5-68
745 Transformer Management Relay
GE Power Management
5.6 S4 ELEMENTS
5 SETPOINTS
5
5.6.12 OVEREXCITATION
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.
a) 5TH HARMONIC LEVEL
y
OVEREXCITATION
y
[ENTER] for more
This message indicates the start of the
OVEREXCITATION
section. To continue
these setpoints press
or press
for the next section.
y
5th HARMONIC LEVEL
y
[ENTER] for more
This message indicates the start of the section describing the characteristics
of
5TH HARMONIC LEVEL
. To continue these setpoints press
or press
for the next section.
5th HARMONIC LEVEL
FUNCTION: Disabled
Range: Disabled / Enabled
5th HARMONIC LEVEL
TARGET: Self-reset
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.
MINIMUM OPERATING
CURRENT: 0.10 x CT
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.
5th HARMONIC LEVEL
PICKUP: 10.0%
ƒ
o
Range: 0.1 to 99.9 (steps of 0.1)
Enter the 5th harmonic current (in %ƒ
0
) above which the 5th harmonic level
element will pickup and start the delay timer.
5th HARMONIC LEVEL
DELAY: 10 s
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.
5th HARMONIC LEVEL
BLOCK: Disabled
Range: Disabled / Logc Inpt 1 (2-16) /Virt Inpt 1 (2-16) / Output Rly 1 (2-8) /
SelfTest Rly / Virt Outpt 1 (2-5)
EN T E R
M E SSA G E
E N TE R
M E SSA G E
Summary of Contents for 745 TRANSFORMER MANAGEMENT RELAY
Page 30: ...2 8 745 Transformer Management Relay GE Power Management 2 3 SECURITY 2 GETTING STARTED 2 ...
Page 210: ...7 36 745 Transformer Management Relay GE Power Management 7 2 BLOCK DIAGRAMS 7 SCHEME LOGIC 7 ...
Page 322: ...9 12 745 Transformer Management Relay GE Power Management 9 3 USING 745PC 9 745 PC SOFTWARE 9 ...
Page 396: ...A 4 745 Transformer Management Relay GE Power Management A 1 FIGURES AND TABLES APPENDIXA A ...
Page 400: ...C 2 745 Transformer Management Relay GE Power Management C 1 WARRANTY INFORMATION APPENDIXC C ...
Page 406: ...vi 745 Transformer Management Relay GE Power Management ...
Page 407: ...GE Power Management 745 Transformer Management Relay NOTES ...
