208 Voltage too low for machine

[marconi]

Just one extra thing to measure using a clamp ammeter - the line and neutral currents at the main breaker with only site load and then with site load and Rottler machine and record them. Please tell us what the four readings are please. What we want to see is the line currents about equal and the neutral current no more than a few amps.

 

[marconi]

also this is the transformer info

The information on this plate enables us to calculate the voltage drop at the output terminals of the transformer as the load current increases. The transformer is a 75kVA with 3 phase Y output of 208V/240V.

The rated secondary phase current is 75000/(3 x 208) = 25000/208 = 120A

The % Impedance figure of 5.54 tells us the percentage of the rated winding voltage which must be applied to it with the the other winding short circuited for the rated currents to flow in each winding. Thus if the primary is short circuited one would have to apply a voltage of 208 x 5.54/100 = 11.5V across the secondary for 120A to flow in the secondary and the transformed down current in the primary winding.

The effective impedance then of each of the secondary phase windings Zs is 11.5/120 = 0.096 Ohms

The volt drop for a particular phase current is Iphase x Zs. This is why I asked you to measure the phase currents.

At full load of 75kVA, or 120A per phase in the secondary windings the voltage drop is 11.5V, which means the terminal voltage is the secondary induced emf (208V) - 11.5V = 196.5V.

If we just consider just the 30kVA load of the Rottler machine fed by the transformer and assume it is balanced 10kVA per phase, the volt drop just due to the supply transformer will be (10/25) x 120 x Zs = 4.6V ...The secondary voltage will be 208 - 4.6 = 203.4V which is out of specification.

There are of course further voltage drops due to all the cabling and switchgear between the transformer secondary terminals and the terminals of the Rottler machine and also the currents for the rest of the site load.

In summary then, primary winding tap changing may be sufficient alone to achieve voltages within specification for the Rottler but be prepared that to supply the site load and the Rottler may require a new higher Kva site transformer or a dedicated transformer for the Rottler - 30kVA is specified. Interestingly the manual states a 60A per phase supply is required which is 208 x 60 x 3 = 37kVA. Whether 30 or 37kVA this is half of the rated capacity of the present 75kVA supply transformer. A review of the site load and power factor may be necessary to see if they can contribute to improve the site voltage using the present transformer.

 

[marconi]

alright i tested the voltage at the subpanel which has a breaker instead of a main lug . at that breaker the voltage is 205v and at the machine the voltage is the same . The cable i ran isnt long the whole run is 40 ft #6 in conduit and 16 ft 6/4 SO cord
there is a transformer that is feeding the subpanel ..its literally suspended above ground i will send picture . my new question is if this transformer might be adjustable. and maybe give me a higher voltage output

I used an online US cable voltage drop calculator:

Voltage Drop Calculator - https://www.calculator.net/voltage-drop-calculator.html?necmaterial=copper&necwiresize=4&necconduit=steel&necpf=0.9&material=copper&wiresize=0.4066&resistance=1.2&resistanceunit=okm&voltage=208&phase=ac3&noofconductor=1&distance=50&distanceunit=feet&amperes=60&x=43&y=23&ctype=nec

For 50ft of 6AWG for the Rottler cable run the voltage drop between start and end at 60A is 2.44V. You can see now how the voltage drops in the transformer (4.66V) and cabling (2.44V) are adding up to cause the problem of low voltage at the Rottler. 208- 4.66- 2.44 = 201V

You may have to run another triple of the same 6AWG (or thicker but not thinner)cables parallel (electrically and physically) to reduce this to 1.22V. Or replace by one thicker complete cable run sized to achieve 'good enough' voltage drop at 60A.



See:

Voltage Drop Calculator​

This is a calculator for the estimation of the voltage drop of an electrical circuit. The "NEC data" tab calculates based on the resistance and reactance data from the National Electrical Code (NEC). The "Estimated resistance" tab calculates based on the resistance data estimated from the wire size. Click the "Other" tab to use customized resistance or impedance data, such as data from other standards or wire manufacturers.

Result​

Voltage drop: 2.44
Voltage drop percentage: 1.17%
Voltage at the end: 205.56

The calculation result above is based on alternating current resistance and reactance data of 3-phase, 60 Hz, 75°C from National Electrical Code (NEC). The actual voltage drop can vary depending on the condition of the wire, the temperature, the connector, the frequency etc.

NEC data Estimated resistance Other Wire material Copper Aluminum Wire size 14 AWG 12 AWG 10 AWG 8 AWG 6 AWG 4 AWG 3 AWG 2 AWG 1 AWG 1/0 AWG 2/0 AWG 3/0 AWG 4/0 AWG 250 kcmil 300 kcmil 350 kcmil 400 kcmil 500 kcmil 600 kcmil 750 kcmil 1000 kcmil Material of conduit PVC Aluminum Steel Power factor (PF) Voltage Phase DC AC single phase AC 3-phase Number of conductors single set of conductors 2 conductors per phase in parallel 3 conductors per phase in parallel 4 conductors per phase in parallel 5 conductors per phase in parallel 6 conductors per phase in parallel 7 conductors per phase in parallel 8 conductors per phase in parallel 9 conductors per phase in parallel Distance (one-way) feet meters miles kilometers Load current Amps

 

[HEXx99]

I used an online US cable voltage drop calculator:

Voltage Drop Calculator - https://www.calculator.net/voltage-drop-calculator.html?necmaterial=copper&necwiresize=4&necconduit=steel&necpf=0.9&material=copper&wiresize=0.4066&resistance=1.2&resistanceunit=okm&voltage=208&phase=ac3&noofconductor=1&distance=50&distanceunit=feet&amperes=60&x=43&y=23&ctype=nec

For 50ft of 6AWG for the Rottler cable run the voltage drop between start and end at 60A is 2.44V. You can see now how the voltage drops in the transformer (4.66V) and cabling (2.44V) are adding up to cause the problem of low voltage at the Rottler. 208- 4.66- 2.44 = 201V

You may have to run another triple of the same 6AWG (or thicker but not thinner)cables parallel (electrically and physically) to reduce this to 1.22V. Or replace by one thicker complete cable run sized to achieve 'good enough' voltage drop at 60A.



See:

Voltage Drop Calculator​

This is a calculator for the estimation of the voltage drop of an electrical circuit. The "NEC data" tab calculates based on the resistance and reactance data from the National Electrical Code (NEC). The "Estimated resistance" tab calculates based on the resistance data estimated from the wire size. Click the "Other" tab to use customized resistance or impedance data, such as data from other standards or wire manufacturers.

Result​

Voltage drop: 2.44
Voltage drop percentage: 1.17%
Voltage at the end: 205.56

The calculation result above is based on alternating current resistance and reactance data of 3-phase, 60 Hz, 75°C from National Electrical Code (NEC). The actual voltage drop can vary depending on the condition of the wire, the temperature, the connector, the frequency etc.

NEC data Estimated resistance Other Wire material Copper Aluminum Wire size 14 AWG 12 AWG 10 AWG 8 AWG 6 AWG 4 AWG 3 AWG 2 AWG 1 AWG 1/0 AWG 2/0 AWG 3/0 AWG 4/0 AWG 250 kcmil 300 kcmil 350 kcmil 400 kcmil 500 kcmil 600 kcmil 750 kcmil 1000 kcmil Material of conduit PVC Aluminum Steel Power factor (PF) Voltage Phase DC AC single phase AC 3-phase Number of conductors single set of conductors 2 conductors per phase in parallel 3 conductors per phase in parallel 4 conductors per phase in parallel 5 conductors per phase in parallel 6 conductors per phase in parallel 7 conductors per phase in parallel 8 conductors per phase in parallel 9 conductors per phase in parallel Distance (one-way) feet meters miles kilometers Load current Amps

UPDATED EDIT**
ah i just saw your post about the transformer .

 

[HEXx99]

Just one extra thing to measure using a clamp ammeter - the line and neutral currents at the main breaker with only site load and then with site load and Rottler machine and record them. Please tell us what the four readings are please. What we want to see is the line currents about equal and the neutral current no more than a few amps.

The technician will not come out to start the machine until we confirm the voltage he wants at the machine lol

 

[HEXx99]

The information on this plate enables us to calculate the voltage drop at the output terminals of the transformer as the load current increases. The transformer is a 75kVA with 3 phase Y output of 208V/240V.

The rated secondary phase current is 75000/(3 x 208) = 25000/208 = 120A

The % Impedance figure of 5.54 tells us the percentage of the rated winding voltage which must be applied to it with the the other winding short circuited for the rated currents to flow in each winding. Thus if the primary is short circuited one would have to apply a voltage of 208 x 5.54/100 = 11.5V across the secondary for 120A to flow in the secondary and the transformed down current in the primary winding.

The effective impedance then of each of the secondary phase windings Zs is 11.5/120 = 0.096 Ohms

The volt drop for a particular phase current is Iphase x Zs. This is why I asked you to measure the phase currents.

At full load of 75kVA, or 120A per phase in the secondary windings the voltage drop is 11.5V, which means the terminal voltage is the secondary induced emf (208V) - 11.5V = 196.5V.

If we just consider just the 30kVA load of the Rottler machine fed by the transformer and assume it is balanced 10kVA per phase, the volt drop just due to the supply transformer will be (10/25) x 120 x Zs = 4.6V ...The secondary voltage will be 208 - 4.6 = 203.4V which is out of specification.

There are of course further voltage drops due to all the cabling and switchgear between the transformer secondary terminals and the terminals of the Rottler machine and also the currents for the rest of the site load.

In summary then, primary winding tap changing may be sufficient alone to achieve voltages within specification for the Rottler but be prepared that to supply the site load and the Rottler may require a new higher Kva site transformer or a dedicated transformer for the Rottler - 30kVA is specified. Interestingly the manual states a 60A per phase supply is required which is 208 x 60 x 3 = 37kVA. Whether 30 or 37kVA this is half of the rated capacity of the present 75kVA supply transformer. A review of the site load and power factor may be necessary to see if they can contribute to improve the site voltage using the present transformer.

This transformer is running power to at least two panels the machines these panels are powering are not ran constantly. they run maybe one of them about 8 times a day and maybe 10 min at the mist each time. the cnc wouldnt be running all day either . but there are also lights getting power from these panels . Im now thinking a 30 kva transformer 3 phase just for this machine is the best bet . unfortunately these are not cheap. unless i just find 240v andpower it from that, right? but then it looks like i made a mistake of supplying inefficient voltage to the machine . which is true, its not enough , but their own manual says 208 v ..im going to look for 240v

 

[marconi]

This transformer is running power to at least two panels the machines these panels are powering are not ran constantly. they run maybe one of them about 8 times a day and maybe 10 min at the mist each time. the cnc wouldnt be running all day either . but there are also lights getting power from these panels . Im now thinking a 30 kva transformer 3 phase just for this machine is the best bet . unfortunately these are not cheap. unless i just find 240v andpower it from that, right? but then it looks like i made a mistake of supplying inefficient voltage to the machine . which is true, its not enough , but their own manual says 208 v ..im going to look for 240v

Do not beat yourself up too much. The rottler electrical spec is far from clear and certainly not definitive in the way the acceptable voltage is written.

Please measure some phase currents and voltages at main breaker for different states of site load to establish what margins exist to supply the demanding rottler load. Would site accept load shedding to allow rottler to power up?

 

[marconi]

HEXx99. I have been reviewing everything you have said and the information in the Rottler manual on the electrical requirements. I have made a mistake because I thought the 205V you mentioned as a low voltage and the 208V mentioned by Rottler were phase voltage. They are actually line voltage. The Rottler requires a 3 phase 3 wire 60Hz supply with a line voltage in the range 208-240V. In terms of phase voltages, this is a range of 208/rt3 to 240/rt3 = 120 to 139V.

The supply transformer line voltage of 205V is a phase voltage of 118V. Tap changing out to be able to bump this up a few volts. At 125V phase voltage the line voltage would be 216V, or 8V above the minimum.

The cable calculation redone using 10kVA per phase at 120V is a current of 10000/120 = 83A.

the #6AWG cable run will drop between its ends 3.9V or a machine phase voltage of 116V or 201 line voltage. Clearly #6AWG is too thin. A double run of #6AWG would halve the volt drop to circa 2 V, thus a machine line voltage of (120-2) x rt3 = 204V - still not good enough.

#2AWG gives a volt drop of 1.71V; (120-1.7) x rt3 = 204V line voltage at the machine.

And this is before we consider the transformer volt drop and volt drop due to site loads. It will be very difficult to achieve the required machine voltage using the current transformer.

I think you are at the stage of placing a transformer 480V/240V - both line voltages - close to the machine to keep the machine's supply cable voltage drop as small possible without having to use a very thick cable and yet stay well within the 208 - 240V specification.

 

[marconi]

The 75kVA transformer with a secondary phase induced voltage of 120V, will have a full load phase current of 25000/120 = 208A.

5.54 percent impedance means 120 x 5.54/100 = 6.5V applied to secondary with primary short-circuited would circulate full load phase current. This Zs is 6.5/208 = 0.031 Ohms.

The Rottler machine when drawing 83A per phase would create a secondary terminal phase voltage of 120 - (83 x 0.031) = 117V.

117V is a line voltage of 202V - unsatisfactory for the Rottler even before any other loads connected to transformer.

The Rottler requires its own transformer. Hope this helps. Happy to discuss.

Regards

Marconi

 

[marconi]

Here is an 8 minute video on the Rottler 5 axis machine cutter - very impressive.