UPS Fault - Turns Off When Mains Fail!

What is the load connected downstream of this UPS?

Were the batteries charged at the time of the main gas genset trip?

A blown fuse inside the UPS panel is the most probable cause.

Now that the power has been restored (a) Check at the Relay display that out sourcing is from UPS or the bypass. (B) Check battery voltage at the Relay display for conformity and simulate mains failure.

As I understand from your question ,Mostly problem will be with your battery bank pl check the individual battery capacity and its inter connections between battery to battery your problem may solved.

Regards,

M.Ayyavaru,

HBL Power Systems Ltd.

Please check first individual cell voltage,when you turn off the UPS weak battery battery voltage drops from its actual value,And when UPS is running you will found these battery voltages increased from its actual value.so replace these battery with new one. Also check the battery fuse in ups panel.

Regards.

The end-voltage on No-Load is not the correct condition of the battery Bank.

Or I should say that off-load Voltmeter indication is not real voltage. Even a bad battery charged [has the minimum energy] will show full voltage but if you put a small load it will drop to end voltage. True test of a battery is with a HRDT that is High-Rate Discharge Tester or under full load.

When power is on battery is not on-load but the converter [AC-to-DC] in UPS is taking load as well as charging the battery bank. These are of a capacity to take full load through the Inverter portion of UPS + Charger for battery.

It is clear from your log that UPS has no problem as it is taking the load on WAPDA power [or your Genset].

The simple test to confirm my statement:

1. Run UPS on Power from Genset [or WAPDA]

2. Switch-off the Critical load [UPS Load]

3. check for sometime to confirm that UPS is running.

4. Swith off input power to ups.

If battery bank has some life ups will keep running.

5. put a small load, then increase load.

Wish you good luck

Downstream Load is the DCS/ESD & workstation. The batteries were charged which was also showed by the UPS display panel before & after the trip (by after i mean after restoring mains). The battery bank was checked. Terminal voltage showed 447 V when connected to the UPS, and 440 V after isolating it from the UPS. True that only a load tester can give true battery status. Nevertheless, even if the battery voltages are low, how much low can they get? 400V, 300V, 200V? Doesn't the electronics inside the UPS or for that matter anywhere else require just 5Vdc, 12Vdc or at maximum 24V dc? right? Weak batteries? OK weak batteries couldn't pick up load, but shouldn't they atleast keep the UPS unit (display panel etc) alive? Why does the UPS goes dead?? Testing cannot be done as the load is main plant DCS. Apologies for my ignorance,but whats Relay Display? Thanx

Normally the end voltage of a 12V battery is 10V. But the End-Voltage level is set on the system and if the battery is capable of taking load some time more it runs after the low warning.

But in your case ups has not taken the load and it behaves OK when run on mains so ir more probably battery bank is suspected.

Why your load cannot be transferred to mains and ups isolated for test.

Is it not auto-transfer or manual transfer provision in your system or a redundant module. Is it a single unit all the system in one module.

Will you please definr your UPS system:

Single Stand-alone system

Multi-modules Redundant system

...

Please do not be after a wild goose chase!

Stand in front of the UPS panel board, you will see some indication lights on the door and a Relay (about one foot in dimensions) with keypad and a small screen display.

Read the UPS manual, you will learn that by scrolling the relay registers (usually you have to enter a password also given in manual) the relay can give you exact time and the nature of the faults in chronological order.

In modern Relays one can enter parameters that the system will only run on bypass mode (irrespective if the manual switch points to AUTO or Bypass) and the UPS must act accordingly.

The Relay has also a function to carry out battery discharge test, that means (if selected) the batteries will be automatically tested without interruption of load to a discharge capacity of about 25% of total capacity and at the end UPS will revert to normal operation.

The Relay screen display also indicates total back up time available and host of other features.

The most sensible advice to you is READ THE EQUIPMENT MANUAL PLEASE AND KNOW YOUR SYSTEM.

It may be that the instantaneous inrush current may be exceeding the UPS capacity and the system is shutting down to protect itself. I've found that to be the case on smaller point load UPS's on occasion.

Inrush current? shouldn't mains breaker trip against that, thereby taking the UPS on load?

Most modern UPS's have dozens of detection systems that will tell you practically everything imaginable that can go wrong. These systems include brief routine battery discharge tests intended to warn you about a weak battery long before you are in a critical situation. I have some older UPS's which I installed many years ago that are still up and running. One such UPS is a SOLA FERRORESONANT model which has very few "bells and whistles" and can only tell you about simple internal problems. If the owners use my services I perform a controlled battery discharge once a year and can usually detect weakened batteries in a timely manner. However some clients prefer to wait for trouble and ignore routine maintenance. The complete failure you described reminds me of these customers. When the batteries are at the end of thier lives they can read a good voltage but will go to zero instantly when power fails. If your UPS is an older model this can be your problem and the fact that everything is OK when it's up and running tends to make me think this is your problem. Place a recording DC voltmeter like a FLUKE 189 across the bank and set it up to record. Then simulate a black out and I'll bet you see nearly zero.

Also remember that most UPS's run thier internal electronics from the inverter and an inverter designed for say 135VDC will crash around 100VDC. Those small voltages you mentioned are derived from AC inverter driven power supplies which can be dual fed, one source from the grid line and a second source from the inverter.

What brand and model is your UPS

Regards

John