User's Manual

Operation: CP1SD/T/L Version

CENTRON® Polyphase Meter Technical Reference Guide 75

Phase Voltage Deviation Check

Once every five seconds, the phase A voltage is combined with a user-defined percentage

tolerance (x) to determine the upper and lower bounds of the acceptable range for the other

voltages. The range of values for the percent tolerance is 1 to 25.

For Diagnostic #2 to pass, the following equations must be satisfied:

ACAc

ABAB

VxVVxV

•−≥•+≤

%)1(lower and %)1(upper

If the above equations are not met for three consecutive checks, the diagnostic check will

trigger. Although the meter is using VA as a reference voltage, it does not need to be correct

for this check to be valid. The percentage difference is the determining factor.

Diagnostic #2 Error Example

This example is for a Form 9S meter wired for a 277 Volt, 4-Wire Wye system, but the site

has an incorrect voltage transformer ratio. The meter was also programmed with a

percentage tolerance of 10%.

The following is the information from the SiteScan snapshot when the Diagnostic #2 error is

triggered.

Phase A Display

(Left Element)

Phase B Display

(Center Element)

Phase C Display

(Right Element)

Voltage Phase

Angles

PhA 0.0° V PhB 119.4° V PhC 240.9° V

Phase Voltage PhA 119.2 V PhB 275.4 V PhC 279.1 V

Current Phase

Angles

PhA 9.0° A PhB 125.5° A PhC 246.0° A

Phase Current PhA 6.8 A PhB 10.2 A PhC 9.8 A

Diagnostic Counters

d1 000

d2 001 d3 000

d4 000 d5A 000 d5B 000

d5C 000 d5T 000 d6 000

The second step to diagnose a Diagnostic #2 error is to compare the different phase voltage

readings. This can be done several ways by simply comparing the readings or plugging the

values into the equation. In this case, A phase is about 120 volts while both B and C phases

are about 277 volts. This could indicate an incorrect voltage transformer ratio or a shorted

voltage transformer winding for the A phase transformer. This could also indicate that A

phase is correct and both B and C phases are incorrect. Also note that diagnostic counter d2

has incremented to “001”.