GE PQMII Instruction Manual page 122

5–38
• VOLTAGE UNBALANCE LEVEL: When the voltage unbalance equals or exceeds this
level, a voltage unbalance condition occurs. See 6.2.2 Voltage Metering for details on
the method of calculation.
• VOLTAGE UNBALANCE DELAY: If the voltage unbalance equals or exceeds the
setpoint value and remains this way for the time delay programmed in
UNBALANCE LEVEL
this setpoint, a voltage unbalance condition will occur.
• VOLTAGE PHASE REVERSAL: Under normal operating conditions, the PQMII expects to
see the voltages connected with a 1-2-3 or A-B-C sequence. If the voltages are
connected with the wrong sequence (e.g. 2-1-3 or B-A-C), a voltage phase reversal
condition will occur. A minimum of 20 V must be applied to the PQMII on all voltage
inputs before the phase reversal feature will operate.
A phase reversal condition is determined by looking at the phase angle at the
occurrence of the peak sample of phase B voltage and subtracting it from the phase
angle at the peak sample of phase A voltage (phase A angle – phase B angle). This
angle is averaged over several cycles before deciding on the condition to avoid any
false triggering of the feature. Only two phases are required to detect phase reversal
because all phase reversal conditions can be covered without the use of the third
phase. The angle to detect phase reversal will vary depending on the connection
being used as described below.
For "4-Wire Wye / 3 VTs", "4 Wire Wye / 2 VTs", "4 Wire Direct", and "3 Wire Direct"
connections, the phase reversal function operates when the angle between phase A and B
becomes ≤ –150° or ≥ –90° as shown below.
Vb(c or n) – 30°
Vb(c or n) = –120°
Vb(c or n) + 30°
FIGURE 5–3: Phase Reversal for 4-wire and 3-wire Direct Connections
For the "3 Wire Delta / 2 VTs" connection, the phase reversal function operates when the
angle between phase A and B is ≤30° or ≥90° as shown below.
shaded area = angle tolerance
allowed before phase reversal
will occur
FIGURE 5–4: Phase Reversal for 3-wire Delta (2 VTs Open-Delta) Wiring
Vc(a or n) = –240°
Va(b or n) = 0°
shaded area = angle tolerance allowed
before phase reversal will occur
Vcb + 30°
Vcb = 60°
Vcb – 30°
Vab = 0°
Vbc = –120°
PQMII POWER QUALITY METER – INSTRUCTION MANUAL
CHAPTER 5: SETPOINTS
VOLTAGE
(reference)
(reference)