Voltage alarm on CNC with lock out in alarm

[jim gage]

I have a customer with voltage issues due to high power provider demand causing my 208 3 phase to drop below 204 volts at times.
When this happens the CNC machine goes into voltage alarm,stops and locks itself out.
I would like to use a boost transformer to bring my voltage up at the CNC to remedy this problem.
The machine is rated for 208/230 does anyone see a down fall to this remedy?

 

[iwire]

I have a customer with voltage issues due to high power provider demand causing my 208 3 phase to drop below 204 volts at times.
When this happens the CNC machine goes into voltage alarm,stops and locks itself out.
I would like to use a boost transformer to bring my voltage up at the CNC to remedy this problem.
The machine is rated for 208/230 does anyone see a down fall to this remedy?

If the machine is really rated for 208 it should not drop out at 204.

But regardless using a boost transformer might work fine or you may find that it provides too much overvoltage during times of low demand. Seeing as the machine is rated up to 230 volts overvoltage will not likely be an issue if you only boost it a bit.

 

[gar]

160722-0850 EDT

jim gage:

All of our CNC machines are HAAS and these all have input transformers with taps to adjust for different nominal input voltages. In the case of our machines I believe the desired DC bus voltage is about 325 V. This bus in monitored for both high and low voltage.

High DC bus voltage occurs primarily from dynamic braking and when the high threshold is reached a shunt resistor is connected across the bus to bleed energy from the filter capacitors. You do not want this to occur from high AC input voltage. I doubt that the power rating on the resistor is designed for a continuous ON state.

The low bus voltage threshold is selected to provide enough power for the main spindle and servo drives to do their power rated tasks.

I am not where the HAAS manuals are so I can not lookup what the allowed input range is for a fixed tap setting.

I would look in your CNC manuals and see if there are internal taps for adjustment to different nominal input voltages.

If your source AC nominal voltage variation is so bad that you can not stay within reasonable input voltage values, then an external voltage regulator might be required.

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[gar]

160722-1156 EDT

From a HAAS on-line manual:

AC Input Power
• Most domestic machines require three-phase power, which may be either wye or delta type. The power source must be grounded: leg or center leg for delta; neutral for wye.
• A separate earth ground is required for three-phase power. Conduit type ground will not be sufficient.
• All phases must be balanced, and voltages must be within ±10%.
• Low-voltage power (208 or 240 VAC) can be set up on the standard machine.
• High-voltage power (480 VAC) requires a high-voltage option to be purchased with the machine

The +/-10% has to apply to the nominal voltage, and not an allowed phase to phase unbalance. Generally the machines seem to be rated from 195 to 250 V. I can not tell you from this information whether nominal could be as low as 195 V. My guess is yes.

This is a very poor statement. What does it really mean?

• A separate earth ground is required for three-phase power. Conduit type ground will not be sufficient.

If it means an explicite EGC to the main panel is required, then OK. But if it just means a local ground rod, then not ok.

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[gar]

160722-1254 EDT

I stopped at the shop and looked at our 1992 HAAS and the voltage taps are labeled 196, 214, 230, and 246. The ratios between these are 1.09, 1.07. and 1.07 . Not quite 10%. Since half of 10 is 5 and they specify an operating range of +/-10 % this seems to imply and internal +/- 15%.

Suppose your nominal voltage was 205 V and you are on the 196 tap, then if nominal is high by 10%, then the DC bus voltage will be high by a ratio of 225/196 = 1.15 . One would really want to use the 214 tap.

Our nominal shop voltage is about 123 (246). Generally does not go over 125, and low might be 118 under very heavy load conditions, like today 90 deg outside. Obviously there are transient conditions where the voltage drops more for a short time, possibly 10 cycles (170 milliseconds).

DTE (Detroit Edison) will be heavily loaded at this time, but my home voltage is at 124.6. So the substation voltage regulator is controlling voltage quite well. At home I am generally between 123 and 125 V.

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