GE Multilin T60 Transformer Protection System 5-25
5 SETTINGS 5.2 PRODUCT SETUP
5
• DEFAULT MESSAGE INTENSITY: To extend phosphor life in the vacuum fluorescent display, the brightness can be
attenuated during default message display. During keypad interrogation, the display always operates at full brightness.
• SCREEN SAVER FEATURE and SCREEN SAVER WAIT TIME: These settings are only visible if the T60 has a liquid
crystal display (LCD) and control its backlighting. When the SCREEN SAVER FEATURE is “Enabled”, the LCD backlighting
is turned off after the DEFAULT MESSAGE TIMEOUT followed by the SCREEN SAVER WAIT TIME, providing that no keys
have been pressed and no target messages are active. When a keypress occurs or a target becomes active, the LCD
backlighting is turned on.
• CURRENT CUT-OFF LEVEL: This setting modifies the current cut-off threshold. Very low currents (1 to 2% of the
rated value) are very susceptible to noise. Some customers prefer very low currents to display as zero, while others
prefer the current be displayed even when the value reflects noise rather than the actual signal. The T60 applies a cut-
off value to the magnitudes and angles of the measured currents. If the magnitude is below the cut-off level, it is substi-
tuted with zero. This applies to phase and ground current phasors as well as true RMS values and symmetrical compo-
nents. The cut-off operation applies to quantities used for metering, protection, and control, as well as those used by
communications protocols. Note that the cut-off level for the sensitive ground input is 10 times lower that the
CURRENT
CUT-OFF LEVEL setting value. Raw current samples available via oscillography are not subject to cut-off.
• VOLTAGE CUT-OFF LEVEL: This setting modifies the voltage cut-off threshold. Very low secondary voltage measure-
ments (at the fractional volt level) can be affected by noise. Some customers prefer these low voltages to be displayed
as zero, while others prefer the voltage to be displayed even when the value reflects noise rather than the actual sig-
nal. The T60 applies a cut-off value to the magnitudes and angles of the measured voltages. If the magnitude is below
the cut-off level, it is substituted with zero. This operation applies to phase and auxiliary voltages, and symmetrical
components. The cut-off operation applies to quantities used for metering, protection, and control, as well as those
used by communications protocols. Raw samples of the voltages available via oscillography are not subject cut-off.
The
CURRENT CUT-OFF LEVEL and the VOLTAGE CUT-OFF LEVEL are used to determine the metered power cut-off levels. The
power cut-off level is calculated as shown below. For Delta connections:
(EQ 5.3)
For Wye connections:
(EQ 5.4)
(EQ 5.5)
where VT primary = VT secondary VT ratio and CT primary = CT secondary CT ratio.
For example, given the following settings:
CURRENT CUT-OFF LEVEL: “0.02 pu”
VOLTAGE CUT-OFF LEVEL: “1.0 V”
PHASE CT PRIMARY: “100 A”
PHASE VT SECONDARY: “66.4 V”
PHASE VT RATIO: “208.00 : 1"
PHASE VT CONNECTION: “Delta”.
We have:
CT primary = “100 A”, and
VT primary =
PHASE VT SECONDARY x PHASE VT RATIO = 66.4 V x 208 = 13811.2 V
The power cut-off is therefore:
power cut-off = (
CURRENT CUT-OFF LEVEL VOLTAGE CUT-OFF LEVEL CT primary VT primary)/VT secondary
= ( 0.02 pu 1.0 V 100 A 13811.2 V) / 66.4 V
= 720.5 watts
Any calculated power value below this cut-off will not be displayed. As well, the three-phase energy data will not accumu-
late if the total power from all three phases does not exceed the power cut-off.
3-phase power cut-off
3
CURRENT CUT-OFF LEVEL VOLTAGE CUT-OFF LEVEL VT primary CT primary
VT secondary
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
=
3-phase power cut-off
3
CURRENT CUT-OFF LEVEL VOLTAGE CUT-OFF LEVEL VT primary CT primary
VT secondary
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
=
per-phase power cut-off
CURRENT CUT-OFF LEVEL VOLTAGE CUT-OFF LEVEL VT primary CT primary
VT secondary
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
=
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