![]() The relations in equations (5), (6), and (7) can be applied to the reactive components I Qx. This results in: iL, tot = i 1 + i 2 … + i x (7) The equations (1) through (3) have been inserted into the equation (5): iL, tot = i 1+ i cir2+…+ i cirx + i 2 - i cir2 + i x - i cirx (6)Īs can be seen in equation (6), all of the circulating currents are eliminated. According to Figure 3, the following is valid: iL, tot = i T1 + i T2 + … + i Tx (5) As a result, the reactive current is obtained which each transformer must yield in order to cover the reactive power requirements of the load. In the case of numerous transformers, the total of all of the reactive currents is determined and is then divided by the number of transformers. The proportion caused by the load is mathematically eliminated in the process. In the case of two transformers operating in parallel, the circulating reactive current is the result of half of the difference between both of the measured reactive currents. In order to maintain the circulating reactive current, it is not sufficient to simply measure the reactive current at the transformer, since this could also be due to an inductive load (refer to i x in Figure 3). In order to attain good regulation results, the relative short-circuit voltages of the transformers may not deviate too strongly (max. However, the same tap positions must then result in the same ratio (= same open-circuit voltages). Transformers with differing capacities can also be operated in this manner. In the master-follower procedure, however, the difference is offset.īoth procedures are particularly suitable for transformers of the same construction. A desired tap difference existing at the beginning of the parallel regulation between the master and the slaves remains intact in the master-slave procedure. It can actively read the tap position of the master via E-LAN and can independently position itself to match the master’s tap position. In the master-follower procedure, the slave is equipped with additional intelligence. In the process, one regulator takes over control while the other regulators follow its position commands (master-slave regulation). These procedures regulate on the same tap positions of the transformers. Master-slave and Master-follower procedures In order to be prepared for such situations, additional measured variables must be found which can be used for the parallel regulation. If the voltages of too highly tapped transformers are compensated for by too lowly tapped transformers, the voltage will be maximally adjusted, but circulating currents will flow. This circumstance greatly complicates voltage regulation. If it is assumed that the impedances Z sc1 to Z scx are all equal and one of the transformers is upset by Δu x in order to regulate the voltage, it follows that: u’ tot = u tot + Δ u x / n (4)Įquation (4) illustrates that, for example, in the case of three transformers connected in parallel (n=3) with the same impedance, a voltage variation at one transformer only affects the busbar by one-third. Since the transformer impedances are strongly inductive and the effective component can be disregarded, such circulating currents are also called circulating reactive currents.Įven more complicating is the fact that the voltage regulation loses sensitivity, since a change in the individual open-circuit voltages u 1 to u x only partially affects the total voltage of the busbar. ![]() This example illustrates that the transformer T1 is additionally loaded with all of the circulating currents while all of the other transformers are relieved by their respective circulating current. Expensive measuring supplements or parallel regulating units are therefore superfluous.įigure 3: Parallel transformers connection – substitute connection diagram ![]() All of the relevant data can be exchanged via the E-LAN regulator bus with two interfaces (RS 485 interface), which enables data communication between up to 255 regulators. The communication interfaces are of particular importance for parallel regulation. The parameterization of the regulator can be carried out menu-driven either directly via the keyboard or via PC with the help of WinREG software. The core of the REGSys ® voltage regulator system (Figure 1) is the REG-D ® voltage regulatorwhich, in addition to its actual regulating function, also performs measuring, recording and statistical functions. Digital regulators, such as the freely programmable REGSys ® voltage regulator system, are in use. Today these tasks are accomplished electronically with high regulation quality. The regulation of transformers with tap changers is a classical subject within the field of power supply and distribution. ![]()
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