Transcript Then what is its effect? Department of Mechanical

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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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How it affects the system?
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Any Analogy in Practical Perspective?
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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:
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•
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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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Then, Where should we use?
Application:
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•
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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
Individual
capacitors
Fixed bank
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Advantages
Most technically efficient,
most flexible
Most economical, fewer
installations
Automatic
bank
Best for variable loads,
prevents over voltages, low
installation cost
Combination Most practical for larger
numbers of motors
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Disadvantages
Higher installation &
maintenance cost
Less flexible, requires
switches and/or circuit
breakers
Higher equipment cost
Least flexible
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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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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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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?
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