Winyah Generating Plant,
Santee Cooper Corona Imaging
by: Wilson Johnson, PE; Darien
T. Salley
Santee Cooper Power
This presentation
focuses on a structure, located near the Winyah Generating Plant
Cooling Towers Unit 3 and 4.
A fault of a phase to ground type occurred, on the Winyah-Charity
230kV Line, on November 29, 2003 at the structure. The corona camera
was used to record data before and after the flashover on the structure
insulators.
The Case:
Location The
Winyah Generating Plant is located in Georgetown, SC. Georgetown
is about 20 miles from the Atlantic Ocean. The structure that this
presentation focuses on is located near two cooling towers.
Environment Due to the location
of the plant (near the Atlantic Ocean) and the location of the structure
(near the cooling towers) the environment is very hostile. The insulators
on the structure are being constantly contaminated with sea water
mist or vapors from the cooling towers.
Cooling Towers The cooling towers
are located a few feet from the tower. Recycle water were used for
the cooling tower. The conductivity*
of the cooling tower water, in the past, reached 12,000uS
The Structure 110 foot height, steel, dead-end pole with a foundation.
It is treated with paint and the last treatment was in 2000.
Outages From 1999 to 2003, the flashover
issue on the Charity – Winyah 230kV transmission line accounted
for 35% of the duration of outages on Santee Cooper 230kV transmission
system. The majority of the outages took place during the month
of November.
Seasonal Variations The flashover
outages usually occur during the winter season due to the change
in the wind conditions. The wind blows the vapors from the cooling
towers across the insulators on the structure.
Contamination on the insulators,
due to water vapor, is causing tracking on the insulator which leads
to the flashover.
Effect on Conductive Contamination on Insulators
- As the water vapor at the cooling towers becomes conductive it
forms a charged cloud around the insulator. Opposite charges attract
to each other. So the negatively charged particles accumulate around
the insulator. This creates a path for the current that is flowing
through the conductor to track on the outside of the insulator.
When the tracking path reaches the structure a flashover occurs
which cause the line to operate for a phase to ground fault.
Corrective Actions:
Corona Camera - In 2002, research
was done to provide a method of recognizing the tracking issue.
A proposal was submitted to purchase the DayCor corona camera and
it was purchased in 2003. The corona camera has been helpful to
assign a qualitative value of the corona on the structure insulator. Insulators - Inside the 230kV substation,
Silguard (a silicon base product – which prevents contamination
from building up on it’s surface) was applied to the insulators.
On the structures, the suspension insulators were changed to a 730kV
rated insulator. Corona rings were placed on the 230kV post insulators.
The replacement of the insulators took place in 2003. Water Quality - The method of recycling
the cooling tower water was discontinued, except for emergency use
only. A water line was built in the summer of 2003 to supply the
cooling towers with fresh water. This reduced the conductivity of
the cooling tower water to 300uS. Maintenance - A monthly maintenance
program of hand washing the insulators was created. This process
removed any build up contaminates from off the surface of the insulator.
Structure #3 video taken on 10/02/2003
Corona image of top conductor. Last time washed October 28, 2003
Conductivity – Unit 3 was 2840 uS; Unit 4 was 3910 uS.
Range – Cooling Tower side was 6700 to 7400 photons/min;
Other side was 1200 to 2800 photons/min. Gain – 150
Flashover – Last operation Jan 2003
Structure #3 video taken on 12/02/2003
Corona image of top conductor. Last time washed November 30, 2003.
Conductivity – Unit 3 was 4900 uS; Unit 4 was 7090 uS.
Range – Cooling Tower side was 6800 to 7900 photons/min;
Other side was 3800 to 4700 photons/min. Gain – 150
Flashover – Last operation Nov, 2003 Distortion / noise due to welding in area.
Structure #3 video taken on 18/02/2003
Corona image of top conductor. Last time washed December 11, 2003.
Conductivity – Unit 3 was 1139 uS; Unit 4 was 1071 uS.
Range – Low readings Gain – 150 Flashover – Last operation November 29, 2003
Summary: The corrective action taken
by Santee Cooper has drastically reduce the quantity of Charity
– Winyah outages. Because of the recycling of cooling-tower
water, due to the failure of the pump on the fresh water system,
the conductivity of the cooling tower vapors was higher than normal.
On November 29, 2003, the cooling tower conductive level was 4400uS
for Unit 3 and 6390uS for Unit 4. Also, due to the season shift
in wind, the insulators on the structure became contaminated. This
lead to a flashover and outage on the line.
The corona camera has helped in determining which insulators and
structures was being contaminated.
In the future, the corona camera will be incorporated in the maintenance
program to focus the cleaning of the insulators and reduce outages.
*Conductivity
- is the ability of a material to transfer a electrical charge from
one point to another. Liquid Conductivity - Conductivity
in liquid is caused by contaminates or substance particles.
Conductivity and temperature are proportionally related: as the
temperature increases, so does the conductivity.
