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UPS is not using Battery directly as standby power
3

UPS is not using Battery directly as standby power

UPS is not using Battery directly as standby power

(OP)
My power plant has a UPS system for our back up power. Capacity rating is 80 kVA. but unlike the usual UPS that i know. the ups itself didn't have a battery as back up of the ac mains. but it use separately dc bus to supply the back to it's inverter. and it use a blocking diode to prevent back feeding to the rectifier. Is there any problem if we use that kind of installation?
here i attach the wiring of ups

RE: UPS is not using Battery directly as standby power

What is the source of the DC bus?
  

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If we learn from our mistakes I'm getting a great education!
 

RE: UPS is not using Battery directly as standby power

If you don't have a battery supplying the dc bus, the Uninterruptible Power Supply will be Interruptible.
 

RE: UPS is not using Battery directly as standby power

(OP)
DC bus is supplied by battery. the battery is charged by other rectifiers. is there any problem  occurs by using this kind of configuration and using of blocking diode. because usually the ups's rectifier also float charging the battery and didn't use blocking diode like this. thank you

RE: UPS is not using Battery directly as standby power

Really this needs to be addressed by the UPS manufacturer. In principle it is possibly ok, but there are enough subtle elements of the design which may make this difficult or impossible for the UPS to operate. For example, the UPS rectifier output will get a large degree of smoothing by the battery, but in this configuration it won't. That sort of thing.
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: UPS is not using Battery directly as standby power

There are many UPS systems where the battery bank is not connected directly to the rectifier output but are charged instead by a separate charger board. Done on systems where the rectifier voltage isn't controlled or in units where the rectifier voltage vastly exceeds the battery voltage. In this case the battery voltage will be boosted by a standard boost circuit in periods when it is required.

There are others that the battery is connected to the rectifier but via a switching component, SCR or similar, for charging purposes and during the discharge cycle the current is fed via the blocking diode. This was done especially on systems which used a 6 or 12 pulse controlled rectifier at the input but where the manufacturer wanted another selling point and could market the UPS as having a high value input power factor. When the battery needed charging the rectifier would be controlled to the correct voltage and the charging SCR turned on, allowing current to flow to the battery.

During this phase of operation the input power factor of the UPS would normally be in the range of 0.8 to 0.85, mainly due to the firing angle (cos theta) of the rectifier thyristors. Once the charge cycle was completed the charging SCR would be turned off. This is achieved by removing the turn on signal to the charging SCR and then lowering the rectifier voltage momentarily to ensure that there is no current flow. Once the charging SCR has been turned off the rectifier voltage can be raised to its maximum level which raises the input power factor.


All that said, I'd be taking what is shown on a very simplified single line drawing with a grain of salt.
 

RE: UPS is not using Battery directly as standby power

(OP)
sir, please explain about ' the UPS rectifier output will get a large degree of smoothing by the battery' i don't really understand about this, and what is other effect of this configuration.

to sibeen :
what is the disadvantage of this configuration? does it have a side effect to the reliability of the ups?


 

RE: UPS is not using Battery directly as standby power

Apart from technical issues there may be regulatory issues. There may be more stringent standards for the UPS than for the station battery. This is not always the case but using the station battery to power a critical load UPS may impose more stringent maintenance and monitoring standards on the station battery.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: UPS is not using Battery directly as standby power

(OP)
waross
What do you think about the technical issues, because The supplier says that it's cheaper to use this kind of configuration. I'm afraid there are many consequences and abnormality because of this unusual configuration.  

RE: UPS is not using Battery directly as standby power

The technical issues have been well addressed by other posters.
When a backup system is installed, it is often mandated by various codes and standards. This may be fire codes, insurance standards, or operating procedures. These authorities often specify minimum standards for monitoring and routine testing.
For example, a standby generator for a private residence just has to start and run most of the time. However, a standby generator for a fire protection pump even though it may be the same basic engine and generator end may, in many jurisdictions, have a monitoring panel which may monitor battery voltage and connections, coolant level, fuel level, water jacket temperature, integrity of the water jacket heaters, mains supply for the water jacket heaters, etc. (It has been awhile since I have seen a spec but it is not trivial.)
In addition, There may be minimum standards for care and testing. There may be a schedule for starting and a minimum run time. Possible weekly or monthly for 1/2 or 1 hour. There may be minimum standards for load testing. Possibly monthly or yearly.
If a UPS is installed for a critical system and another battery system is used, then that battery bank becomes part of the UPS for care testing. If there is a backup generator on the battery bank then the generator may become subject to more stringent care and testing standards.
Some jurisdictions may prohibit feeding non-critical loads from critical battery banks. (In my area I don't believe that I would be allowed to power a personal computer from a battery bank supplying emergency lighting.)
In some jurisdictions the standards may be quite easy to meet and there may not be a problem with a non-critical battery bank feeding a non-critical UPS.
It may be well, however to check the local regulatory requirements for both the battery bank and the UPS.
In regards to the smoothing, The basic wave form of a battery is a pretty straight line. The wave form of a battery being charged by a multi pulse rectifier is the straight line with small peaks corresponding to the peaks of the charging pulses.
The output of a simple single phase rectifier is a series of positive half sine waves.  

Bill
--------------------
"Why not the best?"
Jimmy Carter

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