ABB Relion 670 Series Applications Manual page 180

Section 8
Current protection
t
operate
EQUATION1176 V1 EN-US
where:
t
operate
t
final
I
I
ref

 
operate
I
Bx
I
Trip
θ
n
Consider that the given system has
following settings are used to calculate the operate time:
IRef
IBase1
IBase2
Tau1
Tau2
IHighTau1
Tau1High
ILowTau1
Tau1Low
IHighTau2
Tau2High
ILowTau2
Tau2Low
ITrip
ThetaInit
ResLo
As the cooling system is
as the time constant.
For example, the largest phase load current is taken as 1800 A, then:
174
æ
Q - Q
t
= - × ç final operate
ln
ç
Q - Q
è
final n
2
I
I
ref

2
 
I I I
Bx ref Trip
ON , IBase2 is selected as the base current and Tau2 setting is selected
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ö
÷
÷
ø
is the time to operate
is the time constant
is the steady state heat content
is the largest phase load current
is the given reference load current
is the operate level heat content
is the selected base current based cooling system
ON / OFF
is the operate level load current
is the current heat content
IBase of 1000 A and the cooling system is ON . The
110%
110% of IB
120% of IB
150 min
90 min
110% of IB1
125% of tC1
90% of IB1
75% of tC1
110% of IB2
115% of tC2
90% of IB2
85% of tC2
120% of IBx
50%
60% of Itr
1MRK 511 401-UEN Rev. K
(Equation 65)
Bay control REC670
Application manual