Areva MiCOM P441, Техническое руководство

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P44x/EN AP/E33 Application Notes
Page 24/220 MiCOM P441/P442 & P444
2.7.4 Zone Time Delay Settings
(initiated with CVMR (General start convergency))
•
The zone 1 time delay (tZ1) is generally set to zero, giving instantaneous operation.
However, a time delay might be employed in cases where a large transient DC
component is expected in the fault current, and older circuit breakers may be unable
to break the current until zero crossings appear.
•
The zone 2 time delay (tZ2) is set to co-ordinate with zone 1 fault clearance time for
adjacent lines. The total fault clearance time will consist of the downstream zone 1
operating time plus the associated breaker operating time. Allowance must also be
made for the zone 2 elements to reset following clearance of an adjacent line fault and
also for a safety margin. A typical minimum zone 2 time delay is of the order of
200ms. This time may have to be adjusted where the relay is required to grade with
other zone 2 protection or slower forms of back-up protection for adjacent circuits.
•
The zone 3 time delay (tZ3) is typically set with the same considerations made for the
zone 2 time delay, except that the delay needs to co-ordinate with the downstream
zone 2 fault clearance. A typical minimum zone 3 operating time would be in the
region of 400ms. Again, this may need to be modified to co-ordinate with slower forms
of back-up protection for adjacent circuits.
•
The zone 4 time delay (tZ4) needs to co-ordinate with any protection for adjacent lines
in the relay’s reverse direction. If zone 4 is required merely for use in a Blocking
scheme, tZ4 may be set high.
Remark: In MiCOM S1, timers settable are: tZi but in the DDB corresponding
cells are: Ti
2.7.5 Residual Compensation for Earth Fault Elements
For earth faults, residual current (derived as the vector sum of phase current inputs
(Ia + Ib + Ic) is assumed to flow in the residual path of the earth loop circuit. Thus, the earth
loop reach of any zone must generally be extended by a multiplication factor of (1 + kZ0)
compared to the positive sequence reach for the corresponding phase fault element. kZ0 is
designated as the residual compensation factor, and is calculated as:
kZ0 Res. Comp,

kZ0

= (Z
0
– Z
1
) / 3.Z
1
Ie: As a ratio.
kZ0 Angle,
∠
kZ0 =
∠
(Z
0
– Z
1
) / 3.Z
1
Set in degrees.
Where:
Z
1
= Positive sequence impedance for the line or cable;
Z
0
= Zero sequence impedance for the line or cable.
kZ0 CALCULATION DESCRIPTION
If we consider a phase to ground fault AN with analog values VA and IA.
Using symetrical components, VA is described as above:
(1) VA = V1 + V2 + V0 = Z1I1 + Z2I2 + Z0I0
Z2 = Z1 (for a line or a cable)
(2) VA = Z1 (I1 + I2) + Z0I0
we can write also: IA = I1 + I2 +I0
(3) (I1 + I2) = IA – I0
with (3) in (2) we obtain:
(4) VA = Z1 (IA – I0) + Z0I0
The physical fault current is IR = 3I0 – if put in (4) – we obtain:
VA = Z1 [IA – IR/3 + Z0IR/3Z1] = Z1 [IA + IR (Z0–Z1)/3Z1]
but: (Z0 – Z1)/3Z1 = kZ0