NEC NFPA 70?

To help minimize the possibility of electric fires.

According to NEC article 110.16, where must flash protection markings be located?

Clearly visible to qualified persons before examination, adjustment, servicing, or maintenance of the equipment.

What are the four chapters reorganized in the sixth edition of NFPA 70E-2004?

Chapter 1: Safety-related work practices; Chapter 2: Safety-related maintenance requirements; Chapter 3: Safety requirements for special equipment; Chapter 4: Installation safety requirements.

At what voltage level does NFPA 70E require safety-related work practices to protect employees from flash and contact hazards?

$50\,V$ or more.

Define the 'Limited Approach Boundary' for shock protection.

An approach limit at a distance from an exposed live part within which a shock hazard exists.

What defines the 'Restricted Approach Boundary'?

A distance within which there is an increased risk of shock due to electrical arc over combined with inadvertent movement.

What is the 'Flash Protection Boundary' for systems that are $600\,V$ or less with a clearing time of six cycles and 50 kA fault current?

$4.0\,ft$.

What constitutes the incident energy level for the flash protection boundary at voltages above $600\,V$?

The distance at which the incident energy equals $5\,J/cm^2$ ($1.2\,cal/cm^2$).

Why are PPE ATPV values above $40\,cal/cm^2$ prohibited despite being available?

Due to the sound, pressure, and concussive forces being more severe than the thermal values.

What is the minimum arc rating for PPE Hazard/Risk Category 1?

$16.74\,J/cm^2$ ($4\,cal/cm^2$).

What is the definition of EBT in the context of arc rating?

The average of the five highest incident energy exposure values below the Stoll curve where the specimens do not exhibit break open.

What is the meaning of a red color-coded label in an arc-flash analysis program?

Maximum severity for which no PPE category is available and where energized work is prohibited.

How is 'Arc-flash hazard' defined in the transcript?

A dangerous condition associated with the release of energy caused by an electric arc.

According to IEEE 1584-2002, what potentially hazardous effects were not considered in the analysis methodology?

Molten metal splatter, projectiles, pressure impulses, and toxic arc by-products.

What is the first mandatory step in the sequence for removing a capacitor from operation?

Isolate the capacitors by opening the breakers or isolation devices connecting them to the electrical system.

What is the caution regarding vacuum circuit breaker high-potential testing and X-radiation?

Do not make hipot tests on an open breaker at voltages higher than $36\,kV$ AC across each interrupter.

What are the voltage limits for Class 2 High Voltage rubber gloves?

Tested for $15,000\,V$ for use on $10\,kV$ or less.

What is the visual indication of a two-part neon bulb in a low-voltage tester when energized by AC?

Both parts of the bulb glow.

What is the lowest voltage that can be reliably detected by a proximity type HV tester?

About $2000\,V$.

What is the required minimum size for grounding cables used for personnel protection?

$No. 1/0 American wire gauge (AWG)$ conductor.

What is the recommended maximum duration an employee should work on-site in a single period?

No more than $12\,h$, preceded and followed by a minimum of $8\,h$ of rest.

What dielectric resistance test should be performed on a low-voltage breaker prior to racking in?

A $1000\,V$ megohm meter test phase-to-phase and phase-to-ground.

What is the safety procedure for a technician if a ventilating blower stops while they are in a confined space?

Leave the confined space immediately and remove the hose.

What is the 'inching method' used for in electrical switching?

Opening manually operated disconnects gradually until the operator is sure there is no load current.

When should the inching method NEVER be used?

For load break disconnects, air break switches, or switching devices designed to break load or magnetizing currents.

What is the minimum working and clear hot stick distance for a phase-to-phase voltage range of $46.1$ to $72.5\,kV$?

$3\,ft\,0\,in$.

Why should an operator never reopen a disconnect after a failed attempt at closing it under load?

The lines or apparatus should be de-energized before the disconnect is opened if the alignment is wrong.

What is an 'air break switch' designed to do?

Energize and de-energize load currents, magnetizing current of power transformers, and charging current of transmission lines.

What current value through the body trunk is associated with ventricular fibrillation?

$100$ to $200\,mA$.

What is the threshold of perception for $60\,Hz$ current in an average human?

$1\,mA$, or less.

What is the standard resistance value for 'Internal body Hand-to-foot'?

$400$ to $600\,\Omega$.

What is the required frequency for heart compression during resuscitation?

$60$ times per minute.