Which phase converter is noisy?

Question

I want to get a phase converter to convert single phase 240 to three-phase. There are two types. A static phase converter uses capacitors and electronics and a rotary phase converter uses an idler motor with capacitors and some circuitry. Where my brother-in-law works they use a phase converter and he says it produces a very loud, high pitched whine. I don't want that. Which converter is the loud one? It sounds to me like the rotary phase converter is the better product in terms of the waveforms it produces, but is it also quiet?
I need a phase converter that can deliver 3 Hp.

Answer 1

The phase converter with the moving parts is producing the loud pitched whine. Solid state doesn't produce noises like that. That noise would be the rotary phase converter that you seem to want so badly. It can probably deliver the 3 Hp, but there is nothing wrong with a phase converter that is solid state.

The fidelity of a solid state phase converter will depend on what kind of amplifier it has. Class A amplifiers reproduce the truest fidelity, while Class C amplifiers are the most efficient - and can deliver more power. At the same time? Class C amplifiers produce the poorest fidelity.

And YES - even though I don't deal with phase converters - I am assuming you have amplifiers in a phase converter - even if the amount of power that comes out is exactly equal to the power that goes in. In that case? Then your gain is exactly equal to 1.

You also have Class B, and Class AB amplifiers - but all that means is that your fidelity is somewhere between Class A and Class C. Regardless of which method you use? In a 3-phase circuit, you are reproducing 3 different sinusoidal waveforms - with each waveform being 60 degrees out of phase with the previous one.

So you want 3 Hp? Not a problem.

What you want is your root mean square, or rms voltage to deliver 3 Hp of power. I Hp is equal to 746 watts. You want 3 Hp, so that would be 2238 watts. But wait! That's AVERAGE POWER.

In order to get an rms power of 2238 watts, you have to multiply this by 1.41. That gives your PEAK POWER in watts. Multiplying 2238 watts by 1.41 gives you 3156 watts, rounded off to the nearest watt.

There is a small problem with that however.

You don't want to have both your load and your power supply operating at the same power level. If you do? You are going to get a distortion of your waveform. But if you use a 4 KW power supply, your load will be drawing power at about 78 percent of your phase converter's rated capacity - which gives you a "fudge factor" of about 22 percent. And it's probably a lot easier to get a 4 KW phase converter, than it is to get one that produces exactly 3156 watts of energy.

Ideally, the resistance of the load should match the resistance of the power supply. That maximizes the power delivered to the load. Do you want to know the resistance of both? Even though you are using 3-phase current? Not a problem. Let me know and I will calculate them for you. It involves using Kirchoff's Voltage Law and Norton's Current Theorem.

Confused? Not a problem! I'm about to make it real simple for you.

USE WHAT YOU ARE CALLING THE STATIC PHASE CONVERTER - IT MIGHT ALSO BE CALLED SOLID STATE - AND MAKE SURE IT IS RATED AT 4 KILOWATTS OF PEAK TO PEAK POWER.

Problem solved.

Answer 2

Many solid-state inverters will work with either a single or three-phase input, and use pulse width modulation (PWM) to produce a variable frequency, three-phase output. The PWM frequency is the frequency of the pulses within the pulses of the output. Many times, the default PWM frequency is in an annoying audio range, maybe 2 to 3 KHz. If your inverter's parameters and your application permit doing so, try raising the PWM frequency to about 8 KHz or more. If your "3 HP" application is a single motor, then I would strongly recommend getting a solid state inverter that will accept the single-phase input and give you an acceptable PWM frequency. An inverter-rated motor is recommended for this option, as its windings will handle the additional heat produced by the PWM frequency on the windings. If you choose a solid-state inverter, do your homework before selecting a drive for your application. Vector drives cost more, but that doesn't make them the best choice for every application. Motor generator sets are noisy, high-maintenance, and not very efficient.

Answer 3

The "Add-A-Phase" is a static converter, but I wouldn't recommend it because one time one burned up a valve operator on a pipe line. But it would be quiet. After burning up the valve operator, the electric company was paid to bring in the three phase service.

I have no experience with rotary phase converters, but would expect them to be more reliable than the static ones, especially if the load varies over time. Static ones may be O.K. for constant loads, but I don't trust them anymore.

If noise is a problem, can't you put the rotary phase converter in a small room with some sound-proofing? Or otherwise isolate it?