A parallel connection of capacitors - is a battery, wherein the capacitors are at the same voltage and the total current is equal to the algebraic sum total of currents of said elements.
The main theses
When the parallel connection of capacitors of capacity added, allowing you to quickly calculate the result. Operating voltage capacitors is the same, and the charges are added together. This follows from the formula derived Volta in the XVIII century:
C = q / U, then the C1 + C2 +... = q1 + q2 +... / U.
Parallel connection of capacitors is converted into a single high-capacity capacitor.
Why include capacitors in parallel
- The adjustment to the radio frequency waves is performed switched capacitor blocks providing input resonant circuit resonates.
- The filters powerful power units for the duty cycle will store a lot of energy. Build its inductance is not economically feasible. Apply a parallel set of large electrolytic capacitors.
- Parallel connection of capacitors occurs in measuring circuit. Standards of the branched off portion of the current at nominal value is estimated - the size of the test capacitor capacitance.
- In parallel, periodically set reactive power compensators. This device will block the excess energy into the supply network. What prevents interference overload generators, transformers and wiring excess heating.
Reactive power network
When the induction motor operates, there is a discrepancy between current and voltage in phase. It is noted due to the presence of the winding showing inductive reactance. As a result, part of the power is reflected back into the circuit. The effect may be eliminated if the inductive reactance to compensate for capacitive. Another method - the use of synchronous motors, is effective at voltages of 6 - 10 kV.
If possible, the company should consume all their own produced reactive power. But synchronous motors are not always suitable process conditions. Then put the condenser units. Their expected reactance equal inductance of the motor. Of course, ideally, because the production conditions are constantly changing and it is difficult to find a middle ground.
If you use the parallel connection of capacitors and switching using relays properly, the problem is easy to solve. Individual enterprises of the reflected reactive power is also paid. When not using the anticipated economic losses. Energy suppliers can understand that the reactive power transmission line clogs line, load transformer and if the equipment is not able to give a full load. If every company will upload the channel plus the current economic situation of Power immediately poshatnotsya.
reactive power relay massively distributed and will help determine what part of the capacitors included in the work. Example cost calculation is shown in the graph below. There is an optimum point, step over that is not economically feasible. But it is allowed to do because of other motives.
Connection scheme compensating units
The three-phase networks compensation capacitors put threes on two well-known schemes:
- Star.
- Triangle.
Reactive power in these cases is calculated according to the formulas shown in the figure. After Greek omega denotes the circular frequency of the network (2 x pi x 50 Hz). The relations obtained that the circuit of the capacitors triangle advantageous: power has increased 3 times. Explanation - Star uses a phase voltage is 1.73 times less than linear. Compensated by the reactive power depends on the square of this parameter.
From these considerations, three-phase capacitors are always made a triangle and a star have to beg for an individual order (three-phase capacitor). There is a flip side: the voltage at 1.05; 3,15; 6,3; 10.5 kV all single-phase capacitors. Acceptable splicing, as it pleases. The star, for example, is less than the operating voltage, so each capacitor individually will be cheaper. Both schemes can not be attributed to parallel-connected, like three, however, are united in:
- group;
- section;
- installation.
And in association single phase capacitors can be connected in series and in parallel, and the three-phase - exclusively in parallel. Recommended ratings of all the individual elements to choose the same. This simplifies the calculation, equalizes the load on the electrical circuit parts. Known installations where there is a mixed compound on each phase. Formed parallel branches of series connection of capacitors.
Fitting operate single or three-phase. In networks with a voltage of 380 V is always applied parallel connection of capacitors. An exception is recognized case of equipment use with a single phase 220 V (phase) and 380 B (linear). Then the device is placed under the Individual (or group) to compensate reactive power. The lighting networks capacitors for the most part put after the switch, for obvious reasons. In other cases - depending on the features of the operation of the facility.
For voltages of 3, 6 and 10 kV single-phase capacitors included normal or double star (see. Fig.). One conclusion is grounded (earthed neutral). For this reason, it allowed to use the single-phase capacitors, including a single isolated output. In the latter case, you must make sure that the neutral conductor goes to the cabinet.
The main switch is placed in a particular section of the protected equipment (geographically), and controls the compensation circuit generally uses or removes the additional reactance. If in a particular sector of technological equipment is idle, the main switch will break the compensation circuit. Condensing units usually cost in the dedicated room together, electrically connected in parallel. Before each worth circuit breaker relay regulation to increase or decrease the total capacitance compensators.
Depending on the equipment used now, the amount of reactive power causes the assistance condensing units, respond flexibly to existing needs. Eventually:
- Section of the equipment are connected in parallel. It is easy to understand if you imagine household appliances are powered by an extension cord. All connected in parallel. But installed, for example, various shops, sectors, etc. There are cases when a large power plant (for example, hydroelectric generator) is divided into relatively independent sections.
- Capacitor units are connected in parallel, but generally, in one place, so that succeeded automatically or manually easily adjust the overall capacity by switching switches lightweight type. A capacitor can operate for reactive power compensation of any of the sections, or both at once.
Features capacitor protection
Main switches are generally used in case of accidents and cut down at once the whole section of the equipment. Capacitor installation typed in section parallel connection. Then the main switch once cut down a similar "battery." And the other section condensing units will remain in operation. It is important to understand that the protective equipment, as well as protect, manage to be grouped in different ways. Depending on the convenience and economic feasibility.
Lightweight switches are used, usually in the regulation circuits. Controlled via the relay and increase or decrease the overall capacity of capacitor banks. The vacuum or sulfur hexafluoride is selected as the main switch.
A feature of the chains above 10 kV is to use a single-phase capacitors, collected by the scheme star or triangle, in each branch of which is parallel-sequential group of containers (cm. Fig.). In the presence of products with high working voltage permissible to do the contrary, to apply serial-parallel switching. Then working voltage capacitors are selected so that the number of groups included each other was minimal. The voltage on each of the elements, of course, increases. For reference: the series connection of capacitors.
If you do everything according to the described routine, in case of failure of any circuit element reactive power compensation other will continue to operate in a relatively gentle. Of course, the circuit parameters to be controlled, and operating personnel, according to the procedures, test leads condensing units on serviceability. When designing should take into account a small feature:
The more compensation circuit successive groups of capacitors, the more difficult to each provide a uniform stress distribution. In particular, there may be a certain segment of the frequent congestion.
In addition, the complex electrical connections is not easy to check service personnel. Ornate scheme responds poorly to mounting, frequent mistakes. It is considered an ideal capacitor parallel connection blocks of each phase. Then mount easily and verification procedure is simplified as much as possible.
discharge capacitors
capacitors connected in parallel have a large capacity, at the termination of the work on them is still charged. It is possible to feel, if you touch the connector just off old drill. The new models filter is designed so that the circuit is discharged through a resistor, and the like is not observed.
To reduce the voltage is allowed to use and inductance connected in parallel capacitors. In this case, the grounding resistance of the alternating current is very large, and for permanent - easy to overcome this stretch. During the current operation of the equipment is small, the losses are small. After stopping the production line charge gradually merges via a high resistor or inductance. Of course, not forbidden to put in a relay circuit ground, make contact only after turning off all devices. The design is more expensive and requires automation.
The process of the discharge circuit is important from the viewpoint of ensuring safety. Represent: a condenser from the outlet of charged long stores the potential difference and presents a danger to others. The single phase 220 V discharge is performed via the input filters, provided that the case is properly grounded. The resistance in the circuit, the capacitors connected in parallel is determined by the formula shown below.
Under Q means a reactive power setting in Vary (BAP) and Uf - phase voltage. It is easy to show that the formula given at the rate of discharge time: Q depends linearly on the container being moved in the left part of the formula RC time constant will. In three such periods the battery is discharged by 97%. On the basis of these conditions can be found and inductance parameters. And the best - in series with a resistor her turn, as is often done in real circuits.
