Basler BE1-1051, Инструкция по применению

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FIGURE 20. STATOR TEMPERATURE PROTECTION.
Loss of VT Detection
Two methods in common use to detect loss of
VTs are voltage balance between two VTs and
voltage-current comparison logic. Fig. 21 shows
the use of two sets of VTs on the generator
terminals, with the 60FL (Basler BE1-60) com-
paring the output of the two VTs. One set
supplies the voltage regulator, the other, the
relays. If the potential decreases or is lost from
VT No. 1, the BE1-60 disables the voltage
regulator; if source No. 2 fails, the BE1-60
blocks relay tripping of the 21, 27, 59N, and 47.
In some applications 25, 32, and 40 elements
are also blocked. Overexcitation relay (24),
phase overvoltage (59), and frequency relaying
(81), do not need to be blocked, since loss of
potential leads toward non-operation of these
functions.
FIGURE 21. VARIOUS VOLTAGE PROTECTION
ELEMENTS. VOLTAGE-BALANCE RELAY (60)
DETECTS POTENTIAL SUPPLY FAILURE.
A second means of detecting fuse loss is by
comparing voltage and current (Fig. 22). In a
single phase or two phase fuse loss, voltage
imbalance exists without the corresponding
current imbalance that would exist during a fault.
In a three phase fuse loss, complete voltage
loss occurs without the corresponding three
phase current flow that would occur during a
fault. To prevent a 60FL from being declared
during loss of station power, it may be necessary
to allow a 3 phase 60F to be declared only when
some low level of load current exists.
FIGURE 22. LOSS OF FUSE DETECTION, ALTERNATE
METHOD.
Overexcitation and Over/Under Voltage
Protection
Overexcitation can occur due to higher than
rated voltage, or rated or lower voltage at less
than rated frequency. For a given flux level, the
voltage output of a machine will be proportional
to frequency. Since maximum flux level is
designed for normal frequency and voltage, when
a machine is at reduced speed, maximum
voltage is proportionately reduced. A volts/hertz
relay (24) responds to excitation level as it
affects thermal stress to the generator (and to
any transformer tied to that generator). IEEE
C50.13 specifies that a generator should continu-
ously withstand 105% of rated excitation at full
load.
With the unit off line, and with voltage-regulator
control at reduced frequency, the generator can
be overexcited if the regulator does not include
an overexcitation limiter. Overexcitation can also
occur, particularly with the unit off line, if the
regulator is out of service or defective. If voltage-
balance supervision (60) is not provided and a
fuse blows on the regulator ac potential input, the
regulator would cause overexcitation. Loss of ac
potential may also fool the operator into develop-
ing excessive excitation. The 24 relay can only