Schweitzer Engineering Laboratories SEL-749M, Инструкция по эксплуатации

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4.10
SEL-749M Relay Instruction Manual Date Code 20080918
Protection and Logic Functions
Basic Motor Protection
The function of setting 49RSTP is similar to that of TCSTART, except that
49RSTP asserts only after an overload trip. Setting 49RSTP determines the
running thermal capacity above which the relay does not allow reset
(automatic or manual) following an overload trip.
Equation 4.3
A stopped motor can take longer to cool than a running motor because of
reduced airflow or loss of forced coolant. Based on the setting names, the
cooling time equation is shown in
Equation 4.4 :
Equation 4.4
Round up the result to the next integer.
The factory-default settings assume that the motor stopped cooling time is the
same as the motor running cooling time.
Motor manufacturers sometimes provide cooling parameters for a stopped
motor in the form of either a cooling time constant or a cooling time. If a time
constant is provided, multiply this value by 3 to calculate the motor stopped
cooling time setting (COOLTIME). If a time is provided, use this time directly
for COOLTIME.
NOTE:
In addition to setting
ETHMBIAS := Y, you must set one RTD
location equal to ambient, at least one
RTD location equal to winding, and set
the winding trip level (see
Table 4.20
for details).
You can bias the thermal model by ambient temperature when ETHMBIAS is
set equal to Y. The overload RTD bias is calculated using the ambient
temperature above 40°C and winding RTD trip temperature setting.
Overcurrent Elements
If the SEL-749M is connected to a motor protected by a fused contactor,
disable the phase overcurrent element by setting its trip level to OFF. If the
relay is connected to a device capable of interrupting fault current, use the
element to detect and trip for phase overcurrent faults. Set the phase
overcurrent trip level (50P1P) equal to 2.0 times the motor locked rotor
current with a 0.0 second time delay. Set the phase overcurrent warn level
(50P2P) to a desired value with appropriate time delay.
NOTE:
The cosine filter provides
excellent performance in removing dc
offset and harmonics. However, the
bipolar peak detector has the best
performance in situations of severe
CT saturation when the cosine filter
magnitude estimation is significantly
degraded. Combining the two
methods provides an elegant solution
for ensuring dependable short circuit
overcurrent element operation.
The phase overcurrent elements (50P1 and 50P2; see Figure 4.3 ) normally
operate using the output of the cosine filter, but during CT saturation the phase
current is the output of a bipolar peak detector if the overcurrent element
pickup is equal to or greater than eight times the CT rating and the harmonic
distortion index is high.
where:
RTC = RTC1 or RTC2 (whichever is higher)
49RSTP
100
SF
2
---------
≤
COOLTIME 3 RTC minutes
• ≥
NOTE:
The relay will prompt you
with the minimum allowable
COOLTIME when you attempt to save
a value lower than the minimum.
This is useful when RTC is set to
AUTO.
Table 4.7 Phase Overcurrent Settings
Setting Prompt Setting Range Setting Name := Factory Default
PH OC TRIP LVL Off, 0.10–20.00 xFLA 50P1P := 10.00
PH OC TRIP DLAY 0.00–5.00 sec 50P1D := 0.00
PH OC WARN LVL Off, 0.10–20.00 xFLA 50P2P := OFF
PH OC WARN DLAY 0.00–5.00 sec 50P2D := 0.50
Courtesy of NationalSwitchgear.com