Which method should you use to protect your electronic devices?
Problems related to electrical energy power quality may cause malfunctions or decreases in operating performance in computers and similar devices that process information and sensitive electronic devices; Loss of production and serious financial losses may result.
One of the most commonly observed electrical power quality problems in electrical networks and power distribution systems of enterprises is short or long-term voltage drops. Sensitive electronic devices can operate smoothly only at values within a certain operating range of the voltage they are supplied with. For example, the nominal operating voltage of a device labeled 220V±10% is 220V, but it is guaranteed by the device manufacturer that this device can operate smoothly at all voltage values in the range of 198V-242V. Voltages outside these values may damage the device to which it is applied. Manufacturers clearly state the operating voltage range of the product in the technical brochures and user manuals of the devices they sell and emphasize that if users operate their devices with values outside this voltage range, the product will be out of warranty.
Two methods are generally used to protect sensitive electrical and electronic devices used in commercial and industrial workplaces from voltage drops of the source they are connected to: Voltage regulators and UPSs (Uninterruptible Power Supplies; UPS). These two methods, with their working principles, advantages and disadvantages, will be briefly explained and compared below.
They are also called voltage correctors/regulators. One- and three-phase regulators of different powers are used. They are located between the network and the device whose input voltage will be regulated. Structurally, they are of two types: Dynamic and static voltage regulators. The autotransformer, which generally has a toroidal structure and where carbon brushes sweep the voltage adjustment segments on its upper surface, is the basic structural element of dynamic voltage regulators. As in the regulator shown in the figure, this transformer constitutes an important part of the regulator. When the mains voltage drops, carbon brushes move to the right, for example, to increase the voltage and bring the load voltage to normal voltage; When the mains voltage increases, they exhibit the opposite behavior. The most obvious disadvantage of this system is that its behavior (electrical response) against network voltage changes remains slow. For this reason, dynamic regulators may be insufficient in regulating rapidly changing welding voltages; It is not preferred to use them in businesses where such rapid voltage changes occur. Another disadvantage is that the moving carbon brushes, which are in constant contact with the transformer surface, wear out due to friction and the naturally occurring need for maintenance. The obvious advantage of dynamic voltage regulators is that they are inexpensive and relatively easy to maintain and service.
Static voltage regulators are regulators that contain static semiconductor elements (Thyristor, transistor, etc.) in their structure. Their operating principles are very similar to dynamic regulators. A moving carbon brush or similar moving element is not used in static voltage regulators. Increasing or decreasing the voltage is achieved by controlling the conduction time of static semiconductor elements. Since moving carbon brushes are not used, the maintenance need for these systems is relatively low. Their obvious disadvantages are that they have a complex power and control circuit and that they require experienced technical service personnel for repairs in case of malfunction. Their only advantage is that they can respond quickly to rapid voltage changes and therefore make rapid regulation.
Uninterruptible Power Supplies (UPS), commonly known as UPSs, are one of the most used applications of power electronics today. Its basic function is to apply electrical energy uninterruptedly to critical devices connected to it in case of a power cut. Apart from this known purpose of use, UPSs isolate the expensive and sensitive load they feed from many power quality problems that may arise in the network, including voltage changes; It ensures that it is fed with a clean and regulated voltage and frequency value (220V phase-neutral, 50Hz). As long as the mains voltage remains within the operating range defined for the UPS’s input voltage, the critical load continues to be fed with a regulated pure sinusoidal voltage from the UPS output. When the input voltage of the UPS is cut off (when there is a power outage) or when the operating voltage of the UPS goes outside the tolerances, the UPS continues to operate through its battery system. Battery-assisted operating time is determined by the capacity of the batteries used and the current drawn by the loads connected to the UPS. The battery support time of the UPS operating at full load, in other words at full capacity, is typically 7-10 minutes. is around. This period will increase as the load amount is reduced. Therefore, it is recommended to disable non-critical, unnecessary loads during a power outage.
Online operating models of UPSs perform dual power conversion. First, they convert the sinusoidally changing AC voltage of the network into the form that the batteries can use, that is, DC voltage, with the power electronics circuit called rectifier. While this converted DC voltage keeps the batteries constantly charged, it also feeds the power electronics circuit, that is, the inverter, which is a second power conversion stage. The inverter produces the stable, regulated sinusoidal AC voltage required by the load.
Which one should we choose?
There are certain criteria that determine the selection of a UPS or voltage regulator: how sensitive and critical the application and the devices used are, the current drawn by the device(s) to be fed, the rate and frequency of change of the mains voltage, etc.
If the device you are powering is expensive, sensitive to mains voltage changes, the mission it performs is critical, and the financial and production losses it will cause if it does not work or works undesirably are large, it must be fed from a continuous and well-regulated sinusoidal AC voltage source. The most appropriate power protection solution that can be recommended for such situations is the use of on-line UPSs. Online UPSs protect your critical load not only against network problems such as voltage drops or increases, but also against other problems that may arise in the network (frequency changes, harmonics, transients, etc.). UPS operation is not affected by the mains voltage changing too quickly and too much during the day.
Despite these advantages, UPSs have a complex structure, are expensive and require periodic maintenance.
On the other hand, voltage regulators provide adequate protection for non-critical loads. Voltage correction speeds, that is, regulation speeds, are slower than UPSs. Voltage regulators can only properly regulate slowly varying voltage dips and voltage spikes and apply a voltage to the load at its nominal value. In other power quality-related network problems, it cannot isolate or protect the load.
Before making a purchasing decision for a UPS or voltage regulator, it is extremely important to measure the indoor voltage, monitor the voltage waveform, and detect and identify waveform distortions, if any. For the non-sinusoidal voltage waveform to be observed in the distribution panel, either appropriately selected filters should be used, or an online UPS determined according to the total power of the loads that may be affected by this voltage should be used.
Asst. Assoc. Dr. Vehbi BÖLAT, Tunçmatik A.Ş.