GE D90 Plus Instruction Manual page 188

POWER SYSTEM
Calculating the power cut-off level
178
The Current Cutoff Level and the
metered power cut-off levels. The power cut-off level is calculated as shown here. For delta
connections, the power cut-off is calculated as follows:
where VT primary = VT secondary × VT ratio and CT primary = CT secondary × CT ratio.
For wye connections, the three-phase and per-phase power cut-off values are calculated
as follows:
where VT primary = VT secondary × VT ratio and CT primary = CT secondary × CT ratio.
For example, given the following settings:
Figure 157: Typical power system settings
we have:
• CT primary =
Phase CT Ratio
• VT primary =
Phase VT Ratio
The power cut-off is therefore:
Any calculated power value below this cut-off does not display. As well, the three-phase
energy data does not accumulate if the total power from all three phases does not exceed
the power cut-off.
Voltage Cutoff Level settings are used to determine the
×
Phase CT Secondary
×
Phase VT Secondary
PLUS
D90 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 7: PROTECTION
= 20 × 5 A = 100 A.
= 208 × 66.4 V = 13811.2 V.
Eq. 4
Eq. 5
Eq. 6
Eq. 7