 Home Page News Search Contact Us      Electrical question No.36 - Electrical power distribution load estimation
But in some countries they also use simultaneity factor.

Can anyone explain this? #1
Wed, June 10th, 2009 - 18:43
Demand factor:

The ratio of the maximum demand of an electrical system, or part of a system, to the total connected load of a system or that part of a system under consideration.

Diversity factor:

The ratio of the sum of the individual maximum demands of the subdivisions of a system (or part of a system) to the maximum demand of the entire system (or part of the system).

Coincidence (simultaneity) factor:

In sizing utility distribution capability, the reciprocal of the diversity factor is sometimes used. Called the coincidence factor, this ratio is the maximum demand on a system to the sum of the maximum demands on each component of the system. Note that this differs from a demand factor in that each load is considered on the basis of its expected demand rather than on its maximum rating.

The NEC offers no definition. From the usage context, we might assume that load factor is the ratio of actual power demand by a specific load to the maximum power rating of that load. Such a figure is always less than 100%, and would therefore be equivalent to demand factor.

Actual power :

Actual power is often taken to mean the average load. That seems simple enough until one thinks about what "average" means. If the intent of the load factor is to support a choice of supply conductor ampacity, transformer size, etc., we must recognize that those rating limitations are based on thermal capability. Assume the load is a 300 hp motor, drawing full-load current of 70 amperes at 2,300 volts. If it runs half the time at 150 hp, the "average load" is (300+150)72, or 225 hp. The load factor is 225/300, or 0.75. The relative heating in upstream conductors, just as in the motor winding itself, will be a root-mean-square function of load current-not an average function. On an RMS basis, the electrical load will be the equivalent of 237 hp, not 225. In some applications, "average power" has little meaning    