ABB Relion 670 Series Applications Manual page 159

1MRK 505 370-UUS Rev. K
For the customer tailor-made inverse time delay characteristics (type 17), all three types of reset time
characteristics are available: instantaneous (1), IEC (2 = set constant time reset) and ANSI (3 = current
dependent reset time). If the current-dependent type is used, settings pr, tr and cr must be given.
tResetx: Constant reset time delay in seconds for step x.
tPCrvx, tACrvx, tBCrvx, tCCrvx: These parameters are used by the customer to create the inverse time
characteristic curve. See equation
Technical manual.
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ANSI-EQUATION1261 V1 EN-US
tPRCrvx, tTRCrvx, tCRCrvx: These parameters are used by the customer to create the inverse reset time
characteristic curve. For more information, refer to Technical manual.
HarmRestrainx: Enables freezing of timers of step x from the harmonic restrain function (2nd harmonic).
This function should be used when there is a risk of an unwanted trip caused by power transformer
inrush currents. It can be set to Disabled/Enabled.
7.1.4.2 Setting example
Directional phase overcurrent protection, four steps can be used in different ways, depending on the
application where the protection is used. A general description is given below.
The pickup current setting of the inverse time protection, or the lowest current step of the definite time
protection, must be defined so that the highest possible load current does not cause protection operation.
The protection reset current must also be considered so that a short peak of overcurrent does not cause
the operation of a protection even when the overcurrent has ceased. This phenomenon is described in
Figure 89.
Busbar protection REB670
Application manual
27
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for the time characteristic equation. For more information, refer to
Section 7
Current protection
(Equation 27)
GUID-20729467-24AB-42F0-9FD1-D2959028732E v1
153