The nameplate states a power supply of three-phase 380V, 50 Hz. On a site with fixed distribution that premise holds. On a site with temporary power it does not necessarily hold: the output frequency and voltage of an engineering generator, a temporary power unit or a construction power supply vary with the load and with the model, while the controls, the motors and the heating section of the machine all take the two figures on the nameplate as given.
Where a change of frequency travels
Frequency sets the motor speed, and the motor speed sets the delivery rate of the pumps and the pumping speed of the vacuum pump. When a motor runs below its rated frequency its speed falls, the delivery rate of the ZH screw oil pump falls with it, the pumping speed of the X-100 vacuum pump falls in the same way, and the JRP-500 roots blower follows the same rule.
The consequences of a lower pumping speed are chained: the oil enters more slowly, so the volume in the tank cannot keep up with the treatment rate; the vacuum pumping speed falls, so the working vacuum of -0.08 ~ -0.0999 MPa becomes difficult to hold steadily and the degassing time stretches; and the gas content, which GB/T 423 puts at ≤0.01%, is hard to hold if the treatment time is short.
None of that shows on the machine. The displays on the control panel stay normal, no alarm acts, and the operator only notes that this batch is taking longer than usual. Nobody connects it with the frequency of the supply.
Voltage and phase sequence are checked together
A deviation from three-phase 380V affects the machine as well. With the voltage low the motor current rises and the heating increases, which shortens the winding life over a long run; with the voltage high the withstand level of the components may be exceeded. The effect of voltage fluctuation is more direct, because it acts on the heating load and the motor load at the same time.
The phase sequence deserves separate mention. The machine is fitted with phase failure and phase sequence protection, and when the phase sequence is wrong the protection acts and the machine refuses to start, which is the designed behaviour. But the protection acting only shows that the sequence is wrong; it does not show that the output of the generator is stable in phase sequence. A temporary supply can fluctuate in phase sequence and in voltage as the load changes, and if the protection acts and the machine is reset without any change in the supply conditions, the machine still is not in a position to run steadily.
What to verify before connecting a generator
| Item | Machine requirement | What to confirm on site |
|---|---|---|
| Number of phases | Three phase | Whether the generator output is three-phase four-wire |
| Voltage | 380V | The actual voltage under load, not only the no-load value |
| Frequency | 50 Hz | The actual frequency under load |
| Phase sequence | Matching the protection setting | Confirm with a phase sequence meter before energising |
| Capacity | Total power 72 + 5 kW | The rated capacity of the generator and the load factor |
| Earthing | To the electrical rules | A common reliable protective earth for the generator and the machine |
The row most easily skipped in that table is the voltage and frequency under load. The nameplate figures of a generator are no-load or rated-load values, and the starting surge of the machine makes both of them drift. With the voltage low the motor current rises and the heating increases, which shortens the winding life over a long run; with the voltage high the withstand level of the components may be exceeded. The effect of voltage fluctuation is more direct, because it acts on the heating load and the motor load at the same time.
The conditions for running without concern
When the output of the generator holds 380V, 50 Hz under load, the phase sequence is correct, the capacity leaves enough margin against the total power of 72 + 5 kW, and the earthing is reliable, the machine can be used normally. If the frequency stays well away from 50 Hz for long periods, or the voltage fluctuates noticeably, the treatment result is affected, and in that case the batch size should be reduced, the pace slowed, or fixed distribution used instead.
The requirements the machine places on its supply are clear; whether a generator can be used depends on whether what it delivers under load is the frequency and the voltage the machine needs.
