Power Quality Case Study - A simple fix to a Serious Problem
Power problems that the Utility said may be related to being at the end of the distribution line, more likely was an old system with new electronic loads that brought the problems to light. Regardless, Phaseback VSGR solved the problems without a protracted study, without changing out the existing system components, and with little inconvenience.
Before It was reported that drive faults were occurring as a result of voltage imbalance issues. Variable frequency drives (VFDs) will fault if voltages become unbalanced beyond 10%, or if the phase voltage differential distortion exceeds 6°. Another common cause of VFD faults is overvoltage.
In the data we gathered, we saw a voltage imbalance exceeding 21%, a phase differential distortion of 17°, and a line voltage as high as 503 volts. These statistics create a situation where unreliable operation, lockups, and failures are likely to occur. Additionally, we studied the magnitude of harmonics in the facility. We found that the harmonic distortion was below the nominal threshold of 5% Voltage THD. This value may change depending on the amount of equipment operating, but is presently not the source of the power issues described above.
A Phaseback Voltage Stabilizing Ground Reference (VSGR) was temporarily installed at a welding outlet in the store room, then later in the machine shop, in order to test the VSGR’s effectiveness in solving the power quality issues mentioned above. Voltage imbalance was reduced by a factor of 15 (from 21.3% to 1.4%), and phase voltage differential distortion was reduced by a factor of 16 (Phase C from 257° to 241°). This simple solution will eliminate drive failures, and prevent them from returning, in this extreme case.
With line voltage 5% above nominal, it is recommended to change the drive settings to a higher input voltage. Changing the incoming taps at the Utility transformer may create issues on UPS and other devices, but something to consider.
Adding a Phaseback VSGR to the 480V side of each power transformer will provide the benefits shown below to all equipment in the facility.
Arcing ground faults
Voltage spikes from internal or external sources
Phase voltage imbalance
Phase loss due to high impedance grounds
Phase angle differential distortion
Phase voltage instability
Phase voltage harmonics
Noisy ground reference and frequency instability
Operational efficiency increases
Local ground indication
Remote ground alarm/shunt trip signal
After The facility has (5) 480 volt, 2,500 kVA 3-phase 3-wire delta power transformers. We asked them for their worst problem so we could show how well the power system will function with the addition of a Phaseback VSGR. After the results were shared with the operations and maintenance manager they ordered and installed (5) Phaseback VSGR units. A follow-up visit 6 months after the installation the electrical people explained that this has been the best the power system has ever operated. The year before they had 35 drives fail which shut the facility down. After the Phaseback VSGR installation, they did not have any downtime for drive faults or equipment failure. More charts and data on the following pages.
William Hinton Director of Engineering Applied Energy LLC www.phaseback.com
Power Quality issues & Transformers. Save Lives & Save Money now.
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