Single phase 208V A and B of three phase 208V system PF question

[tyreeinc]

Can someone explain to me why I have multiple 208V circuits using (example) Phase A and Phase B at 120V with a PF on Phase A at 0.63 and Phase B at 0.96 (this is in a data center Remote Power Panel, PDI Model, for a cabinet full of servers with no neutral) The circuit is also showing as bad for the status? Can you also provide me with what issues I might have with these circuits later in laymen terms?

 

[tyreeinc]

Can someone explain to me why I have multiple 208V circuits using (example) Phase A and Phase B at 120V with a PF on Phase A at 0.63 and Phase B at 0.96 (this is in a data center Remote Power Panel, PDI Model, for a cabinet full of servers with no neutral) The circuit is also showing as bad for the status? Can you also provide me with what issues I might have with these circuits later in laymen terms?

 

[iceworm]

Can someone explain to me why I have multiple 208V circuits using (example) Phase A and Phase B at 120V with a PF on Phase A at 0.63 and Phase B at 0.96 (this is in a data center Remote Power Panel, PDI Model, for a cabinet full of servers with no neutral) The circuit is also showing as bad for the status? Can you also provide me with what issues I might have with these circuits later in laymen terms?

As I understand the power system is 208/120 3phase. However, the panel in question has only the three phase conductors run to it and does not have a neutral. The loads are all single phase 208 - wired phase to phase.

Since the panel does not have a neutral, how is it (the panel) measuring 120V and a power factor? The numbers don't appear to mean anything.

ice

 

[GoldDigger]

As I understand the power system is 208/120 3phase. However, the panel in question has only the three phase conductors run to it and does not have a neutral. The loads are all single phase 208 - wired phase to phase.

Since the panel does not have a neutral, how is it (the panel) measuring 120V and a power factor? The numbers don't appear to mean anything.

ice

The monitor is showing you the power factor associated with the current in each of the phase wires. That current and its power factor will be independent of whether the source of that current is a delta or a wye and also independent of whether the loads are wired delta or wye.
However, you have to do some not necessarily simple math to figure out from that information just what the power factors of the actual line-to-line loads are.
In particular, you need to know whether the line currents are leading or lagging, and then do some vector math.

In the case of an unbalanced load, even with a uniform power factor across all phases, I can see the power factor calculated for the line currents to be different for different lines.

Now if the source did not have a neutral conductor to connect the monitor too, it would not be able to give you the readings it is.
Possibly there is a configuration setting on the instrument for showing delta or wye readings and you can just change that?

If there is no neutral at all, then that could cause the error indication you see.

 

[iceworm]

The monitor is showing you the power factor associated with the current in each of the phase wires. .

Okay saw that

...That current and its power factor will be independent of whether the source of that current is a delta or a wye and also independent of whether the loads are wired delta or wye. ...

I'm lost. The loads are all single phase L-L. There are no three phase loads - delta or Wye. 208 source, of course, is always wye.
Infact, the loads are connected:
1-3
5-7
9-11 (this one has something wrong with it)
13-15
17-19
21-23
25-27 (no load)

I don't know how to get a voltage or pf if one is only measuring one lead. There is no direction for the voltage.

In the case of an unbalanced load, even with a uniform power factor across all phases, I can see the power factor calculated for the line currents to be different for different lines. ...

The loads are all single phase. The current going out on ckt 1 is exactly the same as the current going in on ckt 3. True for all the ckt pairs (well except for 9-11. That one is broke.)

... Now if the source did not have a neutral conductor to connect the monitor too, it would not be able to give you the readings it is.

... If there is no neutral at all, then that could cause the error indication you see.

The first one I don't know. The second one - I think that's what I said.

I don't think both can be true.

ice

 

[GoldDigger]

Okay saw that

I'm lost. The loads are all single phase L-L. There are no three phase loads - delta or Wye. 208 source, of course, is always wye.
Infact, the loads are connected:
1-3
5-7
9-11 (this one has something wrong with it)
13-15
17-19
21-23
25-27 (no load)

I don't know how to get a voltage or pf if one is only measuring one lead. There is no direction for the voltage.

I think that what I am trying to say is that the meter is trying to measure the voltage between each of the lines and neutral or ground, and is also measuring the current in each of the hot leads (current transformers?).
It should then calculate exactly the same power factor and VA for each of the paired wires. If it does not, then it is improperly optioned, improperly wired, broken, or more than one of those.

The VA and the power can be measured at each lead, since the phase reference, including polarity, of the voltage is known for each lead.
The theoretical result should be that the real power in the 1-3 load should be the SUM of the lead 1 and lead 3 values since neither lead is at zero volts relative to the neutral reference. This result should be exactly the same as the one that you get by multiplying either line current alone by the line-to-line voltage. Even for a perfect resistive load, the calculated PF for a single lead will not be 1 since the current will not be in phase with that single lead voltage but rather with the line-to-line voltage.
And the VA for the 1-3 load should be a vector derivation from the lead 1 and the lead 3 VA figures. Those do not add as easily as the true power.

 

[tyreeinc]

Hi Ice. I apologize the RPP panel has a 250% neutral and the receptacle has no neutral and is an L6-30

 

[winnie]

I think that what I am trying to say is that the meter is trying to measure the voltage between each of the lines and neutral or ground, and is also measuring the current in each of the hot leads (current transformers?).
It should then calculate exactly the same power factor and VA for each of the paired wires. If it does not, then it is improperly optioned, improperly wired, broken, or more than one of those. [....]

Even for a perfect resistive load, the calculated PF for a single lead will not be 1 since the current will not be in phase with that single lead voltage but rather with the line-to-line voltage.
And the VA for the 1-3 load should be a vector derivation from the lead 1 and the lead 3 VA figures. Those do not add as easily as the true power.

I think that you are clear on what is going on here. The reference for PF are the line to neutral voltages, but the actual power factor of the load should be figured from the line to line voltage.

I actually would _not_ expect the same VA and power factor for the paired measurements. The current flowing in the load is being compared to two _different_ references, at two different angles. For a pure resistive load, one of these measurements would be leading by 30 degrees, the other would be lagging by 30 degrees. An inductive load might show unity power factor on one leg and really lagging on the other leg.

Now that we understand what the PF indication is telling us, the next step is to figure out what to say to the OP about it

-Jon