Installation options for capacitor banks

Installation options for capacitor banks In a low voltage electrical installation, capacitor banks can be installed at three different levels: Capacitor banks - installation, protection and connection options (photo credit: powerstar.co.za) 1. Global installation 2. Segment (or group) installation 3. Individual (or single) installation After installation, we will discuss protection and bonding of capacitor banks.

1. Global installation This type of installation requires a capacitorcompensating device for all indoor substation feeders.

This solution minimizes the total reactive power of the installation and the power factor can be kept at the same level with the use of automatic regulation, which makes the power factor close to the desired one.

This type of compensation method requires the capacitor banks to have a wide range of power regulation , which can be determined by measurements taken 24h at the place of installation of the circuit breaker.

What's good about this solution 1. No reactive energy billing 2. This is the most economical solution, because all the energy is concentrated at one point and the coefficient of expansion makes it possible to optimize the capacitor banks.

3. Makes less demands on the transformer But the disadvantages are:

 

The losses in the cables (RI 2 ) are not reduced.

This is not the best solution for large electrical systems, especially when the distance between the source receiver and the nonlinear receiver is long. The greater the distance, the greater the losses in the transmission system.

2. Installation of segment (or group) The segmental installation of capacitors supposes the compensation of a load segment supplied by the same switchboard. The capacitor bank is usually controlled by the microprocessor-based device called a power factor regulator .

Beside, the requirements of the practice of segmented installation protection of capacitor banks .

In this case, capacitor banks are connected to the bars, which supply a group of loads.

What's good about this solution 1. No reactive energy billing.

2. Requires less feed and reduces heat loss in these feeds (RI 2 ) Includes expansion of each area.

3. Makes less demands on the transformer.

4. Stay economical.

But the downside is: - Solution generally used for widespread factory supplies.

3. Individual (or single) installation In practice, connect the power capacitor directly to the terminals of a device to be compensated. Thanks to this solution, the load on the electrical network is minimized, since reactive power is generated at the terminals of the device .

This method does not require control devices, since the capacitor banks are switched on and off using the same switch as the device .

What's good about this solution 1. No reactive energy billing

2. From a technical point of view, this is the ideal solution, because reactive energy is produced where it is consumed. Heat losses (RI 2 ) are therefore reduced in all lines.

3. Makes less demands on the transformer.

But the disadvantages are: 1. The capacitor is not used when the supply load is not operating.

2. The most expensive solution, given: 1.

The high number of installations

2.

The fact that the coefficient of expansion is not incorporated

Protection and connection of capacitors Operating device In the case of ultra-fast cycling loads (welding machines, etc.), the conventional capacitor control system (electromechanical contactors) is no longer suitable. High speed switching compensation systems using solid state contactors are needed.

The switching current of a capacitor depends on: 1. The power of the capacitor 2. The short-circuit power of the mains supply to which it is connected 3. Whether or not already activated capacitor banks are present In view of these parameters, it is essential to use fast closing and stopping devices (switch, contactor, etc.) . When choosing the operating devices, the user must be informed of the choice of equipment available (for the operation of the capacitors).

Contactors are specially designed by contactor manufacturers to operate capacitors and in particular to assemble automatically controlled capacitor banks. These contactors have auxiliary poles combined in series with precharge resistors which will limit the inrush current upon activation.

Capacitor installation options and tips for protection and connection (photo credit: esugitama.blogspot.rs)

protection In addition to the internal protection devices built into the capacitor:   

Self-healing metallized film Internal fuses Overpressure disconnection devices

it is essential to provide an external protection device to the capacitor .

This protection will be provided by: 1. Either a circuit breaker: 1.

Thermal relay, adjustment between 1.3 and 1.5 × In

2.

Magnetic relay, adjustment between 5 and 10 × In 2. Or HRC type GI fuses , rating 1.4 to 2 × in

Example // i n = nominal current of the capacitor i n = Q c / √3 U Example: 50 kVAr; 400 V three-phase i n = 50 / 1.732 × 0.4 = 72 A Connection - cable sizing The current standards for capacitors are set so that the capacitors can withstand a permanent overcurrent of 30% . These standards also allow a maximum tolerance of 10% on the nominal capacity.

The cables must therefore be at least dimensioned for: I cable = 1.3 × 1.1 (I nominal capacitor) that is to say. I cable = 1.43 × I nominal References // 

Reactive energy compensation and energy quality monitoring by Legrand



Reactive Power Compensation - Master Thesis by Jakub Kępka at the Faculty of Electrical Engineering