Our Zigzag Transformers are designed for your grounding needs and can solve the grounding
challenges you may be facing in your system
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All of our units are built-to-order, in either production-run or prototype quantities. Contact us
with your specifications and we’ll get a design and quote the unit. If you don't know
everything, we can help. Call us at US +1 408-263-8444, or email us by clicking the button
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These transformer are NRTL to UL 506 and 1561. Find out more about our certifications by
clicking here: More on
certifications
Build configurations and capabilities
Electrical Characteristics
Fault current
Fault duration
Continuous current
System voltage up to 15 kVrms
Frequencies at 50/60Hz
***Optionally, can specify X/R ratio + Impedance values
Terminal Configurations (Dependant on transformer specifications)
Copper buss bar
Silicon bronze hardware
Ring-lug compatibility
Touch-safe configurations
Lexan covers
Enclosures and weather
NEMA enclosures
NEMA 1: General purpose
NEMA 3: Weather-resistant (falling dirt, windblown dust, rain, sleet, snow, formation of ice)
NEMA 3R: Same as 3, omits protection against windblown dust
NEMA 4: Watertight
NEMA 4X: Same as 4, but stainless steel
NEMA 6: Submersible
Examples of Zigzag Transformers
370 kVA Zigzag transformer
3-Phase, 60Hz
System voltage = 400 Vrms L-L
CNC = 1,600 Arms in Neutral
ZPS = 0.0006 Ohms
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5 kVA Zigzag transformer
3-Phase, 60 Hz
System Voltage = 480 Vrms
CNC= 18.3 Arms
ZPS = 0.52 Ohms ±1.1 Ohms
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41 kVA Zigzag transformer
3-Phase, 50/60Hz
System Voltage = 480 Vrms
CNC = 41.1 Arms
ZPS = 1.4%
NRTL to UL 1561
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Earthing transformer
3-Phase, 50/60Hz
System Voltage = 480Vrms
CNC = 360 Arms
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370 kVA Zigzg transformer: Description here.
Electrical Characteristics
370 kVA
3-Phase
60Hz
Rated Voltage = 400 Vrms L-L
Rated Current = 1,600 Arms in Neutral, Continuous
Zero Sequence Impedance = 0.0006 Ohms
Features = Designed for low impedance
Terminal Configuration
Copper buss bar for customer connections
Enclosures and features
Designed for low impedance
Certifications: CE, US, NRTL to UL 1561
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5kVA Zigzag Transformer: Description here.
Electrical Characteristics
Power Rating = 5 kVA
No. of Phases = 3
Frequency = 60 Hz
System Voltage = 480 Vrms
Continuous Neutral Current = 18.3 Arms
Impedance = 0.52 Ohms ±1.1 Ohms
Terminal Configurations
Terminal board with silicon bronze terminal hardware.
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41 kVA Grounding Transformer: Description here.
Electrical Characteristics
Power Rating = 41 kVA
No. of Phases = 3
Frequency = 50/60 Hz
System Voltage = 480 Vrms
Continuous Neutral Current = 41.1 Arms
Fault Current = 2,845.9 Arms
Fault Duration = 10 seconds
Impedance = 1.4%
X/R ratio = 4.5 at 100oC/50 Hz
Terminal Configurations
Copper buss terminal connections
Enclosures and weather
NEMA enclosures = NEMA3R enclosure
Certifications = NRTL to UL 1561
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Earthing Transformers
Electrical Characteristics
System Voltage = 480 Vrms
Frequency = 50/60Hz
No. of Phases = 3
Continuous Neutral Current = 360 Arms
Fault Current = 1,600 Arms
Fault Duration = 1 second
Terminal Configurations
Terminal board with silicon bronze hardware
Enclosures and weather
NEMA1 enclosure
Certifications = CE, CUS, NRTL to UL 1561
About Grounding Transformers
The most common connection used in grounding transformers is the Zig-Zag connection. The grounding
transformer is commonly referred to by this connection type, the Zigzag Transformer. Grounding Transformers
are used for obtaining a grounded neutral on three phase, three-wire systems, providing a return path for
zero sequence current generated by the loads in the system or by the fault currents. Sometimes a winding for
auxiliary supply can be added besides the zig-zag winding.
Figure 1: Zigzag Connection
In a case of line-to-ground fault, sufficient current (3I) will flow through the neutral of the transformer,
causing opposite current flow (I) in the zig-zag connected windings of the same core leg. This results in no
magnetizing effect on the core and provides relatively low impedance from path to ground.
Grounding transformers are most commonly used for short-time operation (approx. up to 30 sec) during the
fault currents. However, by connecting reactors they can operate continuously.
The basic parameters required for quoting a grounding transformer are:
Primary Voltage is the system voltage to which the grounded winding is to be connected.
Rated KVA. Because the grounding transformer is normally a short time device, its size and cost
are usually lower when compared with a continuous duty transformer of equal kVA rating. For this reason,
grounding transformers are often not sized by "kVA" but by their continuous and short time current
ratings. Regardless of how you rate it, the grounding transformer must be sized to carry the rated
continuous primary phase current without exceeding its temperature limit. Typical continuous current
values can be as low as 5 amps to as high as several hundred. Be sure to include any auxiliary loading
requirements.
Continuous Neutral Current. The continuous neutral current is defined as three times the phase to
current, or in other words, the zero sequence current. This is usually considered to be zero if the
system is balanced. However, for the purpose of designing a grounding transformer, it is a value that is
expected to flow in the neutral circuit without tripping protective circuits (which would force the
current to be zero) or the leakage current to ground that is not a symmetrical function. Again this
value is needed to design for thermal capacity of the grounding transformer.
Fault current and duration. This value is needed to calculate the short time heating that results
from a fault on the system and should be determined from an engineered system study. Typical values for
this range from a few hundred amps to a few thousand amps with duration times expressed in seconds and
not cycles. For instance, a value of 400 amps for 10 seconds is typical. The fault duration is a
critical parameter for the transformer designer. Where protection schemes use the grounding transformer
for tripping functions, a relatively short time duration is specified (5 -30 seconds). On the other
hand, a continuous or extended neutral fault current duration would be required when the grounding
transformer is used in a ground fault alarm scheme.
Impedance. The impedance can be expressed as a percentage or as an ohm value per phase. In either
case it should be chosen so that the un-faulted phase voltages during a ground fault are within the
temporary over-voltage capability of the transformer and associated equipment, such as arresters and
terminal connectors. This value must come from the system designer.
Secondary connections specify the secondary voltage and connection when applicable.