LV power factor correction

  • 1. Active EnergyOpen or Close

    The form of energy that represents Useful Work, or rather mechanical work, thermal or light energy (heating, lighting, motors) obtained by feeding the user loads. Measured in kWh.

  • 2. Active PowerOpen or Close

    The Electric Power that is converted into useful work, or rather mechanical work, thermal or light energy (heating, lighting, motors). Measured in kW.

  • 3. Ambient air temperatureOpen or Close

    The PFC system and its circuits must be able to bring their rated currents without exceeding the temperature limits tolerated by different components of the system itself. The temperature of the ambient air is the temperature outside the PFC system at which the components inside it can work under nominal conditions without exceeding the limits assigned by the manufacturer to the components.

  • 4. Apparent Power Open or Close

    The Power drawn by a Vector Sum of the Active Power and the Reactive Power. It coincides with the Active Power only in the event that the voltage and current are in phase. Measured in kVA.

  • 5. Automatic PFC controllerOpen or Close

    The control unit with microprocessor technology mounted on the Automatic PFC. It measures the phase displacement of the current absorbed by the load with respect to the voltage (cos phi) and on the basis of the measured values it decides the capacitor banks to be connected or disconnected.

  • 6. BanksOpen or Close

    The number of Capacitor Banks of a Power Factor Correction system necessary to implement a specific Reactive Power at the Operating Voltage Ue.

  • 7. Busbar system Open or Close

    Low-impedance system in Copper or Aluminium that collect the Inductive Reactive Powers generated by the PFC banks.

  • 8. CapacitorOpen or Close

    Electrical component that absorbs a current almost 90° in advance of the voltage, which can therefore be seen as the generator of the inductive reactive power required by the load to be corrected. This quota of reactive power is "discharged" from generation and transformation machines and from all the lines upstream of the PFC distribution point.

  • 9. Centralised power factor correctionOpen or Close

    Consists in installing a single Automatic Power Factor Correction system upstream of all the plant to be corrected. It will be powered by a start of the Low Voltage Panels (Power Center). It allows the minimum value of cos phi 0.95 to be reached such as to avoid penalties due to excessive engagement of reactive energy established by ARERA (Italian Regulatory Authority for Energy, Networks and the Environment). It does not however offer any advantage on the sizing of the plant, nor does it reduce losses downstream of its distribution point.

  • 10. ContactorOpen or Close

    Also called Remote control device, this is a mechanical device having only one rest position, with non-manual operation, able to establish, carry and interrupt currents under nominal conditions, including operating overload conditions. Used to connect or disconnect capacitor banks on controller command.

  • 11. Cos phiOpen or Close

    The relationship between Active Power P1 and Apparent Power S1 absorbed by a single user or a plant, where P1 and S1 are the Active Power and Apparent Power, assuming that the harmonic content is zero and the only fundamental component is present. Coincides with the Power Factor only in the case of absence of harmonics.

  • 12. Degree of protectionOpen or Close

    A code established in standard IEC 60529 that indicates the level of protection foreseen for the PFC system against contacts with active parts, entry of solid foreign substances and liquids.

  • 13. “Detuned” PFCOpen or Close

    In the presence of Harmonics at frequencies capable of triggering Resonance between the PFC and the Plant, it is necessary to install detuning reactors in series inside the capacitive banks within the PFC. This PFC is called “detuned” from the term relating to detuning inductances, "detuned reactors".

  • 14. Dielectric loss of the CapacitorOpen or Close

    All Capacitors are not in their construction pure capacitance; in fact, they have active power dissipations called Dielectric Losses. The ratio between these dielectric losses P and the reactive power of the capacitor Q represents the Loss factor which for our capacitors is lower than 0.2 W/kVAR.

  • 15. Discharge resistorsOpen or Close

    Capacitors cannot be re-energised if they have a residual voltage higher than 10% of their rated voltage. For this purpose, they are provided with resistors which, in accordance with IEC 60831, allow discharge at a voltage equal to or less than 75 V in 3 min starting from an initial peak voltage equal to times the rated voltage Un.

  • 16. Disconnector under Load (Switch Disconnector Device) Open or Close

    An operating switch which, in the open position, ensures the PFC system is disconnected from the rest of the Plant. It can establish and interrupt the current in normal operating conditions and it can also withstand a short-circuit current for some time, but it cannot interrupt it. It is characterised by the value of the short-term Withstand Current (typical period 1 s).

  • 17. Distributed power factor correctionOpen or Close

    This deals with the Power Factor Correction of User Loads of a certain Power, applied locally. It raises the value of the Power factor over the entire network upstream of its distribution point, allowing the reduction of joule losses, advantages on the component sizing and current reduction with the same Active Power on the MV/LV transformers and on the cables with consequent increase in their duration.

  • 18. Filter or detuning reactorsOpen or Close

    The only solution to avoid Resonance problems between the Plant and the PFC system. They are in fact connected in series and tuned to the capacitive banks of the reactors at a frequency lower than the lowest frequency of the harmonics present. The impedance of the Reactor-Capacitor series for a frequency higher than the previous tuning frequency is inductive. Resonance conditions can no longer be created between a Plant that has a typically inductive impedance and the Reactor-Capacitor assembly that also has an inductive impedance to the harmonics.

  • 19. FusesOpen or Close

    A protective device against short-circuit. These protect from short-circuits inside the PFC system involving the switching equipment, wiring and components downstream of their installation point.

  • 20. Inrush currentsOpen or Close

    A transient current surge of high amplitude and frequency that may occur when a capacitor is energised by means of contactor. The amplitude and frequency of this overcurrent are determined by factors such as the short-circuit impedance of the power supply, the capacitance connected in parallel and the instance of insertion. In order to limit this current peak, the contactors are equipped with insertion resistors that limit the value of the current on insertion.

  • 21. Low voltageOpen or Close

    The rated voltage of an electrical system is the voltage for which the system has been designed. In the case of three-phase systems, the effective value of the connected voltage is considered. Low Voltage Systems are those with Rated Voltage up to 1000 V in alternating current and 1500 V in direct current.

  • 22. Mean life expectancyOpen or Close

    The average time up to which useful service of a capacitor is expected at nominal voltage and current conditions and with the power factor correction system installed in an environment with a temperature that does not exceed the value declared in the specification phase.

  • 23. Mixed power factor correctionOpen or Close

    Within the same plant, the use of a centralised PFC system and one or more distributed PFC system on some more energy-consuming users represents the so-called "Mixed power factor correction”.

  • 24. Modular RacksOpen or Close

    This is the "plate" including the Capacitors, the detuning inductances (where present), the contactors (or thyristor modules), the protection fuses and the wiring cables between the components, which can be extracted from the PFC system to facilitate maintenance operations.

  • 25. Operating voltage Ue Open or Close

    The voltage value which, together with the rated current Inc of the capacitor, defines how a power factor correction system is used and the Reactive Power actually generated by the Power factor correction batteries.

  • 26. Overpressure deviceOpen or Close

    At the end of the life of the capacitor, there is an increasing number of internal discharges which determine an increase in pressure inside the cylinder which contains it. To prevent explosion, the capacitor is equipped with suitably prepared connections that cause overpressure and resulting upward thrust of the cover, causing the capacitor to disconnect from the mains.

  • 27. Power factorOpen or Close

    The ratio of Active Power P to Apparent Power S absorbed by a single user or a plant. In the definition of the Power Factor, both Active Power P and Apparent Power S take into account not only the contribution of the fundamental component but also of the harmonics present.

  • 28. Rated Insulation Voltage UiOpen or Close

    The effective value of the Withstand Voltage, assigned by the Power Factor Correction System Manufacturer and which characterises the long-term withstanding of its insulation.

  • 29. Rated Voltage UnOpen or Close

    Effective value of the alternating voltage for which the capacitor has been designed. It is necessary to avoid adopting a rated voltage which is excessive with respect to the Operating Voltage, as this would result in a significant reduction of Reactive Power with respect to the Rated Reactive Power of the PFC system.

  • 30. Reactive EnergyOpen or Close

    The energy that is exchanged between the Network and the User Loads which need the creation of a magnetic field for their operation. Measured in kVARh.

  • 31. Reactive PowerOpen or Close

    The Power used to build up magnetic fields in inductive loads, for example with Motors. Continuously exchanged between the network and the load. Measured in kVAR.

  • 32. ResonanceOpen or Close

    A network connects various components to each other, for example generators, cables, transformers, motors, capacitors (PFC system). When the equivalent inductive reactor of the network and the capacitive one of the PFC system are equal for a frequency that is close to that of the harmonics present, the latter are significantly amplified and there are very high values not only of the current but also of voltage distortion. In case of triggered resonance, there are not only safe failures of power factor correction systems but also current peaks in the plant that can cause untimely operations with resulting, sometimes serious, out-of-service consequences both of the current and then between the rephasing system (equivalent capacitance of the capacitors) and the equivalent network inductance.

  • 33. Short-circuit current (Icc, Icw) Open or Close

    Regarding the Short-circuit Withstanding ability of a PFC system, CEI EN 61439-1 defines two values:

    1) Rated short-time withstand current (Icw) together with the corresponding duration (typically 1s), this value does not depend on the protection device (Automatic Switch) installed upstream.

    2) Rated conditional short-circuit current (Icc), dependent on the Automatic switch installed or as a general device of the Power Factor Correction system or as a starting point for the PFC that supplies the PFC itself.

  • 34. “Standard” PFCOpen or Close

    A PFC installation with insertion systems through electro-mechanical devices (contactors) and without addition of detuning reactors.

  • 35. StepsOpen or Close

    Steps are intended as the number of combinations that an Automatic Power Factor Correction system can be implemented with the capacitor banks available.
    Example: In Power Factor Correction system 400 kVAR with the following banks:
    50 – 50 – 100 – 100 - 100
    The number of possible combinations, and therefore of the different achievable Reactive Powers, is given by the following ratio:
    STEP = Qn/Q1

    Where Qn is the Rated Reactive Power of the PFC system in correspondence to the rated voltage and current values for the capacitors and Q1 is the reactive power of the smallest size bank. In this example therefore:
    STEP = 400/50 = 8

  • 36. THDcOpen or Close

    The capacitors are subjected to current overloads due to overvoltage and the presence of harmonics. At the regulatory level (IEC 60831-1), in order to take into account the causes of overloads and tolerances on capacitance values with respect to their nominal values, it has been established that a capacitor must be able to work at a current of maximum effective value equal to 1.5 times the rated current of the condenser (Inc).
    The regulations therefore take into consideration only the maximum effective value of the current that a capacitor must be able to sustain.
    The THDc reported by all manufacturers of power factor correction systems would like to represent the Total Current Harmonic Distortion Factor that a capacitor can withstand. This is an empirical datum which, however, does not find any confirmation in the regulations and, once the capacitor seal is guaranteed in terms of effective value of the current, obviously also the contribution due to the harmonics is taken into account.

  • 37. THDiOpen or Close
  • 38. THDvOpen or Close
  • 39. Thyristor ModulesOpen or Close

    A thyristor is an intrinsic regulation component in a static module and works in principle as an electronic switch that fulfils a switching process in each half-wave of the supply network. The module is composed of two thyristors per phase (one for the positive half-wave, the other for the negative) connected in antiparallel. The addition of the capacitors and the detuning reactors is thus implemented without moving parts. The thyristors are controlled in correspondence with the natural zero passage of the capacitor current. The capacitors are thus connected to the plant without relevant transients.
    Unlike the traditional solution with contactors in which it is not possible to precisely check the exact switching time, this "static switch" is the ideal choice for rephasing loads with sudden variations in the request for Reactive power.

    Static insertion provides the following advantages:
    • Maximum speed in capacitor bank insertion (< 50 ms)
    • No current peak on capacitors during the bank insertion phase
    • No voltage peak on capacitors during the bank disconnection phase
    • Elimination of problems related to the use of contacts in traditional contactors
    • Extremely silent
    • Very rapid power factor correction
    • Reduction of voltage fluctuations
    • Increased capacitor duration

    Maintenance is reduced to simply a visual inspection of the heat sinks and forced ventilation (if present) on an annual basis. The device self-protects itself from possible overheating.

  • 40. Utility Open or Close

    A term used for an electric or power company or energy authority that supplies electrical energy.