STAR-DELTA Type Starter

5.6 ELECTRICAL SYSTEM (Continued)

By use of the Star-Delta type starter, the compressor motor can be started and accelerated using a greatly reduced “inrush” electric current. The starter is completely automatic and controlled by the Intellisys controller. Refer to the Electrical Schematic 8.1 in Section 8.0.

5.7 STEPPER MOTOR INLET CONTROL

The inlet valve is opened and closed by a stepper motor mounted on the inlet valve. The Intellisys controller regulates the stepper motor to precisely position the inlet valve based upon the demand of the plant air system (See Section 5.8).

The stepper motor is maintenance free. Bearings are lubricated at the factory and sealed for life.

No adjustment of the stepper motor/inlet valve system is required.

5.8 CAPACITY CONTROL

The SSR compressor is supplied, as standard equipment, with three operator selectable capacity control systems, each designed for different plant air requirements:

—MOD/ACS (Modulation/Automatic Control Selector)

—On-Off Line

—Modulation Only

The desired control is selected at the Intellisys control panel (See Section 3.0).

AUTOMATIC UNLOADED START

The compressor will always start in the unload mode. When unloaded, the inlet valve is nearly closed, the blowdown solenoid valve is open (tank vented), and the compressor is operating at minimum power. The Intellisys will open the inlet valve slightly to maintain the proper sump pressure to ensure positive coolant flow and smooth, quiet operation. When the injected coolant temperature is less than 120°F (49°C), a separator (sump) pressure of 45-50 psig (3.1 - 3.4 bar) will be maintained. When the injected coolant temperature is above 120°F (49°C), a receiver pressure of 24-33 psig (1.7 - 2.3 bar) will be maintained. The minimum pressure check valve will prevent any backflow of air from the plant air system during unloaded operation.

ON-OFF LINE CONTROL

For those plants which have a widely varying air demand, on-off line control will deliver air at full capacity (compressor maximum efficiency condition) or will operate at zero capacity (compressor minimum power condition). The compressor is controlled by the Intellisys, responding to changes in plant air pressure. The Intellisys/stepper motor opens the inlet valve and closes the blowdown valve (3SV) whenever plant air pressure drops below the on-line pressure set point. The compressor will then operate to deliver full capacity air to the plant system. If the plant air system pressure rises to the off-line set point of the Intellisys, the inlet valve closes and the blowdown solenoid valve opens the separator vent line, allowing separator pressure to drop. The compressor will continue to run with minimum power draw.

MODULATION/ACS CONTROL

For those plants which have relatively high, constant air-demand relative to the compressor capacity, the recommended control mode is modulation.

The modulation control system retains the features of on-off line control, but provides for throttling of the inlet flow up to the modulation off line air pressure set point.

The throttling position of the inlet valve is controlled by the Intellisys, allowing the stepper motor to “trim” the inlet valve position as dictated by the line pressure.

The modulating pressure range is 10 psig (.7 bar). Modulation begins when the line pressure reaches the maximum modulation pressure setting minus 10 psig (.7 bar) and continues as/if the line pressure rises. Modulation becomes stable when the compressor output equals the plant air demand. When the modulation is at the maximum modulation pressure setting the maximum capacity reduction will be down to approximately 60 percent of the compressor rated capacity. If the air demand has decreased to a level below the 60 percent modulated output, the line pressure will increase slightly to actuate the Intellisys, unloading the compressor and venting the separator.