IEEE Grounding Transformers
IEEE Grounding Transformers
IEEE Grounding Transformers
Medford, Oregon
Medford,
Oregon
John S. Levine, P.E.
Levine Lectronics and Lectric, Inc.
March 2011
February, 2007
1
It is used to provide a ground path on either an
ungrounded Wye or a Delta connected system
The relatively low impedance path to ground maintains the system
neutral at ground potential
On Ungrounded systems you can have
overvoltages of 6 to 8 times normal with
arcing faults
Arcing Ground Faults
Intermittent or Re-strike
V V
Cb Cb
S fa
CONTROL OF TRANSIENT OVERVOLTAGE
It supports the voltage on a faulted
phase
If a single line-to-ground fault occurs on an ungrounded or
isolated system, no return path exists and no current flows
The system will continue to operate but the other two un-
faulted lines will rise in in voltage by the square root of 3,
possibly overstressing the transformer insulation, and
other components, by 173%
Provides a metering point to measure faults
A typical example is a Wind Farm. They utilize
grounding transformers for fault protection on
ungrounded lines
When a ground fault occurs on a collector cable causes the substation
circuit breaker to open, the wind turbine string becomes isolated
Turbines do not always detect the fault and the generators continue to
energize the cable.
Voltages between the un-faulted cable and the ground rise by the 173%
The transformer, placed on the turbine string, provides the ground path
A typical example is a Wind Farm.
WYE CONNECTED
What if no neutral exists (i.e. delta systems)?
A grounding transformer is installed (either a zig-zag or a wye-delta)
from all three phases to create an artificial neutral for grounding
purposes only.
A B C A B C A B C
Zig-Zag
HRG
Grounding
Transformer
Vector diagram of
balanced system
A B C
c C
b
a
c C
A
b
B
a
Each leg of the Zig-Zag
Connection is connected b
to a winding from another which
C is out of phase
c B
The resulting Zig-Zag connection
Is phase shifted with respect to the
incoming three phase source
Az
Cz
Bz
Limits circulation of triplen harmonics
( 3 rd, 6th, 9th, etc)
Can be used without a Delta connected or 5-
legged core
Elimination of secondary winding results in
smaller footprint, lower cost (25-30%)
Includes a Delta or Wye connected secondary
Utilizes 4 or 5 legged core when Wye
connected secondary is specified
Multi-functional, provides benefit of auxiliary
power
Know the basic parameters
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For more information and specification sheets
www. PacificCrestTrans.com