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How can the PowerLogic meters monitor a 3 wire ungrounded WYE system

Issue
In some cases, the user might havea a 3-wire ungrounded WYE system and would like to know what is the most approriate system type for this installation. An ungrounded wye system produce low fault current levels ( for the first ground fault) making it the preferred system in dry docks and ship feeders where earth faults are critical.


Product Line
ION 7300/7550/7650, PowerLogic PM800 series,PM8000 

Resolution

*Warning:  Installation and maintenance of this device should only be performed by qualified, competent personnel that have appropriate training and experience with high voltage and current devices. Failure to follow the instructions / warnings in the Meter Installation Guide can result in permanent damage to the meter, severe injury or death.*


In a 3-wire wye system, the only voltages that matter to the load are the three line-to-line (or phase to phase voltages): Vab, Vbc, and Vca 
The primaries of the two PTs must be connected to all system lines (Va-Vb and Vb-Vc) so that the PT secondaries produce a voltage proportional to the potential difference between the lines. Specifically: Vab and Vcb. Vca is calcuated given the inputs V1 and V2 as shown below :

1- Vab = V1 input, Vbc= V3 input and Vca= 

The 3-wire wye system can be monitored as delta system given that the customer already has ground fault monitoring scheme. A 3 wire wye connected as a delta produces abnormal readings in the event of a ground fault. Furthermore, the meter can either have 2 PTs and 2 CTs, 2 PTs 3 CTs configuration or direct voltage connection if the phase-phase voltage of the system meets the maximum voltage input of the meter. Below are the corresponding wiring diagrams for each meter series :

ION 7330/ION 7550/ION 7650



PM800 series

 
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