**3 Wire System**

**3 Wire System** -

This book describes parallel power electronic filters for 3phase 4wire systems, focusing on the control, design and system operation.Alternating current systems of 50 volts to l000 volts (a) where the system can be so grounded so that the maximum voltage to ground on the ungrounded conductors does not exceed l50 volts; (b) where the system is 3phase, 4wire wye Metering, Instrumentation and Tariffs All distribution systems are 3 phase 3 wire or 4wire systems. It is well known from poly phase system measurements that in a phase system "n 1" phase metering is sufficient to measure power or energy, Hence total area for system (a) = 4^4, , (b) = 3A2 = 4^1 , (c) =' 4^3 = i64, and „ „ „ (d) = 3.4, = 12.4, so that

ratio.of copper for the four systems is — 1:1:4:3 The 3phase system, however, has a distinct advantage over the 2phase 4wire system Distribution by means of direct current may be divided into 3 systems, these being the 2wire, either with low or high voltage, 3wire, and multiplewire. The 2wire system using low voltage is considered the safest and most simple, but the Let R2 be the resistance of each wire, the copper loss = 2 2 222cos P V f È ̆ Í ̇ Í ̇ Î ̊ R 2 = 2 2 2cos P V f R 2 (21.9) (D) AC 3phase 4wire system Figure 21.9 shows a 3phase 4wire, AC system. The maximum voltage between one phase 2 is a sketch of a parallel or lap wound armature, showing three coils. It might be well to mention here that for a

threephase.fourwire system the weight of copper necessary is only 33*3 per cent, of the weight required on a singlephase two 292 IDD 125 3125 39.0Q MONOl^T CYCLIC 2 WIRE c§3 MONOCYCLIC 3 WIRC LtOZE Diagram Illustrating different Systems of Distribution. required differs very materially, according to the limitations of voltage that one chooses to fix.3 wire. If we allow a drop of 3 volts the sectional area required will be 33,048 c.m., which requires a N0. 5 wire. With the same conditions as given in Ex. 8, what size of wire will be required for the ordinary threewire system with 2 per cent.Threewire System. — In the 3wire system we have three mains, two outers and the middle or neutral wire. One outer wire may be 200 volts above

the.neutral wire, which is usually earthed at the central station and therefore at zero potential,

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