There are three commonly used methods for testing insulation resistance: spot reading test, time resistance test, and step voltage test. These three tests are used primarily to test insulation in motors, generators, cables, transformers, and other electrical apparatus. Additionally, there are two ratio test methods that are also helpful when testing rotating machinery, such as motors and pumps.

To perform these tests, it is best to have a megohmmeter with a timed test function and the ability to select from a range of test voltages. It is also helpful to have a thermometer or similar temperature measurement device on hand. If the equipment temperature is below the dew point, a humidity measuring instrument will be necessary, especially when performing a spot test.

As noted in Art. 100 of the 2020 NEC: Fault Current, Available (Available Fault Current). The largest amount of current capable of being delivered at a point on the system during a short-circuit condition.

Informational Note: A short circuit can occur during abnormal conditions such as a fault between circuit conductors or a ground fault. (See Informational Note Figure 100.1 in the NEC.)

Fault current is current outside the usual circuit path and with a magnitude that exceeds the normal circuit current. A fault can be line-to-line, line-to-neutral, or line-to-ground. The new NEC Informational Note, Fig. 100.1, helps explain the differences between “Available Fault Current,” “Short-Circuit Current Rating” (SCCR),” and “Interrupting Rating (AIC).” The available fault current is the largest amount of current available at that point on the circuit. It is important to note that the fault current value is not the same throughout the circuit; it becomes smaller as the impedance is increased between the point of the fault and the source of the power.

The RTO leads to high prices and rolling blackouts.

As Professor William Hogan of Harvard, one of the architects of the Texas system, said in a recent interview with the Harvard Crimson, the state’s electricity market had “worked as designed.” https://www.thecrimson.com/article/2021/2/26/hogan-texas-energy-prices/

Others were upset that rolling blackouts still happened when the auction price was below $9 per kWh. While I am not an economist, it is clear to me that market caps or not, RTOs lead to expensive, fragile grids. It’s not about those crazy people in the Lone State. It’s about the RTO structure. //

Texas didn’t have blackouts because it was unique. It had blackouts because its grid was built on the RTO system. The sooner people understand that fact, the sooner we can do something about the growing fragility of our grids.

Current Transformers produce an output in proportion to the current flowing through the primary winding as a result of a constant potential on the primary //

We can see above that since the secondary of the current transformer is connected across the ammeter, which has a very small resistance, the voltage drop across the secondary winding is only 1.0 volts at full primary current.

However, if the ammeter was removed, the secondary winding effectively becomes open-circuited, and thus the transformer acts as a step-up transformer. This due in part to the very large increase in magnetising flux in the secondary core as the the secondary leakage reactance influences the secondary induced voltage because there is no opposing current in the secondary winding to prevent this.

The results is a very high voltage induced in the secondary winding equal to the ratio of: Vp(Ns/Np) being developed across the secondary winding. So for example, assume our current transformer from above is used on a 480 volt to earth three-phase power line. Therefore:

current transformer secondary voltage

This high voltage is because the volts per turns ratio is almost constant in the primary and secondary windings and as Vs = Ns*Vp the values of Ns and Vp are high values, so Vs is extremely high.

For this reason a current transformer should never be left open-circuited or operated with no-load attached when the main primary current is flowing through it just as a voltage transformer should never operate into a short circuit. If the ammeter (or load) is to be removed, a short-circuit should be placed across the secondary terminals first to eliminate the risk of shock.

This high voltage is because when the secondary is open-circuited the iron core of the transformer operates at a high degree of saturation and with nothing to stop it, it produces an abnormally large secondary voltage, and in our simple example above, this was calculated at 76.8kV!. This high secondary voltage could damage the insulation or cause electric shock if the CT’s terminals are accidentally touched.

Current & voltage in power circuits

If the voltage or current in a power circuit are too high to connect measuring instruments or relays directly, coupling is made through transformers. Such measuring transformers are required to produce a scaled down replica of the input quantity to the accuracy expected for the particular measurement.

Regarding the parallel and series connection of CT's:
Secondary of the CT can be considered as CURRENT SOURCE!
Connecting two CT'S in parallel means two current sources outputs connected to the load, which means the result is the algebraic summation of the two secondaries of the CT's i.e:
If CT1 = 300/5 A
CT2 = 300/5 A
Then output result of parallel connection of the two secondaries of the CT's:
CT3 = 300/10 A, which is equivalent to 150/5 A.
NOTE: any two CT's can be connected in parallel even when they are not similar (they have different ratio)
Connecting two CT's in series is possible just in case if the two CT's are similar to avoid any current circulation between the two CT's!
This connection has an advantage to increase the burden of the output of the CT.
If CT1= 300/5, burden 15 VA
CT2= 300/5, burden 15 VA
Then:
CT3= 300/5, burden 30 VA
I hope this can simplified the idea of parallel and series connection of the CT's

What is needed so that the Occupational Safety and Health Administration (OSHA) would consider your people “qualified persons” — that is, people who are exposed to electrical hazards 50V and greater (Photo 1)? This could be electricians, technicians, HVAC technicians, or any other person who works near 50V or more. OSHA doesn’t care about the job title. If your job title is “Chief Bag Carrier” and you work on or near exposed energized electrical conductors or circuit parts, you need to be qualified.

One important distinction to note is that for a qualified person to work on what is considered to be energized circuits or parts, that circuit would have to be both exposed and energized. Therefore, energized equipment that is not exposed would not have the same requirements as equipment that is exposed. It is considered “guarded” (Photo 2) by OSHA and National Fire Protection Association (NFPA) 70E standards and would present no danger — unless you open the door, rack in or out a circuit breaker, or do something else that would expose the energized part inside. //

There are two sources that provide training requirements for qualified persons:

OSHA regulations in 29CFR1910.399, 1910.332,  and 1910.333
NFPA 70E, “Standard for Electrical Safety in the Workplace”

OSHA uses broad, regulatory, non-prescriptive language. In other words, it can be vague if you are not used to using it. NFPA 70E is very prescriptive. The two documents work together to provide a complete picture.

Industrial Power System Grounding Design Handbook is a comprehensive reference and study guide for the design of global industrial and commercial power systems as dictated by optimized neutral-grounding and ground-fault-protection practices. Except for the noted isolated IEEE references, there are no comparable books currently on the market. In fact, the authors actively contributed to the accrual of the relevant IEEE-paper bibliography.

Benefits for the Reader

This book was written with a dual purpose:

1. As a one-stop reference for budding, as well as practicing electrical engineers/consultants interested in, or responsible for, the design of safe and effective electrical installations for industrial plants.
2. As a text book for a graduate course on industrial and commercial power system design in general, and system grounding and ground-fault protection, in particular.

The reader should find the book self-sufficient as it develops in the first 11 chapters the pertinent preparatory engineering and analytical know-how. In Chapter 12, this collective proficiency will be merged into the formulation of guidelines for the ultimate goal of designing the industrial systems with optimized grounding and protection attributes. Chapter 13 offers a focused synopsis of symmetrical components and a sample of its application.

Considering the reported shrinking base of electrical engineering graduates with a well-developed power background suggests that such engineers would benefit from this comprehensive book; not only as a source of reference but also a study guide for on-the-job training.

What Makes This Book Unique?

Industrial Power System Grounding Design Handbook was authored and published by engineers with life-time experiences as industrial and commercial power system design engineers, who accumulated considerable experience practicing, and teaching the subject. The resulting 584-page manuscript features some 360 detailed illustrations and 19 photographs to facilitate explication.

The scope of this book is not limited to "grounding and ground-fault protection", which is covered in just one of the 13 chapters. Instead, the core subject is the development of an engineering aptitude and rationale to design conceptual industrial and commercial power systems from a grounding perspective; a subject not known to be taught in college, or anywhere else the authors know of. This aptitude is developed only through exposure to comprehensive engineering practices. The appearance of mediocre conceptual designs in contemporary professional papers and journals suggest that the book's subject is in urgent need of revelation to would-be authors, reviewers, and instructors alike.

C37.2-2008 - IEEE Standard Electrical Power System Device Function Numbers, Acronyms, and Contact Designations

The definition and application of function numbers and acronyms for devices and functions used in electrical substations and generating plants and in installations of power utilization and conversion apparatus are covered. The purpose and use of the numbers and acronyms is discussed, and 95 numbers and 17 acronyms are assigned. Function numbers or function acronyms for arc fault detection, high impedance fault detection, human machine interface, communications devices, digital fault and sequence of event recorders, power quality recorders, substation time sources and synchrophasor devices are among those that have been added. The use of prefixes and suffixes to provide a more specific definition of a function is defined. Device contact designations are also covered.

Date of Publication: 3 Oct. 2008

Electronic ISBN:978-0-7381-5778-8

During another site visit — with the electric utility present to allow access to their underground cable junction enclosures — numerous readings were conducted to measure the current on both the underground electric utility energized phase conductors and the concentric neutrals. Voltage measurements were also taken from the ground system in the enclosures to a remote ground. In one particular section (right near the lake), the neutral current on the concentric neutral was less than one-tenth of an ampere, whereas the energized phase current was in excess of 6A. Obviously, the remainder of the return current was flowing through the earth and, in this case, the lake water. In addition, the voltage measured from these same junction enclosures was in excess of 7V to a remote ground test point. These measurements were a clear indication that the concentric neutrals on these underground sections were likely absent due to corrosion.

Using an assumed human body resistance of 300 ohms when immersed in fresh water — and assuming a current range through the human body where muscle control is lost in the range of 6mA to 30mA — and applying Ohm's law, the voltage necessary to cause a drowning in fresh water is in the range of 1.8V to 9V, 60 Hz AC. The above testing results show that the necessary voltage and current levels were at a level well within the range to cause the drowning and near-drowning of the victims.

Any fault voltage going to earth will produce a voltage gradient. If you have a true qualified reference point at zero potential, then your voltage readings will increase (or decrease) as you move to or from the energized object as you make your voltage readings. Using this method, you can frequently pinpoint the actual location of the fault. If your voltage readings are consistent over a large area, then the likely culprit is a voltage on the qualified reference ground.

Arcing ground faults are common on 480Y/277V, 3-phase, 4-wire electrical systems. Arcing ground faults can be caused by human error when working around electrical equipment. When this happens, the results can be devastating. Arcing ground faults, arc flashes, and arc blasts produce high temperatures, high pressures, and acoustic and light energy that can severely injure workers. A large portion of NFPA 70E, Standard for Electrical Safety in the Workplace, is devoted to identifying these hazards and protecting workers from arc flash injuries.

Another cause of arcing ground faults is lack of recommended electrical equipment maintenance. These arcing events typically occur when no one is present. Different types of electrical equipment require different maintenance procedures and frequencies based on the manufacturer’s instructions. Additional guidance for electrical equipment maintenance is available from NFPA 70B, Recommended Practice for Electrical Equipment Maintenance and NETA-MTS, Standard for Maintenance Testing Specifications for Electrical Power Equipment and System.

Unfortunately, many building owners and property managers are not aware of these maintenance requirements and continue to operate electrical equipment in a “set-it-and-forget-it” scenario. This photo gallery is a sampling of electrical equipment that was operated this way, resulting in major equipment losses and long business interruptions. If you are not performing the recommended maintenance on your electrical equipment, now is the time to take action and set up a comprehensive electrical equipment maintenance program.

There is no organization or individual that is responsible for making sure that electricity is generated, transmitted and delivered to customers.

Various organizations, often with competing or conflicting interests, have shared responsibility for different parts of the system that includes generators, transformers, switchyards, transmission lines, distribution lines and billing systems, but “the market” has been assigned the responsibility of supplying wholesale electricity.

And that market is not the free market, but instead is a hybrid that is governed by an ever changing stack of layered rules where many of the important decisions are made by participant groups that do not include customers or even enabled representatives of customers.

A growing portion of the grid’s electricity is dependent on free, but uncontrolled natural flows. Another portion comes from generators whose fuel is delivered by capacity-limited pipes in a “just in time fashion.” When the natural flows are interrupted or something interferes in the pipelines’s capability to deliver fuel, generators stop producing power.

There are processes that can be called into action, but costs can skyrocket in times of scarcity. Some market players thrive in times of crisis and have few incentives to ensure those crises never arise.

To the uninitiated, the term “power breaker” would seem to apply to any circuit breaker. To those more familiar, the term focuses on a range of low voltage circuit breakers. Because breaker nomenclature can seem complex, this article reviews the terms that describe commonly used in low-voltage, backup power systems.

Molded Case Circuit Breakers

Some breaker types are named for the manner in which they are constructed. The term molded case circuit breaker identifies a breaker that is assembled as an integral unit within a supportive enclosure of insulating material … typically, a molded plastic case. Within this category, breakers are differentiated by their trip mechanisms. There are two principle types - thermal-magnetic and solid-state. Molded case breakers are tested according to requirements specified in UL 489 - Molded-Case Circuit Breakers, Molded-Case Switches, and Circuit-Breaker Enclosures. Those that test successfully are listed by UL. Notably, breakers are identified as “80%-rated” and “100%-rated” models. Those rated at 100% undergo thermal testing beyond those listed at the 80% threshold. Consequently, 80%-rated molded case breakers are sometimes called “standard breakers”. //

Insulated Case

Sometimes called a “power” breaker, an Insulated Case Circuit Breaker is similar to a molded case breaker, but Is built on a frame inside an “insulated” molded plastic case. They are tested to the same UL489 standard as molded case circuit breakers. Insulated Case Circuit Breakers can be fixed-mounted or draw-out types. Because of their molded case design, they offer limited serviceability.

ANSI-Rated Breakers

The term “power” breaker more often refers to circuit breakers listed to UL 1066 - Standard for Low-Voltage AC and DC Power Circuit Breakers Used in Enclosures, which in turn references additional standards promulgated by the American National Standards Institute (ANSI). Also known as Metal Frame or Air Frame breakers, these are built as an assembly of parts in a welded metal frame, which is mounted on a draw-out mechanism that enables it to slide out of its enclosure for inspection and service. This enables greater serviceability when compared to other types.

Common Power Breaker Design Elements

Insulated case and ANSI-rated Breakers consist of three principle components: (1) Element, (2) Cell, and (3) Trip Unit. These are explained below.

Ram Kaushik from Schneider Electric replied to questions from “Power event analysis in mission critical facilities,” originally broadcast on July 23, 2020.

West African Power Pool Organization is the association of public and private power entities

The West African Power Pool is a specialized agency of ECOWAS. It covers 14 of the 15 countries of the regional economic community ( Benin, Côte d'Ivoire, Burkina Faso, Ghana, Gambia, Guinea, Guinea Bissau, Liberia, Mali, Niger, Nigeria, Senegal, Sierra Leone //

Developing clear and measurable standards to harmonize electricity planning and operation of pooled electric systems in ECOWAS Member states.

Improving cross-border and reliable flows of electricity in ECOWAS Member states.

2015 Electricity law of Liberia. The Senate and House of Representatives of the Republic of Liberia approved in October 2015 a bill entitled 2015 Electricity Law of Liberia. The new electricity law sets the guiding principles for the power sector organization and gives some guidance on the roles of the different entities without too much detail. The Law offers sufficient flexibility for different institutional approaches regarding rural energy. The Master Plan study evaluated different alternatives, all with pros and cons, and proposes the ones with the potential to be more effective.

Power sector structure. Although now-a-days all power sector activities are provided by Liberia Electricity Corporation, the new Electricity Law structures the power sector in the following different activities which all – except system operation - can now be licensed to the private sector:

• Generation;
• Transmission;
• Transmission system operation;
• Distribution;
• Import and export of electricity;
• Trading of electricity.

Micro-utilities. Micro utilities or operations, such as “Community Current” – common business in Liberia where an entrepreneur operates and distributes power from a small diesel generator – can be exempted from licensing.

LEC. LEC is the State owned Utility which by law continues to be the transmission system operator and the national grid company and is entitled to engage in all other activities at its election. As transmission system operator LEC has to guarantee an instantaneous balance at any given time between the total generation and the total consumption of power taking account of the power exchanges with interconnected foreign systems. The role and scope of the “National Grid Company” is not clearly defined in the Law.

Ministry of Lands, Mines and Energy. Ministry is responsible for the formulation and development of national energy policies and the administration of the Law.

Liberia Electricity Regulatory Commission. LERC is the newly created regulatory agency in charge of licensing activities, issuing regulations to implement the electricity law, approving tariff setting methodologies and to establish, monitor and enforce technical, performance and security regulations and standards.

Rural and Renewable Energy Agency. RREA is an autonomous agency owned by the Government of Liberia with the objective of acting for and on behalf of the Government to promote energy access in rural areas with an emphasis on locally available renewable resources.

The Government of Liberia is working closely with development partners to undertake ambitious measures to rebuild its electricity infrastructure. Liberia’s civil war, which ended in 2003, destroyed much of the country’s power sector. At approximately 12%, Liberia has one of the lowest electricity access rates in the world. In the capital city of Monrovia, less than 20% of the population has access to electricity. By 2030, the Government of Liberia aims to meet an anticipated peak demand of 300 MW and serve 1 million customers, connecting 70% of the population in Monrovia and providing access to 35% of the rest of Liberia.

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BackUPS is a power controller for ensuring reliable AC power to critical equipment that is powered with an Uninterruptible Power Supply (UPS). BackUPS constantly monitors the output of the UPS, and automatically bypasses the UPS if its output fails or becomes unstable. BackUPS has two AC inputs: LINE and UPS. Line is plugged directly into a local AC socket;

UPS is connected to the output of the UPS. If BackUPS senses that there is any interruption in the UPS output, it switches to Line, bypassing the UPS entirely. This keeps the load powered-up, and allows the UPS to be disconnected for battery replacement or other maintenance.

BackUPS includes a Delay timer that ensures the UPS output is stable before the UPS is switched online. Whenever the UPS output comes on, the system monitors its output for a preset time period. The UPS will be switched online only if the UPS output is stable