Power Factor Control Relay
1. General DescriptionThe power factor regulator combines comprehensive operation with
user-friendly control setting. It uses numerical techniques in
computing the phase difference between the fundamentals of
current and voltage, thus precise power factor measurement is
achieved even in presence of harmonics.
The power factor regulator is designed to optimize the control of
reactive power compensation. Reactive power compensation is
achieved by measuring continuously the reactive power of the
system and then compensated by the switching of capacitor banks.
The sensitivity setting optimizes the switching speed.With the builtin
intelligent automatic switching program, the power factor
regulator further improves the switching efficiency by reducing the
number of switching operations required to achieve the desired
power factor.
Usage of the capacitor bank is evenly distributed by the intelligent
switching algorithm. This ensures uniform ageing of the capacitors
and the contactors used.
The four-quadrant operation feature allows the power factor
regulator to operate correctly in the case of active power feed back
to the mains where regenerative power sources are used.
Harmonic current in the system can be harmful to the capacitor
bank. This power factor regulator is capable of measuring the total
harmonic distortion (THD) in the system and produce an alarm if the
THD level is higher than the pre-set value. Other alarms include
under/over compensate alarm, under/over current alarm and
under/over voltage alarm.
Current transformer (CT) polarity is important in determining the
correct phase angle different between the current and voltage
hence the power factor. This power factor regulator will
automatically correct the CT polarity internally in the event that the
polarity is reversed.
2. Light indication
The regulator has a 3-digit numeric display and several light
indicators of which can be functionally divided into 3 categories:-
Power Factor Control Relay User's Guide
A BRIEF OVERVIEW
i. Metering functions - power factor, current & THD for current.
ii. Control parameters functions - power factor, C/K, sensitivity,
reconnection time, rated step, switching program & THD Limit.
iii. Alarm messages function.
To access the above functions, press the "MODE/SCROLL" key until
the light indicator is indicating the desired function. The 3-digit
numeric display will show the value of the selected function. If there
are sub-functions on the selected function such as the function for
"rated step" & "alarm messages", press the "UP" or "DOWN" arrow key
to access these sub-functions.
3. Metering function
3.1 Power Factor
Upon powered up, the numeric display indicates the measured
power factor of the system. If the "IND" LED lights up, it mean the
system is having inductive power factor. On the other hand, if the
"CAP" LED lights up, it means the system is having capacitive power
factor.
If the power factor regulator detects a re-generative condition where
the energy flow is reversed, the power factor display will shown a
minus sign in front of the power factor reading.
When the load current is below the operating range and the power
factor cannot be measured accurately, the numeric display will
shows "---".
If the power factor regulator has been previously set to other display
function, it will automatically return to this power factor display
function if no key is pressed for more than 3 minutes.
3.2 Current
This function display mode is indicated by the "CURRENT" light
indicator. The numeric display shows the true-rms value of the
secondary current measured by the 5A current transformer (CT).
Power Factor
Measurement
Current
Measurement
THD
Measurement
Power Factor
Setting
C/K
Setting
Sensitivity
Setting
Reconnection
Time Setting
Rated Steps
Stepping
Switching
Pragram Setting
THD Limit
Setting
Alarm
Step 1
Coefficient
Step 5
Coefficient
Step 4
Coefficient
Step 3
Coefficient
Step 2
Coefficient
Step 6
Coefficient
Step 7
Coefficient
Step 14
Coefficient
Alarm Message 1
Alarm Message 2
Alarm Message 9
Figure 1: Display Structure
Press "MODE/SCROLL" Press "UP" or "DOWN"
1
a - 3-digit numeric display
b - "CAP " and"IND " indicators(CAP = Capacitive, IND = Inductive)
c - Stepindicator
d - "UP" button
e - "MODE /SCROLL " button
f - "DOWN" button
g - "PROGRAM " button
h - "AUTO " and"MANUAL " indicators
i - Mode indicator
in = nth order harmonic current rms
i1 = Fundamental current rms
Table 1: C/K Table for 415V
E xample:
If a 1000/5A CT is used and the display shows "2.50", the primary
measured current is 500A.
3.3 Current Total Harmonic Distortion (THD)
This mode is indicated by a "THD" light indicator.The numeric display
shows the total harmonic distortion of the current as according to
the formula below.
THD =
This measurement is possible only if the total load is at least 10% of
the rated load. If the THD could not be displayed, the 3 -digit
numeric display will show "---".
4. Control Parameters
4.1 Target Power Factor (SET Cos )
This set the targeted power factor required when the system is
under automatic mode. The power factor regulator will switch the
capacitors in or out in order to achieve this set value.
4.2 C/K
This setting is used to set the switching hysteresis and it is calculated
based on the smallest size capacitor used.
With automatic C/K selection(C/K set to AtC), the reactive power
compensation is achieved without C/K setting. The PFR will measure
and evaluate all steps available when necessary and C/K value is then
computed.
The C/K value can also be obtained manually from table 1 or
calculated with the following formula :-
C/K =
where Q = smallest capacitor step (var)
V = nominal primary system voltage (V)
I = primary rating of the current transformer (A)
Example:-
If Q= 15kvar; V= 415V; I= 800A
=> C/K = (2.88 x15000)/ (415 x 800) = 0.13
4.3 Sensitivity
This parameter set the speed of the switching. A larger sensitivity
value will result in slower switching speed and conversely, a smaller
sensitivity value will result in a faster switching speed.This sensitivity
applies to both switching on and switching off of the capacitor.
4.4 Reconnection Time
This is the safety lockout time which is used to prohibit the
reconnection of the same capacitor step before it is fully discharged.
This parameter is usually set larger than the discharge time of the
largest capacitor size in used.
4.5 Rated Step
Every step in the power factor regulator is programmable except
Step 1. Step 1 is fixed as "1" and it is the smallest capacitor step used.
All other steps were programmed as multiple of Step 1.
Unless all steps are fully used, the unused steps should be set as
"000". The last step can be programmed as alarm/fan output by
setting the step to "ALA" /"FAn". When the last output is
programmed as alarm output, second last output can be
programmed as fan output.
During the programming of the "Step", the corresponding light
indicator for that selected step will light up. Example, number "1"
light indicator indicates rated step for contact output number 1.
If the automatic C/K mode is enabled, the PFR will carry out the
automatic rated step measurement. Therefore, all steps are not
programmable except alarm/fan output.
4.6 Switching Program
This setting allows the selection of one of the four available
switching algorithms.
a) Manual switching (n-A):
b) Rotational switching (rot):
c) Automatic switching (Aut):
d) Four-quadrant switching (Fqr):
The "Manual" light indicator on the power factor regulator lights up
if the switching program is set to Manual switching (n-A). For
Rotational (rot), Automatic (Aut) and Four-quadrant (Fqr) switching
programs, the "Auto" light indicator on the regulator lights up.
Under normal operating condition, the step indicators indicate the
ON/OFF status of every step. A steady ON light indicates the
particular step is switched in. A blinking light indicates that the
particular step is required to switch in but unable to do so
temporary due to reconnection time lockout.
When this switching program is selected, the capacitor steps are
controlled manually by the "UP" or "DOWN" keys. The "UP" key will
connect the capacitor step and "DOWN" key will disconnect the
capacitor step. Steps are switched in a rotational manner based on
first-in-first-out basis.
This switching program is similar to the manual switching method
and it is based on rotational first-in-first-out sequence. Unlike the
manual switching program, this option will automatically switch in
and out the capacitors according to the targeted power factor,
sensitivity setting and the reconnection time setting.
This automatic switching program uses intelligent switching
sequence. The step switching sequence is not fixed and the
program automatically select the most appropriate steps to switch
in or out in order to achieve shortest reaction time with minimum
number of steps. For equal ageing of the capacitor and contactors,
the program will select the least used step to be switched in if
there are two equally rated steps.
Under this switching program, the power factor regulator
automatically detects the CT polarity during power up. Once this
polarity reference is fixed, any subsequent re-generative power
condition detected will cause all the capacitor steps to be
This switching program is similar to the automatic switching
program (Aut) except that this switching program allows the
power factor regulator to operate correctly under both import
power and export power (re-generative) conditions. Under export
power condition, the active power is fed back to the supply mains
by other energy sources such as solar power etc. If this option is
selected, the installer must ensure that the CT polarity is correctly
wired because the automatic CT polarity correction detection
feature is disabled.
