Sola/Hevi-Duty offers a broad range of industrial control solutions
to the most demanding industrial applications. Our products exceed NEMA ratings for
inrush and regulation to ensure control systems are powered correctly.
Electromagnetic control components demand inrush currents up to 10
times the transformer’s nominal rating. While this inrush is
occurring, the output side of the transformer must not fall below 85%
of nominal as specified by NEMA St. 1, Part 4. Using a
transformer that does not meet these ratings may cause erroneous
shutdowns of downstream systems.
To meet your complete control needs, Sola/Hevi-Duty offers four series of control transformers, all of which exceed the NEMA
standards. The Selection Chart can be used to identify the appropriate
transformer for your application.
A printable
version of the following sections is available by selecting the pdf
files to the left.
The
Series
The
SBE series (encapsulated
and open style) is available
from 50 - 5000 VA, 55°C Rise and features copper
windings and encapsulation (through 1000 VA) for longer life and
protection from the environment. This low temperature performance
can mean smaller cabinet size or longer life for any electronic
components that may be nearby.
The SMT
series
are 115°C rise, aluminum wound and for applications
where good voltage regulation and higher power capacities (1000-5000
VA) are required.
The International series meets all
IEC requirements including touchproof covers (IP20 ordered separately)
for European applications. Also available is
the new ICE International series
which combines IP20 touch proof terminations, copper windings
and encapsulation in a design built to match international voltage
combinations.
The HSZ series
rounds out Hevi-Duty’s line with an enclosed series of control
transformers from 1 - 10 KVA that feature either an UL-3R or NEMA
12 enclosure. This unique design, featuring copper windings and
encapsulated construction, can help system designers meet harsher
environmental standards or design for a safer installation outside
of a control cabinet. The HSZ series is for applications where cost
or heat issues make mounting the transformer outside the control
panel necessary.
For proper transformer
selection, three characteristics of the load circuit must be determined in addition to the
minimum voltage required to operate the circuit. These are total steady state (sealed) VA,
total inrush VA, and inrush load power factor.
Sealed
VA - Total steady state, sealed
VA is the volt-amperes that the transformer must deliver to the load circuit for an
extended period of time.
Inrush VA
- Total inrush VA is the
volt-amperes that the transformer must deliver upon initial energization of the control
circuit. Energization of electromagnetic devices takes 30-50 milliseconds. During this
inrush period the electromagnetic control devices draw many times normal current - 3-10
times normal is typical.
Inrush load power factor is
difficult to determine without detailed vector analysis of all the load components.
Generally such an analysis is not feasible, therefore, a safe assumption is 40% power
factor. Until recently, 20% PF was commonly used for transformer
calculations, however, tests
conducted on major brands of control devices indicate that 40% PF is
a safer default assumption.
Determine the supply and
load voltages. The supply voltage is the available voltage to the control transformer. The
load voltage is the operating voltage of the devices that will be connected to the
transformer output.
Calculate the total sealed
VA by adding the VA requirements of all components that will be energized together
(timers, contactors, relays, solenoids, pilot lamps, etc.). Sealed VA data is available
from the control device manufacturer.
Add the inrush VA of all
components that will be energized together. Be sure to include the sealed VA of components
that don't have an inrush, (lamps, timers, etc.) as they present a load to the transformer
during maximum inrush.
Calculate selection inrush
VA in one of the following two ways:
Selection inrush VA =
Square root of [(VA
sealed)2 + (VA inrush)2]
Alternative Method
VA sealed + VA inrush =
Selection inrush
Method
B will result in a slightly oversized transformer.
If your line voltage varies 10% or more, contact
Technical
Services for assistance.
From
Chart A, select
the transformer type needed from the "Transformer VA
Rating" column. Check to be sure that the nameplate VA rating
exceeds the sealed VA of the control circuit calculated in Step 1.
If it does not, select a larger transformer VA that exceeds the
circuit sealed VA.
By
following the above procedure, the secondary voltage delivered by
the transformer will be 90% of the nameplate secondary voltage under
maximum inrush conditions at rated input voltage.
Now refer to the Selection Tables for
the style you have chosen. Select your transformer according to
your required voltage and VA capacity. By following the above procedure,
the secondary voltage delivered by the transformer will be 90% of
the nameplate secondary voltage under maximum inrush conditions
at rated input voltage. You can also use our online
transformer selector to help you select the right transformer.
Chart
A: Regulation Data - Inrush VA at 20% and 40%
Power Factor
Selection
Inrush VA*
Transformer
VA Rating
Type
SBE
Type
SMT
20%
PF**
40%
PF**
20%
PF**
40%
PF**
294
207
N/A
N/A
50
515
363
N/A
N/A
75
696
490
N/A
N/A
100
1362
959
N/A
N/A
150
2131
1501
N/A
N/A
200
2883
2031
N/A
N/A
250
3608
2541
N/A
N/A
300
4777
3364
N/A
N/A
350
7601
5353
N/A
N/A
500
12939
9112
N/A
N/A
750
18703
13171
8277
5829
1000
23814
16066
17182
12100
1500
34586
24356
22834
16080
2000
45633
32770
34506
24300
3000
15800
111000
71284
50200
5000
* Assuming
the transformer is to deliver a minimum of 90% secondary voltage
during inrush conditions.
Industrial Control Transformers