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17. Precautions when using transformer load
Transformer usage objective
1) To match voltage when heater voltage differs from power supply voltage.
2) When it is necessary to insulate the heater circuit from the power supply.
3) To raise ground voltage resistance using a compound transformer when ground insulation deteriorates like vacuum equipment.
17-1. Control type
Transformer load can be used for phase control.
A transformer load cannot be used for cycle calculation zero voltage switching control.
17-2. Transformer magnetic flux density
Excessive current flows when the magnetic circuit becomes saturated when using the transformer (load is limited to transformer winding resistance)
and could destroy the thyristor. With thyristor control, the thyristor is switched (OFF/ON) each half cycle. If the load becomes heavy, the output waveform
tends to become unbalanced and saturated. You should therefore design the system so that magnetic flux density is lower than that of a conventional
transformer.
CAUTION
The applicable transformer is as follows:
Applicable transformer: Isolation transformer (double wound transformer)
Inapplicable single phase transformer: Single wound transformer (slide transformer, etc.)
The secondary side of applicable transformers must, however, be connected to resistance load (power factor 0.8
–
1.0).
Do not connect any equipment between the device and transformer.
Cut off the power supply before replacing the tap of the transformer.
17-3. If using electromagnetic switch (contactor)
If using an electromagnetic switch (contactor) for a circuit connected to the transformer (inductive load), malfunction could result from contact bounce.
If so, you should either use the prescribed noise filter, or connect an X capacitor (0.1
–
0.5
μF)
between the R and U power supply side terminals of
the thyristor, or a Y capacitor (1000
–
3300 pF) between the R and U power supply side terminals and the ground to absorb the noise.
17-4. Rapid fuse usage
We recommend a rapid fuse to protect the thyristor device from excessive current produced when using a transformer due to high frequency wave
noise or load trouble, etc.
See
‘
19-1. Rapid fuse (sold separately).
’
17-5. Prohibition of operating without load
Before conducting operation whereby a load cannot be connected such as test operation, disconnect the transformer wiring and connect a dummy
load such as an electric heater or light bulb. Do not operate the device without a transformer load.
Do not switch loads while the device is powered. Operating without a load may damage the thyristor device.
Note: If using a single heater and it becomes broken, then the device would be operating without a load.
18. Parameter setting function
You can display various setting values, output values, control input
values and settings by connecting with a computer via a
separately-sold PAC communication adapter (S5009).
Note: This device (PAC18A) is not supported by up to PAC
communication adapter (S5009) software version 1.20.
Power
supply
Load
(heater)
Transformer
Electromagnetic
switch
PAC18A
R
U
X capacitor
(0.1 - 0.5
䃛
F)
Y capacitor
(1000 - 3300pF)
