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Size and Location of Capacitor in Electrical System-(Part1)

SIZE AND LOCATION OF CAPACITOR IN ELECTRICAL SYSTEM-(PART1)

TYPE OF CAPACITOR BANK AS PER ITS APPLICATION:

 (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.

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

 (2) 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.

Types of APFC:

  • Automatic Power Factor correction equipment is divided into three major categories: * (1)Standard = Capacitor + Fuse + Contactor + Controller * (2)De tuned = Capacitor + De tuning Reactor + Fuse + Contactor + Controller * (3)Filtered = Capacitor + Filter Reactor + Fuse + Contactor + Controller.

Advantage:

  • Consistently high power factor under fluctuating loads. * Prevention of leading power factor. * Eliminate power factor penalty. * Lower energy consumption by reducing losses. * Continuously sense and monitor load. * Automatically switch on/off relevant capacitors steps for consistent power factor. * Ensures easy user interface. * Automatically variation, without manual intervention, the compensation to suit the load requirements.

Application:

  • Variable load electrical installations. * Compensation of main LV distribution boards or major outgoing lines. * Above the 15% level, it is advisable to install an automatically-controlled bank of capacitors. * Size of Automatic Capacitor bank Qc > 15% kVA transformer.

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

 TYPE OF CAPACITOR AS PER CONSTRUCTION:

 (1) STANDARD DUTY CAPACITOR:

  • Construction: Rectangular & Cylindrical(Resin filled / Resin coated-Dry) * Application: * Steady inductive load. * Non linear up to 10%. * For Agriculture duty.

(2) HEAVY-DUTY:

  • Construction: Rectangular & Cylindrical (Resin filled / Resin coated-Dry/oil/gas) * Application: * Suitable for fluctuating load. * Non linear up to 20%. * Suitable for APFC Panel. * Harmonic filtering

(3) LT Capacitor:

  • Application: * Suitable for fluctuating load. * Non linear up to 20%. * Suitable for APFC Panel & Harmonic filter application.

 SELECTING SIZE OF CAPACITOR BANK:

  • The size of the inductive load is large enough to select the minimum size of capacitors th…