Metrojack (Customer) asked a question.
Need advice/help with
GS23-21P0 (1 HP) DuraPulse GS20 AC drive
- GSDA-DP-D digital potentiometer
- GS23-21P0 (1 HP) DuraPulse GS20 AC drive
- Marathon Y364 MicroMAX AC induction motor
- System operating on 240 VAC, open-loop speed control
We should also note that the building is supplied by an older high-leg delta 3-phase system. However, this should not have any effect on the GS23-21 drive, since the drive is operating on a standard 240 VAC 3-phase input.
Input and Drive Measurements
- AC input voltage to the GS23-21P0 was measured at 242 VAC across all three phases.
- DC bus voltage indicated by the drive was 381 VDC, which appears high; the expected value based on calculation is approximately 342 VDC.
- Speed reference signal from the digital potentiometer measured 10 VDC (max speed setting) both from ACM–AI1 and ACM–+10V, confirming a proper 0–10 V command signal.
Startup Behavior
The drive was enabled by closing DI1/FWD to DCM. When the motor starts, the shaft rotates very slowly, and:
- The GS23-21 output voltage fluctuates between 9 and 42 VAC across all three output phases.
- The output frequency displayed is 0.5 Hz, consistent with the extremely slow rotation.
Intermittent Event Observed
After several repeated start/stop cycles (approximately ten), we observed one instance where the drive started normally.
On that single occurrence:
- The motor accelerated to full speed,
- The drive indicated 60 Hz output,
- The system behaved exactly as expected.
This normal operation occurred only once. All other start attempts—both before and after—resulted in the same slow rotation and ~0.5 Hz output.
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We also observed an interesting condition related to the AC motor. While the motor was mechanically disconnected from the gearbox, there was a period when the motor frame was not grounded. During this time, we measured voltage between the motor body and earth ground:
- 59 VAC with the drive stopped
- 162 VAC with the drive running
Is this normal when the motor frame is ungrounded?
In other words, is this simply capacitive coupling between the stator windings and the motor frame, or does it indicate a potential insulation or wiring problem that we should be concerned about
A couple thoughts,
The GS23-21P0 can be operated from an unbalanced system, but it is recommended to disconnect the filter link.
My first test would be to run the motor without any external speed reference, simply by the VFD keypad Hz command. This will rule out any problem with the external speed reference.
You measure 59VAC between the motor body and earth ground, with the VFD stopped. The motor should have a dedicated grounding conductor connected to the building grounding system, which would include building steel (and technically include concrete rebar). By "earth ground", if you mean any building grounded object, this should not be, and is a safety concern. By "earth ground", if you mean a steak into the dirt outside the building, separate from any grounding rods, then this could be possible, due to different ground potentials. If this were tested during an inspection, the inspector would require an additional ground rod connected to the building grounding system.
We were on a project where we measured voltage (high frequency) between the motor and grounded objects while the VFD was running, (which was causing bearing damage). I believe this is the coupling effect you are referring to. The engineer required additional grounding, including grounding brushes on the shaft.