Low Voltage Products
Power factor improvement
Application guide
Table of contents
3 Basics of power factor
5 Options and solutions
6 Options and solutions, applications and installation
7 Applications and installation
9 Low voltage capacitor construction
11 Sizing capacitors
14 Harmonics
16 Harmonics filtering
17 Appendix
2 Table of contents | Power factor improvement
Basics of power factor
Motor
Basic concepts
Most load on an electrical distribution system can be
categorized into three types - resistive, inductive and capacitive.
On modern systems, the most common load is the inductive
type simply due to the nature of loads that consume electricity.
Typical examples include transformers, fluorescent lighting and
AC induction motors.
Active Power
Reactive Power
Figure 1
Apparent
Power
A common characteristic of all inductive loads from doorbells
to transformers is that they comprise a winding of some kind.
This winding creates an electromagnetic field that allows the
motor or transformer to function. A certain portion of electrical
power goes to maintain this electromagnetic field.
All inductive loads require two kinds of power to function
properly:
– Active power (kW) which actually performs the work
– Reactive power (kVAR) that sustains the electromagnetic field
One common example of reactive power can be seen in an
unloaded AC motor. When all load is removed from the motor,
one might expect the no-load current to drop near zero. In truth,
however, the no-load current will generally show a value between
25% and 30% of full load current. This is because of the continuous demand for magnetizing current by any inductive load.
Active power is the power indicated on a wattmeter. Apparent
power is simply the vector sum or geometrical sum of reactive
and active power (Fig. 2).
What is power factor?
Power factor (p.f.) is the relationship between working (active)
power and total power consumed (apparent power). Essentially,
power factor is a measurement of how effectively electrical
power is being used. The higher the power factor, the more
effectively electrical power is being used.
A distribution system’s operating power is composed of two
parts: Active (working) power and reactive (non-working
magnetizing) power. The active power performs the useful
work... the reactive power does not. It’s only function is to
develop magnetic fields required by inductive devices.
kW (active power)
kV
A
(apparent po
w
er)
kvar (reactive power)
Figure 2
Generally, power factor decreases (angle Φ increases) with
increased motor load. This geometric relationship of
apparent power to active power is traditionally expressed by
the right triangle (Fig 2) relationship of:
Cos Φ = p.f. = kW/kVA
Why improve low power factor?
Low p.f. simply means poor utilization efficiency. CosΦ varies
between 0 and 1, hence a value between 0.9 and 1.0 is
considered good power factor and essentially means that
metered power and used power are almost equal. From a
consumer’s perspective, it simply means you are using what
you paid for, with minimal wastage. When p.f. is low, the
utility must provide the non-productive reactive power in
addition to productive active power. For the utility that means
larger generators, transformers, conductors and other system
devices that pushes up their own capital expenditures and
operating costs, which they simply pass on to industrial users
in the form of power factor penalties. Hence, improved power
factor helps avoid those penalties.
Key advantage of improved power factor = $$$ savings!!
1. Good p.f. minimizes or eliminates utility p.f. penalties
2. Good p.f. helps improve operating life of equipment
3. Good p.f. expands system capacity, hence facilitating
partial deferrment of capital expenditures at plant level.
Power factor improvement | Basics of power factor 3
Basics of power factor
Capacitor
Motor
WITHOUT CAPACITORS
Reactive Power
r
Motor
% Current
5
Power Factor cos-phi
Figure 3 illustrates the relationship of power factor to total
current consumed. With a p.f. = 1.0 given a constant load,
the 100% figure represents the required useful current. As the
power factor drops from 1.0 to 0.9, power is used less
effectively. Therefore, 10% more current is required to handle
the same load. A power factor of 0.7 requires approximately
43% more current; and a power factor of 0.5 requires approximately 200% (twice as much!!) current to handle the same load.
200
150
100
1 0.9 0.8 0.7 0.6 0.
Fig. 3
How capacitors solve the problem of low p.f.
Low p.f. is a problem that can be solved by adding power factor
improvement (PFI) capacitors to the plant distribution system.
As illustrated in Fig. 4, capacitors work as reactive current
generators “supplying” reactive power (kVAR) to the system.
By generating their own reactive power, industrial users free the
utility from having to supply it; therefore, the total apparent
power (kVA) supplied by the utility will be less, which is
immediately reflected in proportionately smaller bills. Capacitors
also reduce the total current drawn from the distribution system
and subsequently increase system capacity.
Capacitor rating
Power factor correction capacitors are rated in electrical units
called “vars”. One VAR = one Volt Ampere of Reactive power.
VARs are units of measurement for indicating how much reactive
power the capacitor will supply. As reactive power is usually
measured in thousands of vars, the prefix “k” (for “kilo”) is added
to create the more familiar “kVAR” term. The capacitor kVAR
rating shows how much reactive power the capacitor will supply.
Each unit of kVAR supplied will decrease the inductive reactive
power demand by the same amount.
Active Power
Available Active Powe
Utility
Motor Motor
WITH CAPACITORS
Utility
Fig. 4
Example (Fig. 5):
A low voltage network requires 410 kW active power at full load,
and the power factor is measured to be 0.70. Therefore, the
system’s full load consumption of apparent power is 579.5 kVA.
If 300 kVAR of capacitive reactive power is installed, the power
factor will rise to 0.96 and the kVA demand will be reduced from
579.5 to 424.3 kVA. Thus, savings can vary from 20~30% or
even more in some cases, which cumulatively translates to
considerable money savings with the PFI equipment often
paying for itself in as little as 6 months.
410 kW
= 15° = .96 P
2
= 45° = .70 P
1
.F
.F
.
579.5 kV
A1
Fig. 5
.
424.3 kV
155.2 kV
Reduction
2
8.901
ravk
A
2
0
C 8.904 = 1ravk roticapa
C 03 = ravk roticapa
A
4 Basics of power factor | Power factor improvement
Options and solutions
Options for improving power factor
The three main options for PFI are as follows:
– Individual capacitor units – One capacitor unit for each
inductive load (in most cases a motor)
– Banks of capacitor units – Several capacitors grouped
in an enclosure that is connected at a central point in the
distribution system. Fixed capacitor banks comprise
multiple capacitors racked in a common enclosure with
no switching while automatic capacitor banks, also called
“cap banks” have capacitors in a common enclosure with
contactor or thyristor (SCR) switched by a controller.
– Combination of above – Where individual capacitors are
installed on the larger inductive loads and banks are
installed on main feeders or switchboards, etc.
Advantages of individual capacitors
– Increased system capacity – When active power
compensation is closest to the load, it opens up system
capacity and also minimizes line losses.
– Cooler operation – Voltage drops cause the current to
increase, thereby cumulative heat losses occur due to
marginally higher current flow. When voltage drops are
corrected/addressed closest to the load itself, such
temperature issues are prevented right from the start.
– Simpler control – Motor and capacitor can be switched
ON and OFF together, which means simpler control logic
and fewer control parts.
– Precise compensation – Since the individual capacitor is
sized to the specific load and switches together with that
load, there is no chance of over compensation.
– Easier selection – Selection of individual capacitors is
simple and straight forward and requires no special
calculations. See relevant charts on pages 11 and 13.
Advantages of fixed or automatic bank systems
– More economical – Cap banks are more economical than
individual capacitor units when the key objective is to reduce
utility power bills and/or reduce the current in primary feeders
from a main generator or transformer. Being a single
installation for power factor compensation simply adds to the
convenience.
– Lower installation costs – The cost of installing one fixed or
automatic capacitor bank unit can be less than installing a
number of individual capacitors next to each inductive load.
– Switching – Automatic capacitor banks can switch all or part
of the capacitance automatically depending on load
requirements. This way, only as much power factor correction
as needed for the given load is provided. (This switching
capability is a primary advantage over fixed capacitor banks
where over-capacitance, leading power factor and resulting
overvoltages can occur should the load decrease.)
– Single point of control – It is easier to manage, monitor and
operate the process when the power factor inprovement (PFI)
equipment is in one physical location.
Low voltage capacitor construction
Combination of individual, fixed and automatic cap banks
A combination of individual and centralized cap banks is often
the best. Individual capacitors are installed on larger motors
and banks are installed on distribution systems. To determine
the total power factor correction required, then, you need to
know the total kVAR requirement for the facility and the desired
power factor. By referring to the Power Factor Correction Chart,
(Table 2), one can calculate the capacitance needed. See
selection instructions on the following pages for more details.
Power factor improvement | Options and solutions 5
Options and solutions, applications and installation
Logic of mechanical protection in QCap
A low-impedence fault rapidly leading to a short-circuit, can be
protected by a fuse. A high-impedance fault on the other hand
may not lead to a current large enough to trip a fuse, it does
cause cumulative resistive heating which increases the pressure
in the sealed can, at a rate directly proportional to the rate of
heating. Likewise, cumulative heating caused by self-healing
action also slowly increases the pressure. Thereby the pressure
threshold can be reached either by the long-term accumulation
of gas released by self-healings (normal end of life) and/or by a
high-impedance fault as described above.
Capacitors special applications
Care should be taken when power factor correction capacitors
Cylindrical capacitors
Functionally very similar to enclosed capacitors (rectangular),
cylindrical capacitors are different in terms of physical dimensions and arrangement of internal parts. ABB cylindrical capacitors, also called QCap. Cylindrical capacitors are packaged
very conveniently and are best suited to plain and detuned cap
banks from 100 to 300 kVAR at 480V or 600V, 60Hz, standard
design for use in commercial market segments in Canada.
are used in the following applications:
– Frequent starts, plugging and jogging applications
– Regenerative loads where load may drive the motor (coasting,
etc.)
– Multi-speed motors
– Motors involving open-transition reduced-voltage starting
– Reversing starters that switch more than once per minute
– Electronic thyristor (SCR) controlled softstarters
QCap mechanical protection feature
A very simple but uniquely effective design feature provides
mechanical protection to each Qcap unit. The device terminals
are internally connected using three notched wires that break
together when the lid rises due to gas pressure. To ensure the
disconnection works reliably, the wires are indirectly anchored
to the lid at one end and to the can at the other. The groove is
designed to support this. The lid itself is has two stable
positions – normal and expanded. When pressure pushes up
the lid, all three wires break and the capacitor is entirely
disconnected.
SNAP on guard
Rigid connections
Locked by groove
SNAP actuated
Typical wiring diagram (detuned)
Plain autobanks are exactly the same as above, only without the reactors R1, R2
and so on.
6 Options and solutions, applications and installation | Power factor improvement
Application and installation
Where should power factor correction capacitors be
installed in a distribution system?
Fig. 6 illustrates multiple options for locating PFI capacitors on
a low voltage distribution system.
Option A: Downstream of the overload relay
Advantages: this is the most efficient location since the
reactive power (kVAR) compensation is produced right where
it is consumed. Line losses and voltage drop are minimized.
The capacitor is switched automatically by the motor starter,
so it is only energized when the motor is running. No separate
switching device or overcurrent protection required. Also,
thermal overload needs to be set carefully, since the capacitor
will cause a reduction in amps through the overload, hence
lower trip setting for the same level of motor protection (see
Table1 for line current reduction as a percent of FLA).
Note: this works only with contactor starters. Special care
needs to be taken in cases where softstarters are used.
Option B: Between the contactor and the overload relay
Advantages: same as Option A except that the overload relay
can be set to the full load amps as per motor nameplate.
This location is often preferred by panel builders as overload trip
setting is simplified.
Option C: Between the circuit breaker and the contactor
Advantages: The capacitor can act as a central kVAR
source for multiple motors fed by the same circuit breaker.
Recommended for frequent jogging & reversing applications.
Disadvantage: as the capacitor stays energized even when the
motor(s) are not running, there is a risk of overcompensation
and leading p.f. at light load. Also, line losses are higher than
with Options A & B as the reactive current is carried further.
Option D: As a central compensation source (cap bank)
connected to the main distribution bus
Advantages: Of the four options,this is the most cost-effective as it
uses a few large kVAR capacitors rather than many small units.
Also, it is a single installation, hence easier to operate, monitor and
control. A power factor controller switches the capacitors in and
out to ensure the correct level of compensation on the network.
Main Feed
Motor
Feed
Fused
Safety Switch
or Breaker
Fused
Safety Switch
or Breaker
PFCC
D
Contactor
L1
L2
L3
Fused
Safety Switch
or Breaker
PFCC PFCCPFCC
Overload
Relay
T1
T2
T3
MOTOR
ACB
Locations for capacitors in motor circuits
Fig. 6
Temperature and ventilation
Low voltage capacitors should be located in adequately
o
ventilated areas with ambient temperature below 40
C. As
capacitors always operate at full load and generate heat of
their own, the better the heat dissipation, the longer the
operating life of the capacitor. Frequency and voltage are key
factors that can cause capacitor temperature to rise.
– Line frequency – variations in mains frequency can result in
temperature stress in the capacitor, though modern power
system frequencies tend to be increasingly stable.
– Operating voltage – if operating voltage exceeds 110% of
the capacitor rating, then overheating and cumulative
damage can occur. In such a case, the voltage must be
corrected or the capacitor must be taken offline in the
shortest time possible.
Note: This overvoltage problem is exactly why it is always
recommended to “undersize” a capacitor’s kVAR rating
during selection. Too much capacitance causes overvoltage
and overvoltage in turn causes excessive heat, the
cumulative effects of which can result in damage to the
capacitor itself.
Discharging time
Low voltage capacitors need a full minute to discharge through
the resistors, but it is still recommended that the terminals be
short-circuited to ground after the 1-minute has elapsed and
prior to human contact.
Power factor improvement | Application and installation 7
Application and installation
Recommended wiring schematics with starter combinations
Autotransformer
Wye-Delta
Part-winding
Softstarter
Note: for softstart wiring, see page 12
2 speed/ 2 winding
Note: standard applicable guidelines and practices shall be used for installation.
8 Application and installation | Power factor improvement
Wire B
Wire B
Low voltage capacitor construction
Principal components of a 3-phase capacitor
The principal components of a 3-phase ABB capacitor include:
1. Sequential protection system:
– Self-healing capacitor elements
Self-healing means that in case of dielectric breakdown,
the fault is cleared by evaporation of the metalized layer.
– Modularity due to multiple elements
Since the average capacitor comprises multiple elements
wired in Y or Δ, the end-of-life failure of one element
does not affect the continued operation of the capacitor,
though the overall capacitance may be reduced slightly.
– Nonflammable dry vermiculite filler
Vermiculite is a dry, granular, inert and non-flammable
insulating material filled around the elements and
compacted down to displace oxygen in the enclosure.
2. Discharge resistors
Discharge resistors (one per phase) are sized for safe
capacitor discharge (<50V in <1 min), as per NEC.
3. Terminal studs
Large terminal studs are located inside the enclosure at the
top of the capacitor for quick and easy cable connections.
4. Enclosure
All ABB enclosures are made of welded heavy gauge steel.
Available enclosure types include Nema 1, 12 and 3R.
Wire A
Electrode
Dielectric
Electrode
Dielectric
Electrode
Dielectric
Electrode
Dielectric
Electrode
Fig. 12
Dielectric
Wire A
Dielectric
Electrode
Dielectric
Electrode
Dielectric
Partial cutaway view of
capacitive element layers
Fig. 13
More about self healing elements
“Self-healing” is a characteristic which is unique to metallized
electrode capacitors. All capacitor normally experience insulation
breakdown as a result of the accumulated effect of temperature,
voltage stress, impurities in the insulating medium, etc. When this
happens in a non-“metallized” design, the electrodes are shortcircuited and the capacitor ceases its production of reactive power.
What is a metallized-film element?
Zinc metallized polypropylene film comprises a very thin layer
of conducting material (electrode) vapour-coated onto a layer
of capacitor grade insulating film. The electrode thickness
averages ~0.01 microns while the film is 5~10 microns thick
depending on design voltage (higher the voltage rating,
thicker the film). The capacitance of an element is inversely
proportional to the separation between electrodes. Hence, if
the electrode separation is halved, the capacitance is doubled
and element size is halved. Two electrode layers separated by
one layer of insulating film are tightly wound around a core,
effectively forming thousands of layers, such that the edge of
one electrode is exposed on one side of the element and the
edge of the other electrode is exposed on the other side (Fig.
12 & 13). Wires are then connected to each side of the element.
The element is enclosed in a plastic canister and sealed.
Key advantages are:
1. Self-healing design (see Fig. 14 & 15)
2. Low internal losses (<0.5 Watt/kVAR including resistors)
3. Small element size but powerful capacitors
4. Smaller environmental footprint at end of life cycle
Dielectric
Electrode
Dielectric
Electrode
Dielectric
Figure 14. Two electrodes short circuit through a fault in a dielectric layer.
In an ABB metallized-film unit, however, these individual insulation
breakdowns do not mean the shutdown of the capacitor.
The faults self-heal themselves and the capacitor continues
operation. The conducting electrode is very thin; when a short
circuit develops as a result of a fault in the insulating dielectric,
the thin electrode vaporizes around the area of the fault. This
vaporization continues until sufficient separation exists between
the faulted electrodes to overcome the voltage level. Fig. 15
illustrates the process of self-healing. The entire process of selfhealing takes “microseconds” and the amount of electrode which
is lost is negligible in comparison to the total surface area of the
element. The result is the metallized-film unit may self-heal
hundreds of times during its long life and still retain virtually all of
its rated capacitance.
Power factor improvement | Low voltage capacitor construction 9
Low voltage capacitor construction
DIELECTRIC
Dielectric
Electrode
Dielectric
Electrode
Dielectric
Figure 15 and the real picture illustrates “self-healing” where electrode layers
around the short circuit (<1μm) are vaporized, hence contained.
The IPE sequential protection system
ABB’s metallized-film self-healing capacitor elements have a
longer life than conventional foil design. However, the effects
of time, temperature, voltage stress and frequency, cumulatively
effect capacitor life. ABB’s sequential protection system with
patented Internally Protected Element (IPE) design provides the
highest possible protection to equipment and personnel. This
proven design ensures maximum reliable service and protection
in each element, which includes an internal fuse link (See Fig. 16)
for individual disconnection in short-circuit conditions.
ELECTRODE
Cylindrical capacitors design (QCap)
QCaps comprice 3 rolls of metallized film stacked vertically and
sealed off with a thermosetting plastic, much like the IPE
described earlier. The sealing not only protects from oxidation
of the electrode, but also provides mechanical rigidity to the
capacitor unit. Discharge resistors are integrated with the cageclamp terminals at the top. One fixing bolt at the bottom is
suitable for vertical or horizontal mounting.
•
•
FUSE LINK
•
•
•
•
•
Figure 16
What are discharge resistors?
As the capacitor elements store electrical charges like a battery,
the capacitor will maintain a near full charge even off power.
As this is a potential safety issue (dangerous on human contact),
discharge resistors are connected between all of the terminals.
When the capacitor is pulled off power, these resistors drain the
stored electrical charge, in the form of heat. It is recommended,
however, that capacitor terminals should always be shortcircuited
before touching the terminals.
What is the significance of dry type design?
ABB low voltage capacitors – both box type and cylindrical –
contain no free liquids. Environmental and personnel concerns
associated with leakage or flammability of conventional oil-filled
units are eliminated while kVAR for kVAR, dry-type units weigh
30% to 60% less than their oil filled counterparts.
•
Enclosed or QCap - which to select?
While both designs are functionally very similar, each is better
suited to certain applications primarily due to design and
construction, availability, etc.
Enclosed/rectangular capacitors are best suited to industrial
applications in Canada for the following reasons:
1. Fully customizable – 208~750V, 50/60 Hz, 2~100kVAR
2. Modular design – longer operating life under stress
3. Servicable, repairable
4. Standalone design, with options (fuse, indications, etc.)
5. Made in ABB Canada
Cylindrical capacitors are best suited to commercial
applications in Canada for the following reasons:
1. Single can size with 6 ratings, 12.5~30 kVAR
2. Suitable for detuned banks (660V available on request)
3. Compact design suitable for smaller cap banks
4. Easy to stock, hence ideal for integrators
5. Made in ABB Belgium
10 Low voltage capacitor construction | Power factor improvement
Sizing capacitors
Selection chart based on motor HP and rpm
Table 1. Suggested maximum capacitor ratings for T-frame EEMAC class B motors (600V and below)
Induction
motor
rating
(HP)
3 1.5 14 1.5 23 2.5 28 3 38 3 40 4 40
5 2 14 2.5 22 3 26 4 31 4 40 5 40
7.5 2.5 14 3 20 4 21 5 28 5 38 6 45
10 4 14 4 18 5 21 6 27 7.5 36 8 38
15 5 12 5 18 6 20 7.5 24 8 32 10 34
20 6 12 6 17 7.5 19 9 23 12 25 18 30
25 7.5 12 7.5 17 8 19 10 23 12 25 18 30
30 8 11 8 16 10 19 14 22 15 24 22.5 30
40 12 12 13 15 16 19 18 21 22.5 24 25 30
50 15 12 18 15 20 19 22.5 21 24 24 30 30
60 18 12 21 14 22.5 17 26 20 30 22 35 28
75 20 12 23 14 25 15 28 17 33 14 40 19
100 22.5 11 30 14 30 12 35 16 40 15 45 17
125 25 10 36 12 35 12 42 14 45 15 50 17
150 30 10 42 12 40 12 52.5 14 52.5 14 60 17
200 35 10 50 11 50 10 65 13 68 13 90 17
250 40 11 60 10 62.5 10 82 13 87.5 13 100 17
300 45 11 68 10 75 12 100 14 100 13 120 17
350 50 12 75 8 90 12 120 13 120 13 135 15
400 75 10 80 8 100 12 130 13 140 13 150 15
450 80 8 90 8 120 10 140 12 160 14 160 15
500 100 8 120 9 120 12 160 12 180 13 180 15
3600 R/MIN 1800 R/MIN 1200 R/MIN 900 R/MIN 720 R/MIN 600 R/MIN
Capacitor
rating
(kVAR)
Line current
reduction
(%)
Capacitor
rating
(kVAR)
Line current
reduction
(%)
Capacitor
rating
(kVAR)
Enclosure type
Line current
reduction
(%)
Capacitor
rating
(kVAR)
Line current
reduction
(%)
Capacitor
rating
(kVAR)
Line current
reduction
(%)
Capacitor
rating
(kVAR)
Line current
reduction
(%)
WARNING
In order to avoid any complications with
the motor or capacitor, never oversize
capacitors or exceed 1.0 power factor.
Problems caused by overcompensation
Overcompensation causes p.f. to cross 1.0, also called as
leading power factor, which must be avoided at all costs.
The main issue is that leading power factor causes overvoltage,
which puts stress on the capacitor
eventually burn out. Also, power factor exceeding 0.95 leading
on generator supply can cause the genset to hunt, enough to
trip circuit breakers and also affect operation of other equipment on the network.
, causing it to heat up and
Example based on motor HP and rpm: A manufacturer needs
to determine the proper capacitors required for a 1200 RPM,
75HP T-Frame EEMAC class B motor.
1. First look up 75 in the horsepower column (Table 1)
2. Then locate the 1200 RPM capacitor rating (kVAR) column.
The result is 25 kVAR. That should improve the power factor
to around 0.95
3. Now refer to the appropriate brochure for capacitor part
number
Note: while selecting individual capacitors or fixed banks,
always select the calculated kVAR rating or a size lower.
On the other hand, for auto cap banks, selecting a size
higher than the calculated value helps to factor in future
expansions or load additions. That is because an auto cap
bank always has the flexibility to adjust its kVAR output
within its range, based on real-time demand.
Power factor improvement | Sizing capacitors 11
Sizing capacitors
Selection methods and examples
Simple thumb-rule calculations based on motor data:
90% of no-load motor amps gives approximate kVAR Hence,
if no-load motor amps = 50A, then capacitor rating shall be
50 x 0.9 = 45 kVAR or less.
If only full-load motor amps is known, then no load amps can
be calculated as 30% of full load amps. Hence, if full load
motor amps = 100A, then no-load amps = 100 x 0.3 = 30A,
then capacitor rating shall be 30 x 0.9 = 27 kVAR or less.
A very rough estimation would be 30% of motor HP, hence for
a 100HP motor, 30 kVAR would be an approximate.
Calculation based on motor kW (see Table 2 next page)
– Starting p.f. = 0.75 and target p.f. = 0.90
– Corresponding factor from table = 0.398
– Motor HP = 100, hence 100 x 0.745 = 74.5 kW
– Required capacitor size = 74.5 x 0.398 = 29.65, rounded to
30 KVAR
– Part number for 600V, 3-ph network would be C603G30 if
installed inside a panel or C605G30 if standalone
What if existing power factor cannot be determined
because kVA is unknown?
Metered demand = 700kW. Ammeter reading indicates 900A.
Existing power factor and apparent power (kVA) are unknown.
How to calculate existing system power factor and capacitance
required to improve p.f. to 0.92 level?
1. kW is known (700kW) apparent power
kVA = ( VOLTS x AMPS x √3 ) ÷ 1000
2. The volts and amps of the distribution system are known so
for 600V and 900A, we have
(600 x 900 x 1.732) ÷ 1000 = 935.28 kVA
3. Now power factor is = 700kW/935.28kVA = 0.746 pf => 0.75
4. Look up Table 2 next page against existing p.f. of 0.75 and
target p.f. of 0.92. Hence multiplier = 0.398
5. Multiply this factor with the kW value.
Hence, 700 x 0.456 = 319.2 kVAR
The general rule as mentioned earlier in this document is to
select a rating below the calculated value if a fixed capacitor
bank is used and to select a rating above the calculated value
if an auto cap bank is uesd. Practically, the best option in this
particular case is an auto cap bank.
Note: in the last example, reactive power compensation of
319.2 kVAR is required to reach a target power factor of 0.92.
Fixed banks always carry the risk of overcompensation in light
load conditions so unless the capacitor is assigned to and
switched with a single load, it is recommended to use automatic
cap banks that can switch the capacitors in stages, especially
for larger values, that is 100 kVAR and above.
Note on using capacitors with softstarters
If individual power factor correction is to be provided to motors
controlled by softstarters, care muct be taken to use correct
interlocking in the control wiring such that the capacitor and
SCR’s are not in the circuit at the same time. Inappropriate
wiring or control logic may result in damage to the softstarter
and equipment. Please consider the following guidelines/logic
while designing the control circuit:
1. Capacitor shall always be located upstream of the
softstarter as indicated in the power schematic on page 8
2. Capacitor shall be switched by a contactor in order to
ensure isolation when required
3. Control logic shall ensure that the capacitor is isolated from
the circuit while the SCR’s in the softstarter are ramping up
as well as when ramping down. That means the capacitor
shall be active only when softstarter’s bypass contactor
is switched ON
4. Most ABB softstarters have a top-of-ramp (TOR) dry
contact that can be used to switch the capacitor contactor
12 Sizing capacitors | Power factor improvement
Sizing capacitors
Selection based on existing and target cos phi values
Generic calculations
Step 1 – Know your starting power factor (cos
power factor (cos
)
Φ
2
Step 2 – Take inverse cosines of both cos
to obtain the angles
Φ
and
1
Φ
2
Step 3 – Take the tangents of the angles
subtract one from the other (tan
and cos
Φ
1
and cos
Φ
1
– tan
Φ
1
Φ
Step 4 – Finally, capacitor size in kVAR = P * (tan
) and Target
1
,
Φ
2
and
Φ
2
)
Φ
2
– tan
Φ
1
Φ
Using the tables
To make it easy, the (tan
Φ
1
– tan
) factors are already listed in
Φ
2
Table 2 below, so simply multiply that value with P (the actual
kW load) to directly obtain the kVAR value of the capacitor.
Note: As we normally use horse power values in North
America, the simple relationship is 1HP = 0.745kW
),
2
where P = load power in KW
Table 2: Power factor correction chart
Starting cos
Φ
0.85 0.90 0.91 0.92 0.93 0.94 0.95 0.96 0.97 0.98 0.99 1.00
0.60 0.714 0.849 0.878 0.907 0.938 0.970 1.005 1.042 1.083 1.130 1.191 1.333
0.61 0.679 0.815 0.843 0.873 0.904 0.936 0.970 1.007 1.048 1.096 1.157 1.299
0.62 0.646 0.781 0.810 0.839 0.870 0.903 0.937 0.974 1.015 1.062 1.123 1.265
0.63 0.613 0.748 0.777 0.807 0.837 0.870 0.904 0.941 0.982 1.030 1.090 1.233
0.64 0.581 0.716 0.745 0.775 0.805 0.838 0.872 0.909 0.95 0.998 1.058 1.201
0.65 0.549 0.685 0.714 0.743 0.774 0.806 0.840 0.877 0.919 0.966 1.027 1.169
0.66 0.519 0.654 0.683 0.712 0.743 0.775 0.810 0.847 0.888 0.935 0.996 1.138
0.67 0.488 0.624 0.652 0.682 0.713 0.745 0.779 0.816 0.857 0.905 0.966 1.108
0.68 0.459 0.594 0.623 0.652 0.683 0.715 0.750 0.787 0.828 0.875 0.936 1.078
0.69 0.429 0.565 0.593 0.623 0.654 0.686 0.720 0.757 0.798 0.846 0.907 1.049
0.70 0.400 0.536 0.565 0.594 0.625 0.657 0.692 0.729 0.770 0.817 0.878 1.020
0.71 0.372 0.508 0.536 0.566 0.597 0.629 0.663 0.700 0.741 0.789 0.849 0.992
0.72 0.344 0.480 0.508 0.538 0.569 0.601 0.635 0.672 0.713 0.761 0.821 0.964
0.73 0.316 0.452 0.481 0.510 0.541 0.573 0.608 0.645 0.686 0.733 0.794 0.936
0.74 0.289 0.425 0.453 0.483 0.514 0.546 0.580 0.617 0.658 0.706 0.766 0.909
0.75 0.262 0.398 0.426 0.456 0.487 0.519 0.553 0.590 0.631 0.679 0.739 0.882
0.76 0.235 0.371 0.400 0.429 0.460 0.492 0.526 0.563 0.605 0.652 0.713 0.855
0.77 0.209 0.344 0.373 0.403 0.433 0.466 0.500 0.537 0.578 0.626 0.686 0.829
0.78 0.183 0.318 0.347 0.376 0.407 0.439 0.474 0.511 0.552 0.599 0.660 0.802
0.79 0.156 0.292 0.320 0.350 0.381 0.413 0.447 0.484 0.525 0.573 0.634 0.776
0.80 0.130 0.266 0.294 0.324 0.355 0.387 0.421 0.458 0.499 0.547 0.608 0.750
0.81 0.104 0.240 0.268 0.298 0.329 0.361 0.395 0.432 0.473 0.521 0.581 0.724
0.82 0.078 0.214 0.242 0.272 0.303 0.335 0.369 0.406 0.447 0.495 0.556 0.698
0.83 0.052 0.188 0.216 0.246 0.277 0.309 0.343 0.380 0.421 0.469 0.530 0.672
0.84 0.026 0.162 0.190 0.220 0.251 0.283 0.317 0.354 0.395 0.443 0.503 0.646
0.85 – 0.135 0.164 0.194 0.225 0.257 0.291 0.328 0.369 0.417 0.477 0.620
0.86 – 0.109 0.138 0.167 0.198 0.230 0.265 0.302 0.343 0.390 0.451 0.593
0.87 – 0.082 0.111 0.141 0.172 0.204 0.238 0.275 0.316 0.364 0.424 0.567
0.88 – 0.055 0.084 0.114 0.145 0.177 0.211 0.248 0.289 0.337 0.397 0.540
0.89 – 0.028 0.057 0.086 0.117 0.149
0.90 – – 0.029 0.058 0.089 0.121 0.156 0.193 0.234 0.281 0.342 0.484
Target cos
Φ
0.184 0.221 0.262 0.309 0.370 0.512
Power factor improvement | Sizing capacitors 13
Harmonics
Problems created by harmonics
– Excessive heating and failure of capacitors, capacitor fuses,
transformers, motors, fluorescent lighting ballasts, etc.
– Nuisance tripping of circuit breaker or blown fuses
– Presence of the third harmonic & multiples of the 3rd
harmonic in neutral grounding systems may require the
derating of neutral conductors
– Noise from harmonics that lead to erroneous operation of
control system components
– Damage to sensitive electronics (eg. ECG in hospitals)
– Electronic communications interference
Origins of harmonic distortion
Any device with non-linear operating characteristics can
produce harmonics. “Non-linear loads” are simply those where
the current does not follow the sinusoidal pattern of the voltage
waveform. An ever increasing demand for stability and precision
in electrical control and protection equipment has led to a
proliferation of diodes, diacs, triacs, thyristors (SCRs), IGBT’s
and similar semiconductor devices in power applications.
Although these solid state devices have brought significant
improvements in control design and efficiency, they do produce
harmonic currents due to their high switching frequency in
operation. Such rapid switching breaks the current waveform
down to a point where it is no longer sinusoidal. Such currents
not only cause a disturbance on the supply network but also
adversely affect the operation of other equipment on the
network, including PFI equipment and capacitors. While we
focus our discussions on harmonics sources associated with
solid-state power electronics, there are other sources of
harmonic currents as well, grouped as follows:
1. Power electronic equipment: Variable Frequency Drives
(AC VFD’s, DC drives, PWM drives, etc.), UPS’s, rectifiers,
switched power supplies, static converters, SCR systems,
diode bridges, IGBT controlled systems, etc.
2. Arcing equipment: furnaces, welding, lighting (CFL, etc.)
3. Saturable devices: Transformers, motors, generators, etc.
The harmonics from such devices are relatively insignificant
compared to power electronics and arcing equipment.
Waveform
Harmonics are defined as integer multiples of the fundamental
60 Hz waveform (i.e., 3rd harmonic = 180 Hz; 5th harmonic =
300 Hz, etc). Multiple waveforms at various frequencies result in
a non-sinusoidal, distorted waveform. Harmonics are continuous
(steady-state) disturbances on the electrical network and very
different from transient disturbances like surges, spikes, sags,
impulses, etc.
Transient problems are usually solved by installing surge
capacitors, isolation transformers or MOVs. These devices help
solve the transient problems but will not affect the mitigation of
low order harmonics or solve harmonic resonance problems.
Harmonic content
IGBT/SCR based converters are often identified by the number
of DC current pulses they produce per cycle. The most common
ones are 6 and 12 pulse types. Several factors influence harmonic
content but some significant harmonic currents, shown as a
percentage of the fundamental current, are listed below (Fig 7).
Order
harmonic
Typical percentage
of
1 100 100
5 35 -
7 14 -
11 9 9
13 8 8
17 6 -
19 5 -
23 4 4
25 4 4
of harmonic
current
6 Pulse 12 Pulse
Figure 7
14 Harmonics | Power factor improvement
Harmonic overloading of capacitors
X
fhz
r
L1
L2 L3
L1
L2 L3
The impedance of a circuit dictates the current flow in that
circuit. As supply impedance is generally considered to be
inductive, the network impedance increases proportionally with
frequency while the capacitor impedance decreases, hence
varying inversely. This causes most of the higher frequency
currents to be absorbed by the capacitor, and other equipment
associated with the capacitor. In certain cases, harmonic currents
can exceed the fundamental (60 Hz) capacitor current. They
can also cause an increased voltage across the dielectric of
the capacitor which could exceed its voltage rating, resulting in
premature capacitor failure.
Harmonic resonance
The circuit or selective resonant frequency is reached when the
capacitor reactance and the supply reactance are equal.
Whenever power factor correction capacitors are applied to a
distribution network, which combines capacitance and
inductance, there will always be at least one frequency at which
the capacitors are in parallel resonance with the supply. If this
condition occurs at, or very close to, one of the significant
harmonics generated, then large currents can oscillate between
the supply network and capacitors. These currents are limited
only by the damping resistance in the circuit. Such currents will
add to the harmonic voltage disturbance in the network causing
increased voltage distortion. This results in a higher voltage
across the capacitor and excessive current through all capacitor
components. Resonance can occur on any frequency, but the
common ones are 5th, 7th, 11th and 13th harmonics or close to
that, for 6 pulse systems. See Fig.8.
High Voltage
X
L
Network
Avoiding resonance
In older systems it used to help to install capacitors in a part
of the system (Fig. 9) with the least probablility of parallel
resonance with supply. Realistically though, with harmonics
increasingly prevalent on most networks these days, avoiding
resonance is not an option anymore as opposed to overcoming it.
Preventing resonance conditions
Ther
e are several ways to overcome resonance. The simplest
solution to overcome resonance is to connect a reactor in series
with each capacitor to ensure the reactance is inductive at the
critical resonant frequencies but capacitive at the fundamental
frequency. For this, the capacitor and reactor must have a tuning
frequency below the lowest critical order of harmonic, which is
usually the 5th, which translates to the 175 Hz to 270 Hz range,
depending on the magnitude and order of harmonics present.
The addition of a reactor in the capacitor circuit increases the
fundamental voltage across the capacitor, hence the voltage
rating of the capacitor needs to be higher. See Fig. 10.
Delta Wye
Detuned Capacitor/Reactor Systems
Fig. 10
X
+X
L
•
f
o
C
Low Voltage
Network
Eliminating harmonic distortion
Harmonic currents can be reduced by using a basic passive
harmonic filter, often packaged with VFD’s mainly to address the
X
fhz– Frequency
C
XL– Supply reactance
XC– Capacitor reactance
f
– Resonant frequency
o
Fig. 8
Motor
Loads
Motor
Loads
Fig. 9
Harmonic
Generator
Capacito
5th harmonic. In order to eliminate harmonics however, it is
necessary to employ more sophisticated filter technology,
especially active harmonic filtering as described on the next page.
Power factor improvement | Harmonics 15
Harmonics filtering
11th5th 7th
Types of filters
Filtering technology has evolved to address harmonics caused by
a proliferation of semiconductor based, electronically switched
devices. Filters in the past involved precisely calculated LC circuits
tuned to different frequencies (see Fig.11) that addressed a limited
number of harmonic orders. Such combinations were almost
always a precarious balance, so any change in load would
necessitate a re-design and modification to the existing filter.
Also, increasingly complex non-linear loads on modern
networks result in higher order harmonics which are beyond
the capabilities of older, reactor based technologies.
Shunt Filters
Fig. 11
ABB solutions for harmonics mitigation
While old filters primarily depended on reactors, newer Insulated
Gate Bipolar Transistor-based (IGBT) solutions are best suited
to actively eliminate harmonics with far greater precision, which
is why ABB only promotes active filtering technology.
Active harmonic filters (AHF) are recommended where harmonic
distortion already exists or if the harmonic distortion is above the
5% limits recommended in IEEE 519-1992, “Guide for Harmonic
Control and Reactive Compensation of Static Power Converters”.
AHF are IGBT-based and can be used in conjunction with tuned
filters and are specifically designed to eliminate harmonics up to
the 50th, thereby improving power quality across the entire network. ABB has a full range of cULus approved active harmonic
filters (PQFM and PQFI versions) for a variety of applications and
environments - commercial, industrial and even marine. PQFI
and PQFM both, have the additional capability of load balancing
as well providing a limited amount of reactive compensation to
augment the power factor correction of standard fixed or
automatic PFI equipment. Full support is provided on request for
product sizing and selection based on the specific requirements
of every application. For more information
Harmonic studies
The first step in solving harmonic related problems is to perform
an analysis to determine the specific needs of the network.
To determine capacitor and filter requirements, it is necessary to
establish the impedance of the supply network and the value of
each harmonic current.
ABB Canada's full offering for low voltage power quality
– Individual capacitor units, fully assembled in Montreal
– Cylindrical capacitors, made in Belgium, with modules
and cap banks assembled in Montreal
– Fixed or automatic capacitor banks, plain or detuned as
required, fully assembled in Montreal
– Dynacomp SCR-switched detuned capacitor banks,
fully assembled in Montreal
– Active harmonic filters, made in Belgium
– All products above are fully cULus approved
– On-site power factor and harmonic studies
– On-site commissioning and startup offerred
– Complete pre-sales and after-sales support
16 Harmonics filtering | Power factor improvement
Appendix
Typical recommended cable sizes and protection device ratings
1503- phase
capacitor
kVAR
240 Volt
480 Volt
2.5
3.5
5
7.5
10
15
20
25
30
40
50
60
75
100
125
150
200
250
300
1.5
2
2.5
3
3.5
4
5
6
6.5
7.5
10
15
20
25
30
35
40
45
50
60
70
75
80
90
100
150
200
250
300
350
400
500
Rated current
per phase (amps)
6
8.4
12
18
24
36
48
60
72
96
120
144
180
241
301
361
481
601
722
1.8
1.8
3
3.6
4.2
4.8
6
7.2
7.8
9
12
18
24
30
36
42
48
54
60
72
84
90
96
108
120
180
241
301
361
421
481
601
Minimum copper
cable size for
75 OC insulation
#14
#14
#12
#10
#8
#6
#6
#4
#3
#1
00
000
250 kcmil
400 kcmil
(2) - 0000
(2) - 250 kcmil
(2) - 400 kcmil
(3) - 300 kcmil
(3) - 400 kcmil
#14
#14
#14
#14
#14
#14
#14
#14
#14
#14
#12
#10
#8
#8
#6
#6
#6
#4
#4
#3
#2
#1
#1
0
00
350 kcmil
400 kcmil
(2) - 0000
(2) - 250 kcmil
(2) - 300 kcmil
(2) - 400 kcmil
(3) - 300 kcmil
Minimum copper
cable size for
90 OC insulation
#14
#14
#12
#10
#8
#6
#6
#4
#3
#1
00
000
250 kcmil
400 kcmil
(2) - 000
(2) - 250 kcmil
(2) - 350 kcmil
(3) - 300 kcmil
(3) - 350 kcmil
#14
#14
#14
#14
#14
#14
#14
#14
#14
#14
#12
#10
#8
#8
#6
#6
#6
#4
#4
#3
#2
#1
#1
0
00
350 kcmil
400 kcmil
(2) - 000
(2) - 250 kcmil
(2) - 300 kcmil
(2) - 350 kcmil
(3) - 300 kcmil
Recommended
fuse amps
10
15
20
30
40
60
80
100
125
175
200
250
300
400
500
600
800
1000
1200
3
3
6
6
10
10
10
15
15
15
20
30
40
50
60
70
80
90
100
125
150
150
175
200
200
300
400
500
600
700
800
1000
Recommended
disc switch amps
30
30
30
30
60
60
100
100
200
200
200
400
400
400
600
600
800
1000
1200
30
30
30
30
30
30
30
30
30
30
30
30
60
60
60
100
100
100
100
200
200
200
200
200
200
400
400
600
600
800
800
1000
Recommended
MCCB trip amps
15
15
20
30
40
60
80
90
110
150
200
225
300
400
500
600
750
900
1100
15
15
15
15
15
15
15
15
15
15
20
30
40
50
60
70
80
90
90
110
150
150
150
175
200
300
400
500
600
650
750
900
Power factor improvement | Appendix 17
Appendix
Typical recommended cable sizes and protection device ratings
3- phase
capacitor
600 Volt
kVAR
2
3
4
5
7.5
10
15
20
25
30
35
40
45
50
60
70
80
90
100
150
200
250
300
350
400
500
Rated current
per phase (amps)
2
3
4
5
7
10
14
19
24
29
34
38
43
48
58
67
77
87
96
144
192
241
289
337
385
481
Minimum copper
cable size for
75 OC insulation
#14
#14
#14
#14
#14
#14
#12
#10
#8
#8
#6
#6
#6
#6
#4
#3
#2
#1
#1
3/0
300 kcmil
400 kcmil
(2) - 3/0
(2) - 4/0
(2) - 300 kcmil
(2) - 400 kcmil
Minimum copper
cable size for
90 OC insulation
#14
#14
#14
#14
#14
#14
#12
#10
#8
#8
#6
#6
#6
#6
#4
#3
#3
#2
#1
3/0
250 kcmil
400 kcmil
500 kcmil
(2) - 4/0
(2) - 250 kcmil
(2) - 350 kcmil
Recommended
fuse amps
3
6
6
10
15
20
25
35
40
50
60
70
80
80
100
125
150
150
175
250
350
400
500
600
600
800
Recommended
disc switch amps
30
30
30
30
30
30
30
60
60
60
60
100
100
100
100
200
200
200
200
400
400
400
600
600
600
800
Recommended
MCCB trip amps
15
15
15
15
15
15
25
30
40
50
60
60
70
80
90
110
125
150
150
225
300
400
450
550
600
750
The above table gives recommended ratings of cables,
disconnect switches, and/or molded case circuit breakers for
use with capacitor loads. For requirements not covered in the
table, the following application guidelines may be used for
capacitor switching duty:
– Power cable sizing 135% of capacitor current
– Disconnect switch 150% of capacitor current
– Molded case circuit breaker 150% of capacitor current
The above ratings are based on the CE code handbook.
ABB assumes no responsibility for inappropriate ratings.
18 Appendix | Power factor improvement
Wire connection
Metal end spray
In-house metallised
polypropylene film (unique profile)
Secondary foil winding
Biaxially oriented
polypropylene dielectric
Thermo-setting encapsulation
Fuse link
Plastic case
Cut-away view of an Internally Protected Element
Installation requirements
For any installation requirements on capacitors, refer to
section 26-200 to 26-222 of the Canadian Electrical Code,
or consult ABB Control’s technical support department.
Separate overcurrent protection
A separate overcurrent device is not necessary when an ABB
capacitor is electrically connected on the load side of the motor
starter fused safety switch or breaker. Personnel and facility
short circuit protection is provided within the capacitor by ABB’s
patented Sequential Protection System. Short circuit protection
between the main feed and the capacitor is provided by the
motor starter fused safety switch or breaker. A disconnect
switch can be provided when the capacitor is connected as
illustrated in Option C (See Fig. 6, page 7). When the capacitor
is connected as in Option C, it remains energized even when the
motor is off. The optional disconnect helps avoid this condition.
Additional information
1. Improved voltage @ transformer due to capacitor addition:
kVAR
% voltage rise =
kVA of transformer
of capacitors x % reactance of transformer
Note: System reactance should be added to the transformer
reactance if available.
2. Reduced power losses in the distribution system due to
capacitor addition:
% reduction of losses = 100 – 100
improved power factor
3. Reduced kVAR when operating 60 Hz unit @ 50 Hz
Actual kVAR = rated kVAR
60
4. Reduced kVAR when operating @ below rated voltage
Actual kVAR = rated kVAR
i.e.
240 V @ 208V = .751 rated kVAR
rated voltage
i.e.
660 V @ 600V = .826 rated kVAR
rated voltage
50
(
original power factor
(
) = .83 rated kVAR
operating voltage)
(
operating voltage)
(
2
)
2
2
Common formulae:
cos Φ = cos Φ (average) =
kVAR = kW
kVA = kVAR =
I
line
Abbreviations and notations:
V = voltage, I = current in Amps, kW = real power
kVA = apparent power, kVAR = reactive power
C = capacitance in microFarad, f = frequency in Hertz
HP = horsepower, k = kilo, π = 3.14159
kW
kVA
tanΦ = kW * tan (cos
*
√
3
V * l
*
1000
1000
kVA
= kW =
√
3
*
V
*
–1
V
1000000/ 1000
√
√
(kWh
)
Φ
2
* 2 * π
3
V * l
*
1000
kWh
2
+ kVARh2)
f
C
*
*
cos
*
Φ
Power factor improvement | Appendix 19
Contact us
ABB Inc.
Low Voltage Products
Note
The information contained in this document is for general
information purposes only. While ABB strives to keep
the information up to date and correct, it makes no
representations or warranties of any kind, express or
implied, about the completeness, accuracy, reliability,
suitability or availability with respect to the information,
products, services, or related graphics contained in the
document for any purpose. Any reliance placed on
such information is therefore strictly at your own risk.
ABB reserves the right to discontinue any product or
service at any time. For additional information on products
or related technical information, please consult with ABB.
The sizing, selection, installation and use of ABB products
shall conform to applicable local codes and/or industry
standards and best practices. Installation or use that is not
in accordance with these codes and standards may be
hazardous to personnel and/or equipment.
© Copyright 2015 ABB Inc. All rights reserved.
1SXP984000M0200 / June 2015
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