Transfer Switch time Delay

Do you have a UPS for your server?

The time delay for switching power supplies depends on all the loads. You do not want to have a positive spike added onto the positive cycle of the old power source. This could cause an overvoltage condition with lots of sparks and fire. It also depends if there are any motors or capacitive loads being fed. When a motor loses power it can become a generator while it loses speed, feeding power back to the source. You may have to wait until it reduces speed enough to avoid an over voltage condition.

A delay could also be required to get the generator up to speed, or synchronized.

Whoever installed the generator should have done all these calculations. Changing the delay could have devastating effects as well as void any warranties. Contact the installer, or get a better UPS and battery back-up for the server to handle the delay.

There are 'make before break' transfer switches, however, the generator controls must be capable of auto synchronization to the utility before transfer. The other way to exercise the generator, done once a week in hospitals, is to do it without actual transfer. There should be a setting on the transfer switch for "exercise" without transfer where the generator starts and runs no load just to check voltage and speed and for leaks. Load test can be set up for once a month. Once a week is too much.

You need to have at least a small UPS system for each important PC (or a big one for all of them!), there is no way round this at all if the mains just drops off, there will be no time for a Sync phase and changeover.....

This smacks of lack of knowledge/planning.....the UPS is the ONLY way to correct this situation and should have been planned from day 1....

As others point out in this thread, you certainly should have a UPS serving critical computer loads. If you have one make sure it's working correctly or even inadvertantly left in bypass. Unless you have a closed transition switch (make before break) you will have momentary loss of power during transfer. The ASCO switches are about the fastest and still, by nature of design, you will get an average open time of 30-35ms depending on the size of the ATS.

You need to determine specifically what type of ATS you have. Over the past several years there have been more and more Delay Transition Transfer Switches sold. Some engineers have been going with this style, simply because it's easier to deal with the current inrush you get from fast out-of-phase switching going hot to hot. If you have a DTTS you can minimize the open delay time but if you have much rotating motor load or tranformer load you'll need to be careful.

It is typically not a good idea to run your gen unloaded for excercise periods. I've seen plenty of engines weeping and drooling oil all over from being wet stacked due to this.

Anyway, check your switch out and respond back here with better specifics. Determine who, what, etc. ASCO, Zenith, Russel, Onan... What catalog number etc and we'll know whether you can do anything.

The main problem as I see it that with "Hot Swop", he needs to know in advance when a power failure is going to happen, how will he get this info??? From God?

Therefore a UPS is the only method that will work properly....

Good post, shows in depth knowledge of the complete problem. I have given you a GA.

Good morning,

When your power goes away (blackout) you will need a UPS to carry your servers, because it takes time for the generator to start and come up to speed and voltage (at least 10 -15 seconds). Now when the power comes back choose a closed transition (which is what you must have had on your old system) switch and you will never know the generator is off line when the power is restored. This is like a form "C" contact i.e. make before break and vice versa. The time delay is probably only for keeping the generator running after the power comes back to insure that it is steady. Once the switch is initiated it is FAST (like 100 ms)! When you exercise your unit, closed transition will always occur because you are starting the generator before making the change - and of course when the unit switches back it's the same thing. Good luck.

Switchman certainly has the answers you need for your problem. I would like to add this though. There was a building built near the fire station where I work. The standard procedure for us is to watch the building details while under construction. The company that was going to use this building was a cell phone service. They built their system to run on rooms full of batteries. Then they used the power company to maintain the charge in the batteries. Their generator was used as backup to charge the batteries. In effect a very large UPS. I do not know what electrical demands your computer system requires, but I would think that for most personal computers a UPS has the added benefit of surge and brown out protection. Even if switchman could talk you through the transfer switch adjustments, UPSs are cheap insurance. Good luck.

Good Post BobC.

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To the original poster, I would just like to add the following to various posts already made on this blog:-

I would just like to add :-

1)that any electronic designed to switch seamlessly from mains to inverter and back, no matter how well designed, may still cause some nasty transients to be produced that could still do nasty things to a running PC.......do not take this risk....they are also usually far more expensive.....

2) If the mains just drops off, there is NO electronics that can handle that transfer in any good manner....no matter what the literature says.....!

3) The mains ---> charger ---> Battery ---> inverter ---> mains Voltage. Is still the best and simplest manner as no particularly high technical quality electronics are required and you are protected from any mains transients as mentioned by others, a further plus.

4) the batteries are "worked" all the time (good for the batteries lifespan) and you can even switch off the mains input from time to time to deplete the battery and then let it charge again. The only requirement here is for a charger that NEVER over charges the batteries under any circumstance.....

I fail to understand why you (seem to be) set on the other sort of UPS with all its possible problems, what are your imagined benefits from this sort? Perhaps we can answer that better......