Automatic voltage regulators

Electrical faults

ELECTRICAL FAULTS: A RANGE OF SOLUTIONS

Electric power supply: a mysterious element with many variables
It is useful to know the more common electrical faults (such as voltage variations, voltage spikes, high frequency interferences, blackouts, harmonic distortions) so as to apply the most adequate protections and avoid productivity drops. Electrical and electronic equipment are designed to properly operate from a clean and constant supply of AC voltage. High deviation from the nominal value or continual voltage fluctuations cause overheating, halts in production, machining defects, loss of data memory and programs, failures and so forth. The electricity board generates high quality electrical energy at its power stations, but cannot prevent it degrading along the distribution lines, which are subject to continual load variation and all kinds of interference. For such reasons, voltage stabilisation and protection against electrical faults are needed. To protect sensitive equipment from electrical faults, several devices are available (line conditioners, automatic voltage regulators, spike suppressors, UPS, etc.) which, depending on their characteristics, complexity and cost ensure different levels of efficacy. The choice should be made by assessing the degree of protection required, the entity of the failures and the direct and indirect costs these may cause. In fact, an overall solution may call for an expenditure that is out of proportion to the value or the function of the equipment requiring a protection, whereas a more economical solution may not be reliable. It is therefore necessary to assess the characteristics of the protection, with the help of experts, or turn to a reputable company that can offer adequate technical support.

COMMON ELECTRICAL FAULTS

Voltage variations
Since they are subject to continual load variations, distribution lines are unable to supply perfectly even voltage levels. This is why electrical machinery is built to accept shifts of at least ±5% as to the nominal value. In fact, in their contracts the electricity boards provide for fluctuations of up to ±10%. Furthermore, this limit is often exceeded due to “slow variations” (voltage drops caused by underdimensioned lines and/or overloads), “overvoltages” (considerable increases in the line value arising when industries drastically cut down their energy consumption), “fast variations” (drops caused by the connection of equipment such as: discharge lamps, punching machines, electric motors etc.).

Voltage spikes

These are very brief pulse disturbances very dangerous for more sensitive equipment because the voltage values may reach thousands of volts. They are caused, not only by the switching of high voltage lines, connection of power factor correction capacitors, lightening, and the cutting off of loads with high reactive powers, but also by limited power loads such as photocopiers and air conditioners connected to the same line that feeds the sensitive equipment. Spikes are not detectable by means of an ordinary voltmeter given their brief duration; however they are one of the main causes of faults and malfunctions.

High frequency disturbances

They are very common and easily detected by anyone who watches television. These are the cause of the “snowstorm” effect and those fastidious lines that sometimes appear on the screen. They are caused by the sparks generated in the AC commutator motors, the “crown effect” on the high voltage lines, the igniters of luminous signs and burners, and the magnetic fields emitted by radio and television stations. Line disturbances, also known as HF noise do not usually create problems on electromechanical equipment, but often cause damage on electronic equipment.

Blackout

This is the most obvious event (though less frequent) because everybody notes it. It may happen accidentally on production plants or on distribution lines, or may be programmed to redu-ce energy consumption. There are also microinterruptions, which may last between microseconds and a few tenths of milliseconds, caused by short circuits or line switching. These faults are not noticed by electromechanical equipment, but they can cause damage to electronic equipment. Usually switching power supplies, installed in almost all electronic equipment, compensate interruptions lasting only a few milliseconds. Longer blackouts can cause loss of data, program cancellations and system failures.Therefore special devices are needed for complete blackout protection.

Harmonic distortions

These are a new type of failure on electric lines that are becoming more and more common. They are caused by the ever increasing use of electrical equipment with non linear absorption such as: rectifiers, converters, drives, switching power supplies. This fault can cause heavy overloads on lines and transformers, explosion of power factor correction capacitors, incorrect indications on measuring equipment and, generally speaking , bad operation of any type of electrical equipment.