Standard for High Voltage eg connections

Standard for High Voltage EG Connections 
 
STNW1175 
Owner: EGM Engineering
Release: 4, 11 Feb 2022 
| 
Document ID: 2946177 
SME: Manager Generation & Customer Standards 
Uncontrolled When Printed
 
56 of 60 
Appendix E: Short Circuit Ratio calculation methods (normative)
Short Circuit Ratio (SCR) 
Short Circuit Ratio is calculated with the following formula: 
SCR =
S
CMVA
P
max
Where
S
CMVA 
is the minimum sub-transient fault contribution in MVA of the studied bus prior to the 
proposed connecting asynchronous (power electronic based) EG System 
Or 
S
CMVA 
is the minimum sub-transient fault contribution in MVA of the studied bus with the 
proposed connecting Rotating Machine EG System; and
P
max
is the maximum EG capacity of the proposed EG System. 
Aggregated Short Circuit Ratio (WSCR) 
Aggregated Short Circuit Ratio means consideration for combined generation in a shared 
Distribution Network which could be based on Weighted Short Circuit Ratio (WSCR), or other 
methods. 
In this Standard, the Short Circuit Ratio also means the aggregated Short Circuit Ratio depending 
on the presence of nearby existing or committed EG Systems. WSCR is used in this Standard for 
assessment when nearby asynchronous EG Systems are present. 
A WSCR calculation should be performed as per the following formula: 
𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊
=
∑ 𝑊𝑊
𝑆𝑆𝑆𝑆𝑆𝑆𝑉𝑉𝑉𝑉𝑉𝑉
∗ 𝑃𝑃
𝑅𝑅𝑆𝑆𝑅𝑅𝑉𝑉
𝑁𝑁
𝑉𝑉
(
∑ 𝑃𝑃
𝑅𝑅𝑆𝑆𝑅𝑅𝑉𝑉
𝑁𝑁
𝑉𝑉
)
2
Where
S
SCMVAi
is the minimum fault contribution in MVA at the connection point with only 
synchronous EG Systems connected;
P
RMWi
is the MW rating of the EG System to be connected;
N is the number of nearby asynchronous EG Systems; and
The EG System index is given by i.