Motor speed drives

Three good reasons to install MOTOR SPEED DRIVES

First, Motor Speed Drives will lower and may possibly eliminate your utility demand charges because they offer built-in soft-start capabilities. This means there will be no inrush current and no voltage sag effect on the rest of the system.

Secondly, we install Drives of the Pulse Width Modulation (PWM) type only, with a diode converter front-end. By installing Drives of the PWM type only, the Displacement Power Factor is high (commonly > 95 % at rated load) and more or less constant throughout the range. This means that drives can reduce energy usage and correct for DPF at the same time. It’s a good thing too, because drives and PF correction capacitors don’t mix. Caps are vulnerable to the higher frequency harmonic currents generated by drives, since their impedance decreases as frequency increases.

Third, Significant electrical energy savings.

Even a small reduction in speed can give significant savings. For instance, a centrifugal pump or fan running at 80% speed consumes only half of the energy compared to one running at full speed.

How to cut energy consumption by nearly 50%

A centrifugal pump or fan running at half speed consumes only one-eighth of the energy compared to one running at full speed. This is because the torque needed to run a pump or fan is the square of the volume. For instance, reducing the pump speed to 80% only requires 64% of the torque (0.8x0.8). Furthermore, to produce 64% of the torque only requires 51% of the power (0.64x0.8), as the power requirement is reduced in the same way.

The explanation for this lies in the pressure difference across the impeller. When less pressure is produced, less acceleration of air or fluid across the impeller is required. It is the simultaneous reduction of acceleration and pressure that multiplies the savings.

High efficiency
Comparing energy consumption of various mechanical and electrical airflow control methods of a typical centrifugal fan reveals that: At 80% airflow, the energy consumption is: 97% of maximum with damper control; and 76% of maximum using guide vanes; but only 51% using motor speed drives. The difference between these figures represents wasted energy.

Low motor losses
The voltage to frequency ratio is automatically adjusted to achieve optimum current for pump and fan loads. This minimizes motor losses and reduces motor noise.

Low running costs
With 50% airflow, the commonly used guide vane system results in the fan motor using over three times the energy (kWh) of a motor controlled by a variable speed drive. These extra running costs, compared to inverter control, are a powerful argument in favor of selecting a variable speed drive.

We install Line Reactors on the line side (Input) as well as the load side (Output).

Input line reactors protect the AC drive from transient overvoltage conditions, typically

caused by utility capacitor switching. The input line reactor also reduces the harmonics

associated with AC drives.

Output line reactors protect the motor insulation against AC drive short circuits and

IGBT reflective wave damage, and also “smooth” the motor current waveform, allowing

the motor to run cooler.