Thyristor exciter ВТСД for synchronous motors

The thyristor exciter ВТСД–ХХХ–ХХХУХЛ4 is designed to supply an excitation winding, control the field current of synchronous motors during mains direct or reactance start; to operate as a part of variable-frequency drives on the basis of a voltage inverter or per ac converter-fed motor circuit, and also as a part of reduced-current start systems for synchronous motors together with starters. It provides operation and protection of an electric motor in synchronous, transient and emergency modes.
 
1. Notation
 
 
2. Technical characteristics
 
Nominal linear voltage, V
380
Mains frequency, Hz
50 ± 2 %
Nominal excitation current, A
20;320; 500
Nominal excitation voltage, V
50 - 230
Nominal auxiliaries voltage, V
380
Current forcing coefficient
2
Cooling
natural
Operation mode
irreversible
Cubicle protection level
IР21
Dimensions (L x B x H), mm
600 х 600 х 1800
Weight, kg
350
 
The cubicle of unilateral maintenance.
 
3. Operation conditions
 
The thyristor exciter is designed for operation at the ambient temperature of +1°С up to 40°С.
Relative humidity – no more than 80% at the temperature +20°С.
With respect to the content of corrosive agents the device can operate in the atmosphere of the type II as per GOST 12150-69.
Concentration of non-conductive dust – no more than 0.2 mg/m3.
Operating conditions group regarding mechanical stress – M2.
Sea level – up to 1000m.
Inclination – not to exceed 5° out of perpendicular.
Free space of no less than 200mm from the side-walls of the cubicle is required.
 
4. Design
 
Structurally the thyristor exciter ВТСД is a metal cubicle of unilateral maintenance (See Fig.1) comprising: power wafer thyristors with coolers of the type O153, power switching units and auxiliary transformers, elements of power signal, control and measurement instruments, control system units, an exciter’s valve part, relay equipment.
Cooling of thyristors – air, natural due to convective streams inside the cubicle.
 
Figure 1. Mounting dimensions for ВТСД–ХХХ–ХХХУХЛ4
 
5. Description
 
The thyristor exciter is designed for continuous operation. The supply voltage of the thyristor exciter – alternating three-phase 380 V, 50 Hz. The output voltage – direct, variable. The nominal rectified current – 20; 320; 500 A.
The thyristor exciter provides direct (reactor) start of a motor as well as smooth start from a starter, frequency start from a frequency converter or quasi-frequency start from a thyristor voltage regulator.
During start/stop of a synchronous motor the thyristor exciter provides:
  • automatic determination of the point when the motor achieves the subsynchronous speed and excitation feeding in the function of stator current or motor slip;
  • starting forcing of the excitation current to provide secure pulling into synchronism;
  • field suppression at motor trips transferring the converter to the inverter mode.
 
With a motor operating from the mains and supplied excitation the following modes of excitation current control are provided depending on the selected operation mode (“Manual/Automatic”):
  • manual setup of excitation and its stabilization on the preset level;
  • base and peak limiting of the excitation current;
  • supply of the forced voltage and current in case of voltage sags;
  • automatic control in the mode of automatic excitation regulator (АРВ mode) with an option to maintain preset values for the excitation current, active and reactive power, cosφ, stator’s voltage;
  • limitation of the excitation current in case of time-current overload;
  • protection of a synchronous motor in emergency operation modes;
  • process protection according to external contact signals.
 
The thyristor exciter provides continuous measurement of the resistance to ground of the excitation winding and the temperature of excitation windings of a motor.
When the power voltage of 380V is given the control system runs automatic self-diagnostic test and checks the power circuits of the exciter. If the result of the control test is positive an on-off signal indicating availability for service is given.
The thyristor exciter provides the following types of protection:
  • output maximum protection – detecting when the excitation current exceeds the set value: 0…2IH for regular operation and (0…3)IH for excitation forcing;
  • input maximum protection – detecting if line currents exceed the set value: 0…3IH for regular operation and (0…3,5)IH for excitation forcing;
  • insulation fault;
  • emergency shutdown;
  • lack of power voltage (of one or several phases);
  • incorrect phase sequence;
  • lack of synchronization to line;
  • supply unit failure;
  • thermal protection (I-IH)∙t. The actuation setting value is programmable;
  • prolonged start. The starting time (0…60 sec) is programmable. If phase currents of a synchronous motor aren’t reduced during the given time limit the start is considered as unsuccessful;
  • field interruption or decrease of the excitation current;
  • protection from asynchronous operation;
  • protection from shut-offs when feeding excitation;
  • unsuccessful exciter run-up;
  • failures in operation of the control system;
  • external emergencies.
 
The control and display panel (ПУ) is placed on the door of the exciter’s cubicle and is supplied with a keyboard to enter parameters, control and display preset and actual parameters for operation of the exciter and motor.
The control and display panel shows:
  • data on exciter’s operation mode;
  • data on motor’s operation mode;
  • results of the availability-for-service tests;
  • causes of emergency shutdowns of the exciter.
 
The software and memory capacity of the master controller allows of archiving data about the operation mode of the exciter and motor, and also of resolving issues connected with additional requirements for control, regulation and diagnostics of the processes in a motor and drive on site.