4.74
SEL-700G Relay
Instruction Manual
Date Code 20170814
Protection and Logic Functions
Group Settings (SET Command)
Off-Frequency Accumulators
When steam turbine prime movers operate at other than design speed,
vibration can cause cumulative metal fatigue in the turbine blades. Eventually,
this fatigue can lead to premature and catastrophic turbine blade failure. For
steam turbine prime mover applications, the SEL-700G records the total time
of operation of the generator at off-nominal frequencies in as many as six
frequency bands. This function satisfies the requirements of the IEEE
C37.106-2003, Guide For Abnormal Frequency Protection for Power
Generating Plants.
If the frequency is within a time-accumulator band, the relay asserts an alarm
bit and starts the 62ACC timer for that band. If the frequency remains within
the band for greater than 62ACC seconds, the relay begins adding time to that
accumulator band timer. If the total time of operation within a particular
accumulator band exceeds the limit setting for that band, the relay asserts a
Relay Word bit (for example, BND1T), which you can use for alarm and/or
trip as necessary.
The accumulator values are nonvolatile and are retained through relay power-
off cycles. You can use the relay serial port GENERATOR command to view
or reset the accumulator values.
Set 62ACC delay long enough for the system frequency to stabilize within a
band before time accumulation starts. Ten cycles or 0.16 seconds is the
recommended setting.
Use the torque control setting 81ACCTC to disable the element for conditions
during which you do not want to accumulate time. For example,
Table 4.14
Frequency Accumulation Settings
Setting Prompt
Setting Range
Setting Name :=
Factory Default
ENABLE FREQ ACC
N, 1–6
E81ACC := N
FREQ ACC DELAY
00.00–400.00 s
62ACC := 0.16
BAND1 UPPER LIMIT
15.0–70.0 Hz
UBND1 := 59.5
BAND1 LOWER LIMIT
15.0–70.0 Hz
LBND1 := 58.8
BAND1 ACC TIME
0.01–6000.00 s
TBND1 := 3000.00
BAND2 LOWER LIMIT
15.0–70.0 Hz
LBND2 := 58.0
BAND2 ACC TIME
0.01–6000.00 s
TBND2 := 540.00
BAND3 LOWER LIMIT
15.0–70.0 Hz
LBND3 := 57.5
BAND3 ACC TIME
0.01–6000.00 s
TBND3 := 100.00
BAND4 LOWER LIMIT
15.0–70.0 Hz
LBND4 := 57.0
BAND4 ACC TIME
0.01–6000.00 s
TBND4 := 14.00
BAND5 LOWER LIMIT
15.0–70.0 Hz
LBND5 := 56.5
BAND5 ACC TIME
0.01–6000.00 s
TBND5 := 2.40
BAND6 LOWER LIMIT
15.0–70.0 Hz
LBND6 := 40.0
BAND6 ACC TIME
0.01–6000.00 s
TBND6 := 1.00
FREQ ACC TRQCTRL
SEL
OGIC
81ACCTC := 1
Summary of Contents for SEL-700G Series
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