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How to Select a Capacitor Banks – Constant/Linear/Non Linear load: Industry Follow

Methods

How to Select a Capacitor Banks – Constant/Linear/Non Linear load: Industry Follow

Methods

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What is power factor ?

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Apr 19, 2023

How it affects the system?

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Apr 19, 2023

Any Analogy in Practical Perspective?

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Apr 19, 2023

Any Analogy in Much Simpler way?

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 (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 a constant 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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Apr 19, 2023

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Apr 19, 2023

Then, Where should we use?

Application:

•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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Automatic type capacitor banks:

 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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Method Advantages DisadvantagesIndividual 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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Apr 19, 2023

System Voltage Minimum rating of capacitor bank

3.3 KV , 6.6KV 75 Kvar

11 KV 200 Kvar

22 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 are practical are as follows:

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Apr 19, 2023

1. Selection of Capacitor as per Non Liner Load:

2.  Effect of series and Parallel Connection of 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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Apr 19, 2023

 Placement of Power Capacitor Bank for Motor:

Location 1 (The line side of the starter): Then what will happen?

 Location 2 (Between the overload relay and the starter): Then what will happen?

Location 3(The motor side of the overload relay):Then what will happen?