Recent content by aemla

Perhaps I should of said "more accurate" out of the two choices. For this example, yes, power supply and transformer will operate near full power. Weight, size, and cost are always considered in real applications. For this example, I ignore those factors. I've seen 480 VDC power supplies...

Thank you for the explanation, that makes complete sense.

If actual supply voltage is 480 vac where a step down transformer is needed.

Good afternoon, How should an upstream isolation transformer be sized for a dc power supply? For example, if we have a power supply with the following specs: Input Voltage: 120 VAC Input Current: 2 Amps Inrush Current: 22 Amps Efficiency: 90% Power Factor: 0.55 Output Voltage: 24 VDC Output...

Hmm, seems that previous wiring was incorrect as well. Changed it and took another set of readings. Performed calculations for each scenario: First scenario appears to be the correct one. Ran a motor with bad bearings with no load, PF seems to be reasonable. Final phase angle also...

How come using Pythagorean Theorem gives a wrong answer?

Hopefully I get this right: 1. Removing one CT. Second CT is required since addition of the scalar values is needed to get the correct answer. 2. Reversing one CT. Phase for that CT will be rotated 180 degrees. This will affect active and reactive power (vector quantities) but not apparent...

One additional follow-up: does this mean that with the exact the same setup, removing one of the CTs will result in incorrect total active power measurement?

Thank you for the detailed explanation. I believe I understand now. What prompted the question was that I knew that the meter was giving incorrect total apparent power value. So I assumed active power would also be incorrect without understanding how the value is actually obtained. Per the...

My understanding as well. If you have a purely resistive load, I would agree. But what if your load has some inductive and capacitive reactance? To make sure we're on the same page. By instantaneous sampling, I mean sampling at a much higher frequency than the actual signal. That way an actual...

Windadct mentioned the reason behind 30 degrees: "when you look at Phase to Phase (L-L) voltages vs the Phase CT - there is a 30 Degree shift in the SENSING". It makes sense to use the phase shift between L-L voltage vs current. What's "Phase CT"? Current Transformer, right? Per my...

Also makes perfect sense. Sensing elements look at waveforms (aka instantaneous values), not like DMM (aka RMS values). Right, L-L voltage is fully defined. So to calculate instantaneous L-L voltages, you would need instantaneous L-N voltages right? So then the question becomes if the meter...

Yeah makes perfect sense. The math that you mentioned, would that need to be done with instantaneous voltages and currents?

This is what the internal wiring of the meter suggests. There are no sensing elements between phases, all of that is calculated. Unfortunately, I'm unable to test with various loads, just have the one 208VAC load. - Sure, I understand that. In a three phase system using a three wattmeter method...

Exactly as you've mentioned before. If my wiring was single phase L-N with 3 phase 4 wire configuration/setup of the meter then it would work (as you've said other two phases would just so happened to have no loads). But my wiring is L-L single phase. With 3 phase 4 wire configuration, meter...