89
Time delayed phase and residual
overcurrent protection (TOC1)
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In case of extremely short or not fully transposed parallel lines, the false residual current
must be measured or calculated when maximum sensitivity is desired. The residual cur-
rent is proportional to the load current.
General criteria for the primary current setting value of the time delayed residual over-
current protection is given in the formula below:
(Equation 34)
The residual protection must not operate under any high load conditions. If the system
is in a stressed situation due to loss of some parallel line the observed line must not be
tripped due to increased residual current caused by load current increase.
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If Is is the primary setting operating value of the function, then the secondary setting
current (Is
SEC
) is:
(Equation 35)
where I
SEC
is the secondary rated current of the main CT and I
PRIM
is the primary rated
current of the main CT.
The relay setting value is given in percentage of the secondary base current value, I
1b
,
associated to the current transformer input I1. The value for IP> and IN> is given from
the formula:
Where:
IRmax
is the maximum permissive residual current flowing in the protection unit
during any service conditions and
Ifmin
is the minimum residual fault current that the relay has to clear.
1.3
and
0.7
are safety factor values.
1.3 IRmax
⋅
Is
0.7 If min
⋅
<
<
Is
SEC
I
S EC
I
PRIM
--------------
Is
⋅
=
Summary of Contents for REO 517
Page 10: ... RQWHQWV ...
Page 16: ...6 Introduction to the application manual KDSWHU QWURGXFWLRQ ...
Page 64: ...54 Blocking of signals during test KDSWHU RPPRQ IXQFWLRQV ...
Page 88: ...78 Scheme communication logic ZCOM KDSWHU LQH LPSHGDQFH ...
Page 146: ...136 Unbalance protection for capacitor banks TOCC KDSWHU XUUHQW ...
Page 166: ...156 Dead line detection DLD KDSWHU 3RZHU V VWHP VXSHUYLVLRQ ...
Page 378: ...368 Monitoring of DC analog measurements KDSWHU 0RQLWRULQJ ...
Page 384: ...374 Pulse counter logic PC KDSWHU 0HWHULQJ ...
Page 412: ...402 Serial communication modules SCM KDSWHU DWD FRPPXQLFDWLRQ ...
Page 440: ...430 LED indication module KDSWHU DUGZDUH PRGXOHV ...