GE Multilin 489 Instruction Manual page 183
Generator management relay
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Also See for Multilin 489:
- Instruction manual (306 pages) ,
- Communications manual (78 pages) ,
- Instruction manual (38 pages)
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CHAPTER 5: SETPOINTS
Note
489 GENERATOR MANAGEMENT RELAY – INSTRUCTION MANUAL
Courtesy of NationalSwitchgear.com
The generator FLA is calculated as:
------------------------------------------------------------------------------------------------------------- -
×
3
Rated Generator Phase-Phase Voltage
The 489 integrates both stator and rotor heating into one model. Machine heating is
reflected in a register called Thermal Capacity Used. If the machine has been stopped for a
long period of time, it will be at ambient temperature and thermal capacity used should be
zero. If the machine is in overload, once the thermal capacity used reaches 100%, a trip will
occur.
The overload curve accounts for machine heating during stall, acceleration, and running in
both the stator and the rotor. The Overload Pickup setpoint defines where the running
overload curve begins as the generator enters an overload condition. This is useful to
accommodate a service factor. The curve is effectively cut off at current values below this
pickup.
Generator thermal limits consist of three distinct parts based on the three conditions of
operation, locked rotor or stall, acceleration, and running overload. Each of these curves
may be provided for both a hot and cold machine. A hot machine is defined as one that
has been running for a period of time at full load such that the stator and rotor
temperatures have settled at their rated temperature. A cold machine is defined as a
machine that has been stopped for a period of time such that the stator and rotor
temperatures have settled at ambient temperature. For most machines, the distinct
characteristics of the thermal limits are formed into one smooth homogeneous curve.
Sometimes only a safe stall time is provided. This is acceptable if the machine has been
designed conservatively and can easily perform its required duty without infringing on the
thermal limit. In this case, the protection can be conservative. If the machine has been
designed very close to its thermal limits when operated as required, then the distinct
characteristics of the thermal limits become important.
The 489 overload curve can take one of three formats, Standard, Custom Curve, or Voltage
Dependent. Regardless of which curve style is selected, the 489 will retain thermal memory
in the form of a register called Thermal Capacity Used. This register is updated every 50 ms
using the following equation:
TC
TC
=
used t
where time to trip = time taken from the overload curve at I
The overload protection curve should always be set slightly lower than the thermal limits
provided by the manufacturer. This will ensure that the machine is tripped before the
thermal limit is reached. If the starting times are well within the safe stall times, it is
recommended that the 489 Standard Overload Curve be used. The standard overload
curves are a series of 15 curves with a common curve shape based on typical generator
thermal limit curves (see the following figure and table).
When the generator trips offline due to overload the generator will be locked out (the trip
relay will stay latched) until generator thermal capacity reaches 15%.
Generator Rated MVA
50 ms
-------------------------- -
×
100%
+
used t 50ms
time to trip
–
(EQ 5.29)
(EQ 5.30)
as a function of FLA.
eq
5–73
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