Schweitzer Engineering Laboratories SEL-700G Series, Инструкция по эксплуатации

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4.66
SEL-700G Relay Instruction Manual Date Code 20170814
Protection and Logic Functions
Group Settings (SET Command)
Figure 4.37 Generator Overload Curve
Volts-Per-Hertz Elements
Overexcitation occurs when a generator or transformer magnetic core
becomes saturated. When this happens, stray flux is induced in nonlaminated
components, causing overheating. In the SEL-700G Relay, a volts/hertz
element detects overexcitation. The SEL-700G has a sensitive definite-time
volts/hertz element, plus a tripping element with a composite operating time.
The relay calculates the present machine volts/hertz as a percentage of
nominal, based on the present and nominal voltages and frequencies. The
VNOM_X, PTRX, and FNOM settings define the nominal machine voltage
and frequency.
Figure 4.38 shows the logic diagram of the volts/hertz elements. If the torque-
control 24TC SEL
OGIC
control equation is true and the volts/hertz value
exceeds the 24D1P setting, the relay asserts the 24D1 Relay Word bit and
starts the 24D1D timer. If the condition remains for 24D1D seconds, the relay
asserts the 24D1T Relay Word bit. Typically, you should apply this element as
an overexcitation alarm.
where
GTC = Generator Time Constant in seconds
I = Generator current in per unit, assuming no
negative-sequence current
Io = Generator preload current in per unit, assuming no
negative-sequence current
49TTP = Overload level setting in per unit
TripTime GTC LN
I
2
Io
2
–
I
2
49TTP
2
–
------------------------------- seconds • =
10000
10
100
1000
2.00
Current (per unit)
1.00
Trip Time (
sec
)
3.00 4.00 0.00
Assumptions:
Pickup Level, 49TTP = 1.05 pu
Time Constant, GTC = 10 min
Preload, Io = 95%
Trip Time