Siemens siprotec 7SA522 - Page 168

2 Functions
168
7SA522 Manual
C53000-G1176-C155-3
Figure 2-73 Characteristic settings of the zero-sequence voltage time dependent stage —
without additional times
Zero Sequence
Power Stage
If you have configured the fourth stage as zero sequence power stage (address 
(DUWK)DXOW2& = 6ULQYHUVH), set the mode first: Address  2SPRGH
,S. This stage can be set to operate )RUZDUG (usually towards line) or 5HYHUVH
(usually towards busbar) or 1RQ'LUHFWLRQDO (in both directions). If the stage is not
required, set its mode to ,QDFWLYH. The zero sequence power protection is to
operate always in line direction. Mode 1RQ'LUHFWLRQDO is not reasonable here
since it would restrict the stage to mere current measurement.
Address  ,S3,&.83 indicates the minimum current value above which this
stage is required to operate. The value must be exceeded by the minimum earth fault
current value.
The zero-sequence power S
r
is calculated according to the formula:
S
r
= 3I
0
· 3U
0
· cos (ϕ – ϕ
comp
)
The angle ϕ
comp
is set as maximum-sensitivity angle at address  3+,FRPS. It
refers to the zero sequence voltage in relation to the zero sequence current. The
default setting 255° thus corresponds to a zero sequence impedance angle of 75°
(255° – 180°). Also refer to Section 2.7 at margin heading “Zero Sequence Power Pro-
tection”).
The trip time depends on the zero sequence power according to the following formula:
Where S
r
is the compensated power according to above formula. S
ref
is the setting
value 6UHI (address ) that indicates the pickup value of the stage at ϕ = ϕ
comp
.
Factor N (address ) can be set to displace the zero sequence time characteristic
in time direction, the reference value 6UHI can be set for displacement in power di-
rection.