single phase

THREE-PHASE GENERATORS FOR SINGLE-PHASE LOADS: DISTRIBUTE A LOAD.

Orefice Generators - Copyright 2017

Orefice Generators - Copyright 2017

When dimensioning the power of a generator, it is necessary to carefully evaluate the type of power to be supplied.

It's very comon that one has  a three-phase generator set and has to supply a single-phase load. How to proceed?

You must have heard that a three-phase generator of Power P = 3 kW can drive a single-phase power load of 1 kW because Pm = P / 3.

This condition is valid for all alternators with Star  windings connection and a voltage of 400 V, where to obtain the single-phase voltage of 230 V, we just power the load between a phase and the Star center.

“Single-phase loads powered by a three-phase generating set must be distributed in such a way that, at each phase, no more than the rated current of the generator is running.

Notice how we talk about power but also about current, because it is important to note that some loads at the time of insertion have a higher absorption, or higher currents. It goes without saying that an experienced technician can rely first on an experimental calculation, but then he must  measure the electrical loads distributed over the phases with the aid of a measuring instrument.

If you do not have a calibration tool, but you have a Generator branded Orefice with VEOTM control panel , you can easily monitor the absorption directly from the Display.

veo control panel

If you do not have a measuring instrument neither a generator  Orefice you will not be able to ascertain the correct distribution of loads between phases.

What if the loads are not properly distributed?

It may happen that the generator will go into distress and that the windings inside the alternator may overheat until they "burn" and interrupt.

To make a comparison, we imagine that electric load is a heavy shopping bag that we carry for hundreds and hundreds of meters with the same arm. We will reach our destination with a tired arm that is more subject to an injury. Dividing the load into two envelopes would not change the work to be done, and perhaps even fatigue, however it would be easier to carry the load to the target avoiding pain and risk.

Unbalanced loads are one of the major breakdown factors in an alternator and consequently in a generator set.

That's not all

An unbalanced load can damage the user connected to it, especially when it is a variable load. An electronic equipment user may not work properly.

That happens especially to Audio Services that hire or purchase a generator to which they then connect their panel without taking care to check how much current they are withdrawing from each phase.

Let's take an example to better explain what can happen:

· Generator with electric power Continuous power of 16 kW; Power factor 0,8; Rated voltage three-phase 400 V.

· Single-phase electrical load to be connected to a total of 8 kW divided as follows:

O Halogen lamps: 5 kW

O Other users with a transformer: 3 kW

Instinctlively the less experienced technician would feel free to connect all the halogen lamps under one stage and the remaining 3 kW under another phase. With this subdivision, considering a current of the halogen lamps that is at least 10 times the nominal current for an average time of 0,12 s, it will not only have problems with the lamps being switched on but will overload the generator for at least 0,12 s will not guarantee voltage and frequency values uitable for feeding the remaining 3 kW with the risk of causing damage to voltage values utside the limits.