EEP - Electrical Engineering Portal http://electrical-engineering-portal.com Electrical Engineering Portal dedicated to el. engineers Wed, 29 Jul 2015 15:19:32 +0000 en-US hourly 1 http://wordpress.org/?v=4.2.3 7 Energy-Efficiency Improvement Opportunities In Lighting Systemhttp://electrical-engineering-portal.com/7-energy-efficiency-improvement-opportunities-in-lighting-system http://electrical-engineering-portal.com/7-energy-efficiency-improvement-opportunities-in-lighting-system#comments Wed, 29 Jul 2015 04:18:15 +0000 http://electrical-engineering-portal.com/?p=65159 7 Energy-Efficiency Improvement Opportunities In Lighting SystemLighting in industrial facilities There are a lot of opportunities to optimise lighting system in (almost) any industrial facility. Seven practical energy-efficiency opportunities to reduce energy use cost-effectively are given below: Lighting controls Replace T-12 tubes by T-8 tubes Replace mercury lights with metal halide or high pressure sodium lights Replace metal halide (HID) with high-intensity fluorescent […]]]> 7 Energy-Efficiency Improvement Opportunities In Lighting System

Lighting in industrial facilities

There are a lot of opportunities to optimise lighting system in (almost) any industrial facility. Seven practical energy-efficiency opportunities to reduce energy use cost-effectively are given below:

  1. Lighting controls
  2. Replace T-12 tubes by T-8 tubes
  3. Replace mercury lights with metal halide or high pressure sodium lights
  4. Replace metal halide (HID) with high-intensity fluorescent lights
  5. Replace magnetic ballasts with electronic ballasts
  6. Optimization of plant lighting (Lux optimization) in production and non-production departments
  7. Optimum use of natural sunlight

1. Lighting controls

Lights can be shut off during non-working hours by automatic controls, such as occupancy sensors which turn off lights when a space becomes unoccupied. Manual controls can also be used in addition to automatic controls to save additional energy in smaller areas.

The payback period for lighting control systems is generally less than 2 years.

Lighting control panel
Lighting control panel (photo credit: cse-distributors.co.uk)

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2. Replace T-12 tubes by T-8 tubes

In industry, typically T-12 tubes have been used. T-12 refers to the diameter in 1/8 inch increments (T-12 means 12/8 inch or 3.8 cm diameter tubes). The initial output for these lights is high, but energy consumption is also high.

They (T-12) also have extremely poor efficiency, lamp life, lumen depreciation, and color rendering index. Because of this, maintenance and energy costs are high.

Replacing T-12 lamps with T-8 lamps approximately doubles the efficacy of the former, thereby saves electricity.

T8 fluoroscent tube 3d structure
T8 fluoroscent tube 3d structure (image credit: solarengineeringltd.com)

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3. Replace mercury lights with Metal halide or High pressure sodium lights

Where color rendition is critical, metal halide lamps can replace mercury or fluorescent lamps with an energy savings of 50%. Where color rendition is not critical, high pressure sodium lamps offer energy savings of 50 to 60% compared to mercury lamps.

Metal halide lamps applied in industrial and warehouse spaces
Metal halide lamps applied in industrial and warehouse spaces

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4. Replace metal halide (HID) with High-intensity fluorescent lights

Traditional HID lighting can be replaced with high-intensity fluorescent (HIF) lighting. These new systems incorporate high-efficiency fluorescent lamps, electronic ballasts and high-efficacy fixtures that maximize output to the work place.

Advantages to the new system are:

  1. They have lower energy consumption,
  2. Lower lumen depreciation over the lifetime of the lamp,
  3. Better dimming options,
  4. Faster start-up,
  5. Better color rendition,
  6. Higher pupil lumens ratings and less glare.
High-intensity fluorescent systems yield 50% electricity savings over standard HIDs. Dimming controls that are impractical in the HIDs can also save significant amounts of energy. Retrofitted systems cost about $185 per fixture, including installation costs.

In addition to energy savings and better lighting qualities, high-intensity fluorescents can help to reduce maintenance costs.

High intensity fluorescent lighting fixture
High intensity fluorescent lighting fixture (photo credit: gea.com)

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5. Replace magnetic ballasts with electronic ballasts

A ballast is a mechanism that regulates the amount of electricity required to start a lighting fixture and maintain a steady output of light.

Electronic ballasts save 12 – 25% of electricity use compared to magnetic ballast.

Electronic ballasts for fluorescent lamps
Electronic ballasts for fluorescent lamps (photo credit: alibaba.com)

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6. Optimization of plant lighting (Lux optimization)

In production and non-production departments

In many plants the lighting system is not specifically designed for the process. There are lux standards for each type of textile process.

For instance, the required lux for weaving is usually higher than that of wet-processing. Even within just one production process, the required lux varies by the process step.

For example, in a cotton spinning process, the required lux in the blow room should be much lower than that of ring frame section. If the lighting provided is higher than the standard (required lux) for any part of the production, this results in a waste of electricity.

Therefore, the plant engineers should optimize the lighting system based on the standard lux specific for each process step.

Cotton spinning production line of clothing manufacturer in Bangladesh
Cotton spinning production line of clothing manufacturer in Bangladesh (photo credit: knitfab.com)

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7. Optimum use of natural sunlight

Many plants do not use natural sunlight to an optimum level. In addition to optimizing the size of the windows, transparent sheets can be installed at the roof in order to allow more sunlight to penetrate into the production area.

This can reduce the need for lighting during the day.

Let the Sun Shine In! Let's incorporate daylighting strategy in industrial facility
Let the Sun Shine In! Let’s incorporate daylighting strategy in industrial facility (photo credit: greshamsmith.com)

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Reference // Industrial Energy Audit Guidebook: Guidelines for Conducting an Energy Audit in Industrial Facilities – Ali Hasanbeigi, Lynn Price

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13 Basic expressions often used in electrical testinghttp://electrical-engineering-portal.com/13-basic-expressions-often-used-in-electrical-testing http://electrical-engineering-portal.com/13-basic-expressions-often-used-in-electrical-testing#comments Mon, 27 Jul 2015 05:06:37 +0000 http://electrical-engineering-portal.com/?p=65147 13 Basic expressions often used in electrical testingTesting of electrical installations // This is the simple list of basic terms you can often hear when testing and measurements of electrical installation (in general) is being performed. While expirienced electrical engineers will find this list short, I hope beginners will catch the essence and continue exploring this field of electrical engineering. Feel free […]]]> 13 Basic expressions often used in electrical testing

Testing of electrical installations //

This is the simple list of basic terms you can often hear when testing and measurements of electrical installation (in general) is being performed. While expirienced electrical engineers will find this list short, I hope beginners will catch the essence and continue exploring this field of electrical engineering.

Feel free to suggest me an expression (along with description) you think it should be listed, it will be my pleasure to add it to the list and to move away from number 13 :)

Ok, so here is the list:

  1. Active accessible conductive part
  2. Passive accessible conductive part
  3. Electric shock
  4. Earthing electrode
  5. Nominal voltage
  6. Fault voltage
  7. Contact voltage
  8. Limit Contact voltage
  9. Nominal load current
  10. Nominal installation current
  11. Fault current
  12. Leakage current
  13. Short-circuit current

1. Active accessible conductive part

Active accessible conductive part is the conductive part of an electrical installation or appliance such as the housing, part of a housing etc. which can be touched by a human body. Such an accessible part is free of mains voltage except under fault conditions.

Switchboard contruction grounded
Switchboard contruction grounded (photo credit: ecsanyi)

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2. Passive accessible conductive part

Passive accessible conductive part is an accessible conductive part, which is not a part of an electrical installation or appliance, like:

  • Heating system pipes,
  • Water pipes,
  • Metal parts of air condition system,
  • Metal parts of building framework
  • etc.
Equipotential bonding of metal pipes
Equipotential bonding of metal pipes (photo credit: diy.stackexchange.com)

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3. Electric shock

Electric shock is the pathophysic effect of an electric current flowing through a human or animal body. Very dangerous, have eyes on your back while testing.

It’s very important to know what to do if electric shock occurs.

What you need to know about electric shock
Electric shock – Emergency resuscitation procedures (photo credit: uksafetystore.com)

Download poster

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4. Earthing electrode

Earthing electrode is a conductive part, or a group of conductive parts, which are placed into earth and thus assure a good and permanent contact with ground.

Earthing electrode
Earthing electrode

Earthing electrode
Earthing electrode (photo credit: wikipedia.org)

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5. Nominal voltage

Nominal voltage (Un) is the voltage which electrical installations or components of electrical installations, such as appliances, loads etc. are rated at. Some installation characteristics also refer to nominal voltage (e.g. power).

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6. Fault voltage

Fault voltage (Uf) is the voltage that appears between the active accessible conductive parts and the passive ones or ideal ground in the case of a fault on appliances connected to the mains installation (connected appliance).

The figure below represents the Fault voltage (Uf) and division of the voltage into the Contact voltage (Uc) and voltage drop on floor/shoes resistance (Us).

Presentation of the voltages Uf, Uc and Us in case of a fault on an electric load
Figure 1 – Presentation of the voltages Uf, Uc and Us in case of a fault on an electric load

Where:

  • ZB – Impedance of human body
  • RS – Floor and shoes resistance
  • RE – Earth Resistance of active accessible conductive parts
  • If – Fault current
  • Uc – Contact voltage
  • Us – Voltage drop on floor/shoes resistance
  • Uf – Fault voltage
Uf = Uc + Us = If × RE
(floor material is placed to ideal ground)

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7. Contact voltage

Contact voltage (Uc) is the voltage to which a human body is exposed when touching an active accessible conductive part. The body is standing on the floor or is in contact with passive accessible conductive part.

Measuring: Contact voltage is measured between the earthing electrode and two measurement electrodes connected together and placed 1m away from tested earthing electrode.

Voltage apportion across the Earth Resistance - voltage funnel
Voltage apportion across the Earth Resistance – voltage funnel

Where:

  • Uo – Ground potential
  • Uc – Contact voltage
  • Ust – Step voltage
  • RE – Earth resistance

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8. Limit Contact voltage

Limit Contact voltage (UL) is the maximum Contact voltage which may be continuously present under certain external conditions e.g. presence of water.

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9. Nominal load current

Nominal load current (In) is the current that flows through the load under normal operating conditions and at nominal mains voltage.

Nameplate of HP printer (I guess) with nominal values of voltage and current
Nameplate of HP printer (I guess) with nominal values of voltage and current

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10. Nominal installation current

Nominal installation current (In) is the current that the installation draws under normal operating conditions.

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11. Fault current

Fault current (If) is the current that flows to active accessible conductive parts and then to ground in case of a fault on a mains appliance.

Download spreadsheet //

Fault Current Calculation Spreadsheet
Fault Current Calculation Spreadsheet

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12. Leakage current

Leakage current (IL) is the current that usually flows through isolation materials or capacitive elements to ground in normal conditions.

Learn more //

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13. Short-circuit current

Short-circuit current (Isc) is the current that flows in a short circuit between two points of different potential.

Short-circuit current diagram
Short-circuit current diagram

Learn more //

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Reference // Guide To Measurements On Electrical Installations in Theory and Practice (Download guide)

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11 Energy-Efficiency Improvement Opportunities In Compressed Air Systemshttp://electrical-engineering-portal.com/11-energy-efficiency-improvement-opportunities-in-compressed-air-systems http://electrical-engineering-portal.com/11-energy-efficiency-improvement-opportunities-in-compressed-air-systems#comments Fri, 24 Jul 2015 05:18:26 +0000 http://electrical-engineering-portal.com/?p=65122 11 Energy-Efficiency Improvement Opportunities In Compressed Air Systems85% of energy lost as waste heat… Instrumentation consumes large amounts of compressed air at many individual locations in a textile plant, but these uses are susceptible to leakage. Most such leaks are at: Threaded connection points, Rubber hose connections, Valves, Regulators, Seals, and in old pneumatic equipment. Air leaks from knitting operations are very […]]]> 11 Energy-Efficiency Improvement Opportunities In Compressed Air Systems

85% of energy lost as waste heat…

Instrumentation consumes large amounts of compressed air at many individual locations in a textile plant, but these uses are susceptible to leakage. Most such leaks are at:

  • Threaded connection points,
  • Rubber hose connections,
  • Valves,
  • Regulators,
  • Seals, and
  • in old pneumatic equipment.

Air leaks from knitting operations are very common and can be quite large; these exact a large invisible cost, and the reduced pressure may impair the operation of the dyeing and finishing machines. Integrated mills that contain knitting operations should check the compressed air systems in knitting as well as in the dyeing and finishing areas.

More than 85% of the electrical energy input to an air compressor is lost as waste heat, leaving less than 15% of the electrical energy consumed to be converted to pneumatic compressed air energy. This makes compressed air an expensive energy carrier compared to other energy carriers.

Many opportunities exist to reduce energy use of compressed air systems. For optimal savings and performance, it is recommended that a systems approach is used.

An example of compressed air plant diagram (click to expand) //

Compressed air plant diagram
Compressed air plant diagram (photo: creditkgpowersystems.com)

In the following, energy saving opportunities for compressed air systems are presented.

Also, Energy Assessment for Compressed Air Systems (ASME) has published a standard that covers the assessment of compressed air systems that are defined as a group of subsystems of integrated sets of components for consistent, reliable, and efficient use of energy. In this standard the procedure of conducting a detailed energy assessment of the compressed air system as well as the energy efficiency opportunities are described.

  1. Reduction of demand
  2. Maintenance
  3. Monitoring
  4. Reduction of leaks (in pipes and equipment)
  5. Electronic condensate drain traps (ECDTs)
  6. Reduction of the inlet air temperature
  7. Maximizing allowable pressure dew point at air intake
  8. Optimizing the compressor to match its load
  9. Proper pipe sizing
  10. Heat recovery
  11. Installing adjustable speed drives (ASDs)

1. Reduction of demand

Because of the relatively expensive operating costs of compressed air systems, the minimum quantity of compressed air should be used for the shortest possible time, constantly monitored and reweighed against alternatives.

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2. Maintenance

Inadequate maintenance can lower compression efficiency, increase air leakage or pressure variability and lead to increased operating temperatures, poor moisture control and excessive contamination. Better maintenance will reduce these problems and save energy.

Service technician at a compressed air system maintenance
Service technician at a compressed air system maintenance (photo credit: endress.com)

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3. Monitoring

Maintenance can be supported by monitoring using proper instrumentation, including following:

  • Pressure gauges on each receiver or main branch line and differential gauges across dryers, filters, etc.
  • Temperature gauges across the compressor and its cooling system to detect fouling and blockages.
  • Flow meters to measure the quantity of air used.
  • Dew point temperature gauges to monitor the effectiveness of air dryers.
  • kWh meters and hours run meters on the compressor drive.
Air-compressor monitoring system
Air-compressor monitoring system (photo credit: airbestpractices.com)

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4. Reduction of leaks (in pipes and equipment)

Leaks cause an increase in compressor energy and maintenance costs. The most common areas for leaks are:

  • Couplings,
  • Hoses,
  • Tubes,
  • Fittings,
  • Pressure regulators,
  • Open condensate traps and shut-off valves,
  • Pipe joints,
  • Disconnects and
  • Thread sealants.

Quick connect fittings always leak and should be avoided.

In addition to increased energy consumption, leaks can make pneumatic systems/equipment less efficient and adversely affect production, shorten the life of equipment, lead to additional maintenance requirements and increased unscheduled downtime.

A typical plant that has not been well maintained could have a leak rate between 20 to 50% of total compressed air production capacity (Ingersoll Rand 2001). Leak repair and maintenance can sometimes reduce this number to less than 10%. Similar figures are quoted by Cergel et al. (2000). Overall, a 20% reduction of annual energy consumption in compressed air systems is projected for fixing leaks (Radgen and Blaustein, 2001).

A simple way to detect large leaks is to apply soapy water to suspect areas. The best way is to use an ultrasonic acoustic detector, which can recognize the high frequency hissing sounds associated with air leaks.

Air compress system pipework and valve
Air compress system pipework and valve (photo credit: teseouk.co.uk)

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5. Electronic condensate drain traps (ECDTs)

Due to the necessity to remove condensate from the system, continuous bleeding, achieved by forcing a receiver drain valve to open, often becomes the normal operating practice, but is extremely wasteful and costly in terms of air leakage.

Electronic condensate drain traps (ECDTs) offer improved reliability and are very efficient as virtually no air is wasted when the condensate is rejected.

The payback period depends on the amount of leakage reduced, and is determined by the pressure, operating hours, the physical size of the leak and electricity costs.

Air compressor automatic drain valve
Air compressor automatic drain valve (photo credit: paragoncode.com)

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6. Reduction of the inlet air temperature

Reducing the inlet air temperature reduces energy used by the compressor. In many plants, it is possible to reduce this inlet air temperature by taking suction from outside the building. Importing fresh air has paybacks of up to 5 years, depending on the location of the compressor air inlet.

As a rule of thumb, each 3°C reduction will save 1% compressor energy use (CADDET, 1997; Parekh, 2000).

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7. Maximizing allowable pressure dew point at air intake

Choose the dryer that has the maximum allowable pressure dew point, and best efficiency. A rule of thumb is that desiccant dryers consume 7 to 14% and refrigerated dryers consume 1 to 2% of the total energy of the compressor.

Consider using a dryer with a floating dew point. Note that where pneumatic lines are exposed to freezing conditions, refrigerated dryers are not an option.

Left: Desiccant compressed air dryer; Right:  Refrigerated compressed air dryer
Left: Desiccant compressed air dryer; Right: Refrigerated compressed air dryer (photo credit: air-compressor-guide.com)

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8. Optimizing the compressor to match its load

Plant personnel have a tendency to purchase larger equipment than needed (that’s true indeed), driven by safety margins or anticipated additional future capacity. Given the fact that compressors consume more energy during part-load operation, this is something that should be avoided.

Some plants have installed modular systems with several smaller compressors to match compressed air needs in a modular way.

In some cases, the pressure required is so low that the need can be met by a blower instead of a compressor which allows considerable energy savings, since a blower requires only a small fraction of the power needed by a compressor.

Air compressor plant
Air compressor plant (photo credit: usequipmentco.com)

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9. Proper pipe sizing

Pipes must be sized correctly for optimal performance or resized to fit the compressor system. Inadequate pipe sizing can cause pressure losses, increase leaks and increase generating costs. Increasing pipe diameter typically reduces annual compressor energy consumption by 3%.

Compressed air energy savings
Compressed air energy savings (photo credit: blog.iqsdirectory.com)

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10. Heat recovery

As mentioned at the beginning of article, more than 85% of the electrical energy used by an industrial air compressor is converted into heat. A 150 hp compressor can reject as much heat as a 90 kW electric resistance heater or a 422 MJ/hour natural gas heater when operating.

In many cases, a heat recovery unit can recover 50 to 90% of the available thermal energy for space heating, industrial process heating, water heating, makeup air heating, boiler makeup water preheating, industrial drying, industrial cleaning processes, heat pumps, laundries or preheating aspirated air for oil burners.

With large water-cooled compressors, recovery efficiencies of 50 to 60% are typical. When used for space heating, the recovered heat amount to 20% of the energy used in compressed air systems annually.

Paybacks are typically less than one year.

In some cases, compressed air is cooled considerably below its dew point in refrigerated dryers to condense and remove the water vapor in the air. The waste heat from these aftercoolers can be regenerated and used for space heating, feedwater heating or process-related heating.

Atlas Copco 280kW double water cooled electric rotary air compressor
Atlas Copco 280kW double water cooled electric rotary air compressor

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11. Installing adjustable speed drives (ASDs)

When there are strong variations in load and/or ambient temperatures there will be large swings in compressor load and efficiency. In those cases installing an ASD may result in attractive payback periods.

Implementing adjustable speed drives in rotary compressor systems has saved 15% of the annual compressed air system energy consumption.

Air Compressor with Adjustable Speed Drive
Air Compressor with Adjustable Speed Drive (photo credit: e3tnw.org)

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Reference // Industrial Energy Audit Guidebook: Guidelines for Conducting an Energy Audit in Industrial Facilities – Ali Hasanbeigi, Lynn Price

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Essential Basics of Total Harmonic Distortion (THD)http://electrical-engineering-portal.com/essential-basics-of-total-harmonic-distortion-thd http://electrical-engineering-portal.com/essential-basics-of-total-harmonic-distortion-thd#comments Wed, 22 Jul 2015 05:17:19 +0000 http://electrical-engineering-portal.com/?p=65107 Essential Basics of Total Harmonic Distortion (THD)THD definition For a signal y, the total harmonic distortion (THD) is defined by the equation: This definition complies with that of standard IEC 61000-2-2. Note that the resulting value may exceed one. According to the standard, h can generally be limited to 50. This equation produces a single value indicating the distortion of a voltage […]]]> Essential Basics of Total Harmonic Distortion (THD)

THD definition

For a signal y, the total harmonic distortion (THD) is defined by the equation:

Total harmonic distortion (THD)

This definition complies with that of standard IEC 61000-2-2.

Note that the resulting value may exceed one. According to the standard, h can generally be limited to 50. This equation produces a single value indicating the distortion of a voltage or a current flowing at a given point in a distribution system. Harmonic distortion is generally expressed as a percentage.

Definition // THD stands for Total Harmonic Distortion. The level of harmonic distortion is often used to define the degree of harmonic content in an alternating signal.

Current and voltage THD

When dealing with current harmonics, the equation becomes:

THD dealing with current harmonics

The above equation is equivalent to the one below, which is more direct and easier to use when the total rms value is known:

THD - total rms value

When dealing with voltage harmonics, the equation becomes:

THD dealing with voltage harmonics


Total harmonic factor (THF)

In certain countries with different work habits, a different equation is used to determine harmonic distortion. In this equation, the value of the fundamental voltage U1 or the fundamental current I1 is replaced by the rms values Urms and Irms respectively.

To distinguish between the two equations, we will call the second the total harmonic factor (THF). Example of a voltage THF:

Total harmonic factor THF

The total harmonic factor, whether for voltage or current, is always less than 100%. It makes analogue measurements of signals easier but is used less and less because the result is very close to the THD defined above when a signal is not significantly distorted.

What is more, it not well suited to highly distorted signals because it cannot exceed the value of 100%, contrary to the THD defined at the beginning of this technical article.


Importance of Mitigating THD

While there is no national standard dictating THD limits on systems, there are recommended values for acceptable harmonic distortion. IEEE Std 519, “RECOMMENDED PRACTICES AND REQUIREMENTS FOR HARMONIC CONTROL IN ELECTRICAL POWER SYSTEMS” provides suggested harmonic values for power systems:

Computers and allied equipment, such as programmable controllers, frequently require AC sources that have no more than 5% harmonic voltage distortion factor [THD], with the largest single harmonic being no more than 3% of the fundamental voltage.

Higher levels of harmonics result in erratic, sometimes subtle, malfunctions of the equipment that can, in some cases, have serious consequences.

The limits on voltage harmonics are thus set at 5% for THD and 3% for any single harmonic. It is important to note that the suggestions and values given in this standard are purely voluntary.

However, keeping low THD values on a system will further ensure proper operation of equipment and a longer equipment life span.


Harmonics: What are they, why do I care, how do I solve?

Low Voltage drive Senor Application Engineer Jeff Fell discusses what cause harmonics and what kind of problems can they cause? Learn about this important issue and how to solve the problems.

This 36 minute education video will walk you through definitions to solutions.

References //

  • Harmonic detection and filtering – Schneider Electric (Download guide)
  • Total Harmonic Distortion and Effects in Electrical Power Systems – Associated Power Technologies (APT)
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Two Circuit-Breaker Types For Automatic Disconnection Of the Supplyhttp://electrical-engineering-portal.com/two-circuit-breaker-types-for-automatic-disconnection-of-the-supply http://electrical-engineering-portal.com/two-circuit-breaker-types-for-automatic-disconnection-of-the-supply#comments Mon, 20 Jul 2015 05:16:38 +0000 http://electrical-engineering-portal.com/?p=65098 2 Most Common Devices For the Automatic Disconnection Of the SupplyAutomatic disconnection The Standard IEC 60364 prescribes automatic disconnection of the supply for protection against indirect contact. What does it mean // The protective device shall automatically disconnect the supply so that, in the event of a fault between a live part and an exposed-conductive-part or a protective conductor, a prospective touch voltage exceeding 50 […]]]> 2 Most Common Devices For the Automatic Disconnection Of the Supply

Automatic disconnection

The Standard IEC 60364 prescribes automatic disconnection of the supply for protection against indirect contact.

What does it mean //

The protective device shall automatically disconnect the supply so that, in the event of a fault between a live part and an exposed-conductive-part or a protective conductor, a prospective touch voltage exceeding 50 V a.c. (25 V in special environments) does not persist for a time sufficient to cause a risk of harmful physiological effect in a person in contact with simultaneously accessible conductive parts.

This protective measure requires co-ordination between the connection to earth of the system and the characteristics of the protective conductors and devices.

This technical article deals with two most common devices suitable for the automatic disconnection of the supply and able to detect earth fault currents, and these are presented below. Note that there are few other types of devices, but they are not mentioned in this article.

  1. Automatic circuit-breakers with thermomagnetic release
  2. Automatic circuit-breakers with microprocessor-based electronic relay

Hereunder there is a description of such protective devices.


Automatic circuit-breakers //

1. With thermomagnetic release

The protections ensured by the automatic circuit-breakers equipped with thermomagnetic release are:

  • Protection against overloads;
  • Protection against short-circuits;
  • Protection against indirect contacts.
Tmax Molded Case Circuit Breaker, type T1
Tmax Molded Case Circuit Breaker, type T1

The protection against overload is provided by the thermal release with inverse time-delay curve, i.e. the higher the overload current, the faster the tripping time.

The protection against short-circuit is provided through the magnetic release with an indipendent time trip curve, i.e with disconnecting time independent from the short-circuit current.

The protection against indirect contacts can be carried out both by the thermal release as well as by the magnetic release since the earth fault current involves at least one phase; if this current is high enough, it can cause the tripping of the circuit-breaker.

It is necessary that the protective device is coordinated with the distribution system and the earthing modality of the exposed conductive-parts, so that tripping is guaranteed to occur in such times to limit the persistence of the dangerous touch voltages present in the exposed-conductive-parts further to the fault.

Figure 1 shows an example of the earth fault current path in a system with the neutral is directly earthed and the exposed-conductive-parts are connected to the same earthing arrangement of the neutral (TN system) and the trip curve of a thermal magnetic circuit-breaker type Tmax T1C160 R160.

Earth current path
Figure 1 – Earth current path

Trip curve Tmax T1C160 In160
Figure 2 – Trip curve Tmax T1C160 In160

As the diagram shows, by assuming an earth fault current of 940 A, the circuit-breaker shall trip in maximum 5s (value read on the curve with the higher tolerance).

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2. With microprocessor-based electronic relay

The protections provided by the automatic circuit-breakers with electronic relays are completely analogous to those assured by the circuit-breakers with thermomagnetic release.

ABB Tmax Circuit Breaker T2
ABB Tmax Circuit Breaker T2

The protection functions implemented by microprocessor-based electronic relay allow protection against:

  1. Overload (protection L),
  2. Short-circuit (protection S and I) and
  3. Indirect contact to be realized.
Protection against overload (protection L), short-circuit (protection S and I) and indirect contact to be realized
Figure 3 – Protection against overload (protection L), short-circuit (protection S and I) and indirect contact to be realized

Electronic releases allow to get an accurate settings both as regards the trip times as well as the current thresholds so that the installation requirements are fully satisfied. Figure 3 shows the same example as before, but a circuit-breaker type Tmax T2 S160 PR221DS-LS/I In160 with electronic release is installed as protective device.

Earth current path
Figure 4 – Earth current path

Trip curve T2S160 PR221DS-LS/I In160
Figure 5 – Trip curve T2S160 PR221DS-LS/I In160

The possibility of setting a low magnetic threshold (at about 750 A) allows to achieve a trip time corresponding to the magnetic tripping (some tens of milliseconds), which is remarkably quicker than the time obtainable under the same conditions with a thermal magnetic circuit-breaker of the same size.

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Tmax molded case circuit breaker (VIDEO)

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Reference // Distribution systems and protection against indirect contact and earth fault – ABB

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Comparision of Direct-on-line (DOL) and Star-delta Motor Startinghttp://electrical-engineering-portal.com/comparision-of-direct-on-line-dol-and-star-delta-motor-starting http://electrical-engineering-portal.com/comparision-of-direct-on-line-dol-and-star-delta-motor-starting#comments Fri, 17 Jul 2015 04:33:36 +0000 http://electrical-engineering-portal.com/?p=65074 Comparision of Direct-on-line (DOL) and Star-delta Motor StartingMotor starting methods // Direct-on-line (DOL) starting Advantages Drawbacks Star-delta starting Advantages Drawbacks Comparision of DOL and Star-delta starting Direct-on-line starting (DOL) As the name suggests, direct-on-line starting means that the motor is started by connecting it directly to the supply at rated voltage. Direct-on-line starting, (DOL), is suitable for stable supplies and mechanically stiff […]]]> Comparision of Direct-on-line (DOL) and Star-delta Motor Starting

Motor starting methods //


Direct-on-line starting (DOL)

As the name suggests, direct-on-line starting means that the motor is started by connecting it directly to the supply at rated voltage. Direct-on-line starting, (DOL), is suitable for stable supplies and mechanically stiff and well-dimensioned shaft systems – and pumps qualify as examples of such systems.

Line diagram for Direct-on-line motor starting
Line diagram for Direct-on-line motor starting

Where:

  • K1 – Main contactor
  • MV1 – Overload relay

Go back to Methods ↑


Advantages of DOL

DOL starting is the simplest, cheapest and most common starting method. Furthermore it actually gives the lowest temperature rise within the motor during start up of all the starting methods.

It is the obvious choice wherever the supply authority’s current limiting restrictions allow for its use.

Power plants may have varying rules and regulations in different countries. For example: Three-phase motors with locked-rotor currents above 60 A must not use direct-on-line starting in Denmark. In such cases, it will obviously be necessary to select another starting method.

Motors that start and stop frequently often have some kind of control system, which consist of a contactor and overload protection such as a thermal relay.

DOL curve - Synchronous speed / Full-load torque
DOL curve – Synchronous speed / Full-load torque

Go back to Methods ↑


Drawbacks of DOL

Small motors which do not start and stop frequently need only very simple starting equipment, often in the form of a hand-operated motor protection circuit breaker.

Full voltage is switched directly onto the motor terminals. For small motors, the starting torque will be 150% to 300% of the full-load value, while the starting current will be 300% to 800% of the full-load current or even higher.

DOL curve - Synchronous speed / Full-load current
DOL curve – Synchronous speed / Full-load current

Go back to Methods ↑


Star-delta starting

The objective of this starting method, which is used with three-phase induction motors, is to reduce the starting current.

In starting position, current supply to the stator windings is connected in star (Y) for starting. In the running position, current supply is reconnected to the windings in delta (∆) once the motor has gained speed.

Line diagram for star-delta motor starter
Line diagram for star-delta motor starter

Go back to Methods ↑


Advantages of Y-Δ

Normally, low-voltage motors over 3 kW will be dimensioned to run at either 400 V in delta (∆) connection or at 690 V in star (Y) connection. The flexibility provided by this design can also be used to start the motor with a lower voltage. Star-delta connections give a low starting current of only about one third of that found with direct-on-line starting.

Star-delta starters are particularly suited for high inertias, where the load are initiated after full load speed.

Start-delta starter curve - Synchronous speed / Full-load torque
Start-delta starter curve – Synchronous speed / Full-load torque

Go back to Methods ↑


Drawbacks of of Y-Δ

But they also reduce the starting torque to about 33%. The motor is started in Y-connection and accelerated and switched to the star-delta connection. This method can only be used with induction motors that are delta connected to the supply voltage.

If the changeover from star to delta takes place at too low a speed, this can cause a current surge which rises almost as high as the corresponding DOL value. During the even small period of switch over from start to delta connection the motor looses speed very rapidly, which also calls for higher current pulse after connection to delta.

The two illustrations to the right show two features which should be taken into consideration when using star-delta starting. The starter first connects the motor in star (contactor K1 and K3). After a time period – which depends on individual needs – it connects the motor in delta contactor K3 open and contactor K2 close.

Star-delta starter curve – Synchronous speed / Full-load current
Star-delta starter curve – Synchronous speed / Full-load current

Starting torque and current are considerably lower at star-delta starting than at direct-on-line starting: one third of the equivalent DOL value.

Mismatching of motor torque speed curve and load torque speed curve. In the example shown here, the motor would slowly accelerate up to approximately 50 per cent rated speed.

Mismatching of motor torque speed curve and load torque speed curve
Mismatching of motor torque speed curve and load torque speed curve

Go back to Methods ↑


Comparision of DOL and Star-delta starting

The following graphs illustrate currents for a Grundfos CR pump started with a Grundfos MG 7.5 kW motor by means of DOL and star-delta starting, respectively. As you will see, the DOL starting method features a very high locked-rotor current which eventually flattens and becomes constant.

Direct-on-line starting of a Grundfos 7.5 kW motor installed on a Grundfos CR pump
Direct-on-line starting of a Grundfos 7.5 kW motor installed on a Grundfos CR pump

The star-delta starting method features a lower locked-rotor current, but peaks during the starting process as the changeover from star to delta is made.

When starting in star (t = 0.3 s), the current is reduced.

Star-delta starting of a 7.5 kW Grundfos motor installed on a Grundfos CR pump
Star-delta starting of a 7.5 kW Grundfos motor installed on a Grundfos CR pump

However, when switching over from star to delta (at t = 1 .7 s), the current pulse reaches the same level as the locked-rotor current seen with direct-on-line starting. The current pulse can even get higher, because the motor during the switching period is un-powered which means it reduce speed before the full voltage (delta voltage) are supplied.

Go back to Methods ↑

Reference // The Motor Book – Grundfos (Download)

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What can a PLC do? Why do we use them?http://electrical-engineering-portal.com/what-can-a-plc-do-why-do-we-use-them http://electrical-engineering-portal.com/what-can-a-plc-do-why-do-we-use-them#comments Wed, 15 Jul 2015 05:08:09 +0000 http://electrical-engineering-portal.com/?p=65051 What can a PLC do? Why do we use them?The meaning of PLC… “PLC” means “Programmable Logic Controller”, that’s clear. The word “Programmable” differentiates it from the conventional hard-wired relay logic. It can be easily programmed or changed as per the application’s requirement. The PLC also surpassed the hazard of changing the wiring. The PLC as a unit consists of a processor to execute the […]]]> What can a PLC do? Why do we use them?

The meaning of PLC…

PLC” means “Programmable Logic Controller”, that’s clear. The word “Programmable” differentiates it from the conventional hard-wired relay logic. It can be easily programmed or changed as per the application’s requirement. The PLC also surpassed the hazard of changing the wiring.

The PLC as a unit consists of a processor to execute the control action on the field data provided by input and output modules. In a programming device, the PLC control logic is first developed and then transferred to the PLC.

So, what can a PLC actually do?

  1. It can perform relay-switching tasks.
  2. It can conduct counting, calculation and comparison of analog process values.
  3. It offers flexibility to modify the control logic, whenever required, in the shortest time.
  4. It responds to the changes in process parameters within fractions of seconds.
  5. It improves the overall control system reliability.
  6. It is cost effective for controlling complex systems.
  7. It trouble-shoots more simply and more quickly
  8. It can be worked with the help of the HMI (Human-Machine Interface) computer

There are many other things this little ‘mean’ thing can do, but one thing I’m sure – that PLCs are irreplaceable in many industry applications and control projects.

Here is an example of wired ABB’s AC500 programmable logic controllers.

Wired ABB's PLCs
Figure 1 – Wired ABB’s PLCs (photo credit: us.profinet.com)

Basic block diagram

Figure 1 shows the basic block diagram of a common PLC system.

Block diagram of a PLC
Figure 2 – Block diagram of a PLC

As shown in the above figure, the heart of the “PLC” in the center, i.e., the Processor or CPU (Central Processing Unit).

  • The CPU regulates the PLC program, data storage, and data exchange with I//O modules.
  • Input and output modules are the media for data exchange between field devices and CPU. It tells CPU the exact status of field devices and also acts as a tool to control them.
  • A programming device is a computer loaded with programming software, which allows a user to create, transfer and make changes in the PLC software.
  • Memory provides the storage media for the PLC program as well as for different data.

Size of the PLC system

Usually they are classified on the basis of their size:

  • A small system is one with less than 500 analog and digital I/Os.
  • A medium system has I/Os ranging from 500 to 5,000.
  • A system with over 5,000 I/Os are considered large.

Components of the PLC system

CPU or processor: The main processor (Central Processing Unit or CPU) is a microprocessor-based system that executes the control program after reading the status of field inputs and then sends commands to field outputs.

I/O section: I/O modules act as “Real Data Interface” between field and CPU. The PLC knows the real status of field devices, and controls the field devices by means of the relevant I/O cards.

Programming device: A CPU card can be connected with a programming device through a communication link via a programming port on the CPU.

Operating station: An operating station is commonly used to provide an “Operating Window” to the process. It is usually a separate device (generally a PC), loaded with HMI (Human Machine Software).


PLC Configurations

There are two basic configurations that commercial manufacturers offer:

1. Fixed Configuration

Fixed PLC configuration
Fixed PLC configuration

2. Modular Configuration

Modular type PLC 'SLC 500'
Modular type PLC ‘SLC 500′ (photo credit: ab.rockwellautomation.com)

PLC Applications (VIDEOs) //

Real world applications


An Application for Industrial Process Control


PLC Bottling Application


PLC application color mixing


PLC Suited To Bottling Line Application


5 guides to study PLCs //

  1. PLC – Programmable Logic Controller – Hugh Jack
  2. PLC Programming – OMRON
  3. PLC – Theory and Implementation – L.A. Bryan; E.A. Bryan
  4. Industrial Training – SCADA System and PLC – Mr. Sonu Kumar Yadav
  5. Programmable Logic Controllers: Programming Methods and Applications – John R. Hackworth and Frederick D. Hackworth, Jr.

References //

  • Industrial Automation Pocket Book – IDC Technologies
  • Overview of Programmable Overview of Programmable Logic Controllers – Dr. Fernando Rios-Gutierrez
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Differences in size and weight of equipment using copper and aluminium conductorshttp://electrical-engineering-portal.com/differences-in-size-and-weight-of-equipment-using-copper-and-aluminium-conductors http://electrical-engineering-portal.com/differences-in-size-and-weight-of-equipment-using-copper-and-aluminium-conductors#comments Mon, 13 Jul 2015 05:13:04 +0000 http://electrical-engineering-portal.com/?p=65028 Differences in size and weight of equipment using copper and aluminium conductorsCommon misconception It is a common misconception that electrical equipment built using aluminum conductors will always be larger than the same equipment using copper conductors. While the actual conductor within the equipment will be larger with aluminum, many times the enclosure for the equipment is the same size whether copper or aluminum conductors are used. […]]]> Differences in size and weight of equipment using copper and aluminium conductors

Common misconception

It is a common misconception that electrical equipment built using aluminum conductors will always be larger than the same equipment using copper conductors. While the actual conductor within the equipment will be larger with aluminum, many times the enclosure for the equipment is the same size whether copper or aluminum conductors are used.

This is true for switchboards, panelboards and most dry type transformers. Oil filled transformers will generally range from 2-5% larger when constructed with aluminum instead of copper windings.

The biggest size impact for electrical equipment when copper and aluminum conductors are considered is for busway. Since the actual conductor is the primary component within the busway, the size difference will be more apparent.

Busbar system inside low-voltage switchgear
Busbar system inside low-voltage switchgear (photo credit: Edvard Csanyi)

For example, GE busway is 4.5” thick, but the width will vary. For 1000A busway, the aluminum bus will be approximately 22% larger than copper bus and for 4000A busway, the size difference increases to almost 27% larger for the aluminum.

Even though the size for the aluminum bus is larger than for the copper bus, the weight difference is more dramatic and favors the aluminum bus.

Using the same examples used for size and assuming 3 phase, 4 wire busway, the 1000A copper is 50% heavier than the aluminum and for the 4000A busway, this value increases where copper is 73% heavier than the aluminum. This weight differential can be a huge factor for both the designer and the installer.

For example a 4000A, 10 foot section of copper bus is approximately 520 pounds, while the same busway with aluminum conductors is only 300 pounds. Installation by the contractor and mechanical support design by the engineer are considerations when the difference between the two products is considered.

The weight difference between equipment items with aluminum or copper conductors is present with all of the equipment types. For switchboards, the actual percentage will vary significantly with the amount of breakers installed in a section; and with a higher count of breakers, the percentage of weight contributed by the busbars diminishes.

However, if you just consider the weight of the steel enclosure and the busbars, copper bussed switchboard sections will be heavier than aluminum bussed switchboard sections, varying between 20% for 1000A sections to 29% for 4000A sections.

Low-voltage switchgear with copper busbars
Low-voltage switchgear with copper busbars

Dry type transformers like switchboards do not typically have a physical size difference between copper and aluminum units, but they like switchboards, have significant weight differences. These differences will vary from 18% for a 45kVA unit to 22% for a 75kVA unit.

This translates to a copper wound 75kVA transformer weighing 130 pounds more than the corresponding aluminum wound transformer.

When considering the differences between copper and aluminum conductors in electrical equipment, size must be acknowledged, but for most equipment types the size is not a delineating feature. The weight of the equipment is generally not apparent, but can be big difference in terms of labor and material for the installation and support of the equipment.


More about Al/Cu comparison…

Reference // A comarison of aluminium vs. copper as used in electrical equipment – GE, Larry Pryor, Rick Schlobohm and Bill Brownell

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MV Metal-Enclosed Switchgear and Loss of Service Continuity (LSC) Categorieshttp://electrical-engineering-portal.com/mv-metal-enclosed-switchgear-and-loss-of-service-continuity-lsc-categories http://electrical-engineering-portal.com/mv-metal-enclosed-switchgear-and-loss-of-service-continuity-lsc-categories#comments Fri, 10 Jul 2015 04:06:16 +0000 http://electrical-engineering-portal.com/?p=64942 MV Metal-enclosed Switchgear and Loss of Service Continuity (LSC) CategoriesAccessibility and service continuity Some parts of a switchgear may be made accessible for the user, for various reasons from operation to maintenance, and such an access could impair the overall operation of the switchgear then decreasing the availability. The IEC 62271-200 proposes user-oriented definitions and classifications intended to describe how a given switchgear can […]]]> MV Metal-enclosed Switchgear and Loss of Service Continuity (LSC) Categories

Accessibility and service continuity

Some parts of a switchgear may be made accessible for the user, for various reasons from operation to maintenance, and such an access could impair the overall operation of the switchgear then decreasing the availability. The IEC 62271-200 proposes user-oriented definitions and classifications intended to describe how a given switchgear can be accessed, and what will be the consequences on the installation.

The manufacturer shall state which are the parts of the switchgear which can be accessed, if any, and how safety is ensured.

For that matter, compartments have to be defined, and some of them are going to be said accessible.

Three categories of accessible compartments are proposed:

  1. Interlock based access: the interlocking features of the switchboard ensure that the opening is only possible under safe conditions
  2. Procedure based access: the access is secured by means of, for instance, a padlock and the operator shall apply proper procedures to ensure a safe access
  3. Tool based access: if any tool is needed to open a compartment, the operator shall be aware that no provision is made to ensure a safe opening, and that proper procedures shall be applied. This category is restricted to compartments where no normal operation nor maintenance is specified.

LSC Classification

When the accessibility of the various compartments are known, then the consequences of opening a compartment on the operation of the installation can be assessed; it is the idea of Loss of Service Continuity which leads to the LSC classification proposed by the IEC:

“Category defining the possibility to keep other high-voltage compartments and/or functional units energised when opening a accessible high-voltage compartment”.

If no accessible compartment is provided, then the LSC classification does not apply.

Several categories are defined, according to “the extent to which the switchgear and controlgear are intended to remain operational in case access to a high-voltage compartment is provided”:

  • If any other functional unit than the one under intervention has to be switched off, then service is partial only: LSC1
  • If at least one set of busbars can remain live, and all other functional units can stay in service, then service is optimal: LSC2
  • If within a single functional unit, other(s) compartment(s) than the connection compartment is accessible, then suffix A or B can be used with classification LSC2 to distinguish whether the cables shall be dead or not when accessing this other compartment.

But is there a good reason for requesting access to a given function? That’s a key point.


Switchgear Examples (by Schneider Electric)

Example 1 – Ex Areva WI

Areva WI - Medium voltage switchgear
Areva WI – Medium voltage switchgear

Here is a GIS solution with in (D) what is said to be “Base section with cable connection area” (AREVA WI). There is no connection compartment, and the only HV compartments are gas filled.

Then, there is no accessible compartment to be considered for LSC classification. LSC is not relevant in that case, and service continuity during normal operation and maintenance is expected to be total.

Example 2 – CGset

Schneider Electric' CGSet -medium voltage switchgear
Schneider Electric’ CGSet -medium voltage switchgear

Here is a GIS solution (Schneider Electric CGset) with an air insulated connection (and possibly VT) compartment. This compartment is accessible (with tools). The other HV compartments are not accessible. Access to the connection compartment is possible with the busbar(s) live, meaning all other functional units can be kept operating.

The LSC classification applies, and such solution is LSC2.


Example 3 – GMset

Schneider Electric' GMSet -medium voltage switchgear
Schneider Electric’ GMSet -medium voltage switchgear

Here is a GIS solution (Schneider Electric GMset) with an air insulated connection (and possibly VT) compartment. This compartment is accessible and interlocked with the earthing function.

The circuit breaker can be extracted (tool access compartment), even if that is not considered as normal operation nor normal maintenance. Access to one functional unit within a switchboard does not require any other functional unit to be switched off. Such solution is LSC2A.


Example 4 – GenieEvo

Schneider Electric' GenieEvo -medium voltage switchgear
Schneider Electric’ GenieEvo -medium voltage switchgear

A mixed technology (Schneider Electric GenieEvo) with an air insulated connection compartment, and an air insulated main switching device which can be extracted with the busbar live, thanks to the disconnector. Single line diagram is similar to example 2.

If both the connection compartment and the circuit breaker compartment are accessible, and access to any of them means the cables are first switched off and earthed.

Category is LSC2A.

GenieEvo, 11KV MV Metal clad Switchgear
GenieEvo, 11KV MV Metal clad Switchgear (photo credit: srec.ae)

Example 5 – MCset

Schneider Electric's withdrawable air-insulated switchgear MCset
Schneider Electric’s withdrawable air-insulated switchgear MCset

A very classic structure of withdrawable air-insulated switchgear (Schneider Electric MCset), with interlock accessible compartments for the connections (and CTs) and the main switching device.

The withdrawing function provides the independence of the main switching device compartment from the other HV compartments; then, the cables (and of course the busbar) can remain live when accessing the breaker.

The LSC classification applies, and category is LSC2B.


Example 6 – SM6

Schneider Electric's secondary distribution switch-disconnector switchgear SM6
Schneider Electric’s secondary distribution switch-disconnector switchgear SM6

A typical secondary distribution switch-disconnector switchgear, with only one interlock accessible compartment for the connection (Schneider Electric SM6).

When accessing one compartment within the switchboard, all other functional units are kept in service. Category is again LSC2. Similar situation occurs with most of the Ring Main Units solutions.

Example 7 – RM6

Schneider Electric's secondary distribution switch-disconnector switchgear RM6
Schneider Electric’s secondary distribution switch-disconnector switchgear RM6

An unusual functional unit, available in some ranges: the metering unit which provides VTs and CTs on the busbar of an assembly (here a Schneider Electric RM6).

This unit has only one compartment, accessible to possibly change the transformers, or their ratio. When accessing such a compartment, the busbar of the assembly shall be dead, then preventing any service continuity of the assembly.

This functional unit is LSC1.

Ring main unit, type RM6, Schneider Electric
Ring main unit, type RM6, Schneider Electric (photo credit: volt-energo.ru)

Reference // Medium Voltage technical guide – Schneider Electric (Download guide)

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Maintenance of Electrical Equipment In Buildingshttp://electrical-engineering-portal.com/maintenance-of-electrical-equipment-in-buildings http://electrical-engineering-portal.com/maintenance-of-electrical-equipment-in-buildings#comments Wed, 08 Jul 2015 04:11:19 +0000 http://electrical-engineering-portal.com/?p=64871 Maintenance of Electrical Equipment In BuildingsPurpose of Maintenance Apart from safety, maintenance is needed to keep plant in an acceptable condition. Maintenance of this kind must be reviewed on an economic and energy efficiency basis. While it is appreciated that breakdown of plant may result in costly interruption of normal building operation, it must also be borne in mind that […]]]> Maintenance of Electrical Equipment In Buildings

Purpose of Maintenance

Apart from safety, maintenance is needed to keep plant in an acceptable condition. Maintenance of this kind must be reviewed on an economic and energy efficiency basis.

While it is appreciated that breakdown of plant may result in costly interruption of normal building operation, it must also be borne in mind that stopping plant for maintenance can also cause a loss in production.

Equipment on continuous and arduous duty, e.g. switchboards, motor control centres (MCCs), air-handling units, chiller plant etc., require more attention than that which is lightly loaded and rarely used.


Initial Steps For Economic and Energy Efficiency

Apart from the above considerations there will be the question of whether to repair or replace faulty equipment. This requires analysis of the past and future maintenance costs and the benefits of new equipment.

There has been much operational research carried out into such things as the probability of breakdown, replacement and repair limits, and overhaul policies. This obviously requires considerable effort and expertise and may need the services of a specialist consultant.

However, some simple initial steps can be taken as far as the economic and energy efficiency is concerned for maintenance of electrical equipment in buildings.


1. Standardisation of Equipment

The use as far as possible of standard items such as switchgear will help both in buying, stockholding and replacement of components on the most economic and convenient basis.

Motor control center at the BCI plant
Motor control center at the BCI plant (photo credit: hotmixmag.com)

2. Establishment of Records on Breakdown

Initially this may be on a simple log book or card system. This information should give some idea of which plant requires attention and at what intervals. It may also lead to improvements to the plant itself which will reduce the frequency of future failures.


3. Frequency of Maintenance

This requires careful organisation to ensure that it fits in with operational requirements. All planned maintenance should therefore have been agreed with the relevant operation manager prior to implementation.


4. Economic of Routine Maintenance

It may not be economic or practical to include some equipment in a scheduled routine although safety inspections will still need to be carried out.

Routine maintenance of transformer
Routine maintenance of transformer (photo credit: leonhard-weiss.de)

Examples of low priority maintenance are equipment that is not subject to breakdown, e.g. electric heater, and equipment that would cause little or no interference with operational routine and could be repair or replaced at any time.

In some cases it may be found that as little as 25% of the plant needs to be maintained on a scheduled routine throughout the year. While the setting up of a successful maintenance operation is not an easy task, the economic advantages can be considerable.

5. Upgrading to More Efficient Plant

Energy saving can be achieved by changing the type of equipment in use, for example:

  1. Replacement of less efficient lamps with more energy efficient lamps.
  2. Replacing electro-mechanical control devices to electronic systems.
  3. Installing new high efficiency motors to replace old motors particularly where extended duty operations prevail.
  4. Retrofitting VSDs for flow control of fans or pumps.

The economics of changing inefficient existing systems, which are continuing to provide a satisfactory operational performance, obviously requires careful consideration. Not only the costs of new equipment need to be understood, but also equipment life can have a significant impact on the overall financial viability of any proposed changes.

Electrical Preventive Maintenance of Air Circuit Breakers
Electrical Preventive Maintenance of Air Circuit Breakers

Emergency Maintenance

The emergency maintenance can hardly be regarded as maintenance in the sense that, in many cases, it consists of an urgent repair to, or replacement of, electrical equipment that has ceased to function effectively.

Obviously, it is better to follow a rigorous ‘Planned Maintenance Programme’ for all essential electrical power distribution installations and equipment in buildings to reduce the frequency of emergency maintenance tasks.

Planned Maintenance

In the use of electrical plant and equipment there are obviously sources of danger recognised in the Electricity (Wiring) Regulations.

These regulations are mandatory and serve to ensure that all electrical plants and equipment areadequately maintained and tested to prevent any dangerous situation arising that could harm the users of such equipment or the building occupants.

Low voltage switchgear maintenance
Low voltage switchgear maintenance (photo credit: elcome.com)

Normally, maintenance carried out solely for safety reasons will be covered by standard procedures, which in some instances will have to fulfil the relevant Code of Practice for the Electricity (Wiring) Regulations.

Planned maintenance can be carried out on the basis of the operation of the piece of electrical equipment itself. For example, it is worth considering whether all electric motors should be periodically cleaned and inspected, making sure that dirt and dust has not interfered with the self cooling of the motor and that there is no oil leakage into the motor’ s windings.

Bearing should also be checked for wear and tear to prevent contact between the rotor and stator. Maintenance can also be based on the complete item of plant, or auxiliary plant, such as the central air conditioning plant of a tall building.

Reference // Guidelines on Energy Efficiency of Electrical Installations – Electrical and Mechanical Services Department – The Government of the Hong KongSpecial Administrative Region

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