What is reactive power compensation?
The ultimate (seeming) power developed by synchronous generators conditionally shares on active and reactive.
Active component of power it is useful it is used, turning into energy mechanical, chemical, light, etc.
The reactive component of power does not perform useful work, it serves only for creation of magnetic fields in inductive receivers (electric motors, transformers , etc.), circulating between the source and the receiver all the time. It can be considered as the characteristic of speed of exchange of energy between the generator and magnetic field of the receiver of the electric power.
From this it follows that the traditional term "consumers of reactive power" which is widely used as electrotechnical personnel in daily practice, and in technical literature is conditional, not reflecting physical essence of reactive power. Especially the concept "reactive energy" is wrong. More exact will be "induction receivers of the electric power" or in some cases "reactive loads".
The electrical power factor is specified on the guard of the synchronous generator. It shows what part from the ultimate power developed by the generator active power is. Influence of electrical power factor on work of electric units is very big. So, for example, the generator with the rated power of 1250 kVA at rated electrical power factor of cos? =0,8 can give to the consumer the active power equal of 1250? 0,8 = 1000 kW.
Power of the prime mover at the direct joint with the generator will be also 1000 kW. Let's assume that this generator works with the same rated power, but with cos? =0,6. In this case it gives to network 1250? 0,6=750 kW, i.e. will be underused on active power for 25%. The same and concerning the prime mover of the generator (the steam or hydraulic turbine) which in this case will also be underused for 25%.
Operational indicators of work of power plant: fuel consumption, waters, couple, lubricant and other auxiliary materials on one developed kW · h - at decrease in cos? also considerably decrease, development of active energy decreases.
Reduction of cos? at the same active power developed by the generator (at invariable active loading at the consumer) leads to increase in ultimate power of the generator. In our example at decrease in cos? with 0,8 to 0,6 the 1000:0,6=1700 kVA generator instead of 1250 kVA, i.e. increase in ultimate power by 27% will be required.
At transformers at reduction of cos? flow capacity on active power owing to increase in the reactive load decreases. For transfer to consumers of 1000 kW of active power at cos? =0,8 the 1250 kVA transformer is required. At decrease in cos? to 0,6 transfer of the same active loading will require the 1700 kVA transformer.
Increase in ultimate power at decrease in cos? leads to increase of current and, therefore, power losses which are proportional to the current square. Increase in current demands increase in section of the transmission line and consequently, the weight of wires and the cable.
Increase in current at decrease in cos? leads to increase in loss of tension in all links of the power supply system that causes undervoltage in consumers of electrical energy.
At the industrial enterprises undervoltage breaks normal operation of electroreceivers. Rotating speed of electric motors decreases that leads to decline in production of working machines and deterioration of products. Productivity of electric furnaces decreases, the quality of welding worsens, the luminous flux of lamps decreases, the flow capacity of factory network circuits decreases.
The considered cases of influence of low power factor for work of electric units show that decrease in cos? has an adverse effect on all links of the power supply system including at work of the industrial enterprise. Therefore questions of increase in electrical power factor have great economic value.
The solution of the tasks connected with availability in the system of the power consumption of reactive loads goes on the way of reactive power compensation. It is caused by holding two mutually supplementing groups of actions: decrease in consumption of reactive power electroreceivers and installation directly at consumers and in nodes of networks of special sources of reactive power - the compensating devices.
For decrease in consumption of reactive power at operation of electric units the following events are recommended:
- the streamlining of technology process leading to improvement of the power mode of the equipment and to decrease in the rated maximum of the reactive load;
- reduction of single operation of asynchronous electric motors, welding transformers and other electroreceivers by implementation of limiters of no-load operation;
- replacement or shutdown of the transformers loaded less than for 30% of their rated power if it is allowed under the terms of working hours of network of electroreceivers;
- replacement whenever possible loaded less than for 60% of asynchronous electric motors by electric motors of smaller power on condition of the feasibility study;
- replacement of asynchronous electric motors synchronous, admissible under the terms of operation of the electric drive if asynchronous electric motors are subject to dismantling owing to wear, changes of technology process or the possibility of use in other installations which are not needing artificial compensation of reactive loads and also in other cases if replacement is proved by technical and economic calculations;
- undervoltage at the low-loaded asynchronous electric motors by switching of the stator winding from the triangle on the star, sectioning of stator windings; undervoltage in the networks feeding asynchronous electric motors by switching of branches of the shop transformer;
- improvement of quality of repair of electric motors (turning of the rotor, reduction of number of conductors in the groove, boring of grooves, burning out of the winding are inadmissible).
For the converting installations which are widely adopted more and more on industrial predpriyaty decrease in reactive power can be reached by reduction of the angle of opening of valves and limits of its regulation, asymmetrical management of valves, application of schemes with artificial switching.
The events for decrease in consumption of reactive power electroreceivers held at the enterprises lower the total reactive load usually no more than by 10%. Therefore the main role is assigned to the compensating devices.
The compensating installations are: cosine capacitors, synchronous electric motors, synchronous compensators, compensation converters. Preferential application at the industrial enterprises was received by cosine capacitors and synchronous electric motors.
Cosine capacitors are manufactured the following types: KM, SQ.KM, KMA, KM2A, KC, KC2, KCA, KC2A, where
- To means cosine;
- M and With - with impregnation by mineral oil or synthetic liquid dielectric;
- And - execution for outside installation (without letter A - for internal);
- 2 - execution in the body of the second dimension (without digit 2 - in the body of the first dimension).
After designation like the condenser digits specify its rated voltage (kV) and rated power (quar).
So, for example, KM-0,38-26 is deciphered as the cosine capacitor (for reactive power compensation in the alternating current main with the frequency of 50 Hz), with impregnation by mineral oil, for internal installation, the first dimension, on voltage of 380 V, 26 quar.
In the IV series the 37,5 and 75 quar. condensers are replaced with the 50 and 100 quar. condensers at the same overall dimensions.
The industry makes complete condenser installations on voltage of 380 V for internal installation and on voltage of 6-10 kV - for internal and outside installation. The majority of types of these installations is equipped with devices for one - and multistage automatic control of power.
More and more broad application is found by the automatic device of regulation of power of condenser APKOH batteries. It allows to include and disconnect sections of condenser batteries depending on the following parameters: reactive power, mains voltage, mains voltage and current.
"Instructions on reactive power compensation" provide control of the following indicators of the mode of reactive power in distribution networks:
- the largest reactive power consumed for the half-hour period in the mode of the greatest active loading of the power supply system;
- the reactive energy given in network of the power supply system during the night failure of the schedule of active loading of the power supply system.
The periods of the greatest active loading of the power supply system and night failure of the schedule of its loading have to be specified by the power supplying organization in the contract for supply of electricity to the consumer.
To economic incentives of consumers for holding actions for reactive power compensation discounts from the rate for electrical energy and extra charges are applied to it.Top