--------+----------------------------------------------------------- | POWER FACTOR SYSTEM +-----+-----+-----+-----+-----+-----+-----+-----+-----+----- | 1.00| .98| .95| .90| .85| .80| .75| .70| .65| .60 --------+-----+-----+-----+-----+-----+-----+-----+-----+-----+----- Single |2,160|2,249|2,400|2,660|3,000|3,380|3,840|4,400|5,112|6,000 phase | | | | | | | | | | --------+-----+-----+-----+-----+-----+-----+-----+-----+-----+----- Two |1,080|1,125|1,200|1,330|1,500|1,690|1,920|2,200|2,556|3,000 phase | | | | | | | | | | (4 wire)| | | | | | | | | | --------+-----+-----+-----+-----+-----+-----+-----+-----+-----+----- Three |1,080|1,125|1,200|1,330|1,500|1,690|1,920|2,200|2,556|3,000 phase | | | | | | | | | | (3 wire)| | | | | | | | | | --------+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----
NOTE.--The above table is calculated as follows: For =single phase= M = 2,160 ÷ power factor^{ 2} × 100; for =two phase= four wire, or three phase three wire, M = ½ (2,160 ÷ power factor^{ 2})× 100. Thus the value of M for a single phase line with power factor .95 = 2,160 ÷ .95^{ 2} × 100 = 2,400.
It must be evident that when 2,160 is taken as the value of M, formula (6) applies to a two wire direct current circuit and also to a single phase alternating current circuit when the power factor is unity.
In the table the value of M for any particular power factor is found by dividing 2,160 by the square of that power factor for single phase and twice the square of the power factor for two phase and three phase.
=Ques. For a given load and voltage how do the wires of a single and two phase system compare in size and weight, the power factor being the same in each case?=
Ans. Since the two phase system is virtually two single phase systems, the four wires of the two phase systems are half the size of the two wires of the single phase system, and accordingly, the weight is the same for either system.
+-------------------+--------------------------------------------+ | | POWER FACTOR | | SYSTEM +--------+--------+--------+--------+--------+ | | 1.00 | .98 | .90 | .80 | .70 | +-------------------+--------+--------+--------+--------+--------+ | Single phase | 1.00 | .98 | .90 | .80 | .70 | +-------------------+--------+--------+--------+--------+--------+ | Two phase, 4 wire | 2.00 | 1.96 | 1.80 | 1.60 | 1.40 | +-------------------+--------+--------+--------+--------+--------+ |Three phase, 3 wire| 1.73 | 1.70 | 1.55 | 1.38 | 1.21 | +-------------------+--------+--------+--------+--------+--------+