GE Multilin F35 Instruction Manual Download

Page: 134 / 486

5-12

F35 Multiple Feeder Protection System

GE Multilin

5.2 PRODUCT SETUP

5 SETTINGS

•

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 F35 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 F35 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

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.

Lower the

VOLTAGE CUT-OFF LEVEL

and

CURRENT CUT-OFF LEVEL

with care as the relay accepts lower signals

as valid measurements. Unless dictated otherwise by a specific application, the default settings of “0.02
pu” for

CURRENT CUT-OFF LEVEL

and “1.0 V” for

VOLTAGE CUT-OFF LEVEL

are recommended.

3-phase power cut-off

CURRENT CUT-OFF LEVEL

VOLTAGE CUT-OFF LEVEL

VT primary

CT primary

VT secondary

------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

3-phase power cut-off

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