Electrical Engineering Circuits

8/11/2019 Electrical Engineering Circuits

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epartmentofMech

anicalEngineering

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ajam

Page -1

How to Select a Capacitor

Banks Constant/Linear/Non

Linear load: Industry Follow

Methods


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epartmentofMech

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GMRInstituteofTechnology,

Rajam

What is power factor ?


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epartmentofMech

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How it affects the system?


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epartmentofMech

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Any Analogy in Practical Perspective?


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epartmentofMech

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Any Analogy in Much Simpler way?


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D

epartmentofMech

anicalEngineering



GMRInstitut

eofTechnology,

Rajam (1) Fixed type capacitor banks

The reactive power supplied by the fixed capacitor bank is constant irrespective of any

variations in the power factor and the load of the receivers. These capacitor banks are

switched on either manually (circuit breaker/ switch) or semi automatically by a

remote-controlled contactor. This arrangement uses one or more capacitor to provide aconstant level of compensation. These capacitors are applied at the terminals of

inductive loads (mainly motors), at bus bars

Disadvantage:

Manual ON/OFF operation.

Not meet the require kvar under varying loads. Penalty by electricity authority.

Power factor also varies as a function of the load requirements so it is difficult to

maintain a consistent power factor by use of Fixed Compensation i.e. fixed capacitors.

Fixed Capacitor may provide leading power factor under light load conditions, Due to

This result in over voltages, saturation of transformers, mal-operation of diesel

generating sets, penalties by electric supply authorities.


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epartmentofMech

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epartmentofMech

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Then, Where should we use?

Appl icat ion:

Where the load factor is reasonably constant. Electrical installations with constant load operating 24 hours a day

Reactive compensation of transformers.

Individual compensation of motors.

Where the kvar rating of the capacitors is less than, or equal to 15% of the

supply transformer rating, a fixed value of compensation is appropriate.

Size of Fixed Capacitor bank Qc 15% kVA transformer


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epartmentofMech

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GMRInstitut

eofTechnology,

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Autom atic type capac i tor b anks:

The reactive power supplied by the capacitor bank can be adjusted

according to variations in the power factor and the load of the receivers.

These capacitor banks are made up of a combination of capacitor steps

(step = capacitor + contactor) connected in parallel. Switching on and off of

all or part of the capacitor bank is controlled by an integrated power factor

controller.The equipment is applied at points in an installation where the active-power

or reactive power Variations are relatively large, for example:

At the bus bars of a main distribution switch-board,

At the terminals of a heavily-loaded feeder cable.

Where the kvar rating of the capacitors is less than, or equal to 15% of the

supply transformer rating, a fixed value of compensation is appropriate.Above the 15% level, it is advisable to install an automatically-controlled

bank of capacitors.

Control is usually provided by contactors. For compensation of highly

fluctuating loads, fast and highly repetitive connection of capacitors is

necessary, and static switches must be used.


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epartmentofMech

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Method Advantages Disadvantages

Individual

capacitors

Most technically efficient,

most flexible

Higher installation &

maintenance cost

Fixed bank Most economical, fewer

installations

Less flexible, requires

switches and/or circuit

breakers

Automatic

bank

Best for variable loads,

prevents over voltages, low

installation cost

Higher equipment cost

Combination Most practical for larger

numbers of motors

Least flexible


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epartmentofMech

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17-Sep-14

System Voltage Minimum rating of capacitor bank

3.3 KV , 6.6KV 75 Kvar

11 KV 200 Kvar22 KV 400 Kvar

33 KV 600 Kvar

Selecting Size of Capacitor Bank:

The size of the inductive load is large enough to select the minimum size of

capacitors that is practical. For HT capacitors the minimum ratings that arepractical are as follows:


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1.Select ion o f Capacitor as per Non L iner Load:

2.Effect of ser ies and Paral lel Connect ion o f capacitor :

3. Can we connect the capacitors in delta? Then what is its effect?

4.Can we connect the capacitors in star connection? Then what is its effect?

5. Can we connect the capacitors in star connection with ground? Then what

is its effect?


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Electrical Engineering Circuits

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