44x/EN AP/Hb6
-44 MiCOM P40 Agile
[(R3G – R4G) – ∆R] ≤ 80% Z min load
With ∆R = 0,032 x ∆f x R load min
∆f: power swing frequency
R load min: minimum load resistance
A typical resistive reach coverage would be 40 Ω on the primary system. The same load
impedance as in section 3.1.2.4.1 must be avoided. Therefore R3G is set such as to avoid
point Z by a suitable margin. Zone 3 must never reach more than 80% of the distance from
the line characteristic impedance (shown as dotted line in Figure 20), towards Z.
For high resistance earth faults, the situation may arise where no distance elements could
operate. In this case it will be necessary to provide supplementary earth fault protection, for
example using the relay Channel Aided DEF protection.
3.1.2.5 Zone setting – Zone time delay
(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 200
ms. 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, zone P or zone Q time delays (tZ3, tZp, tZq) are typically set with the
same considerations made for the zone 2 time delay, except that the delay needs to
coordinate with the downstream zone 2 fault clearance (or reverse busbar protection
fault clearance). A typical minimum operating time would be about 400 ms. 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: The DDBs corresponding to "tZi" (for zone i) time-delays are noted
"Ti" in the PSL.
The following conventional rules are applied:
• Distance timers are initiated as soon as the relay has picked up – CVMR pickup
distance (CVMR = Start & Convergence)
• The minimum tripping time even with carrier receive is T1.
This applies only for standard distance scheme, while in teleprotection schemes
minimum tripping time is separately settable.
• Zone 4 is always reverse
3.1.3 Fault locator
The relay has an integral fault locator that uses information from the current and voltage
inputs to provide a distance to fault measurement. When the fault calculation is complete the
fault location information is available in the relay fault record.
When applied to parallel circuits, mutual flux coupling (section 3.1.2.1.3) can alter the
impedance seen by the fault locator. The coupling will contain positive, negative and zero
sequence components. In practice the positive and negative sequence coupling is
insignificant. The effect on the fault locator of the zero sequence mutual coupling can be
eliminated by using the mutual compensation feature provided. This requires that the
To Next Page
Loading...
