High-voltage starters with microprocessor control 

(voltage regulators)
with capacity of 1.6-3.15MW
 
 
Application
High-voltage starters ВПУ (VPU) on the basis of three-phase high-voltage thyristor voltage regulators are applied for cushion start of high-voltage AC motors in electric drives with ventilatory character of load.
Application of high-voltage starters allows removing restrictions to the number of motor starts during service-time almost entirely. The possibility of ВПУ usage for random (successive) start of uniform electric drives should be mentioned particularly. For example, its application to start compressor station units. Step-by-step adjustment of the efficiency of the whole station is provided with the help of successive activation of units.
Actuation of powerful fans, compressors or pumps with application of ВПУ results in less negative impacts that are typical for the direct start.
ВПУ devices have low cost and small dimensions compared to standard converters, when using them asstarters. It results in minimal payback period with their implementation.
 
Specifications
The power circuit of ВПУ is the combination of anti-parallel coupled thyristors that are connected to each of the three phases of a motor (Fig. 1).
ВПУ devices are supplied with a microprocessor control system that allows implementing more sophisticated algorithms of control over ВПУ.
ВПУ devices used for AC motor control provide:
  • smooth start of a motor with adjustable rate of speed change;
  • smooth stop of a motor with adjustable rate of speed change;
  • decrease of losses in a motor when unloading;
  • limitation of starting currents in the supply network;
  • increase of motor service life due to the substantial decrease of electrodynamic efforts in motors windings when starting;
  • increase in the quality of synchronization of synchronous motors and their re-synchronization after disappearance and subsequent recovery of the supply voltage;
  • increase in service life of switching equipment.
Advantages of ВПУ devices:
  • substantial decrease in  motor starting current (2-4 times);
  • considerable decrease in dynamic loads on motor bearings and kinematics of actuating mechanisms (5-7 times);
  • decrease in voltage dips in the supply network when starting a motor;
  • improvement of operation conditions of electrical equipment;
  • decrease in energy losses in electrical equipment when activating motors;
  • increase in allowable number of starts and energy saving due to the rational use of energy-consuming equipment;
  • increase in reliability and service life of equipment.

The highest economic effect is reached implementing the smooth start system for a group of high-voltage motors. The cost of ВПУ with vacuum circuit-breakers and disconnecting switches is several times lower than the cost of a similar system with a variable-frequency converter. The pay-back period is up to one year.

 
Fig. 1. Functional diagram of ВПУ
(РТ – current regulator, СИФУ – system of pulse-phase control)
 

Performance specification:

nominal line voltage of the supply network, kV
6
supply network frequency, Hz
50±2%
nominal line voltage of auxiliary power supply, V
380
maximum starting current, % of the nominal current
400
maximum duration of starting current flow, sec
30
range of regulation of starting current flow duration, sec
from 1 to 30
allowable number of starts (provided that the current flow equals to 4Inom and there is a 15-minute interval between starts)
unlimited
regulation range of starting current, %
from 100 up to 400
 
The cooling of ВПУ with capacity of 1; 1.6; 2; 3.15MW is air, forced.
The overall dimensions (LxBxH) for all modifications, mm – 1400x1000x2000.
ВПУ modifications are given in the Table 1.
 
Table 1.
 

Name

Nominal voltage, kV

Nominal capacity, kW

 ВПУ – 6/1

6

1000

 ВПУ – 6/1,6

6

1600

 ВПУ – 6/2

6

2000

 ВПУ – 6/3,15

6

3150

 ВПУ – 6/5

6

5000

 ВПУ – 10/2

10

2000

 ВПУ – 10/3

10

3150

 ВПУ – 10/5

10

5000

 ВПУ – 10/8

10

8000

 ВПУ – 10/12,5

10

12500

 
Thyristor voltage regulator functioning
Thyristor voltage regulator functioning is illustrated in the Fig. 2, where:
M – torque characteristic of an asynchronous (at start – synchronous) motor during start with constant voltage on stator terminals;
MC – resistance torque of mechanism load as a function of speed;
M1 –motor torque for mechanism speed-up with the preset pace;
I – starting current of a stator with constant voltage on stator terminals;
I1 – starting current required for starting moment M1.
 
Fig.2
 
From the Figure 2 it is obvious that the efficiency of the thyristor voltage regulators is high when the required motor moment for the preset start type is considerably lower than the moment reached by a motor when connected directly to the supply network.