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5.6 S4 ELEMENTS
A transformer is designed to operate at or below a maximum magnetic flux density in the transformer core.
Above this design limit the eddy currents in the core and nearby conductive components cause overheating
which within a very short time may cause severe damage. The magnetic flux in the core is proportional to the
voltage applied to the winding divided by the impedance of the winding. The flux in the core increases with
either increasing voltage or decreasing frequency. During startup or shutdown of generator-connected trans-
formers, or following a load rejection, the transformer may experience an excessive ratio of volts to hertz, that
is, become overexcited.
When a transformer core is overexcited, the core is operating in a non-linear magnetic region, and creates har-
monic components in the exciting current. A significant amount of current at the 5th harmonic is characteristic
of overexcitation.
This section contains the settings to configure the overexcitation monitoring elements. Included are a 5th har-
monic level, and two volts-per-hertz elements, each with a pickup level and a time delay.
S OVEREXCITATION
S [ENTER] for more
a) 5TH HARMONIC LEVEL
S 5th HARMONIC LEVEL
S [ENTER] for more
5
5th HARMONIC LEVEL
FUNCTION: Disabled
5th HARMONIC LEVEL
TARGET: Self-reset
MINIMUM OPERATING
CURRENT: 0.10 x CT
5th HARMONIC LEVEL
PICKUP: 10.0% ƒo
5th HARMONIC LEVEL
DELAY: 10 s
5th HARMONIC LEVEL
BLOCK: Disabled
5-68
This message indicates the start of the OVEREXCITATION section. To continue
these setpoints press
EN TE R
This message indicates the start of the section describing the characteristics
of 5TH HARMONIC LEVEL. To continue these setpoints press
for the next section.
M E SSA G E
Range: Disabled / Enabled
Range: Self-reset / Latched / None
Select None to inhibit the display of the target message when the element
operates. Thus an element whose "target type" is None will never disable the
LED self-test feature because can not generate a displayable target
message.
Range: 0.03 to 1.00 (steps of 0.01)
Enter the minimum value of current (in units of relay nominal current)
required to allow the 5th harmonic level element to operate.
Range: 0.1 to 99.9 (steps of 0.1)
Enter the 5th harmonic current (in %ƒ
element will pickup and start the delay timer.
Range: 0 to 60000 (steps of 1)
Enter the time that the 5th harmonic current must remain above the pickup
level before the element operates.
Range: Disabled / Logc Inpt 1 (2-16) /Virt Inpt 1 (2-16) / Output Rly 1 (2-8) /
SelfTest Rly / Virt Outpt 1 (2-5)
745 Transformer Management Relay
5.6.12 OVEREXCITATION
or press
for the next section.
M E SSA G E
) above which the 5th harmonic level
0
GE Power Management
5 SETPOINTS
or press
E N TE R
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