The increasing penetration rate of photovoltaics connected to the power grid has brought many problems to utility providers. One of the main issues is that most of the power electronic devices used consume reactive power, which can lead to low power factor and unstable power systems - this problem once again drives the development of power factor correction. Now we will discuss the two most commonly used reactive power compensation methods.
Power Factor
The electricity used to operate equipment is called power or apparent power expressed in volt ampere (S). The apparent power is a combination of active power and reactive power, with active power represented by VA (P) and reactive power represented by VAR (Q).
S2(KVA)=P2(KW)+Q2(KVAR)
The power factor determines the efficiency of a system and is the ratio between active power and apparent power. The lower the power factor, the lower the efficiency of the system. The power factor lags behind inductive loads and leads capacitive loads. Resistive loads have a unity power factor.
Power Factor Correction
Power factor correction achieves uniformity in power factor. The importance behind power factor correction lies in the impact of low power factor on energy prices, instrument lifespan, and accessory sizes (such as cables).
Usually, induction motors used in industrial factories operate under low loads, arc lamps, and different power usage conditions for a short period of time, resulting in low lag power factor. Therefore, utility companies charge these factories using power factor or maximum demand electricity price (KVA electricity price).
Due to their short lifespan, machines, conductors, and electrical components operating at low power factors will experience overheating issues. Considering all of this, utility companies and consumers are seeking a way to ensure that the power factor is close to uniform.
Power factor correction method
There are several methods for power factor correction. The two most commonly used types are capacitor banks and synchronous capacitors.
1. Capacitor bank:
A capacitor bank is a system that includes multiple capacitors used for storing energy and generating reactive power. Capacitor banks can be connected in a triangular or star (Y-shaped) configuration. The rated value of power capacitors depends on the reactive power they can generate. The rated power of the capacitor is KVAR. Since the international unit of measurement for capacitors is Farad, an equation is used to convert the Farad capacitance to the equivalent reactive power of KVAR.
2. Synchronous capacitors:
Synchronous capacitors are only overexcitation synchronous motors that operate without load. When connected in parallel with the load, the synchronous capacitor generates the required reactive power for the system.
The size of synchronous capacitors is directly proportional to the reactive power that the electrical system may consume.
Synchronous motors operate in three different states. Lack of excitement, moderate excitement, excessive excitement. The state changes with the variation of excitation current. Underexcited synchronous motors act as inductive loads, thus consuming reactive power. The intermediate excitation motor acts as a resistive load, so there is no reactive power consumption or generation. Overexcitation state, in which the current sine wave leads the voltage, thus generating reactive power with a leading power factor.
Conclusion
All power factor improvement methods lay under the same principle. For every load with a lagging power factor, a load with a leading power factor must be connected in parallel to ensure a power factor close to unity.
