Dear all,

We are using three supplies for mark vi panels in our cpp
.
1. Floating 125 VDC,
2. 110 VAC ungrounded UPS supply through DACA 1 and
3. 110 VAC non UPS supply with one leg grounded from MCC through DACA 2. Spark plug supply taken from JZ5 before DACA 2.

I wanted to know that is the scheme correct and why is one supply floating and one grounded.

Pls help me here

 

Yes.

The DACAs convert the AC input to ungrounded DC output, and the TCPD selects the higher of the inputs.

This should be explained/detailed in Vol. II of the Mark VI System Guide, GEH-6421, in the Power Distribution section (usually in the back of the manual).

Please note that DACAs are <b>NOT</b> filters. The "normal" DC and AC inputs to the Mark VI (when there are no DACAs) are passed through the <CPF> module, which does minimal input power filtering and is designed to really prevent noise from getting out of the panel on to the DC and AC input (again, if there are no DACAs).

If the AC input to the DACA is noisy (and some UPS outputs are VERY noisy and spikey) then that will be transferred to the Mark VI, and in some cases even magnified through the DACA.

DACAs are a false sense of security--if the DC supply to the Mark VI is lost, then it's likely there is no DC to power the Emer. (DC) L.O. pump, so continuing to run the turbine without DC power for the Emer. L.O. Pump is just begging for a catastrophe.

And, since DACAs do NOT filter incoming power problems--and can even magnify some--they are really a bigger source of problems than they ever were supposed to supplant.

Finally, some Mark VI power supplies (the rack power supplies that convert the 125 VDC to power for the racks and the cards in the racks and for communication between racks) are very prone to failure. GE has issued at least one, if not several TILs (Technical Information Letters) about known problems with some power supplies. (But they've never issued a TIL about DACAs passing power problems to the Mark VI!)

Hope this helps!

If you're having specific problems, we can try to help if you can describe them here and are willing to do some data collection and provide the requested data and information.

 

Thank you CSA sir.

We have recently faced some problems with 125V DC. Since both the supply of MARK VI and EOP are from the same distribution board, starting/stopping the EOP causes a spike of more than 140V which re-boots the panel. Hence this supply is temporarily cut off. Currently the panel running on two AC supplies only.

So sir, pls clarify whether grounded or ungrounded AC should be used for both the DACAs and what is the difference in using these supplies.

 

ppm,

No changes to the AC input(s) required. The DACAs convert the AC input (grounded or not) to ungrounded DC. Simple as that. It's the DC supply that needs to be ungrounded (for the Mark VI).

Sorry to hear about your power supply problems. When the battery charger is powering the batteries it is supplying whatever current is required (up to its output capability) and the battery makes up the remainder if necessary. So, are you investigating the battery charger as the source of the spikes? Isolate the battery charger and run your DC motor test and record the DC voltage and see if the battery charger output capacitors are the cause of the problem.

Please write back to let us know how you fare!