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Banana Skins – February 2024 (#437-444)

437. Financial costs of delayed EMC compliance

A manufacturer of electrical test equipment took an order worth several million dollars for new product to be used worldwide to help service the vehicles manufactured by a major multinational. It failed to meet the EMC standards required for compliance (which had also been made a part of the contract).

Testing and consultancy to discover the causes and find do-able fixes for the EMC problems (several low‑cost options not being possible due to the late stage of the project) cost around $20,000; iterating the PCBs to a compliant build standard cost around $60,000; and refurbishing non-compliant units already supplied to the customer cost around a further $70,000.

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VSWR and its Effects on Power Amplifiers

Voltage Standing Wave Ratio results from an impedance mismatch between a source (an amplifier) and a load (test application). This mismatch can influence the performance of the source.

The delivery of the (eventually) EMC-compliant units was also delayed by five months from the target date, causing equivalent delays in receiving the first payments and incurring greater costs of financing the project (by putting the financial break-even point back around half a year on what was intended to be an 18 month project). Whether any harm has been done to the test equipment manufacturer’s reputation with their customer, or with the marketplace as a whole, remains to be seen.

(A contribution in June 1999, the source wishes to remain anonymous.)

 

438. Pump at ski resort causes interference

In 1996, a ski resort near Silverthorne, Colo, installed a pumping system to lift water up to a river, whose water flows into a lake at the base of the resort and is then used on the mountain for snowmaking. At that time, the pumping system consisted of a 350-hp, 480VAC, 3-phase, SCR, variable-frequency drive (VFD), which was located at the base village. Because the pump and motor were positioned 900 feet below the river and VFD, the resort used 4,1560V as the distribution voltage from the VFD to the motor and pump. The power source for the pumping system was, and still is, a 1000kVA transformer fed by a 25kV, 3-phase overhead power line located five miles from the ski resort. This line also runs beyond the pumping system and serves a local community.

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This pumping system worked well for several years with only the 350-hp pump, but as the ski resort expanded its snowmaking system, more water was needed. As a result, a 750-hp VFD, pump, motor and new pipe to the river were installed in 2002. At this point some real operational problems surfaced.

During the 2002-03 ski season, the resort could not run the 750-hp VFD at full capacity by itself, let alone together with the 350-hp VFD running at full capacity. The drives would drop off-line because of their under-voltage protection. Another concern was that homeowners and businesses in the area and nearby community complained of flickering lights.

(Extracted from: “Solving a Power System Compatibility Problem,” Vaughn DeCrausaz, EC&M, June 1st 2006, https://ecmweb.com. The rest of the article describes how the problem was solved with careful measurement and the application of reactive power factor correction to achieve a unity power factor for the VFD systems.)

 

439. Electric ‘bum’ hazards

I’ve been reading up on various standards relating to test equipment safety and stumbled across BS EN 50110-1 1996 section 3.1.6 Injury (electrical) which cites “electric bum” as a potential hazard! I zoomed in and re-read it several times, it’s definitely B U M and not B U R N.

‘Electric bum’ sounds quite painful, I’m definitely taking all the necessary precautions to avoid that one!

(Sent in by James Toddington of BAE Systems Electronics & Integrated Solutions, Rochester, 9th May 2007.)

 

440. Switching of power‑factor correction capacitor interferes with contactor

A case study illustrates negative impulses of 366V followed by positive impulses of 420V at the terminals of a LV load when a power factor correction capacitor was switched on within an adjacent installation. These transients caused a contactor within a switch panel to fail to latch correctly.

(From subclause 9.2 of IEC/TR 61000-2-14:2006,“Environment – Overvoltages on public electricity distribution networks,” Clause 9: “Case Studies,” https://www.iec.ch)

 

441. Interference from insulation breakdown caused by vibration

This case study shows how high levels of vibration in a three-phase induction motor could cause insulation breakdowns causing momentary earth-faults on one phase. The resulting short voltage peaks on the mains distribution networks caused frequent misoperation of electronic regulators.

(From subclause 9.3 of IEC/TR 61000-2-14:2006,“Environment – Overvoltages on public electricity distribution networks”, Clause 9: “Case Studies,” https://www.iec.ch)

 

442. Switching MV power factor correction trips LV circuit breaker

This case study concerns frequent operation on a circuit breaker protecting a PVC moulding plant, causing lost production. It was found that the cause was the switching of a 120kV power factor correction capacitor in the upstream substation. 

(From subclause 9.4 of IEC/TR 61000-2-14:2006,“Environment – Overvoltages on public electricity distribution networks,” Clause 9: “Case Studies,” https://www.iec.ch)

 

443. Wireless interference problems in the home

Take a look at any Sunday newspaper’s advertising section for stores that sell electronics, and it is clear that wireless devices are everywhere. Visit these stores and listen to the salespeople selling wireless local-area-networks (WLANs), cordless phones, and all else wireless to often-naïve consumers.

What salespeople fail to tell consumers is that before consumers buy the latest wireless gadget, they should make sure that it will function properly in their home environment. For an unknowing consumer, it can be frustrating to buy a microwave, a 2.4GHz cordless phone, a 2.45GHz video transfer system, and a 2.4GHz WLAN, and then find that only some work error-free once installed in the home.

Manufacturers often take the view that as long as their products are certified, interference it the other guy’s problem. What most manufacturers fail to acknowledge is that the consumer ultimately ends up with the problem. Unfortunately, consumers don’t necessarily know why it doesn’t work, just that it doesn’t. These devices often end up as returns or consumer complaints.

(Extracted from: “Residential Spectrum Management: The Manufacturer’s Role,” David A Case, Compliance Engineering 2005 Annual Reference Guide, pages 106-107.)

 

444. Interference with household appliances from living too close to a transmitter

Residents living near the ABC’s main radio transmitter at Liverpool have complained repeatedly of interference from the powerful signals it emits, amid concerns that planners have overlooked the impact of electromagnetic radiation on the area. Residents in a new housing estate at Prestons, which is across the road from the tower, have had the signal from the ABC radio station 702 interrupting phone calls, throwing lines across television screens and turning electronic equipment on and off without warning.

“There would be music at the back of our phone calls,” one resident, Arvin Prasad, said.

“Telstra kept saying it was not their problem but finally they fixed it. They put some kind of filter on the lines.”

Another resident, Marina Baldin, said: “I had one of those touch lamps. It used to go off and on by itself. I got rid of it.”

The Herald reported last week that the five AM radio transmitters at Homebush Bay will have to be moved because Planning NSW has given approval for a multistorey building 200 metres from the 2UE-2SM transmitter. No one is yet living at Homebush Bay, and the issue is who will pay the $40 million cost of moving the transmitters.

But at Prestons people have been living for more than a year in two-storey houses within 350 metres of the ABC tower. The ABC broadcasts at 50 kilowatts – ten times the power of the AM stations at Homebush. The packaging company Amcor, which is investigating a new plant on the old Liverpool showground site 400 metres away, commissioned a study which yielded alarming results.

Readings at ground level were well below safe levels for non-ionising electromagnetic radiation, but at five metres were above the safe limit. The company has been advised it would need to shield equipment in the factory to avoid malfunctions.

The ABC’s director of technology, Colin Knowles, disputed the Amcor findings yesterday, saying the ABC’s own testing at Prestons showed radiation levels were well below those permitted under Australian standards. “This is the same problem that airports experience. People complain about airport noise, but they build out near the airport,” he said.

The ABC tower has been at Liverpool for 67 years. One resident who complained to the ABC was told to direct his concerns to Liverpool Council, which gave permission for the new housing development. A council spokesman was not available yesterday.

(Extracted from: “Neighbours find ABC has turned the radio up too far,” Anne Davies, Urban Affairs Editor, Sydney Morning Herald, 24 February 2003. Also see: “Planning debacle forces radio towers to seek new home,” 17 February 2003, http://www.smh.com.au/articles/2003/02/16/1045330466812.html, and “Government admits radio towers, units were too close”, 18 February 2003, http://www.smh.com.au/articles/2003/02/17/1045330538774.html, also by Anne Davies in the Sydney Morning Herald.)

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