Areva MiCOM P441, Technical Manual

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P44x/EN AP/E33 Application Notes
Page 72/220 MiCOM P441/P442 & P444
2.13.3 Typical Current Settings
The three current thresholds must be set above the maximum expected residual current
unbalance, the maximum negative sequence unbalance, and the maximum expected power
swing current. Generally, the power swing current will not exceed 2.In. Typical setting limits
are given in Table 7 and Table 8 below:
Parameter Minimum Setting (to avoid
maloperation for asymmetry
in power swing currents) Maximum Setting (to ensure
unblocking for line faults) Typical
Setting
IN> > 30% < 100% 40%
I
2
> > 10% < 50% 30%
TABLE 7 - BIAS THRESHOLDS TO UNBLOCK PSB FOR LINE FAULTS
Parameter Minimum Setting Maximum Setting
Imax line> 1.2 x (maximum power swing
current) 0.8 x (minimum phase fault current level)
TABLE 8 - PHASE CURRENT THRESHOLD TO UNBLOCK PSB FOR LINE FAULTS
2.13.4 Removal of PSB to Allow Tripping for Prolonged Power Swings
It is possible to limit the time for which blocking of any distance protection zones is applied.
Thus, certain locations on the power system can be designated as split points, where circuit
breakers will trip three pole should a power swing fail to stabilise. Power swing blocking is
automatically removed after the Unblocking Delay with typical settings:
−
30s if a near permanent block is required;
−
2s if unblocking is required to split the system.
2.14 Directional and non-directional overcurrent protection
The overcurrent protection included in the P441, P442 and P444 relays provides two stage
non-directional / directional three phase overcurrent protection and two non directional
stages (I>3 and I>4), with independent time delay characteristics. One or more stages may
be enabled, in order to complement the relay distance protection. All overcurrent and
directional settings apply to all three phases but are independent for each of the four stages.
The first two stages of overcurrent protection, I>1 and I>2 have time delayed characteristics
which are selectable between inverse definite minimum time (IDMT), or definite time (DT).
The third and fourth overcurrent stages can be set as follows:
I>3 - The third element is fixed as non-directional, for instantaneous or definite time delayed
tripping. This element can be permanently enabled, or enabled only for Switch on to Fault
(SOTF) or Trip on Reclose (TOR). It is also used to detect close-up faults (in SOTF/TOR
tripping logic no timer is applied).
I>4 - The fourth element is only used for stub bus protection, where it is fixed as non-
directional, and only enabled when the opto-input Stub Bus Isolator Open (Stub Bus
Enable) is energised.
All the stages trip three-phase only. (Could be used for back up protection during a VTS
logic)
The following Table shows the relay menu for overcurrent protection, including the available
setting ranges and factory defaults. Note that all tripping via overcurrent protection is three
pole.