Electrical problem question

[Rick Fisher]

I have a 100 amp x 230V breaker supplying a PP-355 20Hp Digital converter. The converter supplies a 3 phase panel, and each machine has its own breaker.

I added a 10hp planer to the mix, I would say its a hard starting machine.. The cutterhead would be well in excess of 100 lbs. The planer has soft start and Star-Delta.. It takes about 4 or 5 seconds to reach speed.

Across from it, again on its own breaker, is a Sliding table saw with a digital screen .. When the converter is on, the digital screen is on, there is no real on - off switch for just power, other than a huge turn switch down on the electrical box. If there is power, the saw is ready ..

When I fire up the new planer, two breakers inside the electrical box of the sliding saw ( different machine ) trip.

Its almost funny .. but not really ..

The planer does have a VFD installed as well, its not for phase conversion, its for variable speed on the feed.

My gut feeling is that the strain of starting the planer is tripping the breakers on the neighbor saw .. Anyone ever seen anything like this ?

Its weird..

I may ask the manufacturer what those breakers actually do .. might help diagnose it.. Also wondering if maybe swapping a power wires around on the saw.. Does Phase Perfect have a manufactured leg or are they all manufactured ?

David K might know ?

[Darcy Warner]

have you measured the legs, a to b, a to c, b to c?
that should tell you what leg is the generated leg, it should be a bit higher voltage under no load.

[Malcolm McLeod]

..., two breakers inside the electrical box of the sliding saw ( different machine ) trip.
...

My suspicion would be this trip is caused by voltage drop. If the saw control circuits are hot all the time, then when the planer starts I would assume the voltage at the saw 'sags'. The saw's controls still need a specific amount of power (P = I x V, simplistically), and with less voltage available, the controls need more current - - so the breakers trip.

I'll get a little ways outside my design experience, but I recall motor loads are usually protected by a circuit protection device with a 'G' trip curve (or slo-blow fuses in the 'old days'). Modern electronics need fast trip CBs, and this may be contributing to your problem as well..?

A simple fix would be to switch off the CB in the 3-phase panel feeding the saw before/during planer operation. ...Or, install a local disconnect at the saw?

[Bradley Gray]

No experience with digital converters but with a rotary converter the control circuit should be powered by the same 2 legs as the input.

Probably already wired that way but worth checking.

[Rick Fisher]

Did a bit closer investigation.. The Slider trips when I shut the planer off .. not on .. I never thought of that .. I hit the power button, motor starts to slow .. and the lights go out on the slider ..

[Rick Fisher]

Malcolm ..

I will install a disconnect if I have too.. Just something I won't always remember.

I wonder if the motor is dumping power back into the grid when its shutting down ?

[Mike Heidrick]

First i would try slowing down how fast the planer stops via the vfd. Then Id wire a braking resistor to the planers vfd. Get its manual and start reading. A free spinning motor is a generator. Vfds have small resistors in them to deal with it but large loads and short stop times require an exrenal braking resistor typically. I wired one to my big 1050 cnc milll.

I would also use the disconnect on the saw. I bet it has one. I know my big tools do but if not I just get a through door disconnect and a box for it. Safety first. I did then when I installed a VFD on my jointer. Allen Bradley AB have some super nice premade ones too. Look up the size needed for you bad boy saw though, it will be a big one i bet. Factorymation used to sell WEG though door setup components. A nema 4/12 steel box with gland plate makes for a fitting mounting box worthy of your quality.

[Mike Heidrick]

You could also wire a mag contactor to the saw as a disconnect before the vfd and saw electronics and install some momentary push buttons by or in the monitors cabinet. If the screen is off you will remember to power it up.

[Malcolm McLeod]

Did a bit closer investigation.. The Slider trips when I shut the planer off .. not on .. I never thought of that .. I hit the power button, motor starts to slow .. and the lights go out on the slider ..

Interesting - - and it blows my voltage sag theory out of the water. Maybe its a voltage spike..?

There can be harmonic noise issues in power lines resulting from the use of VFDs, but the only time I've seen it is when the VFD output wires (to the motor) get relatively long (>100'). And since the VFD is only driving the planer feed, I'd suspect that any noise from it would be insignificant relative the 10hp on the cutter head.

The 100lb+ inertia load of the planer head will make quite a generator when switched off. I don't know how the digital converter will respond to this power flowing 'backwards'. I'll defer to the hard core electrical theorists, but this may be your 'spike'? There may be a way to deal with it by installing filters/reactors/transformers/etc, but I'd be way outside my pay grade to try to recommend specifics.

I do know CBs will wear out if tripped repeatedly, so would that it were my equipment (as I turn subtle shades of envious green), I'd install a local disconnect on the saw if I couldn't find alternative to smooth out the power.

Hope this helps...

[Rick Fisher]

I am remembering that when the planer first ran, I started and stopped it about 5 times and it never tripped up the saw.. The planer cutterhead was running backwards, so I swapped 2 wires at the breaker..

Then it started..

I bet this is a manufactured leg of 3 phase power thing .. It won't take long to swap all the wires down one each and see..

[Rick Fisher]

I moved all the 3 phase wires on the breaker up one .. and the problem went away ..