Soft Starters in Ukraine: Overview and Features
Soft starters (devices for smooth starting) are used significantly more frequently in Ukraine than in European countries. This is related to the fact that frequency drives, which are popular in Europe, have a high cost that may be inaccessible for many consumers. Thus, in Ukraine, the majority prefer devices with a lower cost.
Functions of Soft Starters
Soft starters perform a number of important functions:
- They do not regulate the speed of asynchronous motors;
- They do not provide smooth acceleration or braking;
- They do not compensate for reactive power consumed by asynchronous units.
Limiting Starting Currents
The primary purpose of soft starters is to limit the starting currents of asynchronous machines. This helps to reduce the negative effects of abruptly connecting electric motors to the network.
Types of Soft Starters
Soft starters can have various technical characteristics and parameters:
- Models with control over 2 phases;
- Models with control over 3 phases.
Some soft starters come equipped with a bypass contactor, while others do not. In cases where the start of the asynchronous machine lasts from several seconds to a couple of dozen, smooth starting may not be necessary.
Losses and Heat Transfer
An important point is that losses occur in thyristors, with an average value of 1.5 W per 1 A for one phase. When controlling over 2 phases, losses increase to 3 W, and with 3 phases, it goes up to 4.5 W per 1 A. For example, if the motor current is 100 A, the losses can reach up to 450 W, necessitating heat dissipation.
For this, thyristors are mounted on radiators that have appropriate geometric parameters to ensure effective heat dissipation.
Bypass in Soft Starters
Soft starters with a capacity of 7 to 110 kW are usually equipped with built-in bypasses. This is due to the need to ensure the proper operation of the device when connected to the network.
Devices with a capacity of over 110 kW are often supplied without a bypass element. This is related to the high cost of contactors, which can be more expensive than the soft starter itself. Therefore, manufacturers allow users to decide whether a bypass is needed or not.
Some manufacturers offer starting devices with a capacity of over 110 kW that come with contactors. However, these devices must be equipped with bypass elements for correct operation.