Summary Report for Conduct of Kozloduy NPP Stress Tests

“Kozloduy NPP” PLC
SUMMARY REPORT
for Conduct of Kozloduy NPP
Stress Tests
1.3.2.5.1.1 Main cable routes and sections
Off-site power supply of Units 5 and 6 of Kozloduy NPP is through switchyard 400kV
(working) and 220 kV switchyard (backup).
Connections of 400 kV (to unit transformer) and 220 kV (for startup transformers of Unit 5)
are implemented by overhead lines connecting the transformer of Units 5 and 6 sites with OSY.
Backup transformers of unit 6 are supplied from 220kV switchyard via cable 220 kV, traced in the
underground cable channel. The cable channel is provided with fire alarm system (section 8 from
[7], [8]).
Connections of 6 kV and 0.4 kV cables are made by cable located in protected areas,
corridors, shafts and ducts, with automatic fire fighting and fire doors. All cables are coated with
flame retardant coating. Cable connections from DGS to the safety systems sections are laid in
autonomous cable ducts and premises.
Backup power supply cable connections between the units and part of general plant facilities
are placed on overpasses in special protective metal trays.
1.3.2.5.1.2 Logics, layout and protection against internal and external influences
Auxiliaries of Units 5 and 6 of Kozloduy NPP during normal operation are powered by 24
kV bus after the generator circuit breaker, auxiliary transformer with split coils 24/6/6 kV, power
63/31. 5/31. 5 MW, which supply power to normal operation sections. For normal operation of the
unit simultaneous operation of both auxiliary transformers is required, i.e. both auxiliary
transformers for one unit are considered as one element in terms of reliability.
Electric power supply loads in Kozloduy NPP units 5 and 6 are divided into 3 categories,
according to their consumed electricity and the extent of reliability of power supply:
· Category I loads - AC and DC power loads, not allowing under safety conditions
power outages for more than one semi-period – 20 ms in all modes, including mode of total
loss of alternate current voltage from the working and backup auxiliary transformers
(blackout mode);
· Category II loads - AC and DC power loads, which have increased requirements to
the reliability of electricity supply, and allowing for power outages for a time determined by
the nuclear safety conditions up to 1 min (time for startup of DG and automatic startup of
loads with triggered load system);
· Category III loads – AC power loads, which do not have higher requirements on the
reliability of power supply than the requirements for presence of automatic switch to backup
equipment.
1.3.2.5.2 Backup power supply
1.3.2.5.2.1 Backup power supply sources
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