Part II - IPA SA

REVISTA ROMÂN DE AUTOMATIC
39
PARTIAL DISCHARGE MONITORING
All the components used for the Partial
Discharge (PD) monitoring, including
capacitive couplers, HydroTrac units and
special software, was procured from IRIS
Power, a Canadian company. The Partial
Discharge system was used for two of the
four hydro generators, the generators with a
voltage of 10,5 kV.
In 1994, IRIS [2] installed the world’s first
commercial continuous on-line partial discharge
measuring system for large generators.
The IRIS HydroTrac system was released in
2000. The Partial Discharge testing has
become the most pervasive tool for assessing
the condition of the stator winding insulation
during normal operation of a hydro generator.
Typical winding aging condition, which can be
detected by partial discharge testing, include:
- loose wedges;
- insulation delaminating;
- separation of copper-insulation bond;
- deterioration of semi-conducting
coating;
- damaged semi-conducting/grading
coating overlap area;
- cracks on winding insulation;
- problems related to thermal,
mechanical, and/or electrical aging of
the insulation.
The results of PD testing are generally
summarized by two key indicators or
summary numbers: NQN and Qm. These two
factors are derived from the standard pulse
height analysis plots obtained from a PD test.
- NQN is the area under the pulse
height analysis curve, and represent the total
PD activity and indicate the increasing
insulation aging.
- Qm is the magnitude, in mV, of the
largest PD pulses detected and is indicative of
the worst deterioration within the machine.
For each of the two 10,5kV hydro generator
was allocated a HydroTrac unit. The two
units were connected, via an RS-485 network,
to the central DS2 diagnosis station.
OTHER DATA MONITORING
The other data, which were necessary to be
monitored, are obtained from the SCADA
system, elaborated by ABB Germany, via an
OPC server – OPC client connection in which
ABB is the server and IPA is the client.
As OPC client, IPA has used the RSView32
base software from the Rockwell Automation
Company. The process parameters, which are
taken over in this way, for analysis, are the
following:
• Hydro generator stator winding, iron
core and bearing temperature;
• Cooling water, cooling air and oil
temperature;
• Guide vane opening;
• Grate clogging level;
• Water upstream and downstream
level;
• Circuit breakers and protections
state;
• Voltage and current in the 0,4 kV
circuits;
• Oil and cooling water pumps
running hours.
These information are used to give, for
example, a statistical image about the
frequency of circuit breakers disconnecting or
about how many times a winding temperature
has exceed a certain value and at what time.
All these data are archived, to be used for a
long time diagnosis trend display, or to be
edited in a printed report.
REFERENCES
[1] VibroSyst M “On line monitoring of
hydro generating units for optimized
operations and maintenance”.
[2] B.A. Lloyd and G.C. Stone – Iris Power
Engineering – “Experience with continuous
on-line stator winding partial discharge
monitoring of hydro generators”.
AR934-8.doc