Schweitzer Engineering Laboratories SEL-352-1 - Maximum Magnitude Nulling (Kmag); Maximum Phase Error to Null (Kang); Thermal Logic Enable (THLOG)

Date Code 20010731 Breaker Logic 3-27
SEL-352-1, -2 Instruction Manual
The output of the logic includes the adjusted difference voltage, a magnitude of the amount of
error that is nulled, and an angle of the amount of error that was nulled.
A recommended voltage nulling delay setting is VNpu = 10 minutes.
Maximum Magnitude Nulling (Kmag)
Range: 0.0–30.0% in 0.1% steps
Use SET <ENTER> to access the Kmag setting and establish a limit to the amount of acceptable
voltage nulling. Kmag is set in percent and is compared to the absolute value of 1–(VAY/VAX).
When this limit is reached, the voltage nulling remains at that threshold, and the potential
transformer disagreement (PTD) alarm asserts. Tracking continues when the nulling drops
below Kmag again.
Select the Kmag setting based on the accuracy of your potential measurement device and actual
field measurements during steady-state conditions. A recommended setting is Kmag = 5%.
Maximum Phase Error to Null (Kang)
Range: 0.0–15.0° in 0.1° steps
Use SET <ENTER> to access the Kang setting and establish a limit to the acceptable angle of
voltage nulling. Kang is set in degrees and is compared to the absolute value of the angle
difference between VAX and VAY. When this limit is reached, the voltage nulling remains at
that threshold and the potential transformer disagreement (PTD) alarm asserts. Tracking
continues when the nulling drops below Kang again.
Select the Kang setting based on the accuracy of your potential measurement device and actual
field measurements during steady-state conditions. A recommended setting is Kang = 10°.
Thermal Logic Enable (THLOG)
Range: OFF, ON, CUSTOM
Use SET <ENTER> to access the THLOG setting. Enable, modify, or disable the thermal logic
for protecting the breaker trip and close resistors.
Set THLOG = ON to enable the thermal logic for protecting the breaker trip and close resistors.
Refer to Figure 3.19 for a logic diagram of the scheme.
If the breaker does not have trip and close resistors, or if you do not want thermal protection, set
THLOG = OFF. If you need logic for your application different from that available with either
of the two schemes, set THLOG = CUSTOM. When CUSTOM is selected, all thermal settings
are shown including the SEL
OGIC control equations. Modify these settings to meet your specific
application needs.