1.1 was undergoing troubleshooting and was out

1.1      
PARTIAL SYSTEM
COLLAPSE

The Network Interconnected Transmission
System (NITS) suffered a partial system collapse on the 21st and 25th
of January, 2016. The following is a summary of the

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1.1.1     Cause of  the 21st
January, 2016 system collapse

The system collapse was caused by loss of the 330kV
Aboadze Volta line. This was due to defective Glass insulators on the 330kV
Aboadze Volta line. These insulators have been observed as cause of the System collapse experienced
in the country.

As a result of the increased dust from the
Harmattan (dry) season this year, the defective insulators have been causing
flashovers to ground from the dust, creating transient faults and for that
matter surges which results in breaker isolation of the Aboadze – Volta line.

 

By this isolation, which had been preceded by
tripping of the Aboadze Cape Coast 161kV line, supply from the generating power
plants located in Aboadze were cut off from reaching the eastern side of the
country which bears the larger amount of load in the country. The Aboadze Coast
line was undergoing troubleshooting and was out of circuit at the time of
failure of the Aboadze – Volta 330kV line.

 

The isolation therefore resulted in frequency
swings precipitating
widespread tripping of transmission lines by distance relays. This was followed
by the various thermal plants, being Sunon
Asogli, KARPOWER, CENIT, TT2PP tripping to shutdown. Subsequently, with the
three Akosombo units not being able to support the load, they also tripped on
51VT, over-speed.

 

The collapse did not however affect the whole
country.  Customers in the Western Region
were not affected by the collapse as the thermal plants and the lines serving
these areas were still in service.  This
is attributed to the fact that the GTs appropriately deloaded thereby
containing the remaining load within the isolated network. However high
frequencies were experienced. These were still within the frequency band of the
GTs thereby allowing them to continue operation. With existing path through the
inter-tie excess generation of about 250MW went across the border.

 

1.1.2     Cause of 25th January, 2016 system collapse

 

The events of the 25th
January 2016 could be considered as similar to that of the 21st
January, 2016 being that it was triggered by loss of transmission from the
Aboadze enclave generators to the eastern part of the country where much of the
national load is located. Demand for Accra is currently about 700MW.

 

A transient fault on the
Takoradi to Cape Cost line had caused the line to trip. Prior to this the 330kV
Aboadze – Volta line had tripped at about 06.12Hrs due to a suspected flashover.
The line was therefore out of circuit for maintenance when the Takoradi Cape
Coast line tripped. This resulted in other lines supplying the eastern part of
the country from Aboadze to trip. 

 

These trips caused sudden
surges in the system resulting in the partial system collapse.

 

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