Wattmeter is a measuring instrument used to determine how much real power in the load that is operating in an electrical system with several load conditions, such as DC load, single phase AC load and three-phase AC load.<\/span> In operation must pay attention to the instructions in the manual book or table listed on the wattmeter.<\/span> Similarly, in the case of reading should refer to the existing manual book.<\/span><\/p>\n Electricity in the sense can be grouped in two groups according to their power supply, namely DC power and AC power.<\/span><\/p>\n DC electrical power is formulated as:<\/strong><\/span><\/p>\n P = V.<\/b><\/span> I.<\/span> While AC electric power there are two kinds, namely: power for one phase and power for three phases, which can be formulated as follows:<\/span><\/p>\n On a single phase system:<\/strong><\/span><\/p>\n P = V. I.<\/b><\/span> cos \u03c6<\/b><\/span> On a three phase system:<\/b><\/span><\/p>\n P = 3 .V.<\/b><\/span> I.<\/b><\/span> cos \u03c6<\/b><\/span> Generally speaking, electrical power contains elements of resistance and reactance or complex impedances so that the absorbed power depends on the nature of the load.<\/span> This is because the absorbing power is a resistive load, while the reactive load does not absorb power.<\/span> Thus the multiplication of effective voltage with effective current is the apparent power (S).<\/span> While the real power magnitude (P) is:<\/span> Also the power caused by the reactive load (Q), the magnitude is:<\/span> The relationship between the three apparent power, pseudo power and reactive power can be illustrated by the following power triangle:<\/span>
\n Where :<\/span>
\n P = Power (Watts),<\/span><\/p><\/blockquote>\n
\n Where :<\/span>
\n V = Working Voltage (Volt),<\/span>
\n I = The current flowing to the load (Ampere)<\/span><\/p><\/blockquote>\n
\n Where :<\/b><\/span>
\n V = Neutral phase voltage (volt),<\/b><\/span>
\n I = The current flowing to the load (Ampere)<\/b><\/span><\/p><\/blockquote>\n
\n S = VI<\/b><\/span><\/p>\n
\n P = V.<\/b><\/span> I.<\/b><\/span> Cos<\/b><\/span>
<\/a><\/p>\n
\n Q = V.<\/b><\/span> I.<\/b><\/span> Sin<\/span>
<\/a><\/p>\n
\n
<\/a>
\n Figure 45. Power Triangle<\/span><\/p>\n