power factor unbalanced measurements once again 1

[mag100]

I have resently submitted a post on this but I have more information for review. Stated in my resent post we had a contractor read our power factor on each phase. he claims that the power factor in phase A is 50% phase B is 98% and phase C is 80%.
The meter he used is a Fluke 43B.
The incoming power from our main switchgear is 480 volt 2000amp 3phase wye connection.
The contractor insists we reinstall this meter. I was given directions on how to install the meter. Install current probe on phase A. No mention on direction of current arrow on current probe.install voltage probes on phase B and one on Phase C.
Question will that give us the correct power factor on Phase A?
How do you get the power factor readings on the other phases? Do you need to move the voltage probes in respect to the CT?
What i really need to know is this meter able to read the power factor in a three phase wye connection accuratly?
I realize a three phase quality analizer would do the task but i need to prove to "management" this is the incorrect meter to do the job.

 

[rbulsara]

Best friend is the manual of the meter. Correct phase relationship between the current and voltage reference needs to be entered in the meter settings.

It does sound like a wiring error.


Rafiq Bulsara

http://www.srengineersct.com

 

[waross]

This is a single phase meter.
This meter will only measure three phase power on a balanced system.
The connections that you were given are for measuring a balanced three phase system.
Remember RTFM (Read The Flukin Manual)
If there are unbalanced line to line loads, this meter may not even measure single phase power factor accurately.
To measure the power factor on A phase, connect the Voltage leads from A phase to neutral and put the current probe on A phase.
However, a load between A phase and B phase may cause an error.
Even though the power factor of both loads may be unity, the current probe will see the vector sum of the currents and compare it with the voltage angle of A phase to neutral and report a power factor of less than unity.
If the meter is reading different power factors on a three phase connection, that is a prima-facia indication that the phases are not balanced and the meter is not suitable.
This meter is suitable for measuring single phase power from a single circuit breaker.
This meter is NOT suitable for measuring combined lone to neutral and line to line loads.
This meter is not suitable for measuring unbalanced three phase loads.
This meter may be useful to check balanced three phase circuits such as a healthy three phase motor.
This meter is more suitable for measuring individual circuits than for feeders to a mixed single phase/three phase panel.
PS RTFM

http://assets.fluke.com/manuals/43b_____umeng0200.pdf

http://assets.fluke.com/manuals/43b_____gseng0000.pdf

http://www.fluke.com/Fluke/caen/support/manuals/default.htm

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

 

[edison123]

Bill- RTFM

Muthu

http://www.edison.co.in

 

[7anoter4]

One could calculate the active power using the three-phase kwh counter. [The old fashioned -with rotating disk was better.] But let's say it is a modern digital kWh counter with minimum display of 0.1 kWh.
Let's say [for the example] we know the pf [cos (fi)] =0.8 I=2000A and voltage 480 V.
P=SQRT (3)*0.480*2000*.8=1330.2 kW*sec/sec
In 10 sec will be 1330.2*10/3600=3.7 kWh reading on the counter.
The same procedure we could use with reactive power counter [kVARh counter].
and we'll get Q=SQRT (3)*0.480*2000*.6=997.7 KVARsec/sec.
In 10 sec will be 997.7*10/3600=2.8 kVARh on the counter.
Tan(fi)=Q/P=2.8/3.7=0.7567 for fi= 0.6478 radians
Now average cos(fi)=cos(0.6478)= 0.797.

 

[waross]

Hi 7anoter4:
For clarification are you proposing to use the utility revenue kilo-Watt-hour meter? Good suggestion.
Another variation is to use the information on the power bill. It should show both KWHrs and KVARHrs. From that you may calculate the average PF.
I have worked with cooperative utilities who would download the internal memories and either send them to me on a disk or by e-mail.
As well as three phase measurements I would get single phase voltage, current and kW. The measurements would be at 15 minute intervals for about 30 days.

Try rolling the meter connections. If the meter is capable of measuring the three phase PF, then the PF should stay the same for each "roll". I suspect that the phase on which the current probe is attached will read high despite "rolling" the connections.
Rolling:
Move the current probe from A to B.
Move the voltage probe from B to C.
Move the voltage probe from C to A.


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