Page 41 - North American Clean Energy July August 2015

SOURCES & REFERENCES
trip preventing higher temporary over- front and long-term savings, while increasing system Steven W. Saylors, P.E., “Large Wind Plant Collector Design “Wind Farm Collector System
voltage values from developing.
eiciency and reliability.
Grounding, IEEE PES Transmission and Distribution Conference 2008.
For comparison purposes, a temporary Reigh. A. Walling, P.E., “Overvoltage Protection and Arrester Selection for Large Wind Plants”
overvoltage was simulated three ways.
Carlos Ober is an international sales executive and appli- IEEE TD2008-000728
IEEE Standard 142-1991: IEEE Recommended Practice for Grounding Industrial and
• Without any grounding reference;
cations engineer at EMA Electromechanics
Commercial Power Systems.
• With a conventional breaker with a 1000
Enernex “Comparison of the Technical and Economical aspects of the Combined 34.5 kV
kVA wye-delta grounding transformer;
EMA Electromechanics
Vacuum Circuit breaker & High Speed Grounding Switch VDH/GSMI vs. grounding
and
Transformers” 2013
www.emaelectromechanics.com
• With a combined vacuum circuit breaker
Advance Energy “Neutral Connections and Effective Grounding” white paper
and mechanically interlocked grounding
switch, in the collector circuit.

For all three simulated scenarios, a single-
phase-to-ground fault is applied to phase
A, and then the collector feeder is tripped.
he wind turbine generators continue to

operate while the feeder becomes isolated
(Figure 4). Without a ground reference but
with one phase connected to ground, the
unfaulted phase B voltage (Red Trace) rise

well over the typical 1.82 per unit tempo-
rary overvoltage capability of a surge ar-
rester (Pink Trace).

he (Blue Trace) shows the transient
and temporary overvoltage on Phase B
with a conventional breaker and a ground-
ing transformer in the circuit. When the

substation circuit breaker is replaced by a
combined circuit breaker and mechanical-
ly interlocked grounding switch, the volt-
age on Phase B (Green Trace) rise to about

1.15 p.u. and then drops to zero. Both
grounding methods are efective in limit-
ing the temporary overvoltage. However,
the overall system stress and absorbed en-

ergy by the surge arrestors will be further
reduced by the combined circuit breaker
and mechanically interlocked grounding
switch. As an added bonus, a grounding

breaker will also mitigate overvoltage
caused by a high generation to load ra-
tio event. Load rejection, occurs when a
signiicant portion of the load becomes

separated from the generation source. E.g.
If a high voltage breaker trips at the point
of interconnection, the wind generating
plant will be islanded. he remaining con-

nected load will be the wind farm itself
which is much lower than the output of
the system and a voltage rise can occur.
When the substation high voltage breaker

opens all feeder breakers will trip clamp-
ing each and every feeder to ground pre-
venting a possible overvoltage. Installing

a grounding breaker on every feeder will
reduce equipment, risk of environmental
issues (transformer oil spills, ire), labor,
engineering, and installation costs, as well

as the substation’s footprint.

Conclusion
Combined circuit breakers and mechani-

cally interlocked grounding switches are
an emerging alternative to grounding
transformers. he industry is steadily
increasing the use of grounding break-

ers in wind plant collector systems with
positive results. By eliminating grounding
transformers’ high costs and core losses,
grounding breakers provide signiicant up-

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