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Waveform of the Month

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Prescribing unbiased power and environmental solutions since 1995!

November 2007

~ Waveform of the Month

~ In the waveform below, the Uni-Polar Current is most likely due to a saturated transformer in the system.

~ Why Monitor Current?

~ Most monitor manufacturers try to reduce the cost of their monitor and they eliminate the current channels because it cost five as much to support a monitor with 15 channels (10 voltage and 5 current) instead of 3 channels (voltage Phase-ground only). This is the number one reason engineers are not accustomed to monitoring current (the cost of the monitor prior to RxMS was always too high). That created a false sense of need for why current is so critical. By simultaneously monitoring both voltage and current, you can answer the customer’s biggest question; didn’t your system cause that distortion? It is impossible to convince a customer that the distortion is not from your equipment without monitoring the current.

~ The next best reason to monitor current is to document if the system was being used at the time of the event. One of the scenarios that we see weekly is an event that occurs over the weekend but the error is not reported until the operator tries to use the equipment on Monday morning. Therefore looking at the event log for something Monday morning is futile since the real event that caused the problem may have occurred earlier in the weekend. Having the current data, it is easy to see that the system was not used prior to that time and it is easy to find the actual event knowing this.

~ Ground current is a very critical justification for monitoring current as this is one of the major problems with sophisticated electronics; ground loops. By monitoring the current on the ground, you not only get to see the wave shape but also the actual amplitude and can use this information to find the source of the ground current.

~ The last reason to monitor current is for sizing the power protection device properly and to see sudden changes that may be occurring on the feeder or within the system itself. RxMS has actual document with a customer that their manufacturer for a PDU (Power Distribution Unit) actually implemented a cost reduction plan that involved changing the grade of steel used in the transformer. While it must have passed their internal testing when the unit got to the field, it became obvious that the steel was now saturating and causing the current pulse to go uni-polar (one direction). This caused the current to rise tenfold and caused major issues with power protection devices trying to protect the equipment causing them to have to really oversize the conditioner (costing a lot more money) all because the PDU manufacturer wanted to make more margin on their sale. By saving approximately $70 per unit, it ended up costing the customer over $8,000 on each system that they had to protect!  If we did not monitor current for this client, they would have never known what was occurring.

~ Remember that knowing is better than guessing!