ABB Relion 670 Series Applications Manual page 228

Section 9
Frequency protection
300
250
200
150
100
50
IEC12000611 V2 EN-US
Figure 96: Typical stress magnification factor curve according ANSI/IEEE C37.106-2003
Each turbine manufactured for different design of blades has various time restriction limits for
various frequency bands. The time limits depend on the natural frequencies of the blades inside
the turbine, corrosion and erosion of the blade edges and additional loss of blade lifetime during
the abnormal operating conditions.
The frequency limitations and their time restrictions for different types of turbines are similar in
many aspects with steam turbine limitations. Certain differences in design and applications may
result in different protective requirements. Therefore, for different type of turbine systems,
different recommendations on the time restriction limits are specified by the manufacturer.
However, the IEEE/ANSI C37.106-2003 standard "Guide for Abnormal Frequency Protection for
Power Generating Plants" provides some examples where the time accumulated within each
frequency range is as shown in Figure 97.
222
-
1.0
Frequency or Resonant Frequency
Ratio
Standard
+
IEC12000611-2-en.vsd
1MRK 511 358-UUS A
Application manual