Woodward HighPROTEC - I2> and %I2;I1> - Unbalanced Load [46]

Protective Elements
I2> and %I2/I1> – Unbalanced Load [46]
Elements:
I2>[1] ,I2>[2]
The I2> Current Unbalance module works similar to the V 012 Voltage Unbalance module. The positive and
negative sequence currents are calculated from the 3-phase currents. The threshold setting (either » I2>« or
»I 2/FLA« ) defines a minimum operating current magnitude of I2 for the 46 function to operate, which insures that
the relay has a solid basis for initiating a current unbalance trip. The » %(I2/I1)« (option) setting is the unbalance trip
pickup setting. It is defined by the ratio of negative sequence current to positive sequence current » %(I2/I1)« .
All I2> Current Unbalance modules are identically structured.
The condition for a trip of this module is that the negative sequence current I2 is above the set threshold and – if
configured – the percentage current unbalance is above the setting » %(I2/I1)« . The module initiates a trip if this
condition is fulfilled for a specific tripping delay time.
For this tripping delay time, there are two characteristics available as configuring options, a definite time
characteristic (DEFT, where the tripping delay is a setting value) and an inverse characteristic (INV, where the
tripping delay is calculated).
The setting of »CurrentBase « decides about whether » I2>« or »I 2/FLA« is used as the threshold value. This rating
value – » I2>« or »I 2/FLA« – is the permitted continuous unbalanced load current, and it is specified in units of either
I
n
(for » CurrentBase « = “ Device Rating ” ) or I
b
(for » CurrentBase « = “ Protected Object Rating ” ).
The principle of the definite time characteristic (DEFT) is as follows:
• The module trips if for the tripping delay time (which is set as the Setting Group parameter »t « ) the negative
sequence current I2 is above the set threshold and (if configured) the percentage current unbalance is
above the setting » %(I2/I1)« .
The principle of the inverse time characteristic (INV) is as follows:
• The protective device permanently calculates the heat (thermal) energy θ of the object to be protected. This
happens all the time, independent of any alarm or tripping decisions.
The module trips if for the tripping delay time t
trip
– which is dependent on θ – the following conditions are all
fulfilled:
1. The negative sequence current I2 is above the set threshold (» I2>« or »I 2/FLA« ) and
2. the percentage current unbalance is above the setting » %(I2/I1)« (if » %(I2/I1)« is set to active ) and
3. the calculated thermal energy θ exceeds a maximum value θ
max
,, which is calculated based on the
setting K for the thermal load capability.
• For θ = 0 the tripping delay time is calculated as follows:
for » CurrentBase « = “ Device Rating ” for » CurrentBase « = “ Protected Object Rating ”
t
A
=
K ⋅ I
n
2
I
2
2
−I
2 ›
2
t
A
=
K ⋅ I
b
2
I
2
2
−I
2 ⁄ FLA
2
where
t
trip
= tripping delay in seconds,
744 MCDGV4 DOK-HB-MCDGV4-2E