Basler BE1-CDS220, Instruction Manual, Page: 367 / 476

BE1-CDS220 Testing And Maintenance 13-53
To change from group 0 to group 1, execute the following commands.
CS-GROUP=1 select setting group 1
CO-GROUP=1 execute setting group 1
Using the basic information in Table 13-41, program the pickup of the elements for setting
group 1 and, optionally, proceed with group 1 testing.
Sidebar 13-10. Negative Sequence Overcurrent Element Pickup
A three-phase electric power system can be modeled using a set of balanced equations known as
symmetrical components. These components provide a practical method of analyzing power system
operation during unbalanced conditions such as would occur during a fault.
The symmetrical components of a power system are segregated into positive, negative, and zero
sequence components. At any given time, all of these components may be present in load current due to
unbalanced load, etc. In practice however, asymmetrical current or voltage conditions are more typical
due to unbalanced loads, unbalanced system faults, open conductors, etc. In the case of an unbalanced
load, this condition may be detrimental to the operation of a power system and the equipment. Under
unbalanced fault conditions, these components will very likely be harmful to equipment and potentially, to
personnel. Positive sequence components are comprised of balanced three-phase currents and line-to-
neutral voltages supplied by power system generators. Under any of these scenarios, negative sequence,
and zero sequence components will be present. The associated figure shows the sequence components
in phasor form.
positive negative zero
I
c1
I
b1
I
a1
I
c2
I
b2
I
a2
I
a0
= I
b0
= I
c0
Sequence Components in Phasor Form
These sequence component quantities are very useful in that they can be measured and used as
operating parameters to help safeguard equipment. Proper management of the power system conserves
resources and minimizes potentially harmful exposure to the public and operating personnel.
Using symmetrical components, we can say the following about phase currents.
I
a
= I
1
+ I
2
+ I
0
(see the associated figure)
I
b
=
α
2
I
1
+
α
I
2
+ I
0
I
c
=
α
I
1
+
α
2
I
2
+ I
0
where
α
is an operator equal to 1.0
∠
120
o
.
From this we can derive that the equation for negative sequence current I
2
, is
I
2
=
1
/
3
(I
a
+
α
2
I
b
+
α
I
c
)
Under balanced conditions, this value would be zero. If a single-phase input is applied, then a negative
sequence quantity will appear to the relay. If we let I
b
= I
c
= 0, then, I
2
= I
a
÷
3 .