Slide 1

MV & LV Capacitor Sizing1Fundamental Circuit Elements

Resistor Current in phase with Voltage

InductorCurrent lagging voltage by 90 deg

CapacitorCurrent leading voltage by 90 deg

Basics....Capacitor Sizing2Electrical Power has 2 components

Active PowerPower used for the functional output requirements

Reactive PowerPower consumed by load to meet its magnetic field requirement

Reactive Power....Capacitor Sizing3What is Power factor

Cosine of the angle by which apparent power (KVA) is out of phase with respect to active Power

Basics....Capacitor Sizing4Overloading of transformerHigher voltage drop throughout systemIncrease I2R lossesIncreased rating of equipmentHigher kVA demandLevy of Penalty by EBs

Effect of reactive Power on the system....Capacitor Sizing5KVA = (kW2 +kVAR2)Cos = kW / kVA ie. kW/ (kW2 +kVAR2)

As we can see as the power factor increases the reactive power reducesHence power factor improvement is the key to reduction of reactive power. The best method for this is using capacitors

Some more basic formulas....Capacitor Sizing6KVAR requirementType of compensationWhere to compensate

Selection of capacitors....Capacitor Sizing7HV level or LV levelCapacitor at individual loads or central compensationGroup compensationLoad characteristicsReactor required

Where to compensate....Capacitor Sizing8Fixed (For HT motor terminals)Variable ( LT bus level )

Type of compensation

Capacitor Sizing9Calculation LT capacitor

KVAR required = Connected load x Demand factorDemand factor = [Tan (cos-1 initial pf) - Tan (cos-1 Final pf)]

KVAR requirement

Capacitor Sizing10Calculations - HT capacitor

KVAR requirement

Capacitor Sizing11Capacitor kVAR should be less than the No load kVA of the motorIn case series reactor is used, capacitor voltage to be increased to account for reactor voltage drop

Points to be noted

Capacitor Sizing12