How to Choose Transformers is an important area to consider when you begin the journey toward a transformer investment. How to Choose Transformers begins by determining the transformer’s capacity which is rated in volts-amps (VA). Operational voltage for most appliances and/or equipment should be visibly labeled as follows:
Current (Amps), Frequency (Hz), Voltage (Volts), Wattage (Watts or VA)
This voltage labeling is usually located on the back of the appliance. If labeled voltage cannot be located, it is fine to use the wattage in most cases. If the appliance labeling shows starting amps and running amps, it is best to use the running amps to calculate the wattage (VA).

How to Choose Transformers continues with the result of a basic Voltage x Amps calculation. With the resulting number, you now know How to Choose Transformers--with a VA rating equal to or larger than the VA listed on the appliance. It is always fine to use a transformer with a larger VA listing but using a transformer with a smaller VA rating could lead to overheating and/or burning out the transformer, which is not advisable.
In general, it is more cost effective to use one large transformer for several appliances than to have several transformers for each appliance. However, if you have an appliance that is frequently running (washing machine, freezer, etc.) and the transformer is permanently placed, that transformer should be left attached and dedicated solely to that one appliance.
Harmonics are electric voltages and currents that appear on the electric power system as a result of certain kinds of electric loads. Harmonic frequencies in the power grid are a frequent cause of power quality problems.

Causes
In a normal alternating current power system, the voltage varies sinusoidally at a specific frequency, usually 50 or 60 hertz. When a linear electrical load is connected to the system, it draws a sinusoidal current at the same frequency as the voltage (though usually not in phase with the voltage).
When a non-linear load, such as a rectifier, is connected to the system, it draws a current that is not necessarily sinusoidal. The current waveform can become quite complex, depending on the type of load and its interaction with other components of the system.
Regardless of how complex the current waveform becomes, as described through Fourier series analysis, it is possible to decompose it into a series of simple sinusoids, which start at the fundamental power system frequency and occur at integer multiples of the fundamental frequency (as described in the main harmonic article).AC Power Conditioner
Power quality is simply the interaction of electrical power with electrical equipment. If electrical equipment operates correctly and reliably without being damaged or stressed, we would say that the electrical power is of good quality. On the other hand, if the electrical equipment malfunctions, is unreliable, or is damaged during normal usage, we would suspect that the power quality is poor.

As a general statement, any deviation from normal of a voltage source (either DC or AC) can be classified as a power quality issue. Power quality issues can be very high-speed events such as voltage impulses / transients, high frequency noise, waveshape faults, voltage swells and sags and total power loss. (See Glossary for definitions.) Each type of electrical equipment will be affected differently by power quality issues. By analyzing the electrical power and evaluating the equipment or load, we can determine if a power quality problem exists.

We can verify the power quality by installing a special type of high-speed recording test equipment to monitor the electrical power. This type of test equipment will provide information used in evaluating if the electrical power is of sufficient quality to reliably operate the equipment. The process is similar to a doctor using a heart monitor to record the electrical signals for your heart. Monitoring will provide us with valuable data, however the data needs to be interpreted and applied to the type of equipment being powered. Lets look at two examples of interpreting data for such as a USA location (other countries use different voltages but the same principal applies).



Example No. 1.

A standard 100-watt light bulb requires 120 volts to produce the designed light output (measured in lumens). If the voltage drops to 108 volts (-10%), the light bulb still works but puts out less lumens and is dimmer. If the voltage is removed as during a power outage, the light goes out. Either a low voltage or complete power outage does not damage the light bulb. If however the voltage rises to 130 volts (+10%), the light bulb will produce more lumens than it was intended to, causing overheating and stress to the filament wire. The bulb will fail much sooner than its expected design life; therefore, we could conclude that as far as a standard light bulb is concerned, a power quality issue that shortens bulb life is high voltage. We could also conclude that low voltage or a power outage would cause the lumen output to vary, which effects the intended use of the bulb.

A standard 100-watt light bulb requires 120 volts to produce the designed light output (measured in lumens). If the voltage drops to 108 volts (-10%), the light bulb still works but puts out less lumens and is dimmer. If the voltage is removed as during a power outage, the light goes out. Either a low voltage or complete power outage does not damage the light bulb. If however the voltage rises to 130 volts (+10%), the light bulb will produce more lumens than it was intended to, causing overheating and stress to the filament wire. The bulb will fail much sooner than its expected design life; therefore, we could conclude that as far as a standard light bulb is concerned, a power quality issue that shortens bulb life is high voltage. We could also conclude that low voltage or a power outage would cause the lumen output to vary, which effects the intended use of the bulb.



Example No. 2.

A CRT or monitor for a personal computer uses a 120 volt AC power supply to convert the incoming voltage to specific DC voltages required to run the monitor, these voltages include 5 VDC for logic circuits and high voltage DC to operate the cathode ray tube (CRT). If the incoming voltage drops to 108 volts (-10%), the power supply is designed to draw more current or amps to maintain the proper internal voltages needed to operate the monitor. As a result of the higher current draw, the power supply runs hotter and internal components are stressed more. Although the operator of the monitor does not notice a problem, the long term effect of running on low voltage is reduced reliability and increased failures of the monitor. If the power drops below the operating range of the power supply, the monitor will shut down. If the voltage goes above 132 volts AC (+10%), the power supply will not be able to regulate the internal voltages and internal components will be damaged from high voltage; therefore, we conclude that the power quality requirements for the PC monitor are much higher than for a light bulb. Both high and low voltage can cause premature failures. The economic issues are much greater for the PC monitor in both replacement cost and utilization purposes.

A CRT or monitor for a personal computer uses a 120 volt AC power supply to convert the incoming voltage to specific DC voltages required to run the monitor, these voltages include 5 VDC for logic circuits and high voltage DC to operate the cathode ray tube (CRT). If the incoming voltage drops to 108 volts (-10%), the power supply is designed to draw more current or amps to maintain the proper internal voltages needed to operate the monitor. As a result of the higher current draw, the power supply runs hotter and internal components are stressed more. Although the operator of the monitor does not notice a problem, the long term effect of running on low voltage is reduced reliability and increased failures of the monitor. If the power drops below the operating range of the power supply, the monitor will shut down. If the voltage goes above 132 volts AC (+10%), the power supply will not be able to regulate the internal voltages and internal components will be damaged from high voltage; therefore, we conclude that the power quality requirements for the PC monitor are much higher than for a light bulb. Both high and low voltage can cause premature failures. The economic issues are much greater for the PC monitor in both replacement cost and utilization purposes.

The above examples can be applied to any electrical or electronic systems. It is the task of the power quality consultant to determine if the power, grounding, and infrastructure of a facility is inadequate to operate the technological equipment. Once this assessment is made steps can be taken to remediate the problems. To use the physician example, the diagnosis has to be made before the medicine is prescribed. Many clients are buying power quality medicine without a proper diagnosis. This is both costly and many times ineffective.



Power Quality Events

Power quality issues can be divided into short duration, long duration, and continuous categories. The computer industry has developed a qualification standard to categorize power quality events. The most common standard is the CBEMA curve (Computer Business Equipment Manufacturing Association). Other standards include ANSI and ITIC.

Figure 1 is an example of the CBEMA curve for site. The various power quality events are plotted on the curve based on time and magnitude. Any event outside the curve would be a suspect power problem.


Figure 1
Figure 2 is a table of the power quality data divided into time categories.

Figure 2
By qualifying the events, we can determine what type of power protection equipment is required to protect the technology.

See Glossary for descriptions of power terms.



What can cause power quality problems?

We have found that the majority of power quality problems are related to issues within a facility as opposed to the utility. Based on over 20 years of field experience, we have found that 90% of power quality problems are caused within the site. Typical problems include grounding and bonding problems, code violations and internally generated power disturbances.

Other internal issues include powering different equipment from the same CVCF & VVVF Power Source. Lets take an example of a laser printer and a personal computer. Most of us would not think twice about plugging the laser printer into the same power strip that runs the PC. We are more concerned about the software and communication compatibility than the power capability; however, some laser printers can generate neutral-ground voltage swells and line-neutral voltage sags every minute or so. The long term effect to the PC may be power supply failure. We have to be careful in how technology is installed and wired.

The case studies give examples of how we found and solved power quality problems for our clients. Please go to this section for more information.
For most people, power quality problems are anything related with electric power that interferes with the proper operation of their electrical devices. There are numerous specific types of power quality problems, each with their own causes and effects. Read more about power quality problems.
The causes of poor power quality run the gamut from squirrels or hot summer days to the failure of equipment on the electric utility’s system. Some causes can be corrected or eliminated while many others are out of anyone’s control, at any price.Read more about the causes of poor power quality.
The symptoms of poor power quality can be as subtle as motors that prematurely fail every few years or as obvious as equipment that shuts down or as catastrophic as burned out circuit boards.
Solutions to power quality problems are dictated by

1) the cause of the problem and its effect,

2) to what extent the problem needs to be corrected,

3) most importantly, the financial value of correcting the problem. There is no single solution to any power quality problem, but the first and most critical step is to understand the problem and it’s effects.

Read more about correcting power quality.
Yes and no.
Yes - as long as they, the utility, are the cause of the problem and it is within their capability to fix it. But, electric utilities are only required to provide power within a broad set of limits.
NO - the electric utility can’t and won’t take responsibility for problems that are outside of their control or are acts of nature, God, etc.
The long and short of the matter is that most electric utilities deliver power as they are required to do: nothing more and nothing less. It is very easy to determine if a problem is the fault of utility, which it rarely is. The vast majority of the time, power quality problems arise due to situations and conditions downstream from the electric meter (where the utility's responsibility ends).
MODERN produces a unique line of products to solve a broad range AC voltage problems for commercial and industrial applications. Sizes range from 3 to 2,000 kVA and up to 600 volts. Chronically high, low or fluctuating voltages, deep voltage sags, unbalanced voltages and unbalanced currents are just some of the power quality solutions provided by MODERN. Read more about MODERN products.
Contact us. We will be happy to help you find a solution to your power quality problem. Even if we don’t have a solution within our product line, we will do our best to point you to someone who does.
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