Compensation is the process of balancing reactive power generated by loads during the transmission and consumption of electrical energy to eliminate their negative effects on the system. This process is based on the principle of balancing the reactive power caused by inductive devices with capacitive reactive power. As a result, the apparent power of the system decreases, the current level drops, and losses in transmission lines are minimized.
Power Triangle and Reactive Power Definition in Alternating Current
To properly analyze reactive power and compensation, it is first necessary to understand the basic structure of alternating current (AC). Alternating current (AC) is a type of current that changes direction periodically over time and exhibits amplitude variability. Its widespread use in modern energy transmission and distribution systems stems from its ability to provide lower losses during transmission over long distances at high voltage levels. Therefore, electrical energy is transported from power plants to distribution points in the form of alternating current.
Alternating current circuits have three fundamental power components related to energy transmission: active power (P), reactive power (Q), and apparent power (S). Active power represents the power component where actual work is done and is measured in Watts (W). In circuits that generally contain only resistors, there is no phase difference between current and voltage; therefore, all the energy in the system is actively used.
However, if reactive elements such as inductance (L) or capacitance (C) are also present in a circuit, a phase angle is created between the current and the voltage. Due to this phase difference, some of the transmitted power acquires a reactive character. Reactive power is the power component required for the creation of a magnetic or electric field but not directly converted into work. It is expressed in volt-ampere-reactive (VAr) units. In alternating current circuits, apparent power is calculated by multiplying the phase voltage by the effective values of the current flowing through the circuit and represents the total power requirement of the circuit. Apparent power is expressed in VA (Volt-Ampere) units.
Active Power (P) – In Watts (kW) and is the energy that is directly converted into work.
Reactive Power (Q) – In kVAr, does not contribute to energy transfer but produces a magnetic field.
Apparent Power (S) – In kVA, is the vectorial combination of active and reactive power.
Since the relationship between these power components is shown in a triangular shape, this structure is called the “power triangle”.
The power formulas for alternating current are as follows:
For single-phase circuits:
S = U x I
P = U x I x cosα
Q = U x I x sinα
For three-phase circuits:
S = V³ x U x I
P = V³ x U x I x cosα
Q = V³ x U x I x sinα
Here:
S is the apparent power (VA),
P is the active power (W),
Q is the reactive power (VAr),
U is the phase-to-phase voltage (Volt),
I is the current (Ampere),
α represents the phase angle between the current and voltage.
An increase in the phase angle leads to an increase in reactive power and a decrease in active power. This lowers the power factor, negatively impacting system efficiency. At this point, compensation applications improve the power factor by reducing the α angle and minimize energy losses.
Electrical grids are not solely structures carrying active power. Due to inductive or capacitive loads, reactive power constantly circulates within the system. Maintaining this balance is critical for both grid stability and energy efficiency. Compensation is the fundamental solution for achieving this balance.
Since electrical systems are dynamic structures, the reactive power requirement constantly changes throughout the day due to the influence of different loads. Automatic compensation systems, used to balance this change, monitor the power factor of each phase via three-phase reactive power control relays and activate capacitors or reactors accordingly.
Basic Principles of Reactive Energy and Compensation
Every system that consumes electrical energy requires a certain amount of reactive energy in addition to active energy. Reactive energy is used to create magnetic or electric fields, but it is not directly converted into work. Alternating current, produced in power plants and transmitted through the grid, requires reactive power to operate in devices such as generators, transformers, and motors. This power increases the apparent power by creating a phase difference in the system.
Since reactive energy is not consumed, it returns to the transmission lines, causing unnecessary load on the lines. This load leads to voltage drop and additional energy losses in the transmission system. Through compensation, this reactive component is met by capacitive elements, reducing the load on the grid.
Especially in systems with inductive loads, such as elevator motors, water pumps, ventilation fans, transformer substations, and ballasted lighting, equipment generates a high amount of inductive reactive power. In this case, capacitive reactive energy is supplied to the system through parallel-connected capacitor banks. Thus, the reactive energy required by inductive loads is directly met by these capacitors.
When controlled generation of inductive reactive power is required in the system, shunt reactors are included in the circuit to balance the existing capacitive effect. Similarly, maintaining grid balance is essential for capacitive devices such as UPS systems, electronic lighting, and LED fixtures.
How is compensation performed?
The primary goal of power factor compensation in inductive electrical systems is to minimize the apparent power (S) of the system and, consequently, the phase angle (α) between current and voltage. A reduction in the phase angle causes compression of the power triangle, which can only be achieved by reducing the reactive power component (Q). This is because active power (P) represents the actual power demanded by consumers and, being dependent on the load characteristic, cannot be changed by compensation.
Most electrical loads, by their nature, are inductive and draw positive reactive energy from the grid. Therefore, to balance the inductive reactive power generated in the system, capacitive elements capable of generating negative reactive power are integrated. This is usually done by connecting capacitors in parallel to the loads. With this method, the reactive energy required by the system is supplied directly through the capacitors, thus significantly reducing the amount of reactive power drawn from the power grid.
When capacitors are activated, the total reactive power component in the system decreases, leading to a reduction in apparent power. As apparent power decreases, the amount of current flowing through transmission lines also decreases; this minimizes transmission losses and increases the overall efficiency of the energy system.
Capacitors are passive circuit elements created by placing a dielectric insulating material between two conductive plates. Although they are often referred to as “capacitors” in electronic circuits, these components are called “condensers” in energy systems. Modern UPS systems, LED-based lighting products, and various electronic equipment are generally capacitive in nature and cause capacitive reactive power load on the grid. To maintain reactive power balance in such systems, capacitor banks with appropriate values are designed and integrated into the system.
Compensation is a strategic energy management method applied to eliminate reactive power imbalances in the electrical system and improve the power factor of the grid. Capacitive elements (capacitor banks) or shunt reactors used to increase inductive effects are connected to the system according to the reactive load requirement. In this way, the total reactive power of the system is kept within the targeted limits, transmission losses are reduced, voltage stability is maintained, and energy quality is improved.
What are the benefits of compensation?
The primary goal of power factor compensation is to improve the performance and efficiency of energy systems by bringing the power factor as close as possible to the ideal value, i.e., one (cosφ ≈ 1). The power factor represents the ratio of active power to apparent power in a system; as this ratio increases, the transmission and distribution infrastructure is used more effectively, and the system operates more efficiently.
What problems arise if there is no compensation?If compensation is not implemented in the system, or if the existing compensation capacity is insufficient, the following problems will be encountered:
Electricity suppliers apply a “reactive power penalty fee” to facilities that draw reactive energy above the specified limits. These costs create a significant financial burden for large facilities.
Full efficiency cannot be obtained from active power due to a low power factor, and system performance decreases.
Voltage imbalances occur, which can cause damage to sensitive equipment.
Equipment such as transformers, generators, cables, and switchboards overheat due to carrying excessive current, increasing the risk of malfunction. Fire risk may arise due to the heating of the installation.
Why Should Compensation Be Applied?
Elektrik sistemlerinde yaygın olarak bulunan endüktif ve kapasitif karakterli yükler, güç faktörünü olumsuz etkileyen faz farklarına sebep olur. Bu fark, sistemde reaktif güç oluşmasına neden olur. Reaktif enerjinin şebekede yarattığı olumsuz etkileri ortadan kaldırmak, sistem verimliliğini artırmak ve enerji maliyetlerini düşürmek için kompanzasyon uygulaması kaçınılmazdır.
Özellikle sanayi tesisleri, alışveriş merkezleri, büyük ofis yapıları ve üretim hatları gibi yüksek enerji tüketen yerlerde kompanzasyon sistemlerinin kurulması teknik ve ekonomik açıdan zorunludur. Doğru tasarlanmış bir kompanzasyon sistemi sayesinde hem enerji kalitesi iyileştirilir hem de işletme maliyetleri optimize edilir.