Functions
2.19 Impedance Protection (ANSI 21)
SIPROTEC, 7UM62, Manual
C53000-G1176-C149-7, Release date 03.2010
159
Impedance Stages
The protection has the following characteristics which may be set independently:
1. Zone (fast tripping zone Z1 ) with parameters
ZONE Z1 Reactance = reach,
T-Z1 = 0 or short delay, if required.
Overreach zone Z1B, externally controlled via binary input, with parameters
ZONE Z1B Reactance = reach,
T-Z1B T1B = 0 or short delay, if required.
2. Zone (zone Z2) with parameters
ZONE Z2 Reactance = reach,
ZONE2 T2 The user must select a value for T2 above the grading time of the network
protection.
Non-directional final stage with parameter
T END The user must select T END so that the 2nd or 3rd stage of the series-con-
nected power system distance protection is overreached.
As the user may assume that impedance protection measurement extends into the unit transformer, parame-
trization must be selected to sufficiently consider the transformer control range.
Therefore ZONE Z1 is normally set to a reach of approx. 70 % of the protected zone (i.e. about 70 % of the
transformer reactance), with no or only a small delay (i.e. T-Z1 = 0.00 s to 0.50 s). Protection then switches off
faults on this distance after its operating time or with a slight time delay (high speed tripping). A time delay of
0.1 s is preferred.
For ZONE Z2 the reach could be set to about 100 % of the transformer reactance, or in addition to a network
impedance. The corresponding ZONE2 T2 time stage is to be set so that it overreaches the power system pro-
tective equipment of the following lines. The T END time is the last back-up time.
The following formula is generally valid for the primary impedance (with limiting to the unit transformer):
with
k
R
Protection zone reach [%]
u
SC
relative transformer short-circuit voltage [%]
S
N
Rated transformer power [MVA]
U
N
Machine-side rated transformer voltage [kV]
The derived primary impedances must be converted for the secondary side of the current and voltage trans-
formers. In general:
The nominal current of the protection device (= secondary nominal current of the current transformer) is auto-
matically considered by the device. You have already communicated the transformation ratios of the current
and voltage transformers to the device by entering the nominal transformer values (see section 2.5).
To Next Page
Loading...
Need help?
General
