Learn about UL 1008 short-circuit testing and passing criteria, and know how to apply the short-circuit withstand and closing rating in a power system

Electrical engineers must concern themselves with power quality issues in buildings and electrical systems. Learn how to mitigate power quality issues in this webcast.

Electrical engineers should understand what power factor correction is, why engineers should correct power factor, the evolution from power factor to true power factor and various power factor correction techniques. The presenter will also examine applications that involve power factor correction in harmonic-rich networks and how it can be used to mitigate flicker. The discussion will conclude by looking at the future of power factor correction by exploring electronic VAR compensation.

When designing backup, standby and emergency power systems for mission critical facilities, there are several considerations beyond NFPA 70: National Electrical Code, NFPA 110: Standard for Emergency and Standby Power Systems and other building code requirements that must be addressed. Electrical engineers must understand the owner’s project requirements for the building’s power systems. Mission critical facilities can include data centers, hospitals, laboratories, semiconductor manufacturing, pharmaceutical and other facilities where interruption of power would have a severe impact on operations and business.

Engineers also need to be mindful of the overall new construction or existing building retrofit process and ensure equipment replacement is coordinated, temporary power strategies are identified and phasing concepts are developed.

When selecting protection devices, consideration must be given to the prospective short-circuit current (PSC) at the location the device is to be installed in (AS/NZS 3000:2018 clause 2.5.4.1). The PSC can be determined by measurement or by calculation. Many multi-function testers are able to measure the PSC.

PSC can also be calculated by undertaking a Live Fault Loop Impedance measurement (in ohms) and dividing the voltage by this measurement.

Example

Voltage tests as 240 volts and the measured fault loop impedance between incoming line and neutral is 0.08.

Max PSC = E/R

240/0.08 = 3000 A or 3kA

Three Phase Supplies
Where there is a three phase supply, the PSC is likely to be between line conductors. In this case, the PSC can be calculated by multiplying the single phase reading by the square root of 3 or 1.73. Therefore in the example above, the PSC would be 3000 x 1.73 = 5190 A or 5.19kA.

Example: Calculate Size of Bus bar having Following Details

Bus bar Current Details:
Rated Voltage = 415V,50Hz ,
Desire Maximum Current Rating of Bus bar =630Amp.
Fault Current (Isc)= 50KA ,Fault Duration (t) =1sec.
Bus bar Temperature details:

Schneider Electric's Fault Current Calculator -- Single phase or three phase

The wireless telegraph is not difficult to understand. The ordinary telegraph is like a very long cat. You pull the tail in New
York, and it meows in Los Angeles. The wireless is the same, only without the cat." - Albert Einstein ///

Possibly apocryphal, like m good quotes

Everything an apprentice needs to know about applying the NEC requirements in Art. 230 ///

Corrections:

• 480/277 delta should be 480/277 wye
• 600/480 delta should be 600/377 wye

Electrical engineers should understand what power factor correction is, why engineers should correct power factor, the evolution from power factor to true power factor and various power factor correction techniques

To properly sizing the amount of capacitor (kVAR) required to correct the lagging power factor,we must have three (3) important of information below:

• kW (kilowatts)

• Existing Power Factor ( % )

• Desired Power Factor ( % )

From this information,now we can calculate the capacitor size for power factor correction.The formula to calculate the required kVAR is:

Calculation Example :

1 unit air-compressor ( 3 phase 415 VAC ) used an average of 90 kW with an existing power factor of 80%.The desired power factor is 95%. The factor value for this case is 0.421 to raise the power factor from 80% to 95% using table 1.

0.421 x 90 kW = 38 kVAR

In order to calculate power factor correction for your installation, your should follow the steps below: //

At the end of the spreadsheet you will get the calculation of the energy savings for above power factor correction.

I once watched two engineers/technicians argue for two hours about what power definitions should be displayed on a HMI interface. One of them argued that VARs were being EXPORTED during lagging conditions, so a lagging current should be shown as POSITIVE VARS and Power Factor! The other argued that VARs were IMPORTED during lagging conditions, so a lagging current should be shown as NEGATIVE VARs and Power Factor!

I was fairly new to the business and had no skin in the game, so I couldn’t contribute at the time, but I did find both arguments compelling and the whole scene was hilarious. Now that I’ve had some experience, I realize that they were both correct… from their perspectives.

Here’s an excerpt from The Relay Testing Handbook: Generator Relay Protection Testing that should help clarify how Phasor Diagrams can be interpreted differently by electrical workers with different backgrounds, and why you should NEVER plot a phasor on a Power (P-Q) Diagram:

New NEC requirement and stirring of state/local initiatives seek to address dangers DC power in rooftop PV systems pose to firefighters.

210.8 Ground-Fault Circuit-Interrupter Protection for Personnel. ...(F) Outdoor Outlets. All outdoor outlets for dwellings, other than those covered in 210.8(A)(3), Exception to (3), that are supplied by single-phase branch circuits rated 150V to ground or less, 50A or less, shall have ground-fault circuit-interrupter protection for personnel. This requirement shall become effective January 1, 2023, for heating/ventilating/air-conditioning (HVAC) equipment.

Substantiation: GFCI protection was expanded in the 2020 NEC without HVAC component and equipment safety standards being harmonized with GFCI amperage limits. Currently, the UL standard that HVAC equipment is listed to (UL 1995) has no requirements for leakage current if the unit is hard wired, as most residential air conditioners/heat pumps are. In the future, HVAC equipment will be listed to UL 60335-2-40, which sets a limit of 10 milliamps of leakage current. However, this new standard is not mandatory until 1/1/2024. UL 943 is the standard to which GFCI breakers are listed and are required to trip at 5 milliamps of current. Even if HVAC equipment is listed to the UL 60335-2-40 standard, there is no guarantee it will be compatible with UL listed GFCI breakers This lack of coordination is what is leading to the nuisance tripping that customers are dealing with.

Until both equipment and component standards are updated, designers, installers, AHJs, and consumers are forced to choose between an NEC 2020 compliant installation or an operational installation. In jurisdictions that have adopted 2020 NEC with 210.8(F) intact, there have been numerous instances of field tripping of the GFCI breaker on ductless mini splits, units containing power conversion equipment, and on many single-stage units.

The “PPE First” Fallacy

This is the belief that some electrical workers have related to the idea that their employer gave them the arc flash PPE, so let’s just put it on and get the work done. PPE should be viewed as the last line of defense and used only after all other options have been exhausted. Article 130 of the NFPA 70E requires an arc flash risk assessment to include evaluating electrical tasks using the hierarchy of risk control method. Electrical professionals should always evaluate methods for eliminating the hazard, shielding themselves from the hazard, and any other step to keep workers out of the line of fire. If our risk assessment results in no other option than being exposed to the potential arc flash hazard, then the employee determines the appropriate PPE needed to execute the task safely.

An example of managing this mindset to drive a positive culture can be seen in an approach I have used for voltage-rated tools. When managing a group of electrical workers, I provided them with electrical safety training, which included the requirement for voltage-rated tools when working inside the restricted approach boundary (RAB) of exposed energized conductors. After the training, I was told that they all needed to be provided with individual sets of voltage-rated tools because on any given day they could receive a maintenance task that would require performing work inside the RAB. Knowing that I was the author and provider of the electrical safety training that taught them the requirement, you can imagine their surprise when I declined their request.

I explained that if I provided each employee with their own set of voltage-rated tools, I am implying that I expect them all to perform repair-type work within the RAB when, in fact, my expectation is the exact opposite. Instead of individually issued tools, I provided two toolboxes with voltage-rated tools that were kept locked, and I retained the keys. Working inside the RAB for non-diagnostic tasks requires an energized electrical work permit (EEWP). A task that would require voltage-rated tools also required an EEWP approved by me. If the EEWP and hazard risk assessment process resulted in verifying that the task was infeasible to complete in an electrically safe work condition, then I would approve the plan and provide a key to the voltage-rated tools. The result was that those tools rarely were used because the process worked as intended. Instead of jumping right in and executing the task with PPE, we took some time to think about what needed to be done and determine if there was a way to do the work while minimizing the need for PPE. In most cases, we found ways to execute the task with significantly reduced exposure to electrical hazards.

That scenario demonstrates the goal of the requirements for an electrical safety program. The goal is to drive a culture of continuous evaluation of how we execute our tasks with the mindset of minimizing our exposure to hazards. The days of ‘taking risks because we are electrical workers and we knew the risk when we signed up for the job’ is over. There is no task in the electrical industry that is important enough to risk our life to execute. Given what we understand about electrical hazards and the procedures and technology available, there is no reason for anyone to ever be injured or killed by an electrical hazard. There is always a method for protecting workers from the hazard. The solution is in driving a culture that prioritizes safety at work and home so that taking risks is replaced with taking time to plan the work to be executed safely.

The Independent System Operator for the New England power grid (ISO-NE) has produced a summary brief describing the challenges associated with Arctic Outbreak 2017-2018, a period of substantially below normal temperatures that lasted from Dec.25, 2017 until Jan. 8, 2018.

After describing the intensity of the cold wave with a number of graphs, charts, images and words, the brief made the following sobering statements about the fuel mix used to supply power demand.

Overall, there was significantly higher than normal use of oil
– Coal use also increased over normal use
Gas and Oil fuel price inversion led to oil being in economic merit and base loaded
As gas became uneconomic, the entire season’s oil supply rapidly depleted

NEW ORLEANS — The entire New Orleans area south of Lake Pontchartrain is expected to be without power for weeks because all eight of Entergy’s transmission lines delivering electricity from the outside world failed simultaneously.

Hurricane Ida’s intense winds turned one of the main transmission towers into a heap of twisted and rusted metal along River Road at the edge of Bridge City. //

It was a staggering sight for a tower that rose 400 feet above the Avondale Shipyard and supported power lines across a 3,800 foot span to a tower across the Mississippi River in Harahan. On Monday, those same power lines could be seen in drone footage overhead, dunked into the muddy river.

That’s only one of the entry points that failed, leaving Entergy customers on what the utility officially calls an “island.” Entergy says it’s trying to assess and investigate what it acknowledged was a “catastrophic transmission failure” and scrambling to figure out how to restore power.

Entergy Louisiana CEO Phillip May said that assessment period will take at least four days, after which more than 20,000 restoration workers will pursue at least two tracks to get the lights back on:

Getting at least one of the failed transmission lines back up and running, or by generating power from within the island itself, using the power station at Nine Mile Point, or by firing up the new power plant at Michoud, in New Orleans East. //

The second option, creating a self-generated power source from within the “island,” is not ideal, but will be pursued at the same time. First, to use the 230 megawatts of power that can be generated at the New Orleans Power Station, Entergy still needs to restore enough transmission lines to deliver electricity to customers. //

In addition to the New Orleans Power Station, Entergy hopes to generate another 400 megawatts at the Nine Mile power station and use large generators to push the total electricity on the “island” above 600 megawatts. That would be enough to provide critical power to services and infrastructure but not enough for all customers to be restored, Moreno said.

A mere ½ in. closer, and this screw could have done some serious damage to the EMT and the conductors inside. This is a great example of why Sec. 300.4(E) requires raceways, cables, and boxes to be installed and supported to provide no less than 1½ in. of separation between the lowest surface of the metal-corrugated sheet roof decking and the top of the raceway cable or box. //

I will certainly give this installer credit for installing the Class 2 control wires in a raceway separate from the power wires feeding this air-conditioning equipment. Section 725.136 generally requires Class 2 and Class 3 circuits to be kept separated from power conductors and provides several methods to achieve this separation. However, the choice to install liquidtight flexible nonmetallic conduit (LFNC) in this outdoor, sun-drenched area may need to be reviewed. Section 300.6(C)(1) requires nonmetallic raceways exposed to direct sunlight to be listed or identified as being sunlight resistant. Section 356.10(3) does permit LFNC to be installed in outdoor locations if the LFNC is listed and marked for this purpose. According to the product standards, LFNC suitable for installation outdoors is marked “outdoor.”

If I pass a current through a copper conductor, how can I calculate how hot the conductor will get?

For example, if I have a 7.2kW load powered by 240VAC, the current will be 30A. If I transmit this power to the load via a 2.5mm2
copper conductor, how do I calculate how hot this conductor will get?