Technical information on issues of concern

5 июля 2015
Technical information on issues

improve the quality of three-phase power systems and applications

filtersettings transformers (normalizers)

AC voltage type TST and TST2-R.

Why three-phase devices that provide improved power quality, improve the reliability of power supply system and reduction of losses, preference should be given to the normalizers of a variable voltage type TST2 and TST2-R?

It is known that more than 35% of electricity generated, distributed in low voltage networks with a neutral conductor. The study of modes of operation of such networks shows that the quality of electricity in many cases does not meet the requirements of GOST 13109-97, and below the level of acceptable international standards.

The main factor which influences the mode of voltage at consumers and increase cost of electricity is the imbalance of three-phase power supply system of the displacement of the neutral phase voltage and high harmonics. This is facilitated by the following reasons:

   1. The almost universal use of transformers with the output line voltage 380 V circuit connections "star" with zero, which has a 10 times larger value of resistance zero sequence than the resistance value of direct and reverse sequences;

   2. The increase in the number of single-phase high power loads, non-linear, which leads to the appearance of the third harmonic with the zero order of the phases, which can reach 100% of the current of the fundamental frequency. Normal loads are replaced by non-linear , a feature which is pulse and high-frequency power consumption;

   3. The large extent of the urban and especially rural networks 380V.

Unbalance the stresses due to the large resistance of the low-voltage zero-sequence networks, cannot be excluded with symmetrical control means mode. Moreover, the symmetrical voltage regulator is implemented in the power center under the unbalanced voltage system, inevitably leads to an increase in variance of voltage at consumers one or two phases. Additional voltage deviation caused by the offset of the neutral phase voltages, significantly contributed to the installation of individual voltage regulators. Along with the high cost of scarce materials, their use causes an increase in power loss and power in electrical networks, the additional power consumption.

The presence of higher harmonics in the nonlinear loads, leads to additional energy losses, reducing the service life of electrical equipment, and in some cases - to the output of the equipment.

In four-wire electrical networks of Russia and other CIS countries are mainly used transformers with winding connection star-star" with zero. However, these are the cheapest to manufacture transformers in operation is economical only if the symmetric load phase. Real non-symmetric load phase and non-linear single-phase loads – one of the main reasons for the growing losses in power transformers and in reducing the quality of electricity supplied to consumers fed from these transformers. In recent times, this problem is particularly acute in connection with the spread of modern power systems power consumers, clearly and significantly distort the mains voltage, such as a controllable actuator, welding machines, computer and other electronic equipment.

Loss short circuit RK power transformers depend on the amount of current in the zero wire and it increases sharply. The zero current in the wire causes a flow of zero sequence in three-phase magnetic systems and is in the nature of the leakage flux of similar threads short circuit, but the value is significantly large, as evidenced by the ratio of full resistance for types of transformers TM, TMA, TSMA - Zкз and Zо first Zкз in (7 – 15) times less Zо.

Thus to solve power quality in networks low-voltage 0,4kV, appropriate to the conduct of activities on reduction of the equivalent resistance zero sequence network, and the use of individual and group filtering and corrective devices.

One of the effective ways to reduce the displacement of a neutral phase voltages and filtering of higher harmonics is a significant decrease in resistance and zero sequence impedance of the loop phase is zero, accomplished by applying filtersettings normalizers AC voltage type TS2T and TST2-R.

Filtercartridge normalizers AC voltage type TST2 and TST2-R provide:

      1.The normalization phase (or line) voltages;

      2.The reduction in electricity consumption;

      3.Filtering of higher harmonics;

      4.The increase in the service life of the used equipment;

      5.Provide greater reliability and security;

      6.The payback period is less than 24 months.

In many cases the use of filtersettings normalizers TST2 and TST2-R allows to exclude from power system voltage stabilizers. In those cases, when without the use of voltage regulators can not do - the combined use of three-phase group of single-phase stabilizers and filtersettings transformers TST can stabilize the phase and line voltages at the same time. At the same time the use of three-phase stabilizer is composed of three single-phase during the stabilization phase voltages, can lead to significant asymmetry of the line voltages with extremely adverse consequences for three-phase loads, such as motors.

Filtercartridge transformers (normalizers) AC voltage type TST2 are manufactured in two variants of execution, namely: vers. 1 - with series-parallel switching and use 2 – parallel and normalizers TST2-R only with series-parallel switching (vers. 1).

When a series-parallel operation of the Normalizer TST2 (TST2-R) is placed between the source of electrical energy (supply or self-contained source of energy) and power consumers – consumers of electrical energy.

With the parallel connection TST2 is connected in parallel with an electric power source and the load.

The use filtersettings normalizers TST2, with series–parallel switching, also be useful in a system with Autonomous sources of electric power: diesel-generator sets and uninterruptible power supplies, greatly affecting the increase of service life, the reliability of these products and reducing losses of electric energy. Filter-balun transformer eliminates the flow of zero sequence currents through the windings of the generator and the UPS and reduces nonlinear distortion .

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