SECTION
DRY-TYPE DISTRIBUTION TRANSFORMERS
ACME ELECTRIC
•
MILWAUKEE, WI
•
800.334.5214
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acmetransformer.com
8
25. Can transformers listed in this catalog be reconnected
as autotransformers to increase their kVA rating?
Several
standard single phase transformers listed in this catalog can
be connected as autotransformers. The kVA capacity will
be greatly increased when used as an autotransformer,
in comparison to the nameplate kVA as an insulating
transformer. Examples of autotransformer applications are
changing 600 volts to 480 volts in either single phase or three
phase; changing 480 volts to 240 volts single or three phase
or vice versa; or the developing of a fourth wire (neutral) from
a 480 volt three phase three wire system for obtaining 277
volts single phase. This voltage is normally used for operating
fluorescent lamps or similar devices requiring 277 volts. For
further details showing kVA and voltage combinations for
various autotransformer connections refer to Page 30 and 31
in this catalog.
26. Are ACME Transformers shown in this catalog U.L.
Listed?
All of the transformers, with few exceptions, are
listed by Underwriters’ Laboratories and have met their
rigorous requirements. We are also prepared to have
transformers, which are not presently listed, submitted for
listing to Underwriters’ upon the customer’s request. Please
contact the factory for details.
27. Is CSAcertification available for transformers shown in
this catalog?
Most ACME transformers shown in this catalog
are certified by Canadian Standards Association. They have
been designed and tested in accordance with the latest
specifications. Please contact the factory if further details
are required.
28. What is BIL and how does it apply to transformers listed
in this catalog?
BIL is an abbreviation for Basic Impulse Level. Impulse tests
are dielectric tests that consist of the application of a high
frequency steep wave front voltage between windings, and
between windings and ground. The Basic Impulse Level of
a transformer is a method of expressing the voltage surge
(lightning, switching surges, etc.) that a transformer will
tolerate without breakdown. All transformers manufactured
in this catalog, 600 volts and below, will withstand the NEMA
standard BIL rating, which is 10 KV. This assures the user
that he will not experience breakdowns when his system is
properly protected with lightning arrestors or similar surge
protection devices.
29. What is polarity, when associatedwith a transformer?
Polarity is the instantaneous voltage obtained from the primary
winding in relation to the secondary winding. Transformers 600
volts and below are normally connected in additive polarity —
that is, when tested the terminals of the high voltage and low
voltage windings on the left hand side are connected together,
refer to diagram below. This leaves one high voltage and
Example:
Determine the interrupting capacity, in amperes, of
a circuit breaker or fuse required for a 75 kVA, three phase
transformer, with a primary of 480 volts delta and secondary
of 208Y/120 volts. The transformer impedance (Z) = 5%. If the
secondary is short circuited (faulted), the following capacities
are required:
Normal Full Load Current =
Volt Amps
75,000 VA
√
3 x Line Volts
√
3 x 480 V
90 Amps
Maximum Short Circuit Line Current =
Full Load Amps =
90 Amps
5%
5%
1,800 Amps
The breaker or fuse would have a minimum interrupting rating of
1,800 amps at 480 volts.
NOTE:
The secondary voltage is not used in the calculation.
The reason is the primary circuit of the transformer is the only
winding being interrupted.
21. Can Single Phase Transformers be used for Three Phase
applications?
Yes.
Three phase transformers are sometimes
not readily available whereas single phase transformers can
generally be found in stock. Three single phase transformers can
be used in delta connected primary and wye or delta connected
secondary. They should never be connected wye primary to wye
secondary, since this will result in unstable secondary voltage.
The equivalent three phase capacity when properly connected
of three single phase transformers is three times the nameplate
rating of each single phase transformer. For example: Three
10 kVA single phase transformers will accommodate a 30 kVA
three phase load.
22.Does ACME provide “Zig-Zag” Grounding Transformers?
Yes.
Please refer to Page 31 for a special diagram which
can be used to connect standard single phase off-the-shelf
transformers in a three phase zig-zag manner. This system can
be used for either grounding or developing a fourth wire from
a three phase neutral. An example would be to change a 480
V — three phase — three wire system to a 480Y/277 V — three
phase — four wire system.
23. What color are ACME Dry-Type Transformers?
ASA 61 (NEMA) light gray is used on all enclosed transformers
from .050 to 1000 kVA.
24. How do you select a transformer to operate in an ambient
higher than 40° centigrade?
When the ambient exceeds 40°C use the following chart for
de-rating standard transformers.
Instead of ordering custom built transformers to operate in
ambients higher than 40°C, it is more economical to use a
standard transformer of a larger kVA rating.
Maximum Ambient
Maximum Percentage
Temperature
of Loading
40°C (104°F)
100%
50°C (122°F)
92%
60°C (140°F)
84%
H1
H2
x2
x1
120 VOLT
OUTPUT
240 VOLT
INPUT
VOLT
METER
360
VOLT
READING
ADDITIVE
POLARITY
