Power Quality Issue

What is the nature of the frequent failures?

What are the nature of failures for each equipment? What components were found to be affected. Nature of component failure. Answers to these will help.

Dear Madhu,

The problem may mostly be because of the electro magnetic interference (EMI) of any one of the instruments on load. This can be tested by changing the location of all equipemnts or get the instruments tested for EM radiations.

Thanks

Make sure the neutral of the UPS is solidly grounded. If not, the neutral is shifted for unbalace load condition, and the phase to line voltages become unbalanced leading some phase to neutral voltage higher and it cases the equipment failure.

- MS

Get a Power Quality logger with event loggin capability.
It would be best located at the UPS output board.

This will quickly show if there is a power quality issue or something els is causing your problems.

Regards,
Sapper

There is a high possibility of unbalancing of load at times resulting in shifting of neutral and thus tripping as per settings. Need to observe the tripping times and load pattern at that time- Sudden imbalance of load. Check if there are too many single load connectiions on load side. This should be balanced. Timing could be start up, shut down, luch and tea break machine loading / unloading, street lighting and evening lights. lods adjacent to the equipmenst in consideration, earthing strips if getting shorted etc . Log the loads on three phases for 24 hours minimum and see the pattern

You may check by removing the single phase loads and check the performance. Mostly it should not trip.

30kVA seems like a heck of a lot for the loads you described...maybe you have a lot of kit....doesn't really matter.

Can you describe these "black streaks" a little more please?

What type of plant is this located in?

May please check whether sudden voltage pulses/ spikes are generating (due to IGBTs in UPS ) and fed to the loads/ instruments for which instruments/ meters became faulty.If so, remedy is to use proper filters.

Thanks,

Manindra

with all due respects,

1. what would be filter like for a UPS system having two 3oKVA UPS in parallel? please provide more info on this.

2. I guess, is it valid to do solid grounding of UPS neutral? that too at supply end?

3. Nature of load, load list consists of Quality control instruments like HPLC, GC, Muffle furnace, weighing balances, pH indicator etc

4. regarding type of failure, i would like to bring few recent issues. Black Horizontal lines on LCD screens of weighing balances, PCB component failures etc

5.Regarding EM Interference, how can we check it and more over all the instruments that we have do not have any specific EMI requirements mentioned on it.

Having had a lot of troubles myself with a large number of electronic devices sharing a common power circuit, I will describe my issues and what I did to resolve them. And please, as there are many people on this forum far more educated and experienced in this field, correct or elaborate on anything I write to provide a more useful solution.

Firstly, I was using a single phase 110V line and not a 3 phase xxxV line so some things may not apply.

Initial Problems consisted of:

1. Hum and Noise in audio

2. Irregular Video interference patterns

3. 70v-110v showing across case grounds from unit to unit. Inconsistant from device to device.

4. Scrambled data on MIDI path managers and consistantly scrambled digital audio effects settings.

Corrective measures:

1. Be certain that all devices are in common polarization. Just because a device is working does not mean that all legs of the power are configured identically. This can apply to multiphase power as well.

2. Try to keep the main power source, as in the transformer at the outside power line, common to all the equipment. Large companys have multiple power transformers from their service providers to handle the load. Try not to mix them on these multiple devices.

3. Use isolation transformers and/or power supply filters between the individual units. There are many reasonably priced units that can provide isolation and noise filtration.

4. Try to remove any motorized or pulsed coil devices from this circuit. Some furnaces have a pulsed coil for their burner system and can play havoc with the local power system. Many motors can "ripple" the local circuit power and cause surges when starting up. Brushed motors can have worn brushes/commutators and create RF and other voltage spikes all while running seemingly normal.

5. Starting at the main input supply, remove and clean all connections. If any aluminum wire is found, pay special attention there with an anti- corrosive treatment after cleaning. Replace if practical.

6. Experiment with shielding of individual power cords and device cabinets. Stray RF signals from the most unlikely sources can become a factor. An old microwave oven is a common problem with stray radiation.

7. Any of your devices can have a degraded power supply circuit, with a leaky capacitor or the like, and feed "crap" back into the supply line. This device may seem to be working normally but still be creating an issue.

8. I see you have had your UPS checked, but I will add that these units do not seem to be fool proof. I have 4 small units (500VA-1.5KVA), and 2 additional filter/conditioner/regulators. Occasionally on startup, one of these devices actually creates a spike of it's own and shuts down 1 monitor and 1 computer requiring a manual restart of only these devices. This can be solved by starting up each device individually, but that is not practical on my system.

Good Luck!! It took me 2 years to solve my issues but it was well worth it.