Every month our electrical energy provider sends us a bl for the amount of elect

Question

Every month our electrical energy provider sends us a bl for the amount of electrical energy that we have consumed. The rate is often expressed in cents per kWh and consists of at least two components: (1) the demand charge, which covers the cost of lines, poles, transformers, and so on, and (2) the energy charge, which covers the cost to produce elec- tric energy at power plants. The energy charge is the subject of the deregulation of the elec- tric utility industry where you, as a customer, choose your energy provider. It is common for an industrial facility operating at a poor power factor to be charged more by the electric utility providing electrical service. Let's suppose that our industrial facility operates at 277 V rms and requires 500 k W at a power factor of 0.75 lagging. Assume an energy charge of 2c per kWh and a demand charge of $3.50 per kW per month if the power factor is between 0.9 lagging and unity and S5 per k VA per month if the power factor is less than 0.9 lagging. The monthly energy charge is 500 x 24 X 30 x $0.02 $7200. Let's calculate the monthly demand charge with the 0.75 lagging power factor. The complex power absorbed by the industrial facility is

Explanation / Answer

Demand charge is calculated on the basis of peak load of the consumer. So Demand Charge will be 500×24×30×$0.035×0.75 = $9450

VIcos(theta)=500

277×0.75×I=500

I=2.4 amp

Reactive power= VIsin(theta)= 277×2.4×0.66=438.76 kvar

Complex power= 500+436.76j kva

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