Soft Starter Characteristics

Smoother control – unique to Moeller

[picture of DM4 Soft Starters] The conveyor belt starts without vibrations and operates smoothly using both the DS4 and DS6 soft starters. The asymmetrical trigger control developed and patented (PCT/EP00/12938, 19.12.2000) by Moeller makes it possible. It avoids DC components which normally result on a two-phase controlled soft starter (see diagram below). They suppress the formation of an elliptical rotating field, which leads to an irregular acceleration of the motor and which unnecessarily extends acceleration times. With the devices of the DS4 and DS6 series the start with asymmetrical trigger control is active in the start phase, with DS4-340-...-M(R) in uninterrupted operation also.

Current characteristic in the uncontrolled phase

[graph of current characteristic]
Conventional methods:
Symmetrical control with high level of DC components

New process from Moeller:
Asymmetric control without DC components

Motor voltage – softer start

[graph of motor voltage]
With a soft starter the motor voltage is reduced by phase angle variation and increased to the value of the mains voltage from an adjustable start voltage (U_START) within a preselected ramp time t_START. The soft run up and run down protects the coupled mechanical parts from abrupt loading, and avoids current peaks and voltage dips on the electrical power network.

1 DOL start · 2 Star-delta start · 3 Soft start

Motor current – dampened peaks

[graph of motor current]
More and more electrical power supply companies demand conformity to defined current limit values. The loading of networks caused by high inrush currents should be avoided with DOL starting, or current peaks should be avoided with star-delta start, in order to prevent unwanted side-effects, such as voltage dips. The adjustable current limitation of the soft starter is the ideal solution here.

1 DOL start · 2 Star-delta start · 3 Soft start

Motor torque – reduced loading

[graph of motor torque]
During switch-on, fluctuations in the current and voltage cause problems on the power network. The resulting abrupt divergences in torque cause stress for your machines. It leads to higher maintenance costs and effort, and influences the quality of production. These disadvantages can be minimised by using a soft starter. It guarantees a more gentle torque progression and reduces your operating cost expenditure.

1 DOL start · 2 Star-delta start · 3 Soft start

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This page last updated: 7 September 2007