Smooth start systems
Smooth start and frequency regulation devices
"NG-Energo" develops, produces and supplies to a customer the alternating and direct current starters. They include:
1. Smooth start devices for asynchronous motors.
2. Rotation frequency regulators for asynchronous motors.
The range of the said devices ensures the performance of these functions for electric drives of up to 1200 kW, 400 V and 5 MW, 6.3 kV with respect to the following types of equipment:
- Centrifugal mechanisms;
- Pumps;
- Ventilators and air-conditioning units;
- Compressors;
- Conveyors;
- Crushers;
- Lifting and transporting equipment;
- Filling and packing equipment, etc.
Smooth start system
Smooth start system is an SCR switching device (voltage regulator), ensuring the smooth start and the shutdown of three-phase cage asynchronous motors. It combines the functions of a smooth start and stop, mechanism and engine protection, as well as connection to automation systems.
A smooth start system ensures:
- The possibility of starting large consumers in situations of limited capacity of electric power sources;
- Energy resources economy;
- Decreasing the impact of starting engines to the electric network due to limited current rushes and voltage dropouts in the network.
The entire range of starters is divided into dimension types depending on the operation mode - normal or heavy.
A smooth start system is supplied ready to use, to be applied regularly in accordance with the engine protection class.
The system has a built-in terminal, allowing to rearrange the programmable functions, settings and guards in order to adjust to the electric drive application conditions.
Performed functions:
- Controlling the start and slowdown moment according to the given algorithm.
- The possibility to use a bypassing contactor shunting the voltage regulator after the start is completed with the support of electronic guards.
- The engine heat protection.
- Starting time control.
- Controlling current values of controlled parameters.
- Protecting from underload and overload in the established mode.
- A built-in self-control, etc.
Within the limits of the starter capacity, a parallel connection of engines is allowed, while the total current of connected engines must be lower than the rated current of the starter selected in the application type function.
A smooth start system can work with the wound rotor engine, whose rotor chain resistance is fully or partially short-circuited. In this case the starting moment depends on the value of this resistance.
In this case, when the engine is started, in order to gain moment necessary to overcome the load resistance moment, the resistance in the rotor chain must be partially short-circuited. The wound rotor engine with a short-circuited rotor winding has a very weak starting moment and in order to gain a sufficient starting moment, strong current of a stator winding is needed. In this case the starter of a larger dimension type is selected in order to have the clamping current equal to 700 % of the rated current.
Application range
The table gives example applications of devices depending on their starting characteristics, classified in accordance with the mechanism type as normal or heavy operation mode.
| Mechanism type | Operation mode | Functions realized by a smooth start system | Starting time (sec) |
| Centrifugal pump | Normal | Slowing down (reducing hydraulic impact). |
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| Preventing underload and change in the order of phase alternation. |
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| Piston pump | Normal | Controlling the pump failure and rotation direction |
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| Ventilator | Normal | Determining overload due to passages plugging, or underload (kinematic connection to the engine, ventilator fault). |
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| Heavy, if > 30 sec | Braking torque when stopping |
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| Refrigerant compressor | Normal | Protection for special engines |
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| Screw compressor | Normal | Preventing change in the order of phase alternation. |
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| Contact for automatic unloading. |
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| Centrifugal compressor | Normal | Preventing change in the order of phase alternation. |
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| Heavy, if > 30 sec | Contact for automatic unloading. |
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| Piston compressor | Normal | Preventing change in the order of phase alternation. |
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| Contact for automatic unloading. |
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| Conveyor, transporter | Normal | Controlling overload in case of faults or underload in case of a tape breakage |
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| Screw jack | Normal | Controlling overload in case of faults or underload in case of a breakage |
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| Lifter | Normal | Controlling overload in case of jamming or underload in case of a breakage |
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| Elevator | Normal | Controlling overload in case of jamming or underload in case of a breakage |
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| Permanent acceleration in case of load changing. |
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| Circular saw, band saw | Normal, Heavy, if > 30 sec | Braking for quick stop |
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