That's a good idea. I'll discuss it with my superior. I'm going to recommend more testing (ensuring the leads are attached properly), and maybe an analysis of the motor control cabinet.
Thanks again to everyone who offered info and advice.
If I see any further conclusion to these issues I'll...
OKAY, here's what the "technical representative" said in his reply:
"Yes, it looks like the PT may have been reversed. Hard to say for sure, but it is either that or you have a more serious power problem that we first thought! <G>"
I'm not sure what the "<G>" means.. but it looks like I might...
Well the fact that the waveforms are not as expected, and the powerfactor is significantly lower than I think they should be, I'd say the leads were hooked up wrong.
The thing is, I remember when he hooked them up, he said "the tester won't allow them to be backwards, it'll beep or something"...
We have a piece of metering equipment installed in the switchgear which shows the instantaneous kVA, kVAr, kW, pf, etc. of the SG bus. It claims a pf of 0.77, which is okay. Why would the pf on the transformer primary be so bad (0.5pf)? I'm starting to get the feeling that the test equipment...
I just collected the info off the DC motor:
Brand: Thrige-Scott Ltd.
Type: Shunt Motor
Power: 150kW
RPM: 2000
Armiture: 460V - 350A
Exciter: 360V - 6.1/4.85A
Again, the control cabinet also powers some small melt-pumps and heats.
I checked the power factor stated by the switchgear and it said...
I will contact the person that performed the testing and point out the waveform issues mentioned. I agree that the vector sum of the waves should be zero, and clearly this is not the case.
Thanks for your input everyone!
I'll try to collect a few more load specifications which might help us find a solution.
The puzzling thing is that we have 8 other similar extruders, a few with dedicated 175kVA tranformers, and they don't seem to make nearly as much noise. Of course, those ones...
The transformer is fed from a large piece of switchgear (in the same room). The fuses are Ferraz Shawmut A6D300R. And the switchgear is fed from a 5MVA (25kV/600V) transformer. I'm not sure what you mean by an upstream rectifier? There's nothing else inline with the tranformer.
It was proposed by the company that did the testing that the source of the bad current harmonic distortion could be a result of bad iron core laminations. From the email I recieved:
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It is possible that these harmonics are at least partly responsible for the noise level in the...
The sound level isn't really variable. It's either on or off: loud or quiet. If's definitely more than a hum, like a loud buzzing. We have a larger 750kVA in the same electrical room which makes half the noise but runs way hotter.
As for reactors or thyristors, my knowledge of the internals of...
Hmm that's an interesting thought. We had some professional maintenance guys do a visual inspection when the plant was shut down last month. They said everything was tight (probably referring to the connections), but as you say, perhaps something is too tight!?
I still think it must be...
The testing was performed on the primary side only.
It's not an autotransformer. It's a K-Factor 13 as described at http://www.marcustransformer.com/vw/fs/p017.htm
The Marcus site claims its design is aimed at non-linear loads. And it's 'features' are listed as:
§ Specifically designed copper...
The primary voltage readings stayed below 347V for the duration of the 24 hour test. At some points the voltage dipped to as low as 338V, but only for short time periods. The voltage %THD stayed between 1.0% and 1.7%. So I don't believe the voltage is the problem.
The loading on the transformer...
Hey all,
I have a 300kVA Marcus brand transformer with an excessively high sound output. The sound output has been metered at ~85dB, which is well over the rated 65dB. The transformer was only purchased and install a little over 1 year ago. It was physically inspected and is clean as a whistle...
The "worst" fault is known as a "bolted" three phase fault. "Bolted" refers to the phases being connected via a zero impedance connection. In reality this is not physically possible, since there will always be a resistive componant with a fault occurs.
On the other hand, it depends what you...
Great, thanks for all the tips, everyone.
I'm fairly comfortable with my method now.
In the end of all things, I'll probably have an electrical firm which specializes in arc flash analysis double check my numbers.
As was said earlier, arc flash is still in its infancy. Here at our facility we're...
RonShap,
The values I gave were for 100% arcing current/100% bolted fault current. I have been performing my calculations at 100% AND 38% bolted fault current. 38% is the lowest fault level at which an arc can sustain itself on a 480V system (note: "industry accepted level", see: Annex D.6(1)...
Sorry, dpc, I got my numbers mixed up. The 5.61 and 2.74 values are actually the Flash Protection Boundry distances (in meters). This is, for those who don't know, the distance at which a curable burn will be recieved in the even of an arc flash.
Here are the proper numbers:
@ 24 seconds, E =...
"the upstream fuse that will attempt to clear the fault during that event downstream, will carry the calculated value at the fuse location."
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This idea is new to me. The calculated current value (bolted 3ph fault) at the fuse is much larger than the arcing current...
