The main objective of this paper is to balance a threephase unbalanced load on supply system. Variable reactive power compensation of nonlinear and/or poor power factor loads is an important issue in the modern distribution system. In recent years, there has been a great increase in demand for controllable VAr sources to compensate large industrial loads such as electric arc furnaces, electric traction, commercial lighting, air conditioning etc. If not compensated, these loads create system unbalance and lead to wide fluctuations in the supply voltages. Such supply system cannot be used to feed sensitive loads like computers, electronic equipment, etc.

Said and Pirouti (2009), discuss the presence of unbalanced load results in reactive power burden and excessive neutral current, which in turn results in low system efficiency, poor power factor and disturbance to other consumers. Czarnecki, Hsu, and Chen (1995), have discussed innumerable control methods proposed to draw balanced supply currents if reactive load is fed from balanced supply system. The vast majority of the work is restricted to single phase loads, three phase, and three- wire loads. However, this paper discusses on an attempt to correct the power factor and balancing of three phase unbalanced delta connected load by means of compensation. Ghosh and Joshi (2000), had proposed a new approach to load balancing and power factor correction in power distribution system. Mayordomo, Izzeddine, and Asensi (2002) had discussed a load and voltage balancing in harmonic power flows by means of static VAr compensators. Pan, Peng, and Wang (2005) had discussed the power factor correction using a series active filter. Husain, Singh, and Tiwari (2010) presented balancing of unbalanced load and power factor correction in Multi-phase (4-phase) load circuits using DSTATCOM. A four-wire three-phase load balancing with static VAr compensators were discussed and presented by Quintela, Arévalo, Redondo, and Melchor (2011).

A unity power factor is desirable for better economical and technical operation of the system. Usually power factor correction means to generate reactive power as close as possible to the load which requires it rather than generating it at a distance and transmitting it to the load, as this results not only in large conductor size but also in increased losses.

A very important concept of load compensation is load balancing. It is desirable to operate the three phase system under balanced condition, as unbalanced operation results in flow of negative sequence current in the system and is highly dangerous, especially for rotating machines.

The balancing of an three phase unbalanced active load of a three-phase distribution network, by a three-phase unbalancing compensation was discussed for the first time by Steinmetz (1917) mentioned by (Otto, Putman, & Gyugyi, 1978) for a resistive load supplied between two phases. The method was generalized for three-phase unbalanced loads, the elements of the compensator being determinate starting from the analytical condition of cancellation of negative sequence component of the currents on the load phases, through its real and imaginary parts, (Figure 1). This condition can be accomplished by an unbalanced three-phase compensator in delta connection, which contains only reactive elements (capacitive susceptances and/or inductive susceptances), able to cancel in the network, a three phase currents set with a negative sequence component equivalent to the negative sequence component absorbed by the unbalanced load. The compensator determines the redistribution of active and reactive power between the phases, which can be obtained only by a delta connection of its elements. In the same time, the compensator can get involved on the positive sequence, for the symmetrical compensation of the reactive power in order to correct the power factor or voltage control. The total compensation of reactive power absorbed by the load can be analytical in the form of imaginary part of the positive sequence component of the current on the phases of the load compensator. Considering all the conditions presented above, the following relations for the susceptances of the compensator are obtained (Miller, 2010).

where B_ABcomp, B_BCcomp, B_CAcomp are the equivalent susceptances of the compensator, and B_12load, B_23load , B_31load, G_12load, G_23load, G_31load the equivalent susceptances (Gueth, Enstedt, Rey, & Menzies, 1987), respective conductances corresponding to a delta connected three-phase load as in Figure 1.

Figure 1. The Schematic of Electrical Equivalent of the Load and the Balancing Compensator

Depending on the nature of the load, the type and the level of unbalancing, results in four cases for the three susceptances of the compensator: (i) three capacitive susceptances; (ii) two capacitive susceptances and one inductive Susceptance; (iii) two inductive susceptances and one capacitive susceptance; (iv) three inductive susceptances. The last two cases can result for active and/or capacitive reactive loads, situations extremely infrequent in practice. The study presented in (Otto et al., 1978), refers to the first case, which is the most common practical case, when the load has active character and strong reactive character on all three phases, the unbalance is not very significant, so that balance can be achieved with a compensator containing only capacitors in delta connection (Figure 1).

The simulation model of unbalanced inductive load connected to supply system is shown in Figure 2.

Figure 2. Unbalanced Inductive Load

Table 1 shows unbalanced load details.

The simulation model of balanced load connected to supply system is shown in Figure 3.

Table 1. Unbalanced Load Data

Figure 3. Balanced Compensator

Table 2 shows measurement of source side voltage (V) and current (I), with magnitude and phase angle.

Table 2. Source Side Measurement

Table 3 shows measurement of load side voltage (V) and current (I), with magnitude and phase angle.

Table 3. Load Side Measurement

Figure 4 represents balanced voltage (V) and current (I), of phases A and C with same in phase angle (Source Side).

Figure 4. Balanced Voltage and Current of Phases A and C with same in Phase Angle (Source Side)

Figure 5 represents unbalanced voltage (V) and current (I), of phase B with variation in phase angle (Source Side).

Figure 5. Unbalanced Voltage and Current of Phase B with Variation in Phase Angle (Source Side)

Figure 6 represents balanced voltage (V) and current (I), of phase A and C without variation in phase angle (Load Side).

Figure 6. Balanced Voltage and Current of Phases A and C without Variation in Phase Angle (Load Side)

Figure 7 represents unbalanced voltage (V) and current (I), of phase B with variation in phase angle (Load Side).

Figure 7. Unbalanced Voltage and Current of Phase B with Variation in Phase Angle (Load Side)

Figure 8 represents balanced voltage (V) and current (I), of phase A and C without variation in phase angle (Source Side).

Figure 8. Balanced Voltage and Current of Phases A and C without Variation in Phase Angle (Source Side)

Figure 9 represents balanced voltage (V) and current (I), of phase B with phase angle (Source Side).

Figure 9. Balanced Voltage and Current of Phase B with Phase Angle (Source Side)

Figure 10 represents balanced voltage (V) and current (I), of phase A and C without variation in phase angle (Load Side).

Figure 10. Balanced Voltage and Current of Phases A and C without Variation in Phase Angle (Load Side)

Figure 11 represents balanced voltage (V) and current (I), of phase B with phase angle (Load Side).

Figure 11. Balanced Voltage and Current of Phase B with Phase Angle (Load Side)

This paper analyzes the power factor correction and balancing of unbalanced delta connected load using simplified mathematical model. The results are validated using Matlab simulation. The proposed approach can be used for power factor correction and balancing of unbalanced load in power system. This improves the overall power quality and reliability of the supply system.