Pursuant to Article 116 of the Energy Law

4.2.11.2.4. Main and backup fault protection should be installed to protect 110 kV also two-
phase transmission lines (e.g. railway substations). Required protective functions by 
protection devices should be 
a) for main protection devices: 
- multi stage overcurrent protection; 
- multi stage earth fault overcurrent protection. 
- automatic reclosure for breaker;
- overload protection; 
- breaker failure protection; 
- pole discordance protection (if not completed by an internal breaker’s scheme ) 
- trip circuit supervision of the breaker (as external device for each tripping coil ) 
a) for backup protection devices: 
- multi stage overcurrent protection; 
- multi stage earth fault overcurrent protection. 
4.2.11.2.5. If the facility of the transmission system user has 110 kV plant with embedded 
grid tone command (PLC), standard field with three current transformers and at least one 
voltage transformer (for controlling the level of signal) shall be used. Such plant shall be 
fitted with the three-phase multi stage overcurrent and earth fault overcurrent protection 
4.2.11.2.6. Capacitor batteries in the external PLC filter shall be protected by the protection 
against the instantaneous current misbalance that is connected on the current transformer 
between the neutral points of two groups of the capacitor banks in star shape connection. If 
there are coupling inductive elements with oil insulation, protection with gas relays needs to 
be applied. 
4.2.11.2.7. Local bus bar protection is not required for protection of 110 kV bus bars in the 
facilities of the transmission system users in conventional plants and GIS plants, if not 
required by the manufacturer, but the respective buss faults should be eliminated by trips of 
110kV supply lines in adjacent facilities (remote protection).
4.2.11.2.8. Local differential bus bars protection will be used in 110 kV GIS plants of the 
transmission system user when required by the manufacturer.
4.2.11.2.9. 110 kV plants with installed differential protection of bus bars shall also have the 
function of the protection against the breaker failure.
4.2.11.2.10. In 110 kV plants with several bus bars, protection devices should be installed in 
bus coupler bay, with multi stage three-phase overcurrent and multistage earth fault 
overcurrent protection including breaker failure functions. 

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