With a development of modern power electronics, equipment based on semiconductors, powerful arc steel melting furnaces, rolling mills and other consumers with nonlinear and sharply variable loads in power supply systems (PSS) of enterprises, there are problems associated with the appearance of non-sinusoidal distortions of current and voltage curves.
Non-sinusoidal distortions adversely affect the operation of electrical equipment, relay protection and emergency controls, telemechanics systems and the reliability of PSS as a whole. This is primarily due to deterioration in the company’s energy indicators, a decrease in reliability of electric grids operation and a reduction in a service life of the equipment in operation.
Harmonic distortions are formed by a sum of signals of fundamental harmonic (50 Hz) and the harmonic components of higher frequencies. The harmonic spectrum is obtained by decomposing of received current or voltage signal into its harmonic components. The voltage or current curve in this case is described by Fourier:
where I0– constant component, Iυmsin(υɷt+Ψυ) – higher harmonics components of the υ-th order.
Distortions of the supply voltage curve
The degree of influence of harmonic component reflecting the quantitative content of a particular harmonic is described by non-sinusoidal coefficient of the n-th harmonic voltage component KU (n) and the total harmonic component coefficient KU.
where Un – voltage of n- th harmonic component, U1 – voltage of main harmonic.
Normally permissible and maximum permissible values over the presented coefficients are regulated by the requirements of the existing state standards.
At fulfilling the activities regarding reactive power compensation, attention should be paid to the problem of higher harmonic components for a number of reasons:
- a resistance of capacitors is inversely proportional to the frequency of supply voltage, as a result of a small resistance there is an increase of current through the capacitor at harmonic frequency, which leads to accelerated aging of the insulation, shortening the service life of equipment, an occurrence of non-admissible overloads and as a result capacitor failure;
- when a phase of resulting current and voltage in the oscillatory circuit “capacitance of capacitors – network inductance” coincides, a parallel resonance occurs accompanied by a sharp current increase and equipment failure.
Decrease in the level of higher harmonics in electrical networks is one of the main tasks of reducing the influence of nonlinear loads onto supplying network and improving the quality indicators of electrical energy.
One of the most effective and economically feasible technical solutions in the field of reactive power compensation in the presence of higher harmonic distortions of current is the use of filter mismatching/detuned capacitor banks of ERVA type.
where I0– constant component, Iυmsin(υɷt+Ψυ) – higher harmonics components of the υ-th order.
To prevent the emergence of resonant modes, it is necessary to use the banks representing in-series resonant circuit formed by a throttle connected in-series with capacitors. Such banks are called mismatched filters of higher harmonics.
The purpose of this connection is to reduce a resonance frequency of network to a value below the lowest higher harmonic. The power of throttle is expressed as a percentage of capacitor power. The most common application is throttles of 5.67%, 7% and 14%. Its own resonance frequency corresponds to each value of throttle’s power. For example, for a 7% mismatch, the resonant frequency is 189 Hz. This means that for all harmonics whose frequency lies above 189 Hz, the network is an inductive resistance and a resonant mode appearance is unlikely for them. This solves the problem of expensive equipment repairing that failed due to the effects of higher harmonics currents.
Capacitor banks of UKMF type are designed for automatic reactive power compensation of consumers’ loads in the networks of general purpose with voltage 0.4 kV at a frequency 50 Hz, using an electrical load with a nonlinear voltage-current characteristic.
| Type designation |
Quantity and power of steps |
Overall dimensions, mm | Rated current, A |
Weight, kg, not more |
Normative document |
||
| length | width | height | |||||
| UKMF1(2,3)-0,4-50-12,5 U3 | 2×12,5+25 |
800
|
600
|
1550
|
70 | 150(150,165) | СТ 2347- 1917-01- ТОО-4- 056-2016 |
| UKMF1(2,3)-0,4-62,5-12,5 U3 | 12,5+2×25 | 90 | 160(170,175) | ||||
| UKMF1(2,3)-0,4-75-12,5 U3 | 2×12,5+2×25 | 108 | 165(170,185) | ||||
| UKMF1(2,3)-0,4-75-25 U3 | 25+50 | 165(165,185) | |||||
| UKMF1(2,3)-0,4-87,5-12,5 U3 | 12,5+25+50 | 126 | 175(170,195) | ||||
| UKMF1(2,3)-0,4-100-12,5 U3 | 2×12,5+25+50 | 144 | 180(180,205) | ||||
| UKMF1(2,3)-0,4-100-25 U3 | 2×25+50 | ||||||
| UKMF1(2,3)-0,4-125-25 U3 | 25+2×50 | 1700 | 180 | 230(235,250) | |||
| UKMF1(2,3)-0,4-150-25 U3 | 25+50+75 | 217 | 250(225,270) | ||||
| UKMF1(2,3)-0,4-150-50 U3 | 3×50 | 250(250,270) | |||||
| UKMF1(2,3)-0,4-175-25 U3 | 2×25+50+75 | 253 | 260(250,285) | ||||
| UKMF1(2,3)-0,4-200-25 U3 | 25+2×50+75 | 2000 | 289 | 335(340,370) | |||
| UKMF1(2,3)-0,4-200-50 U3 | 4×50 | 345(320,375) | |||||
| UKMF1(2,3)-0,4-225-25 U3 | 25+50+2×75 | 325 | 345(360,390) | ||||
| UKMF1(2,3)-0,4-250-25 U3 | 2×25+50+2×75 | 361 | 365(360,405) | ||||
| UKMF1(2,3)-0,4-250-50 U3 | 2×50+2×75 | ||||||
| UKMF1(2,3)-0,4-275-25 U3 | 2×25+3×75 | 397 | 380(380,420) | ||||
| UKMF1(2,3)-0,4-300-25 U3 | 2+50+3×75 | 1600 | 1700 | 433 | 435 (420, 465) | ||
| UKMF1(2,3)-0,4-300-50 U3 | 6×50 | 490 (460, 530) | |||||
| UKMF1(2,3)-0,4-350-25 U3 | 25+2×50+3×75 | 505 | 480 (475, 525) | ||||
| UKMF1(2,3)-0,4-300-50 U3 | 7×50 | 2000 | 630 (590, 680) | ||||
| UKMF1(2,3)-0,4-400-25 U3 | 25×+50+4×75 | 577 | 680 (660, 735) | ||||
| UKMF1(2,3)-0,4-400-50 U3 | 8×50 | 680 (630, 740) | |||||
* As per customer’s request, it is possible to produce banks with different requirements from the table.
Symbol structure designation of filter capacitor banks of UKMF type:
| UKM | UKM | – capacitor bank upgraded; |
| F | F | – filter; |
| Х- | 1- | – order of mismatching factor: 1-5,67%, 210 Hz; 2- 7%, 189 Hz; 3-14%, 134 Hz; |
| XX- | 0,4- | – rated voltage, kV; |
| ХХ- | 250- | – rated power, kVAr; |
| ХХ- | 50- | – control step, kVAr; |
| Х | U3 | – climatic performance and location category as per GOST 15150-69. |
For example: UKMF1-0,4-250-50 U3 – Filter capacitor bank upgraded for voltage class 0,4 kV with mismatching factor 5,67% (210 Hz), rated power 250 kVAr with a control step 50 kVAr, climatic performance and location category as per GOST 15150-69 – U3.
For climatic performance UHL1 all equipment is located in warmed block-modular building.