Switching by Capacitor duty contactors with necessary protection.
Low loss EPCOS capacitor banks with inductance in series to prevent high inrush current.
Dry type - soft resin - self healing - low loss - over pressure disconnected type reputed make capacitors are used. It gives compact and high safety construction.
On consumer request as well as depending on site condition heavy duty capacitors can be used to operate in continuous high voltage
Schneider, L&T and GE switch gear components manufactured according to IEC standards are used in panel.
Micro controller based PF controller with 4 quadrant measurement and built in protections is used to select capacitor banks.
Continuous display of instant power factor and other related data such as kVAr, required kVAr etc.
Panel design is available for 1:1:1:1, 1:1:2:2, 1:2:2:2, 1:2:4:4, 1:2:4:8 capacitor steps. Hence smooth and accurate compensation is possible with minimum switching operations.
Facility to operate in Auto/Manual mode.
Customized panel construction is possible
Rating from 50 kVAr to 300 kVAr for 3 phase 415 V, 50Hz applications.
Introduction
Majority of the loads in the industries are highly inductive in nature such as induction motors, AC/DC drivers, welding machines, arc furnaces, fluorescent lightings, electronic controls and computers. There may be a few resistive loads for heaters and incandescent bulbs. Very rarely industries may have capacitive causing a very poor lagging power facor. If this poor power factor is left uncorrected, the industry will require a high maximum demand from Electricity Board and also will suffer a penalty for poor factor will inflate the monthly Electricity Bill. Since power factor can be corrected to near unity there can be huge saving from the Electricity Bill. standard practice is to connet power capacitors in the power system at appropriate places to compensate the inductive nature of the load. The relation between the different power parameters kW, kVA, kVAr, kWh, kVArh, average power factor and other basic detail are given
Disadvantages of having poor power factor are generally understood as follows:
More kVA demand for the given kW load and penalty for poor power factor -
hence higher running cost (electricity bill).
More line current for the given kW load and hence higher rated transformer,
switchgears and cables are required - hence higher capital cost.
More line current for the given kW load and hence higher losses at the
transformer, switchgears and cables - hence higher running cost.
More line current for the given kW load - Poor utilization of all electrical distribution
network and hence poor return on investment.
Higher voltage drops in the distribution network - hence poor performance of
electrical equipments resulting in production loss.
Higher voltage fluctuations - hence damage to electrical equipments resulting in
production loss.
Options
1)Digital ammeter for capacitor current
2)kVArh meter to show the kVArh pumped.
3)Harmonic Indicator and Load managers.(Grid as well as panel side)
Need to correct The Poor Power Factor:
Hence if we are able to correct the poor power factor to near unity on all occasions at all loads, we can bring down the kVA demand, line losses, increase the utilization of the distribution equipments, increase the performance of electrical equipments, avoids damages to electrical equipments and avoid production losses due to power related problems. Another major advantages is that near unity power factor not only avoids penalty, but also brings in incentive from Electricity Board for higher power factor. All the above savings in revenue expenditures improves the bottom line of the company directly adding to the profit. Hence the investment on a good power factor correction system will have an attractive pay back. Subsequently the return on the investment will be high.
Various Methods of Power Factor Correction System
Using Power Capacitors, the poor power factor can be corrected in the following method.
By providing fixed value of capacitors to the distribution network at various points. They will be switched in/out as per the load manually.
Using APFC panel at the various points of the distribution network - Here automatic power factor correction takes place with the help of power factor controller and power contactors by switching in/out 4/6/8/12 steps of capacitor bank as the power factor varies.
Comparision of methods:
Advantages and disadvantages for the above various methods are analyzed as under.
Fixed value capacitors - simple and cheap, but effective correction not possible. Over compensation at lean loads result in high voltages, transients and leading power factor which are detrimental to the system. Huge inrush currents due to capacitor switching are not limited and hence failure of capacitors and other switch gears in the circuit takes place frequently. Transients damages the sensitive electronic equipments. Power harmonics present in the system may get increased with capacitors connected due to resonance.
APFC Panel using Power contactors - Effective correction in reasonably possible . But capacitors switching with inrush currents with power contactors are having limitation and also the damages to capacitors and contactors are frequent due to bouncing of contacts. Failure of sensitive electronic equipments may show a downward trend. Even though certain amount of resistive/inductive air cored coils are included in each step to reduce the in rush currents, they are not mitigated to satisfactory levels. Hence capacitors, contactors and switch gears are likely to fail. Power harmonics present in the system may get increased with capacitor connected due to resonance.
however in rush current produced due to switching of capacitors using contactors can be avoided by using SSR's as switching element. The harmonics can be reduced by using detuned capacitors banks.
Fast PF Regulator
The power factor controller accepts voltage and current signal, computes kVAR of the load, requirement of the compensation as per the set point and activates the relays to switch in/out the capacitors banks.
System Function
Automatic Power Factor Correction Panel is used for centralised power factor correction in systems serving mainly linear load. They are installed in switch boards or distribution boards.
The Control Panel consists of Electronic Power Factor Controller equipment which measures reactive power of the feeder. When the load power factor differs from the preset value, the PF relay activates contactors to switch capacitors in and out in steps as required.
The Capacitors banks are selected in order to have better accuracy of PF tuning automatically. No. of steps can be minimum 4 to max. 12 steps. Total capacitors bank required to reach desired Power factor is divided into several steps depending on the loads and to avoid over compensation and frequent ON/OFF operations. More No. of steps ensure better accuracy and reduces No. of operations of capacitor banks.
