Control & Communications
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Figure 6.4 Voltage Balance Threshold
Monitoring is done when the maximum voltage is larger than the voltage balance pickup value. The voltage is considered balanced and will not cause an alarm if the voltage min/max ratio is larger than the voltage balance factor. The voltage is unbalanced and will cause an alarm if the min/max ratio is smaller than the voltage balance factor.
Failure of this check will cause an event Voltage Balance Error. This event can activate an output contact.
The voltage balance pickup value (3402) can be set from 40 to 120 V in steps of 1 V. If one of the three phase voltages is above the preset threshold, the function checks for balance.
The voltage balance factor indicates the amount of unbal- ance tolerated before the function generates an alarm (3404). It ranges from 0.58 to 0.95 and can be set in steps of 0.01.
Current Summation
The Current Summation function can be enabled or disabled (3411). When enabled, it monitors the instantaneous sam- ples of the A/D converter using the currents flowing into all four relay CTs regardless of whether there are four primary CTs connected or not. The calculation is therefore valid for systems with both residual connections or explicit neutral/ ground/zero sequence CTs.
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Figure 6.5 Current Sum Threshold
Failure of this check will cause an event Current Summation Error. This event can activate an output contact.
The pickup value (3412) for the current summation check depends on the secondary phase CT rating and the value is in secondary amperes. The value for 5 A CTs ranges from
0.5A to 5.0 A; and the value for 1 A CTs ranges from 0.1 to
1.0A. Both values can be set in steps of 0.1 A. If one of the three phase currents is above the preset threshold, the mon- itoring function is activated.
The current summation factor indicates allowable compen- sation for differences between primary CTs (3414). It ranges from 0.1 to 0.95 and can be set in steps of 0.01. This factor is important under high fault currents or when CTs are oper- ated closely to their rated current.
Current Balance
The Current Balance function can be enabled or disabled (3421). When enabled, the function monitors the phase cur- rents to see if they are approximately balanced (of equal magnitude). Balance is defined as the ratio of minimum to maximum current, where the maximum current is the largest and the minimum current the smallest of the three phase cur- rents.
Current balance monitoring is done when the maximum cur- rent is larger than the current balance pickup value. The cur- rent is considered balanced and will not cause an alarm if the current min/max ratio is larger than the current balance fac- tor. The current is unbalanced and will cause an alarm if the min/max ratio is smaller than the current balance factor.
38 | Siemens Energy & Automation, Inc. |
