Transformers are one of the primary components for the transmission, distribution, and control of electrical energy. Their design results mainly from the range of applications, the construction, the rated power, and the voltage level. While operating principles of transformers remain the same, the advantages and disadvantages have evolved along with transformer design and construction.
Advantages of transformers
Transformers have many benefits. Some of them are explained below.
Simple working principle and construction
A transformer is a static device consisting of a winding, or two or more coupled windings, with different numbers of turns on a magnetic core, for inducing mutual coupling between circuits. The alternating current magnetic field created in one winding induces a current in the other is proportional to the number of turns.
Transformers are exclusively used in electrical power systems to transfer power by electromagnetic induction between circuits at the same frequency with very little power loss, voltage drop, or waveform distortion.
Stepping up / down voltage and current
Transformers are important equipment in the power distribution system as well as in the power electronic system. They can step down high voltages in transmission at substations or step up currents to the needed level of end-users.
Isolation and efficiency
The traditional transformer has a simple construction, high efficiency, and reliability. Moreover, it provides galvanic isolation as well. Transformers are useful in providing electrical isolation between the primary circuit and the secondary circuit because there is no electrical connection between the two windings. In a transformer, energy is transferred entirely by magnetic coupling.
During the last decade, the basic construction has remained the same, but the improved material technology allowed higher saturation densities and lower hysteresis losses to be achieved, which resulted in very efficient transformers. The efficiency of a transformer is considered to be 97%.
Transmitting and distributing power
Power generation, transmission, and distribution are the three main constituents of the modern power system, in which the transformer plays a most critical role. Transformers have made possible economic delivery of electric power over long distances. Transformers enable high efficiency and long-distance power transmission by boosting the voltage to a higher one on the generation side with the so-called power transformer. On the distribution system side, this high voltage is stepped down for industrial, commercial, and residential use with the so-called distribution transformer.
The traditional transformer provides a cheap and very efficient method for voltage level transformation and isolation. The total cost of a transformer is not expensive. (except big distribution transformers)
Various types and wide usage areas
Transformers have various types such as distribution, power, current, potential, isolation transformers. Each of them works on the same principle but has different usage areas. For example, current transformers are used to step down currents for the measurement instruments.
No moving parts and starting time
A transformer has no internal moving parts, and it transfers energy from one circuit to another by electromagnetic induction. It ensures under normal conditions, a long and trouble-free life. Besides, it does not require any starting time.
Most transformers can be “reverse connected” which means the same transformer can be wired to be a “step-up” or “step-down, depending on how it’s installed. This reversing capability must be allowed and specified by the manufacturer.
To accommodate various input voltages, some transformers may be equipped with multiple taps on the primary. These taps are sized for standard voltages (220, 230, 240….etc.), or they can be only slight variations to adjust for consistent over or under voltage at a particular location. These taps are most commonly provided as a percentage of the primary voltage, such as 2-1/2% and 5% (up or down from nominal)
Disadvantages of transformers
Transformers have some drawbacks. Some of them are explained below.
High temperatures in a transformer will drastically shorten the life of insulating materials used in the windings and structures. Increasing the cooling rate of a transformer increases its capacity. Therefore, the maintenance of cooling systems is critical. External cooling may include heat exchangers, radiators, fans, and oil pumps.
Works only in AC
A transformer does not pass DC, therefore a transformer can be used to keep the DC voltage on the output of an amplifier stage from affecting the bias of the next amplifier. The ac signal is coupled through the transformer between amplifier stages.
Transformers are widely used electrical machines to step up and down voltage levels in transmission and distribution systems. Even if they operate with very high efficiencies, due to reached high VA values and numbers of the transformers installed in a power system, loss minimization studies gain great importance. Among the losses, iron losses are particularly important, because the transformer is continuously energized, and therefore, considerable energy is consumed in the core, while load losses occur only when the transformer is on load.
Although the transformer is in global use, many of its characteristics are unwanted in the modern distribution grid. To meet the requirements of the future intelligent network management systems a new concept of a distribution transformer is needed. One possibility is to implement an intelligent transformer.
The transformer is very bulky and heavy. It needs space. There have been inclusive studies to reduce the size and weight of the transformer. It transforms the voltage directly. It also transfers the unwanted voltage sags, dips, and frequency variations to the output.
Low power quality
The transformer has a very limited voltage and power quality regulation and needs additional flexible AC transmission systems for power quality control.
Voltage dips and frequency variations
The output voltage is a direct representation of the input. Any unwanted characteristics from the input, such as voltage dips or frequency variations, will be represented on the output. Whatever frequency is on the primary will appear on the secondary.
The output current will likewise influence the input current. In a practical distribution environment, the input current will be a reflection of the sum of the connected output currents. The presence of harmonics on the load currents will manifest themselves in the input current. For single-phase, residential customers odd harmonics especially the 3rd, 5th, and 7th are notably present with values above 15 % of the fundamental. As with the total load, the harmonics are rarely balanced among the three phases. With delta-connected primary transformers, the 3rd harmonic circulates in the primary winding and does not propagate to the network, but it does add to the primary winding losses.
Many transformers are damaged every year due to various reasons. Accelerated degradation and failure of transformers can occur because of several conditions such as oil leakage, overloading, unbalanced loading, and harmonics. However, the majority of failures are caused by a combination of these electrical, mechanical, and thermal stresses acting upon the power transformer components over time. Therefore, it is important to study and develop effective methods of monitoring the condition and health of transformers.
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