Control is very dynamic and follows the load
fluctuations without any delay.
Zero current switching technique is used, so there are
no voltage transients or surge currents during switch
IN/OUT - Hence improved life span of capacitor.
Thyristors are used for switching-Hence there is no
limit on number and frequency of switching.
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 customer request as well as depending on site
condition heavy duty capacitors can be used to
operate in continuous high voltage.
Low loss reputed make detuned reactors are used as
decided by the presence of harmonics in the system.
(RPD 9530 Only)
Scheneider and GE switch gear components
manufactured according to IEC standards are used in
the 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.
Rating from 50 kVAr to 600 kVAr for 3 phase 415 V, 50 Hz applications.
Customized panel construction is possible.
Introduction
Majority of the loads in the industries are highly inductive in nature such as induction
motors, AC/DC drives, welding machines, arc furnaces, fluorescent Lighting, electronic
controls and computers. There may be a few resistive loads for heaters and incandescent
bulbs. Very rarely industries may have capacitive loads such as synchronous motors. Net
industrial load is highly inductive causing a very poor lagging power factor. 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 power factor. These two factors of
high kVA demand and 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 connect 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
details are given
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, avoid
damages to electrical equipments and avoid production losses due to power related
problems. Another major advantage 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. This method is 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.
Using APFC Panel at the various Points of the distribution network. Here automatic
Power factor correction takes place with respect to load power factor with the help of
Power factor controller and Power contactors. Here effective correction is reasonably
possible. In both the methods high inrush currents are produced during switching ON/OFF
of capacitors. Hence capacitors, contactors and switchgears are likely to fail.
By Dynamic PFC panel with power factor controller and Thyristors instead of power
contactors .4/6/8/12 steps of capacitor banks will be switched in/out as the power factor
varies. Zero current switching of capacitors is possible with Thyristor switch.
By Dynamic PFC Panel with detuned capacitor banks. Here instead of plain capacitor a
detuning reactor is used in series with the capacitor. This method is recommended where
the industrial loads are predominantly non linear and causing power harmonics more than
that of the stipulated standards.
TYPE RPD 9520
FAST PF REGULATOR:
It is a high end power factor controller suitable for switching the
Thyristors. It accepts voltage and current signals, computes kVAr
of the load, requirement of the compensation as per the set point
and activates the Thyristor switching modules to switch IN/OUT
the capacitor banks. A special logic is written in the software for
selection of required compensation.
DYNAMIC SWITCHING MODULES
This module consists of an electronic card to see the Thyristor
switch in a capacitor with minimum voltage so that the switching
current is near zero. This, hence prevents heavy in rush current
in the capacitor and in the system. Even with phase reversal
this module functions normally. This module switch OFF the
capacitors during any phase failure condition.
POWER BLOCK
This is nothing but two Thyristors connected in antiparallel model
for use in AC system. Adequate dv/dt protection is provided by
snubber circuit. Over current protection and isolation of the bank
are achieved by MCCB. Thyristors are mounted on heat sinks with
proper cooling arrangements.
CURRENT LIMITING REACTOR
Suitable Iron core reactor is used in series with the capacitor for
di/dt protection of Thyristors.
CAPACITOR
Dry type - soft resin - self healing - low loss - over pressure
disconnected type reputed make capacitors are used. On
customer request as well as depending on site condition heavy
duty capacitors can be used to operate in continuous high voltage.
In this model Effective correction is possible as Thyristors
can be operated as many times as required. Inrush currents while
switching can be contained to a very low level as zero current
switching logics are employed for each step. This method is very
much adequate, if the power harmonics are within the limits
stipulated by the standards. Otherwise, power harmonics will get
amplified due to resonance.
EFFECTS OF HARMONICS
ON CAPACITORS
Capacitor reactance Xc decreases with the increase of
frequencies. Xc = 1/(2 ∏fc). Hence it offers low impedance
for harmonic frequency. So even smaller amplitudes of the
harmonic voltages result into higher current through the
capacitor which are detrimental to them.
More critical is the capacitor may cause parallel
resonance with transformer impedance at harmonic
frequencies. At resonance high current flow between the
capacitor and transformer and voltage magnification
takes place which is harmful to the system.
TYPE RPD 9530
One of the better solution for improving power factor under
harmonic conditions is by employing de-tuned capacitor banks.
De-tuned capacitor bank consists of a series circuit of capacitor
and a specific filter circuit reactor. The resonance frequency of the
de-tuned bank does not match close to any of the existing
harmonic frequency, it is normally lower than the lowest harmonic
frequency present in the system, usually 5th harmonic.
The main purpose of the de-tuned filter is to avoid resonance
condition of the capacitor with transformer inductance and to
prevent amplification of original harmonics. More or less harmonic
currents will be sucked from the grid depending on the de-tuning
frequency. Very common is a de-tuning to a frequency of 189 Hz
(7%) with reduction of harmonics approximately 30 – 50%.
At the fundamental frequency (50 Hz), which is well below the
resonant frequency, the de-tuned filter is capacitive and it
produces capacitive reactive power. Above the resonant
frequency the de-tuned filter is inductive and it cannot amplify the
typical harmonic frequencies such as the 5th, 7th, 11th, 13th, and
so on.
DE-TUNED REACTOR
ICD will make a study of power harmonics present in the system
and suitably select the de-tuned reactor according to the
harmonics present and the mitigation of harmonics required.
Dynamic PFC Panel using Thyristors employing
de-tuned capacitor banks is an excellent solution for the power
factor correction at all conditions of load whether it is fluctuating or
it contains power harmonics. Power harmonics are mitigated with
this system and power factor is corrected to the desired level
without any amplification of power harmonics. With this system
power quality will be much better and the performance of electrical
equipments will have their normal function with minimum
damages. Investment on this system will see a very good return
and add directly to the profit of the industry.
