Inverter Selection

The inverter is a commercial item not manufactured by TCD Systems. TCD Systems has presently selected the Mitsubishi FR-S500 series inverter if an inverter is ordered with a system. However, most sales are control cards only and the customer purchases locally available inverters and does the wiring in plant.

Virtually all inverters now meet minimum requirements to operate with the Synphase system. If selecting a new brand of inverter, confirm its adaptability using the following list.

  • Input Power Is Compatible:
    The inverter must be able to use the incoming 3-phase power available in the factory. This is typically between 230 VAC 50 Hz and 500 VAC 60 Hz. In some cases, low line voltage may cause the inverter to “under voltage trip”. This condition is especially probable if the mains voltage is constantly near the low end of the inverter’s acceptable range. A simple and inexpensive fix is to insert 2 low power single-phase boost transformers wired for 5% or 10%.
  • Voltage Output Power Must Match The Motor:
    The inverter must have an output capable of driving the motor to which it is attached. The inverter’s Volts/Hertz adjustments can be used to match any motor type.
  • Amount of Output Power (HorsePower):
    A synchronous motor will consume much higher currents than the same HP induction motor. Select an inverter based on current ratings instead of HP ratings if using a synchronous motor. If the motor is driving an oscillating load (like a cam) it is possible that a mains voltage dip occurring at the same time as heaviest torque requirement may cause the inverter to “low voltage trip”. Select an inverter 1 size larger than the motor requirement because the greater capacitance on its DC buss will help ride through this situation. It will also allow the inverter to be used in hotter environments, as the ripple current in the DC buss capacitor bank will be reduced by ½.
  • 0-10 Volt Input Signal Compatible:
    The inverter must be capable of accepting a speed reference command of 0-10 volts to control output between 0-90 hertz. The input resolution must be 8 bits (½ %) or better. 12 bits is recommended.
  • Acceleration / Deceleration Rates = 2 sec. or less
    (0.5 sec. is desirable).
  • Start / Stop Switches:
    Is the selected inverter capable of utilizing the start/stop switches selected for your factory? Most inverters are.
  • Heritage Systems:
    For older Synphase systems, the inverter must have a dry contact output that will switch from open to short when the inverter is running. Newer Synphase cards without the terminals for this connection do not require this option.
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Inverter Selection.pdf

Inverter Installation

Factors to be considered when selecting a location and method of installing the inverters includes the following:

  • Temperature (Location):
    Hot air rises. The temperature at catwalk level is hotter than at floor level. Keep all inverters near floor level.
  • Temperature (Radiant Heat):
    Check for direct radiation heating as well as the ambient air temperature in the proposed mounting area. If the inverters must be mounted near a conveyor where hot ware is only a few feet away, consider a heat shield to prevent direct radiation.
  • Temperature (Mounting Inside Another Enclosure):
    Inverters do NOT need to be installed in an air-conditioned room. With a few common sense precautions, they can be mounted directly on the factory floor. Also, choosing the next larger HP inverter for the motor being driven allows operation on the derated end of the temperature graph (higher ambient temperature). If you decide to mount the inverter inside another enclosure, you must consider the heat dumped into that enclosure by the inverter and the subsequent ambient temperature rise inside the enclosure.
    Note: TCD Systems has chosen a design that mounts the inverter ½ inside and ½ outside an enclosure. By placing the inverter’s heat sink outside the enclosure, the ambient rise inside the enclosure is minimized.
  • Environmental Rating:
    If you intend to mount the inverter on a rack or wall in the production area, consider using a NEMA 12 (gasketed) inverter. Mounting the inverter inside another enclosure in the production area or in an air-conditioned room allows the use of a NEMA 1 or chassis style inverter.
    Note: As most air born contamination is suspended in the air, an enclosure with openings in the bottom is satisfactory. As long as the air inside the enclosure is stagnant (especially NO fan) it need not be gasketed.
  • Wiring the Inverter to the Motor:
    It is almost impossible to purchase an inverter that does not use IGBTs as output drivers to the motor. Because of their rapid turn on/off switching characteristics, internal heating (and thus size and cooling problems) have vastly improved compared to inverters available in the 1990’s. However, this rapid switching does come with a down side. The high frequencies generated can cause voltage doubling in improperly terminated wires to the motor. Keeping the motor leads 300 feet (100 meters) or less allows this problem to be ignored. It does however prevent you from installing the inverters too far from the production area.
  • Wire Selection:
    Some of the motor lead wiring is in high temperature areas, high temperature wiring is generally used to connect the inverters to the motors. If FEP (Teflon coated) wire is used and if it is pulled through rigid conduit, microscopic cracks can develop in the Teflon insulation. Although these cracks do not show up when a sine wave meggar is used for testing, any water condensing in the conduit will find its way into these microscopic cracks and appear as a high frequency (MHz) short circuit. The inverter will “ground fault trip”. A glass braided insulation wire should have the glass braid stripped an additional 1 inch (2 cm) more that the underlying insulation to prevent the same problem caused by wicking of moisture.
  • Wiring Synphase Control Card to Inverter:
    There is only one connection between the Synphase card and the inverter, the 0-10 volt speed reference command. Use a twisted shielded 2-conductor wire and connect the shield to the negative terminal of the inverters 0-10 volt input. Wire size is not important as current is minimal. Do not exceed the inverter manufacturer’s recommendation for length of wire (usually around 10 feet or 3 meters).
  • Wiring Start/Stop Switches:
    If you decide to use separate switches to start or stop the motor instead of the switches on the inverter’s front panel, wire them according to the inverter manufacturer’s instructions.
    Note: There is no connection of this function to the Synphase card. The Synphase logic determines motor run status by observing the tachometer attached to the motor.
  • Additional Devices:
    Local codes vary. Branch circuit protection and motor disconnect devices are the responsibility of the plant.
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Inverter Installation.pdf
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