In article” Power Factor CorrectionCapacitors Sizing Calculations – Part Fifteen” we indicated that The
Main Components of PFC Panel are as follows:
1 The Main Components of
PFC Panel

A Panel for
power factor correction (PFC Panel) is constituted essentially from the
following main components:

And we explained how to select the first three
items (protective devices, contactors and capacitors) in the past article. Today
we will explain the following:
 How to Select a Discharge Resistor,
 How to Calculate the Value of Discharge Resistor,
 How to Select Power Factor Controller,
 How to Calculate the Number of Physical Steps, Electrical Steps and Electrical Control.
Fourth: How to
Select a Discharge Resistor

IEC
Requirements for Discharge of capacitors

How
to Calculate the Value of Discharge
Resistor

Fifth: How to Select Power Factor Controller

Function Of PF Controllers

Difference Between Old And Modern PF
Controllers

PF
Controller and Step Combinations
The PF controllers
continually measure installation reactive power and monitor on/off of
capacitor steps in order to obtain the relevant power factor. Therefore, the
capacitor steps are arranged in step combinations, these combinations will
give many advantages like:
Meaning Of
The Step Combinations
For example, If we have
(7) step PF controller, it will have one of the following step combinations
There are many other step
combinations and in the same manner as above you can know the meaning of each
step combinations, for example:
1.2.3.6.6.6 etc.
1.2.4.8.8.8 etc.
The
Control Programs Of The Step Combinations
The below table shows the
possible control programs for each type of step combinations:

Electrical
Steps, Physical Steps And Electrical Control

Difference
Between Electrical Steps, Physical Steps And Electrical Control
1 Physical
Steps:
They represent
the Physical/real capacitor units seen by you inside the PFCC panel where
their KVAR sum is equal to the total KVAR required for power factor
correction and each physical step is tripped individually by a contactor.
2 Electrical
Steps:
they represent
the KVAR power seen by the electrical installation according to the connected
physical steps KVAR at each time, so
their total KVAR is varying according to the load variations of the
installation and their quantity =total
KVAR required/smallest physical step KVAR.
3 Electrical Control:
This is equal to the
number of electrical step, multiplied by the power of step no. 1 which is
always the smallest step.
For example, if we need
100 KVAR for power factor correction of an installation, and we plan to get
this 100 KVAR on 10 stages to give 10, 20, 30, 40, 50, 60, 70, 80, 90, 100
KVAR as per the load variations. So, we have two case solutions as follows:
Case solution#1:
Using 10 capacitors
with 10 KVAR each to get the 100KVAR = 10 x 10 KVAR, in this case we say that
the number of physical steps = the number of electrical steps. The step
combination in this case will be 1.1.1.1.1.1.1.1.1.1 and this case called the
physical steps method.
Case solution#2:
Using 4 capacitors with
ratings 10, 20, 30 and 40 KVAR to get the 100KVAR = 1 x 10KVAR + 1 x 20KVAR+
1 x 30KVAR + 1 x 40KVAR, in this case we say that the number of physical
steps = 4 and their step combination in this case is 1.2.3.4 and the number
of the electrical steps will be 10 steps as follows:
Case# 2 is called the
electrical steps method. Comparing the two above case solutions, we will
find the following:
So, using the electrical steps method gives
the following advantages:

How to Calculate the Number of Physical Steps, Electrical
Steps and Electrical Control

The number of electrical
step depends on:
Using the below table1,
you can find the number of electrical step.
Table1
Example#1:
A capacitor bank made up
of 7 physical steps:
1 of 30 kvar
6 of 60 kvar
Find the used step
combination, calculate the number of electrical steps and calculate the
possible power for each electrical step?
Solution:
* Step no. 1 is always
the smallest
Also, you can find the
Number of electrical step from table1 by look up for the column of 7
controller outputs with the row of step combination 1.2.2.2.2.2.2 which will
give the Number of electrical step = 13
Electrical control: 13
times the power of step no. 1 = 13 x 30 kvar = 390 kvar
The possible power for
each electrical step will be as follows:
Operating cycle:  = step
disconnected & 1 = step in operation
Conclusion:
Example#2:
Consider an APFC System of 250 kvar, calculate the number of electrical steps
and calculate the possible power for each electrical step and Find the used
step combination using the physical steps method and the electrical steps
method?
Solution:
Using the physical step method:
10 physical steps will be used each 25 KVAR to get 250 KVAR = 10
steps x 25 KVAR
Using the Electrical step method:
4 nos. electrical steps will be used with the following ratings 25,
50, 75, 100 KVAR.
Conclusion

Notes for designing a capacitor bank with PF controllers

In the
next article, we will explain how to choose Cables for Power Factor Correction Capacitors. Please, keep
following.
The
previous and related articles are listed in below table:
Subject Of
Previous Article

Article

Glossary of Power Factor Correction Capacitors


Types of Loads,
The Power
Triangle,
What is a power factor?
Types of power
factor
Why utilities
charge a power factor penalty?
Billing Structure.


What causes
low power factor?
Bad impacts
of low power factor,
Benefits of
Power Factor correction.


How to make
Power Factor Correction?
Types of
Power Factor Correction Capacitors
Individual compensation


Group compensation,
Central compensation,
Hybrid compensation.
Summary for Power Factor Correction
Capacitors Sizing Calculations Steps


Step#1: Collect Monthly Billing Data
Step#2: Make Some Preliminary Measurements
For Current And Voltage


Step#3: Fill the Economic Screening Worksheet


Step#4: Make Preliminary Measurements
For Harmonics
Step#5: Repeat the Economic Screening
Worksheet
Step#6: Compare the Savings with the
Probable Cost of Capacitors' Installation
Second: Design Phase
Step#1: Performing a Detailed Plant
Survey
Step#1.A:
Review the one line diagram
Step#1.B:
Take into consideration the loads that produce harmonics
Step#1.C:
collect sufficient data Inventory by using measuring instruments


Step#2: Select Economical Capacitor Scheme
Step#3: Checking the "No Load" Voltage Rise
Step#4: Select Capacitor Switching Options
Step#5: Check the Harmonic Distortion and make Harmonic
Mitigation Options
Step#6: Use the Economic Screening Worksheet again


Power Factor Correction Capacitors
Sizing Calculations Steps For New Designs


Factors Affecting The Rated KVAR For a Capacitor
Calculation of the Capacitor KVAR Rating for Compensation at:
1Transformer
2Individual Motors


3 Calculation Of The Capacitor KVAR Rating For Buildings
And Power Plants(Group Compensation)


Harmonics Effects On Power Factor Capacitors
Harmonic Limits in Electric Power Systems (IEEE 5192014)
Options to Reduce Harmonics for PFCC
Power Factor Compensation In Case Of Harmonics


Power
Factor Correction Capacitors Calculators:
1 Arteche Reactive Power and Harmonic Resonance Point
Calculator,
2 Eaton Power Factor Correction Calculator,
3 AccuSine Sizing
Spreadsheet,
4 SquareD (Schneider Electric) Calculator.


The Main Components of PFC Panel
How to select Circuit Breakers for PFC Panel
How to select Fuses for PFC Panel
How to select Contactors for PFC Panel


How to select a capacitor for PFC Panel and Capacitors’
rules
Capacitor compensation with a detuned reactor
How to Select a Detuned Reactor

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