Power Factor Correction With H

7/30/2019 Power Factor Correction With H

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Power factor correction with

Harmonic Filters


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Modern electrical equipment demands Power Quality

Modern electrical equipment imposes stringent demands

on voltage stability and power quality. The power

network has to be free from harmonics and other

electrical disturbances.

By installing harmonic filters several benefits are

obtained:

- Higher power factor, improved voltage stability and

network losses

- Filtering of harmonics in the system

- Avoidance of resonance problems and amplification of

electrical disturbances.

A clean network also imposes much less strain on

equipment and lengthens its life span. This means lower

maintenance cost and lower cost for replacing worn-out

equipment.

What problems can harmonics cause?

- Increased losses, e.g. machines will operate at

increased temperature and can be overheated

- Resonance problems between the inductive and

capacitive parts of the power network

- Malfunctioning of control systems since electronic

meters, relays, etc. are matched to the fundamental

frequency

- Overloading of capacitors, leading to malfunctioning

and premature ageing

- Interference with telecommunications and computers

- Disturbances in ripple control systems

- High currents in neutral conductors.

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Harmonics become apparent when a distorted sinus

curve is mathematically analysed. Through Fourier

analysis, an arbitrary periodic function can be dividedinto a number of sine waves. The example below shows

that the red distorted curve consists both of the

fundamental frequency (e.g. 50 Hz) and of super-

imposed 5th (250 Hz) and 7th (350 Hz) harmonicfrequencies.

What are harmonics?

= + +


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Where do harmonics come from?

Most types of equipment common in electrical systems

today generate harmonics:

- Equipment containing electronics that control other

apparatus, e.g. variable speed drives, soft starters,

static compensators, rectifiers, etc.

- Arc furnaces

- In certain cases, transformers, reactors and rotatingmachines.

Harmonics are not only found in industrial networks.

They can also spread into the distribution network and

cause problems for other power users.

Variable speed drives...

...rolling mills... ...and paper machines are examples of industrial equipment generating

harmonics.

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Each plant needs its own solution

Thorough know-how and experience is required to design

harmonic filters properly. Each plant is unique and needs

its own special technical solution. Both system and

component know-how are essential to find the optimum

solution in each individual case. An important component

in the filter is the capacitor. Since it copes with the whole

harmonic content, it must be designed with the greatest

care.

From analysis to commissioning

ABB Capacitors has the competence to support filter

projects from beginning to end. During the entire course

of the project we concentrate on cooperation and dialogue

with our customer, so that the best solution possible is

selected and attained.

Analysis

We analyse the plant using as inputs single-line diagrams,

type and size of loads and mode of operation. The

analysis culminates in a measurement plan.

Measurement

We carry out measurements in the plant under differing

operating conditions. The type of activity pursued

determines the scope of measurements. Complex

processes can take several days to measure, whereas

static processes do not normally involve much time. We

utilize sophisticated harmonic analysis equipment and

store information for subsequent processing.

Calculation

The measurements are then mathematically evaluated,

using computer programs. Various filter configurations

and operation modes are simulated. The calculations

result in a report containing a recommendation as to how

the filter installation should be designed to achieve the

best results and where it should be located. We also

calculate the distortion level anticipated after the

proposed installation.

In simple terms one might say that the filter absorbs

harmonics.

The filter is built up from passive RLC components, i.e.

resistors, reactors and capacitors. They are designed to

form a tuned circuit. The tuning frequency is matched to

the harmonics in question; normally of the 5th, 7th and

11th order. To avoid resonance, the tuning frequency is

usually placed lower than the harmonics occurring in the

network.

What is a harmonic filter?

There are basically three types of filter:

- The band-pass filter is tuned to one frequency. A

special case primarily occurring in low-voltage

systems is the de-tuned filter.

- The double-tuned filter is tuned to two frequencies.

- The high-pass filter filters frequencies above thetuning frequency. In certain cases a high-pass filter can

be installed as a C-type filter, which is used when

compensating arc furnaces or cyclo converters.

A filter installation normally consists of 1 - 3 band-pass

filters that filter one frequency each. Combinations with

high-pass filters, which is open to higher frequencies, can

also be applied.

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Design

ABB Capacitors calculates and designs the filter. Our

own production plant manufactures the capacitor units

and we enjoy close cooperation with prominent producers

of other components such as reactors and resistors.

We can also supply the relay protection for the filter, so

that the correct protective level is attained.

Commissioning

We supervise erection and commissioning. Our under-

taking can also include verification measurements to

check that the performance the equipment was designed

for has been achieved.

The filter design is arrived at with the aid of modern computer equipment.

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Band-pass filter Doubble-tuned filter High-pass filter


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High power quality pays!

A tough competitive climate leads to stringent availability

demands being imposed on all industrial installations.

Profits are dependent on the avoidance of downtime and

breakdowns as far as possible. A reliable and consistent

power supply is an important condition for this. The

expression high power quality is of vital concern to

utilities and industrial plants.

A harmonic filter represents a dependable method of

achieving high power quality in the form of stable voltage

and low distortion. This ensures reliable power supplies

and a high degree of availability.

Highly automated industry...

...and sensitive computer equipment require power supplies that are free

from harmonics for operations to run smoothly.

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...switchgear...


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We have unique experience

ABB Capacitors has been manufacturing power

capacitors since the early 1930s. We have considerable

experience in the design of harmonic filters for different

plants and industrial sectors. Further, we have

comprehensive know-how from all other types of

capacitor applications, e.g. HVDC, SVC, shunt and

series compensation etc.

Our capacitors are of the very highest quality. They areusually equipped with internal fuses, i.e. each capacitor

element has an individual fuse. In this way a stable tuning

frequency, high availablity and long service life are

achieved.

Capacitor filter projects imply close collaboration on our part with thecustomer since filters must be specially matched to each plant.

The maximum acceptable voltage distortion and total

harmonic distortion (THD) have been specified in

various national and international standards and

recommendations. In the table below, for example, the

values recommended by IEC for industrial plant are

given.

Recommendations and standards regarding power network distortion

ABB Capacitors designs and manufactures filters

according to various specifications. We will discuss with

and advise our customers on the choice of suitable

requirements. Differing national requirements and

technical considerations may determine the optimum

choice.

Odd order Odd order

non-multiple of 3 multiple of 3 Even ordern Dn (%) n Dn (%) n Dn (%)

5 6 3 5 2 2

7 5 9 1,5 4 1

11 3,5 15 0,3 6 0,5

13 3 21 0,2 8 0.5

17 2 >21 0,2 10 0,5

19 1,5 >10 0,2

23 1,5

25 1,5

>25 0,2 + 12,5/h

Compability levels for harmonics in MV industrial networks (class 2)

Maximum THD 8% (IEC 61000-2-4)

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ABB Capacitors AB

SE-771 80 LUDVIKA, Sweden

Phone +46 240 78 20 00

Fax +46 240 78 36 77

www.abb.com/powersystemsSECAP A03.en

Edition 2, 2000-05

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Support

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For more than seventy years, ABB Capacitors has

manufactured power capacitors for small and large

installations all over the world. ABB Capacitors in

Ludvika bears overall responsibility for the capacitorbusiness of the ABB Group.

ABB Capacitors is certified according to ISO 9001

(quality) and ISO 14001 (environment).

The product range of ABB Capacitors covers most types

of capacitors for power applications, for instance:

- High voltage shunt banks

- Harmonic filters

- Series compensation

- Static var compensators

- High voltage direct current

(HVDC) installations

- Capacitive voltage dividers (CVDs).

Cover photo:

5:th Harmonic Filter,

36 Mvar, 145 kV,

Sweden.

Power Factor Correction With H

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