Auxiliary Converter Technical Data PDF

6. AUXILIARY CONVERTER 1.0 INTRODUCTION Each locomotive is equipped with two boxes enclosing the static auxiliary converter system. 1. BOX1 containing BUR1 2. BOX2 containing BUR2 & BUR3 and battery charger, which may be, fed from one of the two converters and wh...

6. AUXILIARY CONVERTER 1.0 INTRODUCTION Each locomotive is equipped with two boxes enclosing the static auxiliary converter system. 1. BOX1 containing BUR1 2. BOX2 containing BUR2 & BUR3 and battery charger, which may be, fed from one of the two converters and which may be considered to be a functional part of the converter system. Fig.6.1 shows the converter function within the locomotive and Fig 6.2 the essential parts of the auxiliary converter and battery charger. Three auxiliary converters are designed for connection to the auxiliary services winding of the main transformer. Each converter is rated for 100 KVA output and has short circuit proof three-phase output at 415 V. The output frequency of converter BUR1 & BUR2 is variable from 0 to 50 Hz while BUR3 gives fixed frequency output at 50 Hz. The battery charger is supplied from the converter BUR3. In case of the fault in the converter, BUR2 will feed the battery charger. The battery charger with a rated output of approx. 111 V charges the locomotive batteries and supplies the low voltage loads. The low voltage output is electrically insulated from the input and from the three-phase output. The converters are provided with external forced convection cooling (5 m/sec approximately). Thermostats are provided inside the box. When the temperature goes above 50C, fans run until temperature decrease below 35C. Both boxes and three phase output chokes are mounted in the machine room of the locomotive. The intermediate chokes are incorporated in the main transformer tank for convenience and in order to save weight. TRACTION ROLLING STOCK : THREE PHASE TECHNOLOGY Page 64  Fig. 6.1 TRACTION ROLLING STOCK : THREE PHASE TECHNOLOGY Page 65  TECHNICAL DATA Input Supply voltage : 1000 V AC +200 V -300 V Apparent power : 100 KVA Current (r.m.s.) : 150 A (100 KVA and 700 V) Frequency : 50Hz + 3% Rated insulation voltage : 1200 V Test voltage (50Hz/60 sec) : 4250 V Intermediate circuit Voltage : 550 VDC Rated current : 155 ADC Short term overload : 190 ADC Rated insulation voltage : 900 V (capacitor) Test voltage (50 Hz/60 sec) : 2600 V TRACTION ROLLING STOCK : THREE PHASE TECHNOLOGY Page 66  Fig. 6.2 TRACTION ROLLING STOCK : THREE PHASE TECHNOLOGY Page 67 2.3 Output AC DC Rated voltage (fundamental r.m.s) : 415 V --- (DC voltage) : --- 111 V Rated frequency (BUR1 & 2 ) : 50 Hz --- (BUR3) : 50 Hz --- Rate current (AC includes battery charger) : 140 A --- Max. battery charger current (only battery) : --- 80 A (user + battery) : --- 110 A No. Of poles (conductors) : 3 3 Rated insulation voltage : 900 V 150 V Test voltage (50 Hz/60 sec) : 2600 V 1500 V 2.4 Control unit Supply voltage: 77..137.5 V (operating range) Power consumption : 120 W 2.5 Thermal losses and cooling by forced air Thermal losses at rated power Box1 : 2 KW Box2 : 5 KW Ventilator supply voltage : 36….56 V Ventilator power losses : 5W Air rate : 5 m/sec TRACTION ROLLING STOCK : THREE PHASE TECHNOLOGY Page 68  Fig. 6.5 TRACTION ROLLING STOCK : THREE PHASE TECHNOLOGY Page 69  3.0 CIRCUIT DESCRIPTION The main parts of the converter are:  The half controlled rectifier bridge [50.11]  The intermediate filter (inductor [51.3] and capacitor [51.1])  Three inverter legs, connected as three-phase inverter [50.12]  The electronic control unit  The three phase output inductor [50.9]  The battery charger (three phase transformer [107.1] and rectifier ) The other components serve to detect the actual values required to control the process and to ensure that the necessary operating condition are maintained for reliable operation of the power electronics. 3.1 Rectifier The half controlled asymmetrical type GTO rectifier is used. The rectifier converts AC to DC and maintains output dc voltage of approx. 550 V. The input & output voltage waveforms are shown in fig.6.3 and currents through devices are summarized in fig.6.7. Average value of rectifier output voltage: √2 U2 = --------- x Un rms x (1 + cos )  The active power transmitted through the converter amounts to P = UZ x IZ, IZ being the average value of the link filter current. TRACTION ROLLING STOCK : THREE PHASE TECHNOLOGY Page 70  Fig. 6.6 TRACTION ROLLING STOCK : THREE PHASE TECHNOLOGY Page 71 3.2 DC link filter DC link filter consists of intermediate circuit reactor and capacitor. The intermediate circuit reactor smoothes the pulsating energy flow from the input rectifier and supplies DC current (IZ) with superposed ripple. The choke is equipped with two coils in order to keep voltage spikes away from the inverter and the connected load. The intermediate circuit capacitor (CZ) absorbs the component of the current, with little fluctuation in terminal voltage. In addition, CZ represents the low impedance voltage source, essential for functioning of three phase inverter. CZ also supplies the magnetization current to the inductive load. The intermediate circuit capacitor consists of 2-stage series circuit of 6 parallel-connected electrolytic capacitors each. The voltage across the series connected stage is balanced with resistors. These are dimensioned so that the current passing through them is several times larger than the capacitor leakage current and they thereby determine the voltage sharing. At the same time they act as discharge resistors. Fig.(4) shows the voltage waveforms across the filter input and output. 3.3 Three phase inverter The three-phase inverter consists of three single-phase inverter modules. They generate a three phase AC voltage from the intermediate circuit DC voltage by being approximately switched ON and OFF Fig.5 shows the switching sequences of the three modules is steady state conditions. The rectangular output voltage of inverter may be represented as an infinite sum of sine waves as follows: U(t) = UZ x [(√6 x √2 ) / ( x n)] x  sin ( n x 2 f1 x t ) TRACTION ROLLING STOCK : THREE PHASE TECHNOLOGY Page 72  Fig. 6.7 TRACTION ROLLING STOCK : THREE PHASE TECHNOLOGY Page 73  With f1 = inverter frequency as understood conventionally fundamental component and n being 1,5,7,11,13,17….( = 6k ±1, k = 1,2,3,4……) The shaft power of motor is function of fundamental component √ 2 U1rms = UZ x ------  In case of resistive loads, the heating will be function of total rms value. V (total) rms = UZ x √ 2/3 In steady state operating conditions, both frequency and amplitude of output voltage correspond to set point, while in dynamic conditions these values can be set away from the reference value by PWM for better control of the process. 3.4 Three phase inductors The inductor slightly attenuates harmonics but mainly provides the converter with the required capability of withstanding load short – circuits. 3.5 Battery Charger The diode bridge (107) rectifies the voltage supplied from one of the auxiliary inverter through 107.1 A capacitor of 2.2 mF located on 107 smoothes the charger voltage and limits the transient voltage rise when some major load is switched off. The current transducers 107.2 and 107.3 transmit the actual current values to the control unit of inverter BUR2 while the transducers located on the charger module transmit the same values to inverter BUR3 (normally supplying the battery charger) control unit (Ref. Fig. 6.8). TRACTION ROLLING STOCK : THREE PHASE TECHNOLOGY Page 74  Fig. 6.8 TRACTION ROLLING STOCK : THREE PHASE TECHNOLOGY Page 75 3.6 Protective devices I. Battery charger circuit breaker – The battery charger is protected against overload by magnetic circuit breaker 100. the breaker isolates the battery charger from the inverter output through magnetic tripping in case of short circuits inside the battery charger. The converter need not be switched off and locomotive can continue to run until the battery capacity is exhausted. II. Input fuse – The fuse protects from serious consequential damage, which result in the event of failure of power components in the rectifier bridge or defects of the regulation or the actual value monitoring. III. Surge arresters [40.1] – The surge arresters protect the semiconductors of the rectifier bridge [50.11] from over voltage spikes. IV. Damping filter RC [49.2/49.1] – The small filter is intended to limit the rate of rise of voltage spikes in order to avoid spurious thyristor firing. 3.7 Measurement devices I. Input voltage measuring transformer. It provides the electronic control unit with information about amplitude and phase of input. II. Voltage transducer. It is used to measure intermediate circuit voltage. 3.8 Auxiliary Converter control unit It handles all control and electronic protection functions. The control unit communicates with the vehicle control unit (FLG) via MVB optical bus. The rack contains:  A power pack with electrical insulation between input and outputs, which converts the battery voltage varying over a wide range into the various stabilized voltages e.g. +24 V for gate unit supply, +15 V for analog circuit and transducer supply and +5 V for digital circuit. All voltages have a common ground.  The microprocessors unit including binary input / output card. This unit provides the regulation of the link voltage (i.e., it controls the input rectifier) and of the battery voltage. It is in charge of the higher-level protective functions, of the contactor control and of the communication with the FLG.  The bus interface board converting the electrical signals elaborated by the microprocessor unit into the optical ones and vice-versa. TRACTION ROLLING STOCK : THREE PHASE TECHNOLOGY Page 76