EDR-5000
IM02602007E
47 - Voltage Unbalance Protection
Available elements:
47[1] ,47[2]
This is the 47 device Voltage Unbalance setting, which consists of the Threshold, %(V2/V1), and Delay settings. The
voltage unbalance function is based on the Main VT system 3-phase voltages.
The positive and negative sequence voltages are calculated from the 3-phase voltages. The Threshold setting defines a
minimum operating voltage magnitude of either V1 or V2 for the 47 function to operate, which ensures that the relay
has a solid basis for initiating a voltage unbalance trip. This is a supervisory function and not a trip level.
The %(V2/V1) setting is the unbalance trip pickup setting. It is defined by the ratio of negative sequence voltage to
positive sequence voltage (% Unbalance=V2/V1), or %(V2/V1) for ABC rotation and %(V1/V2) for ACB rotation. The
device will automatically select the correct ratio based on the Phase Sequence setting in the System Configuration
group described above.
This function requires positive or negative sequence voltage magnitude above the threshold setting and the percentage
voltage unbalance above the %(V2/V1) setting before allowing a voltage unbalance trip. Therefore, both the threshold
and percent settings must be met for the specified Delay time setting before the relay initiates a trip for voltage
unbalance.
The voltage unbalance pickup and trip functions are reset when the positive and negative sequence voltages V1 and
V2 drop below the Threshold setting or (V2/V1) drops below the %(V2/V1) setting minus 1%.
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