Product Overview

Industrial Control Power Transformers
10/3
Siemens ICP · 2011
Transformer Selection Process
Selecting a transformer for industrial
control circuit applications requires
knowledge of the following terms:
Inrush VA is the product of load volt-
age (V) multiplied by the current (A) that
is required during circuit start-up. It
is calculated by adding the inrush VA
requirements of all devices (contactors,
timers, relays, pilot lights, solenoids,
etc.), which will be energized together.
Inrush VA requirements are best
obtained from the component
manufacturer.
Sealed VA is the product of load
voltage (V) multiplied by the current (A)
that is required to operate the circuit
after initial start-up or under normal
operating conditions. It is calculated by
adding the sealed VA requirements of
all electrical components of the circuit
that will be energized at any given
time. Sealed VA requirements are best
obtained from the component manufac-
turer. Sealed VA is also referred to as
steady state VA.
Primary Voltage is the voltage avail-
able from the electrical distribution sys-
tem and its operational frequency,
which is connected to the transformer
supply voltage terminals.
Secondary Voltage is the voltage
required for load operation which is
connected to the transformer load
voltage terminals.
Primary Fuse Kit
In addition to factory installed secondary
fusing, Siemens offers a primary fuse
kit for class MT transformers Size
50–750 VA for field installation. The
primary fuse kit includes a 2-pole class
CC fuse block, instructions and all
associated mounting and wiring
hardware. Additionally, this fuse kit
will fit most competitors’ units. To
order this kit, use catalog number
KCCFPX2R. The primary fuse kit,
when installed, will add a maximum of
0.69 in. (18 mm) to the transformer “A”
dimension and 1.94 in. (49 mm) to the
“C” dimension.
Primary Fuse Kit Installation—Class MT Transformer with Primary Fuse Kit, KCCFPX2R
Fuse Clip Kit KCCFPX2R
Once the circuit variables have been determined, transformer selection is a simple
5-step process as follows:
1. Determine the Application Inrush VA by using the following industry accepted formula:
Application Inrush VA =
3
(Inrush VA)
2
ѿ (Sealed VA)
2
2. Refer to the Regulation Chart. If the primary voltage is basically stable and does
not vary by more than 5% from nominal, the 90% secondary voltage column
should be used. If the primary voltage varies between 5% and 10% of nominal,
the 95% secondary voltage column should be used.
3. After determining the proper secondary voltage column, read down until a value
equal to or greater than the Application Inrush VA is found. In no case should a
figure less than the Application Inrush VA be used.
4. Read left to the Transformer VA Rating column to determine the proper
transformer for this application. As a final check, make sure that the Transformer
VA Rating is equal to or greater than the total sealed requirements. If not, select
a transformer with a VA rating equal to or greater than the total sealed VA.
5. Refer to the following pages to determine the proper catalog number based
on the transformer VA, and primary and secondary voltage requirements.
Regulation Data Chart
——————————–
To comply with NEMA standards, which require all magnetic devices to operate successfully at 85% of rated voltage, the
90% secondary voltage column is most often used in selecting a transformer.

For units with Class 105°C insulation systems.

For units with Class 180°C insulation systems.
Inrush VA At 20% Power Factor
NEMA/IEC NEMA/IEC NEMA/IEC
Transformer 95% Sec 90% Sec 85% Sec
VA Ratings Voltage Voltage Voltage
25 100/––– 130/––– 150/–––
50 170/190 200/220 240/270
75 310/350 410/460 540/600
100 370/410 540/600 730/810
150 780/860 930/1030 1150/1270
200 810/900 1150/1270 1450/1600
250 1400/1540 1900/2090 2300/2530
300 1900/2090 2700/2970 3850/4240
350 3100/3410 3650/4020 4800/5280
500 4000/4400 5300/5830 7000/7700
750 8300/9130 11000/12100 14000/15400
1000

15000/––– 21000/––– 27000/–––
1000

9000/––– 13000/––– 18500/–––
1500 10500/––– 15000/––– 205000/–––
2000 17000/––– 25500/––– 34000/–––
3000 24000/––– 36000/––– 47500/–––
5000 55000/––– 92500/––– 115000/–––
Class MT, MTG
General
ICP_2010_10_2_012810Edit_ab.fm Page 3 Tuesday, September 20, 2011 8:44 AM