Toshiba GRZ100-211B, Инструкция по эксплуатации

Страница: 85 / 463


84

6 F 2 S 0 8 3 4
Positive phase sequence current I
1F
, negative phase sequence current I
2F
and zero phase sequence
current I
0F
at fault location in a single-phase series fault are given by:
I
1F
+ I
2F
+ I
0F
=0 (1)
Z
2F
I
2F
−
Z
0F
I
0F
= 0 (2)
E
1A
−
E
1B
= Z
1F
I
1F
−
Z
2F
I
2F
(3)
where,
E
1A
, E
1B
: power source voltage
Z
1
: positive sequence impedance
Z
2
: negative sequence impedance
Z
0
: zero sequence impedance
From the equations (1), (2) and (3), the following equations are derived.
I
1F
=
Z
2
+ Z
0
Z
1
Z
2
+ Z
1
Z
0
+ Z
2
Z
0
(E
1A
−
E
1B
)
I
2F
=
−
Z
0
Z
1
Z
2
+ Z
1
Z
0
+ Z
2
Z
0
(E
1A
−
E
1B
)
I
0F
=
−
Z
2
Z
1
Z
2
+ Z
1
Z
0
+ Z
2
Z
0
(E
1A
−
E
1B
)
The magnitude of the fault current depends on the overall system impedance, difference in phase
angle and magnitude between the power source voltages behind both ends.
Broken conductor protection element BCD detects series faults by measuring the ratio of negative
to positive phase sequence currents (I
2F
/ I
1F
). This ratio is given with negative and zero sequence
impedance of the system:
I
2F
I
1F
=
|I
2F
|
|I
1F
| =
Z
0
Z
2
+ Z
0
The ratio is higher than 0.5 in a system when the zero sequence impedance is larger than the
negative sequence impedance. It will approach 1.0 in a high-impedance earthed or a one-end
earthed system.
The characteristic of BCD element is shown in Figure 2.4.10.2 to obtain the stable operation.
I
1
I
2
0
0.01
×
In
0.04
×
In
|I
2
|/|I
1
|
≥
BCD
setting
|I
1
|
≥
0.04
×
In
&
BCD
|I
2
|
≥
0.01
×
In
In: rated current
Figure 2.4.10.2 BCD Element Characteristic
www
. ElectricalPartManuals
. com