4.102
SEL-751 Relay Instruction Manual Date Code 20170927
Protection and Logic Functions
Group Settings (SET Command)
Equation 4.14
The settings used are listed in Table 4 .37.
The SEL-751 provides three curve options for each of the 27I elements, setta-
ble via the 27InCRV setting—CURVEA, CURVEB, and COEF (user pro-
grammable curve). CURVEA is compliant with IEC 60255-127 and is the IEC
standard curve as shown in Figure 4.64. CURVEB is a non-standard curve as
shown in Figure 4.64. The curve option COEF is the user programmable
curve. Set the coefficient related settings 27InCFA, 27InCFB and 27InCFC to
realize the curve that meets your application needs. Table 4.38 shows the
parameters of the three curves. Note that when 27InCRV is set to CURVEA or
CURVEB the coefficient related settings 27InCFA, 27InCFB and 27InCFC
are forced to the values shown in Ta ble 4 .3 8 and hidden.
When the operating quantity exceeds the pickup level, 27InP, then the output
remains deasserted. If the operating quantity exceeds the pickup level for the
reset time setting, 27InTTR, then the time integrator resets to 0.
Table 4.37 Inverse-Time Undervoltage Settings
Setting Prompt Setting Range
Setting Name :=
Fac to ry Default
27I ENABLE Y, N E27In := N
OPERATING QTY Refer to Ta ble 4.36 27InOQ := VAB
PICKUP LVL Refer to Tab le 4.36 27InP := 120.00
CURVE CURVEA, CURVEB, COEF 27InCRV := CURVEA
COEFF A 0.00–3.00 27InCFA := 1
COEFF B 0.00–3.00 27InCFB := 0
COEFF C 0.01–3.00 27InCFC := 1
TIME DIAL 0.00–16.00 27InTD := 1.00
RESET TIME 0.00–1.00 sec 27InTTR := 0.01
TRQ CONTROL SEL
OGIC 27InTC := 1
Table 4.38 Specification Of Inverse-Time Undervoltage Protection Element
Curve Description
Curve Defining Constants
27InCFA 27InCFB 27InCFC
Curve A 101
Curve B 0.98 1.28 2.171
Programmable Curve 0.00–3.00 0.00–3.00 0.01–3.00
n = 1 or 2.
TTT
n
27InTD
27InCFB
27InCFA
1
27InOQ
27In P
---------------------–
27InCFC
--------------------------------------------------------+
=
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