Introduction:
10% of the electrical energy used by industry is used to drive air compressors.
Compressed air is ten times the cost of electricity. With traditional systems
precise & efficient air control can not possible. Typical loading of the
compressor is 70-80% of the rated capacity.
Traditional compressor system:
Star-Delta starters are used to start & drive the compressor motors. Once
the compressor starts it start dumping the air in air storage tank from
where the air is supplied to the outside shop floor. Return line from the
outlet of the tank is taken to the compressor differential air controlling
pressure switch as a feedback. Pressure switch monitors the outlet air
pressure from the tank. Pressure switch has differential pressure setting
where user can set the range as per his requirement. Depending upon the
pressure switch setting, valve mounted in the airline from compressor to
air tank gets activate or deactivate & start or stop the airflow to the
air tank. As this is open loop system it wait for loading the compressor
till the outlet pressure doesn’t falls below the preset loading point. If
the air demand from shop suddenly increases, pressure level in tank suddenly
falls down, when it falls below the preset lower limit compressor goes on
loading & start dumping the air in tank. As the compress or loading Time is
comparably more, required air pressure cannot maintain. Also during compressor
no load condition motor run with rated speed, it is unnecessary wastage of energy.
Our solution to overcome the drawbacks of old system:
Purpose of this system is to maintain the precise & efficient air
pressure in the outlet pipe of the compressor & maintain the low
motor RPM during no load conditions. This system consists of 2
compressors that is one is of 37kw and second is of 45kw out of
which one is running on VFD continuously & other is running on
star-delta as per customer choice, which is to be selected manually
by a change over switch on panel. Pressure transmitter is connected
at the outlet pipe giving the true feedback of the air pressure passing to the field.
Set-up for the system:
VLT 5000 series ac drive with 160% overload torque operating in closed loop
for automatic speed controlling of the compressor with respect to the air
pressure feedback from the pressure transmitter that is connected to the
outlet pipe of the air tank, And the other is on stand by or can be run
on star-delta. Pressure meter and RPM meter provided on panel to show the
status of the out going air pressure and RPM of the motor to operator.
10 turn POT for required air pressure set point for PID.
Operating sequence:
By making the panel mains supply ON the drive gets power on and the start command
to the drive gets from the relay that is activated from the NC contact of existing
star delta contactor of same compressor. (when to run the compressor on VFD the
star-delta of the same compressor should be off.). After getting the start command
to the drive, compressor pump starts running, internal PID of drive check the
present air pressure in pipe & base on that it decides the RPM of the motor to
be maintain.
