GE EPM 6000 Multi-function Power Metering System instruction manual Power, Energy, and Demand

CHAPTER 2: ELECTRICAL BACKGROUND

2.3Power, Energy, and Demand

2.3.1 Description

It is quite common to exchange power, energy, and demand without differentiating between the three. Because this practice can lead to confusion, the differences between these three measurements will be discussed.

2.3.2Power

Power is an instantaneous reading. The power reading provided by a meter is the present flow of watts. Power is measured immediately just like current. In many digital meters, the power value is actually measured and calculated over a one-second interval, since it takes some amount of time to calculate the RMS values of voltage and current. However, this time interval is kept small to preserve the instantaneous nature of power.

2.3.3Energy

Energy is always based upon some time increment – it is the integration of power over a defined time increment. Energy is an important value because almost all electric bills are based, in part, on the amount of energy consumed.

Typically, electrical energy is measured in units of kilowatt-hours (kWh). A kilowatt-hour represents a constant load of 1000 watts (1 kW) for 1 hour. Stated another way, if the power delivered (instantaneous watts) is measured as 1000 W, and the load was served for a one-hour time interval, then the load would have absorbed 1 kWh of energy. A different load may have a constant power requirement of 4000 W. If this load were served for one hour, it would absorb 4 kWh of energy. Likewise, if it were served for 15 minutes, it would absorb ¼ of that total, or 1 kWh.

The following figure shows a graph of power and the resulting energy that would be transmitted as a result of the illustrated power values. For this illustration, it is assumed that the power level is held constant for each minute when a measurement is taken. Each bar in the graph represents the power load for the one-minute increment of time. In real life, the power values are continually moving.

2–8 EPM 6000 MULTI-FUNCTION POWER METERING SYSTEM – USER GUIDE