In your daily routine, you come across various electronic devices to save time. To work efficiently, they need enough power. However, more than required can cause wire insulation damage and a short circuit in the machine. Then, what can you do then to balance out voltage fluctuation? Place a Capacitor Bank so that they can get enough amount of needed electricity.
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What is a Capacitor Bank?
Capacitor Bank is the group of capacitors of the same range, joined in series or parallel to store more electrical energy. A single capacitor can store few charges, and a device can have one embedded on it. However, when you have to support bigger devices or a group of them, you require a capacitor bank.
-Diagram of a Capacitor bank-
Previously, power substations used them to provide adequate energy to the consumers without power lag or current phase shift. Now, this technology has spread to its household usage to support your devices as well.
How Does it Work?
Manufacturers design capacitor banks to correct AC fault currents or provide a DC power supply. A single capacitor has two conductive sheets separated by a capacitor dielectric such as air or any other material. Electricity charges the plates oppositely so that they can maintain a static electrical field between them.
Over time, charges start to move from one plate to another, dissipating energy and thus providing electricity to the connected devices. In a bank, these little capacitor units have parallel or series connections in them. This increases their due capacitance and so, they can dispense energy to power stations and big factories.
Capacitor Bank Types
According to their manufacturing, capacitor banks have the following types.
In this arrangement, each capacitor unit has its fuse unit connected externally. Upon any issues, this fuse is blown out and disconnects the faulty capacitor unit. Bank continues its work without any interruption but provides lesser voltage than before. In addition, even if all the units are healthy, a faulty fuse unit could affect the performance of the capacitor bank.
The internally fused type connects every element of the capacitor with the fuse, all enclosed in the same box. You can easily install and maintain it as it has low-rating units. Upon failure of any single element, the bank can continue to work. The major drawback is if more elements stop working, you cannot change each of them; instead, you have to buy an entirely new bank.
To eliminate the need to fuse the bank’s capacitors, “fuse less” connects all the capacitor units in series with each other to form a string. Then, it connects each string in parallel to form the bank. Upon failure of one capacitor, other capacitors in series camouflage its absence. Thus, this type does not require fuses to operate.
What are its uses?
-Picture of Wiring of a typical power source-
Capacitors banks are ideal for sustained running of electrical appliances. You can use a capacitor bank for
Compensating Reactive Power
Adding an inductive load across the system lowers the quality of power given through the main supply. To improve the power factor lag, you can add capacitors. Thus, they can reduce the load of the actual power supply and overcome the lack of reactive power.
Power Factor Correction
In the power distribution process, capacitors improve the power shift phases. It appears as an additional load in the system and reduces the wastage of unused power. As the power factor is the ratio of used power to the total provided power, this adding of capacitor makes both the quantities equal so that pf can reach 1.
Capacitor banks save energy in the form of electric charges that a system could waste without them. Greater is the capacitance of a bank, larger is the amount of energy it can store. Electric devices that require DC supply also use capacitors to maintain the power supply while charging their batteries.
The capacitor is a source of high resistance when placed across a circuit, not for higher frequency signals. Therefore, you can use shunt capacitor banks to block noise. Therefore, signals of higher carrier frequencies do not reach out to the appliances, and abrupt fault current does not occur.
-Picture of a Shunt Capacitor Banks-
Reducing Fault Current Cost
As the system has a low power factor, friction inside the wires wastes a larger amount of energy as heat and opposing force. Nevertheless, electricity providers have no concern with this issue, and you get lesser than what you are paying off your bills. Installing a capacitor bank can reduce this issue, and save the extra energy to complete the requirement of your devices.
Substation Capacitor Bank
As capacitor banks can improve power factor, hence provided voltage quality, people install them at substations. They connect several capacitors in series to improve the voltage profile. By its addition, the power factor angle is reduced as the current is now leading the voltage. As the angle reduces, you know that the power factor is improving.
By increasing the inductive load on the consumer side, the demand for reactive power increases. The load, e.g., water pump, requires more reactive e power to create magnetic flux and make its coil moving. This increased demand causes the power factor to drop and imbalances the power consumption. More energy losses become a burden on the plant.
When you use a capacitor bank on the production side, it becomes a source of the consumers’ reactive power, thus making the plant more efficient in its work.
Can we only use Capacitor Banks on a larger scale?
With time, the capacitor banks have expanded their usage to a smaller scale as well. Mobile phones use small-power capacitor banks with super-capacitors to reduce their charging time. A super-capacitor can hold its charges a hundred times more than an average capacitor, we use it as low voltage rechargeable batteries in most cases too.
In wireless spaces, tiny micro-electro-mechanical systems, also known as MEMS, replace full-sizeable capacitors. Research shows that the capacitors can also supply large pulses of current that many pulse power devices and weapons need. A high-energy bank with a modern semiconductor switch can create pulse up to hundreds of kilojoules and a high amp electric pulse. Radar, fusion research, and Marx generators are the common and exotic applications of such high-density pulses.
What to do for Capacitor Bank protection
During installation, to limit the inrush current, reactors are attached in series with the capacitor banks. These reactors can protect it.
Overcurrent (unbalance) relay
Due to blown fuses or short-circuiting inside the bank, some capacitor units may get faulty. These units no longer remain the part of the connection that causes burden to fellow units inside the chain. It may not be a problem at first but as the number of faulty units increases, the asymmetry becomes more visible.
Overcurrent relays detect this unbalancing inside the capacitor banks so that you can replace it on time without causing any damages all over the circuitry.
Capacitors are in series with the reactors so if there is over-voltage; you cannot easily detect it. As it can stand only 110% of rated voltage, after this increase, the capability curve starts following an inverse time characteristic, that is, current starts decreasing.
To detect this, an overload relay is introduced that measures the current from the bank and converts it into corresponding voltage. It prevents the capacitor to discharge the energy on a short supply of voltage, even though there is no need.
Short circuit protection
Other than over-current and voltage issues, the capacitor is also vulnerable to short-circuiting and earth faults. For this situation, a 2-phase or 3-phase short circuit protection and an earth overcurrent relay can be a good solution.
What to consider while choosing a Capacitor Bank?
While choosing a capacitor bank for any situation, you have to consider few parameters that are
- Voltage Rating, to sustain voltage peak and surge voltages. It has up to 110% of normal peak voltage and 120% of normal RMS voltage.
- KVaR Rating, to ensure that the system gets sufficient reactive power. Capacitor Bank Calculation needs the initial and desired power factors.
- Temperature Rating, to sustain the temperature of the bank while it is working. To calculate this rating, you have to observe the increase in temperature during sunlight and other energy losses.
- Insulation Level, as the medium used will play a huge role in determining energy provided, just like in any other electrical device.
- Rated current level, or RMS value of a current that is normal for charging the capacitor.
- Discharge time, to see in how much time the capacitor will run out of energy.
- Single-phase or three-phase, as both are useful for specific reasons.
As you know, electric energy travels from the main power source to your home via wires. In this process, the friction inside the wires converts this energy into heat and other energy forms. This is not a concern of the company, as they bill you based on the meter, which reads how much energy you have used in a month.
Here, if you have a capacitor installed, the energy heating up wires and straining your devices is redirected  towards it. Hence, it lowers your bill and you save yourself from repairing motors affected by power faults.