Isolation transformer requirements for PQM

[BrianW]

Hi,

Is there any requirement for using isolation transformers when feeding the power source (control power) to PQMs? Isolation transformers had been used previously to eliminate "phantom" readings on the display of the PQMs, but that may have been historic. 

Can anyone suggest or point to a definitive answer to say if isolation transformers should be used as a precaution to eliminate the phantom readings? 

Thanks in advance,

Brian

[Charles_Murison]

Hello @BrianW ,

If I understand your question you are asking if connecting an Isolation transformer to the control power of PM8000 meter will prevent the Phantom Voltage phenomena from occurring. The answer is no. The design inside the meter is what will cause this phenomena. How the meter's control power is connected will not change the behavior inside the meter.

It may be possible to make a wiring change outside the meter that can address the phantom voltage.

The coil selection would need to be done by electrical engineer that is familiar with local electrical requirements. 

Regards,

Charles

[BrianW]

Hi Charles,

Many thanks for responding to my message. What I actually mean is in relation to the auxiliary power supply to the meter, the L1 and L2 that power up the meters. What I gather is that there is no galvanic separation between the meter auxiliary power supply and the Voltage References therefore a voltage may 'appear' on the voltage reference terminals via the neutral circuit, this only applying to 3P&N circuits. Clients of our were unhappy with approx. 30V displayed when a circuit was off, so isolation transformers were introduced to provide that galvanic isolation. I had been informed by SE previously that this should not be a problem any more because of the isolation built into the meters that should eliminate this issue. 

Regards,

Brian

[Charles_Murison]

Hello @BrianW ,

You mentioned PQM but did not say what type of meter, PM5000 series PM8000 series, ION7400 series etc. Different meters have different designed and will have different options. For example, some PM5000 meters can have a grounding module attached that will eliminate the Phantom voltage. 

PM8000 and ION7400 meters do not have a grounding module nor do they have any changes to the internal design that I know of to address the Phantom voltage. So a lot may depend on what meter you are talking about.

Regards,

Charles

[BrianW]

Hi Charles,

Thanks again for the response. We use PM5000, PM8000 and ION9000 mostly. The PM5000 grounding module is an optional extra, I am presuming, and if the 8000 series do not have a grounding module or internal design that may rectify any phantom voltages being displayed, what would be an appropiate fix for the PM8000 meters.

Thanks again,

Regards,

Brian

[Charles_Murison · Accepted solution]

Hello @BrianW ,

Most customers are satisfied once the explanation of the phantom voltage is given. If customer is not satisfied and requires action the only option is to do something outside the meter, see image in my previous post for example of relay coil.

Regards,

Charles