WATTS NEW

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Power Measurement In AC Circuits

Posted on May 16, 2012 by via Edvard

GE Watthour MeterPower measurement in AC circuits can be quite a bit more complex than with DC circuits for the simple reason that phase shift complicates the matter beyond multiplying voltage by current figures obtained with meters.What is needed is an instrument able to determine the product (multiplication) of instantaneous voltage and current. Fortunately, the common electrodynamometer movement with its stationary and moving coil does a fine job of this.Three phase power measurement can be accomplished using two dynamometer movements with a common shaft linking the two moving coils together so that a single pointer registers power on a meter movement scale. This, obviously, makes for a rather expensive and complex movement mechanism, but it is a workable solution.An ingenious method of deriving an electronic power meter (one that generates an electric signal representing power in the system rather than merely move a pointer) is based on the Hall effect.

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Why You Need an Uninterruptible Power Supply

Posted on May 16, 2012 by dave manney

Many people would agree that a power loss in their home is an inconvenience. But for businesses, a power loss can be disastrous; it leads to downtime where a business is losing potential income every second their electrical equipment is not running. While many businesses would wait for the power to come back on, this is hardly ideal and can easily be remedied. All is needed to solve this problem is an Uninterruptible Power Supply.

An Uninterruptible Power Supply , commonly referred to as a UPS, is a power protection system designed to provide clean, stable power to critical application equipment throughout mains power disturbances and power failures.

Common Problems with Electricity

Blackouts: Blackouts are caused by the collapse of the main power supply resulting in a devastating effect on all connected equipment.
Spikes: Spikes are caused by short, but rapid, voltage changes resulting in hardware damage and/or software corruption.
Noise: Noise is disturbances caused by various conditions resulting in computers “freezing” and premature electrical components failure.
Sag: Sag is caused by a drop in the main power supply often triggered by turning on a large load, and is quite common for businesses resulting in an unnecessary computer systems reboot.
Surge: Surge is caused by a large load being turned off or a load being swapped at substation leading to corrupted files or computer system failures.
Brownouts: Brownouts are caused when the mains supply is unable to deal with the load demand resulting in a voltage drop. Similar to a Sag – computer systems reboot unnecessarily, although this can last for a longer period of time.

All it takes is a small blackout, surge, spike, or any other fluctuation in the voltage for your equipment to be permanently damaged, your operating system files corrupted, and your data lost – all this can happen in the blink of an eye.

Types of UPS Systems

Typically, businesses can choose from three types of USPs, which are as follows:

1. Standby UPS

A Standby UPS is the least expensive and simplest Uninterruptible Power Supply. This type of UPS obtains its primary power from the AC line and switches to the backup battery when any drop in voltage is detected – this is done automatically. The moment the power is restored, the UPS then switches back.

Being the simplest and cheapest option, standby UPS is considered to be a “no frills” approach as there is nothing to regulate the electricity through, although some manufacturers include some sort of line filter.

A “ferroresonant standby” can also be purchased for those looking for an improvement upon the design of the typical standby UPS. A ferroresonant UPS transformer is used in order to switch from line power to battery power. A source of stored energy is used while the unit switches between the battery power and line power.

2. Line-Interactive UPS

Many businesses consider a Line-Interactive UPS to be the most efficient type of uninterrupted power supply; and is therefore, the most popular type of UPS used by businesses. The moment the input power fails, the AC input is disconnected by the transfer switch, and the bi-directional charger is then able to provide output power. This ensures that a faster response time than a standby UPS is obtained when a power failure transpires.

3. Online UPS

An Online UPS is considered to be the best option, but it is also the most expensive option. Unlike other types of UPS, the battery is used as the main source of power and the line power as the secondary source of power.

The moment the line power goes out, an Online UPS just stops charging the battery, rather than converting from one power source to another. It works in a similar way to a laptop when it is disconnected from the charger; the battery will continue to power the system until the stored power is depleted.

The benefits of using an UPS are as follows:

Minimization of direct sales revenue losses
Peace of mind that in a power failure, backup power is available
Protection against the risk of permanent data loss
Avoidance of the excessive costs for replacing/repairing systems affected by power supply issues
Reduction in staff inactivity
The life of expensive electrical hardware can be prolonged

Companies, such as Liebert, provide many solutions and answers you may have regarding your specific UPS need. For more information regarding an uninterruptible power supply, contact L&S Electric today!

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Transformer Repair

Posted on May 16, 2012 by dave manney

The need for transformer repair

Transformers are normally varied in sizes and they are the heart of all the power systems. Due to the fact that they are critical and very expensive, they play a very important role in the delivery of power in the network system as a whole. If the transformers are subjected to some adverse conditions, than damages may occur. Therefore, transformer maintenance and their proper installation is very critical in extending the life of the transformer. Getting skilled and experienced technicians to do this may be of good help and service.

Before looking at the need for transformer repair service, it is important to first of all look at the economic impacts of a transformer failure. There are two major types and they include the direct economic impact of replacing the transformer and the indirect economic impact because of the production loss. The operating conditions of the transformer like overloads often lead to the failures. Abnormal operating conditions also play a major role in its operations. Adequate protection is therefore imperative in the qualitative life of a transformer.

Any machine that is man-made is prone to wear and tear. It is for this reason that having a qualified repair person on your speed dial in case anything occurs. We cannot prevent transformer damages and wear because some of the situations are unavoidable. The important thing that should be noted is getting a qualified repair person.

There are many requirements for transformer repair. Some are:

To increase the efficiency of the transformer . Transformers need to be repaired so to increase their efficiency. If ignored, the transformers may develop further complications and lead to total breakdown. Some of the repair areas that help in increasing the efficiency of the transformers include the AC and DC motors, the gearboxes and blowers, wound rotor and submersible motors.
Another requirement for transformer repair is in regards to in saving of time and money . An effective preventive transformer maintenance and repair program involves the scheduling of routine inspections and checkups done on a regular basis. Even the small problems can be very severe if they are left untouched. This leads to the harsh damages that results in expenses that could have been avoided if they were repaired in time. Big gadgets like transformers can be a dangerous hazard if proper repair is not done. It can lead to fires and deaths if care is not taken.

Repairs done on transformers lead to a safer environment . Not only will preventive transformer maintenance save time and money, but it enhances a safer environment. The risk of any hazard is efficiently reduced and the vicinity of the transformer remains safe.

Transformers need repair now and then in order to keep them working properly. A transformer that does not work properly is not very safe. If an industry depends on it as a source of power transmission, then losses can be incurred. Transformer repair is very important so as to keep everything in an industry running very well.

Some causes of transformer failure include the following:

Terminal failures these are as a result of open leads, loose connections and short circuits.
Winding failures that result from short circuits.
Core faults, external faults and abnormal operating conditions.

L&S Electric provides thorough repair services for almost all types of transformers. For more information, please contact us.

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Posted in Power Services, Transformer Services | Tagged Electricity distribution, Transformer types | 1 Comment

Tip: Root Cause Analysis – keep an ear out

Posted on May 16, 2012 by dave manney

Here’s a tip from Reliability Web:

When it comes to looking for failures during a Reliability Study or for causes during a Root Cause Analysis investigation, ‘Listen to your operators’.

They are the eyes and ears of your production facility. It doesn’t matter if you are running a chocolate factory, bottling beer, or drilling for oil, they all have one thing in common – operators on the front line.

These valuable members of your team are often the first to notice problems occurring; these problems may only stop the machine once a shift for a few minutes while they go and hit the reset button. These ‘high frequency short duration’ issues often get reported but are not seen or considered as critical because we have not yet witnessed a major stoppage. After all, we hit the reset button and the machine starts again.

A few things start to naturally happen at this stage.

• Operators stop reporting faults because nobody does anything about them
• Operators start to change the operating practice of the machine to allow for these issues during their shift. This then becomes normal operating practice, without any form of risk assessment having been performed. These changes are usually only identified following a major incident investigation. When it is often too late.

Reliability is like Safety – Ignore the little things and before long it could be something major.

Typical comments used by operators during Reliability Studies and RCA investigations are:

• ‘We’ve been doing it that way for years’
• ‘We kept reporting it to management’
• ‘I used to do that task but we removed it from our check list because we never found anything’

Great examples exist like the operator who used to carry out torque checks on a rotating piece of equipment at the end of shift, only to be told it was no longer required. Two years later the Reliability investigation into downtime on the machine revealed ‘sheared bolts’ as the number one failure mode on the machine. We re-introduce the torque checks and the problem disappears.

Or the Root Cause Analysis performed on a ‘light curtain trip’ that stopped the machine once a shift for five minutes. The downtime lost on this ‘insignificant’ problem was quantified to be worth over $1 million in losses to the business. The solution identified during the Root Cause Analysis equalled $34,000! The problem solved.

So during Reliability Studies and Root Cause Analysis, listen to your plant engineers, equipment specialists and OEMs, but, whatever you do, don’t forget to ‘Listen to your operators’.

Tip Provided by: Gary Tyne, Apollo RCA Trainer, ARMS Reliability

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Posted in Root Cause Analysis | Tagged Reliability engineering, Root Cause Analysis | 1 Comment

Finding Rebates & Incentives for VFDs

Posted on May 15, 2012 by dave manney

One of the greatest benefits variable frequency drives (VFDs) offer is the ability to save you money by running your equipment in a most efficient manner. There are, however, additional benefits, such as receiving incentives or rebates from federal, state, and local agencies.

In an article* entitled, “No hot air about VFDs,” Kay Dekker, from Yaskawa Electric America, writes about locating and applying for those incentives.

To briefly review, VFDs are electronic controls that manage three-phase AC electric motor speed. By regulating speed, a VFD assures that a motor dissipates only the amount of energy needed to handle the instantaneous load. The alternative to VFDs in most AC motor applications is a single-speed motor consuming its fully rated nameplate power regardless of what the application needs. Throttling is often handled with clutching or braking.

For example, many commercial and industrial building HVAC systems use single-speed AC motors to run fans. The fan air is controlled by an inlet vane or an outlet damper. A better alternative is to replace the vane or damper with a VFD that continuously regulates motor speed.

All three approaches consume about the same amount of energy at 100% air flow. But at reduced air needs, the VFD approach uses much less energy. When an HVAC system demands 50% of air flow, tests have shown that a VFD uses 21% of unrestricted full-flow energy. At the same 50% flow, inlet vane control would use 65% of full-flow energy and outlet damper control would consume 87% of full-flow energy.

Differences are even more pronounced at low air flows. At 20% of air flow, a VFD design only consumes 5% of full-flow energy. By contrast, an inlet vane system would use 51% and an outlet damper would use 64% of full-flow energy. A calculation engine that generates energy savings at various levels of flow can be found here.

Besides saving energy, Dekker writes, VFD control reduces maintenance costs and extends operating life by letting a motor run at less than its fully-rated speed when possible. VFDs also allow more precise control of air flow, which helps to increase the comfort level in a building.

The Yaskawa A1000 VFD Family

Buildings account for more than a third of U.S. energy use, so they are an important target for energy efficiency improvements. Research by the American Society of Heating, Refrigeration and Air-Conditioning Engineers shows that approximately 50% on all energy used in a typical building goes into HVAC operation. Using VFDs to reduce HVAC energy consumption can thus result in significant energy savings, and the payback on investment can be substantial.

Even without rebates, payback periods for installing VFDs are usually less than three years and sometimes can be less than a year. Rebate programs can reduce payback periods to a matter of months. The Database of State Incentives for Renewables & Efficiency is one resource that offers comprehensive information on federal, state, local and utility incentives that promote renewable energy and energy efficiency.

States often lead the way in adopting progressive policies promoting energy efficiency. Many states offer incentives for energy efficiency upgrades that include a direct rebate payment due upon installation. The federal government also offers tax deductions or credits for attaining defined levels of efficiency or for supporting specific energy-saving technologies, and many states do as well.

Rebate levels vary widely within the U.S., but the American Council for an Energy Efficient Economy (ACEEE) estimates that rebates usually cover from 15 to 35% of installed cost. However, the ACEEE warns that utility and government-funded rebates are not guaranteed. Such rebates often depend on funding accessibility and are often doled out based on a competitive ranking system. Because of the energy market’s volatility, the ACEEE suggests applying for rebates in the planning stages of construction or upgrades, but to keep potential rebates out of the installation budget.

Although each utility can have its own variations, rebate programs generally contain similar standard features. For example, Austin Energy offers rebates of 20% for qualified VFD use in HVAC applications. These levels are typical of those available from other utilities.

*Article published with permission.

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Posted in A1000, Variable Frequency Drives, Yaskawa | 1 Comment

Bearing Lubrication

Posted on May 14, 2012 by dave manney

Bearing lubrication is the act of applying a lubricant on the surface between the rolling bearings parts ant the metal surface. Lubrication seeks to reduce direct contact between the rolling and the sliding surfaces. When applied, the lubricant separates the two surfaces, reducing friction.

In some cases, the sliding surfaces are not totally separated by the lubricant; as a result, there are some small cases of wear and tear between the metal surfaces. Friction between the metallic parts generates high temperature thus causing tribal chemical reactions. As a result, a tribochemical layer forms that acts as a lubricant hence are reducing friction.

Lubrication condition dictates friction wear and tear. The following are the main lubrication conditions.

1. Full fluid film lubrication

This is a lubrication condition where the lubricating surface continually separates the lubricating fluid. Fluid lubrication is the other name of full fluid film lubrication. The friction experienced is normally between the fluids.

2. Mixed lubrication

Sometimes the lubrication fluid layer may become too thin. As a result metal, to metal contact occurs hence causing mixed friction.

3. Boundary lubrication

Boundary lubrication occurs when the lubricating materials contains additives that enhances lubrication. Due to friction the temperature of the lubricating service increases.as a result, lubricating additives in the lubricants causes some chemical reaction. After the chemical reaction a chemical lubrication layer is formed that prevents friction. Prevention of friction due to the chemical layer is the one referred to as boundary lubrication

All types of lubrication occurs when using both oil and grease lubricants. The strength of a lubricating material depends on the viscosity of the lubricating fluid.

Inadequate bearing lubrication

Proper bearing lubrication is essential. The following are the main symptoms of poor bearing lubrication and the resultant side effects.

1. Noise

Noise is one of the major symptoms of inadequate lubrication. Noise can be caused by three things namely starved lubrication, contamination of the lubricant and unsuitable lubricants. Starved lubrication results to one on one contact between metal services which causes the wear. The viscosity of the lubricating material determines the suitability of the lubricating material. Use of an unsuitable lubricating fluid will result to a thinner layer of the lubricant. Local metal contact formed will result to noise production. The last cause of noise is contamination contained in the lubricant. Dirt particles and other impurities in the lubricant disrupt the lubricating film and hence producing noise.

2. Cage wear

Cage wear is another symptom of inadequate lubrication. Cage wear result from starved lubrication and poor choice of lubricating materials which result to local metal contact.

3. Wear on rolling elements, raceways and lip surfaces

The other symptom of poor lubrication is wear, on the rolling services. Similarly to the other symptoms, starved lubrication, unsuitable lubricants use and impurities in contained in the lubricants are the major causes. Starved lubrication causes chemical corrosion due to oscillating relative motion and slip marks. Unsuitable lubricants may not contain the anti-wear also known as the EP additives hence causing wear on the rolling parts. Contamination in the lubricants may contain solid hard particles which are corrosive.

4. Fatigue

Poor bearing lubrication will cause fatigue. Starved lubrication result to a thinner lubricating fluid layer hence causing direct contact between the lubricating fluids, as a result, fatigue will obviously occur. Unsuitable lubricants may also contain may contain substances whose viscosity increases slightly under pressure, as a result the bearing will experience some fatigue.

5. High temperature and discoloring bearing parts.

Due to friction, the temperature of the system increases causing some of the colored substances to melt. Bearing discoloring occurs. High temperature results from starved lubrication and use of unsuitable lubricants.

6. Damaged lubricant

Another symptom of poor lubrication is damaged lubricant. The lubricants may solidify, discolor or lose the lubricating ability. This result from starved lubrication and the use of unsuitable lubricant. Other possible cause of this includes excessive operating time of the system.

Importance of proper lubrication

1. Saves cost

Lubrication saves the costs of replacing bearing balls and installing new equipment. This is because, the use a lubricant, eliminates friction hence reducing the wear on rolling surfaces.as A result the surfaces life spun increases hence reducing the cost of replacing them. Apart from the cost of buying new equipment’s, lubrication also saves the maintenance costs.

2. Efficiency

Lubrication improves the efficiency of a bearing. When one uses suitable lubricants, friction between the rolling parts is minimized this in turn eliminates fatigue. A fatigue free machine provides maximum performance and works according to the required standards.

3. Saves time

Non lubricated bearings are slow in their operation. When using a lubricated bearing, the bearing moves faster provide the needed services at a higher speed hence having a positive impact on the productivity. Also, bearing lubrication saves time spent repairing the rolling parts in a system.

4. Reduces noise pollution

One of the most irritating things about friction is the noise produced. Noise has a negative implication on the working environment and may influence other workers performance. When done, bearing lubrication reduces one to one metal contact hence reducing the noise produced.

5. Reduces wear and discoloring

Lubrication reduces wear of the rolling material and also reduces discoloring of the operation surfaces.

6. Increases the life of the bearings

As a result of reduced wear and tear, the life of a bearing increases with a considerable margin

Over-lubrication

Over-lubrication is one of the main culprits behind electric motor failure.it Occurs when due to excessive use of a lubricant on rolling surfaces. Over-lubrication result to pressure building .pressure causes temperature increase which can result to bearing failure. Also over lubrication can result to lubricant spill which result to the lubricant going to unexpected areas.As a result the oil spill may cause damage to sensitive parts and result to system breakdown. So when doing bearing lubrication, it is advisable to avoid over lubrication.

Conclusion

Bearing lubrication is essential mechanical maintenance activity. Bearing lubrication should be carried out by expert in the field to maintain high standards. The above article enlightens about bearing lubrication and symptoms of ineffective lubrication.

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Sizing of power cables for circuit breaker controlled feeders (part 2)

Posted on May 13, 2012 by via Edvard

Sizing of power cables for circuit breaker controlled feeders (part 2) Continued from article Sizing of power cables for circuit breaker controlled feeders (part 1) 2. Criteria-2 Continuous current capacity (Ampacity)This criterion is applied so that cross section of the cable can carry the required load current continuously at the designed ambient temperature and laying condition. Ampacity is defined as the current in amperes a conductor can carry continuously under the conditions of surrounding medium in which the cables are installed. An ampacity study is the calculation of the temperature rise of the conductor in a cable system under steady-state conditions.Cable ampacity, if required to be calculated than it is calculated as per the following equation givenin IEEE -399, section 13.This equation is based on Neher-McGrath method where,Tc’ – allowable conductor temperature (ºC)Ta’ – ambient temperature (either soil or air) (ºC)∆Td – temperature rise of conductor due to dielectric heating (ºC)∆Tint – temperature rise of the conductor due to interference heating from adjacent cables (ºC)Rac – electrical ac resistance of conductor including skin effect, proximity and temperature effects (µ_/ft)R’ca – effective total thermal resistance of path between conductor and surrounding ambient to include the effects of load factor, shield/sheath losses, metallic conduit losses, effects of multiple conductors in the same duct etc (thermal- Ωft, ºC-cm/W).

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Question from the Field: Maintenance Ready Backlog

Posted on May 12, 2012 by via Reliability Now

So what is maintenance ready backlog,

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Sizing of power cables for circuit breaker controlled feeders (part 1)

Posted on May 12, 2012 by via Edvard

Low voltage switchboard with circuit breakers (incomers, feeders) The following three criteria apply for the sizing of cables for circuit breaker controlled feeders:I. Short circuit current withstand capacityThis criteria is applied to determine the minimum cross section area of the cable, so that cable can withstand the short circuit current.Failure to check the conductor size for short-circuit heating could result in permanent damage to the cable insulation and could also result into fire. In addition to the thermal stresses, the cable may also be subjected to significant mechanical stresses.II. Continuous current carrying capacityThis criteria is applied so that cross section of the cable can carry the required load current continuously at the designed ambient temperature and laying condition.

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