GE EPM 5300 User Manual download pdf (Page 7)

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CHAPTER 1: AC POWER MEASUREMENT

GE Multilin EPM 5000 series Advanced Power Meters 3

Voltages between the phases vary depending on loading factors and the quality of distribution

transformers. The three-phase system is distributed in different voltage levels: 208V AC, 480V AC, 2400V

AC, 4160V AC, 6900V AC, 13800V AC, and so on.

Power measurement in a poly phase system is governed by Blondel's Theorem. Blondel’s Theorem

states that in a power distribution network which has N conductors, the number of measurement elements

required to determine power is N-1. A typical configuration of poly phase system has either a Delta

connection or a Wye connection (see Figure 1.4, below).

2) Wye

E I

CN C

P = E I + E I + E I

BN CN

E I

BN B

E I

AN A

1) Delta

E I

CB C

E I

AB A

P = E I

AB A

+ E I

CB C

ABC

Figure 1.4: Poly Phase System: (1) Delta, (2) Wye

1.3: Consumption, Demand and Poor Power Factor

CONSUMPTION:

T W=WH × W = instantaneous power T = time in hours

The total electric energy usage over a time period is the consumption of WH.

Typically, the unit in which consumption is specified is the kilowatt-hour (KWH): one thousand watts

consumed over one hour. Utilities use the WH equation to determine the overall consumption in a billing

period.

DEMAND: Average energy consumed over a specified time interval. The utility determines the interval,

typically 15 or 30 minutes. The utility measures the maximum demand over a billing period. This

measurement exhibits a deviation from average consumption, causing the utility to provide generating

capacity to satisfy a high maximum consumption demand. The highest average demand is retained in the

metering system until the demand level is reset.

POOR POWER FACTOR: Results in reactive power consumption. Transferring reactive power over a

distribution network causes energy loss. To force consumers to correct their Power Factor, utilities

monitor reactive power consumption and penalize the user for Poor Power Factor.

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GE EPM 5300 User Manual Page 7

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