Medha Servo Drives Privite Limited Nacharam, Hyderabad, Telangana

Vigilance Control Device (VCD) is a microcontroller based safety device which will automatically apply penalty brakes in case the driver is incapacitated. Similar operation is available in older locomotives in the form of Deadman’s Lever.Operating PrincipleInstalled on locomotive, VCD gives cyclic warning to the driver. Based on drivers reaction to this warning (in terms of any of the pre-defined sets of actions to be done by the driver), the system automatically resets the alerting cycle. In case, the driver fails to acknowledge the initial alert signals, a set of additional alert indications are given. Even failing to respond to these additional alert signals also will result in automatic application of penalty brakes.Some of the pre-defined set of actions to reset Alerter cycle can include: Change of notch position/ Master Handle Reverser Increase / decrease of level of dynamic braking Normal application of formation brakes Operation of locomotive horn Operation of sanding valves Pressing of VCD reset button Other customized actions based upon locomotive type These pre-defined set of actions are regularly monitored by VCD system and VCD cycle is reset whenever any of the above actions takes place.In case the driver fails to acknowledge the Alerter warning signal during initial time period (say 60 sec), an additional indication in form of blinking LED will be given for a pre-defined time. After the predefined time if acknowledgement is not yet received, an additional audio alarm is given. If the driver further fails to acknowledge the alarm, automatic application of brakes will take place and Engine is brought to IDLE speed.

Medha and Traktionssysteme, Austria entered into a Joint Venture agreement (Medha Traction Equipment Pvt. Ltd.) to manufacture 3 phase AC Traction Motors and Traction Alternators in India. Medha Traction Equipment Pvt. Ltd. produces AC Traction motors which complement Medha's existing and growing portfolio of traction and propulsion products. Implemented product range for applications including diesel and electric locomotives, DMU, EMU, Metro, High Speed, Tram and Trolley bus Recently made motors for 1600 HP DMU, 1.3 MW EMU, and 4500 HP diesel locomotive Customer's benefits Price competitiveness with manufacturing facility in India Large database of designs from projects all over the world; can be easily customized for any new requirement Class 220 insulation allows compact motors Long operating life and low life cycle cost Any motor rating from 40 kW to 1600 kW Option to have single manufacturer taking responsibility for all propulsion equipment including converter, alternator, motor and controls Applicable International standard : Testing : IEC 60349-2 Rating and performance : IEC 60034-1 Losses and efficiency from tests : IEC 60034-2-3 Degrees of protection : IEC 60034-5 Method of cooling : IEC 60034-6 Terminal marking : IEC60034-8 Noise Level L IEC60034-9 Mechanical vibration level : IEC 60034-14 Different thermal classes of insulation systems : IEC 60085 Designation of terminal & direction of rotation : IEC 60034-8

Newer generation Diesel / Electric locomotives, EMUs, DMUs and Metro cars equipped with AC Traction Motors require sophisticated Traction Converters to control these motors as part of propulsion system.Diesel locomotive and DMU propulsion system architectures provide rectified alternator output as stable DC link bus voltage input to the Traction Converter. Traction Converter could be a combination of one or more inverters each controlling one or more traction motors. EMU and Electric locomotive propulsion system architectures typically provide secondary winding of traction transformer as input feed to the Traction Converter. Traction Converter would have multiple line converters which convert single phase AC input to a stable DC link bus voltage. A combination of one or more inverters converts this DC bus voltage to 3-phase power controlling one or more traction motors each. For Metro cars, depending on OHE voltage or third rail DC voltage, traction converter may include line converters and inverters or only inverters.   Traction Inverter Technology Traction Inverter drives/brakes one (independent motor control) or multiple (bogie control) Traction Motors. DSP is used for implementing Vector motor control using Space Vector PWM for complete VVVF control of traction motor in both motoring and dynamic/regenerative braking operation. Input power is typically taken from stable DC Link voltage (from diode rectifier or line converter) and torque command is received from locomotive control system.  Independent motor control typically used in locomotives has the advantage of better wheel slip control (better adhesion), better Tractive effort independent of wheel diameter variations and also better availability of locomotive power in cases of inverter or motor failures. Medha uses IGBT devices in all Traction Inverters for better efficiency and reliability. Gate drive cards control IGBTs and protect them against various short circuit conditions. Optic fiber communication is used between Traction Computers (DSPs) and Gate drive cards for noise immunity. Various current, voltage and temperature sensors are used for monitoring and protection of both inverter and motor.

Medha is one of the leading manufacturers of Speed Recorders for Railway applications. These recorders are used on Locomotives and are similar in function to Black boxes in aeroplanes. Speed Recorders are used for monitoring the performance of Loco Driver and especially in the event of an accident the recorded data becomes vital for establishing the cause of accident.Medha designed it's first Speed Time Distance Recorder MRT 912 in 1989. It was an innovative technology in Strip Chart Recording using a microprocessor, developed as a substitute for the Secheron, Switzerland made mechanical Speed Recorder used by the Indian Railways at that time. It was the first microprocessor based system on the Indian Locomotives.Today Speed Time Distance Recorders are available in different models based on their application and Locomotive. For Diesel Locomotives various models like Memory based Speed Recorder and Event Recorder are available. Medha also supplies Test Equipment for these systems and custom speed sensors  that work with these Speed Recorders.Basic Principle : The Axle mounted Speed Sensor generates a signal, whose frequency is proportional to the RPM of axle. Microcontroller in the Recorder computes speed and distance continuously and records in the internal memory as well as in the plug-in type memory card. A quartz crystal controlled, battery backed, RTC generates time signal for recording. Various locomotive parameters viz., Motoring Status, Dynamic Brake Application, Throttle Position, GR0, Horn Status, Transition Status etc. can be fed into the digital inputs of the system which will be recorded. All parameters are indicated in the Recorder and also they are transmitted from Recorder to Indicator Unit, mounted in the second drive cab, for display.

Electronic Governor is a maintenance free alternative to the mechanical Governors popularly used for this application. The Governor consists of a Control Unit mounted in the Driver cab, and an Actuator Unit mounted on the Engine. The Actuator Unit can be mounted exactly on the same Engine base as mechanical Governors. The Governor controls the engine speed, based on throttle handle position (popularly known as notch) selected by the Driver on the Driver Desk. Engine RPM is measured from a Tachogenerator or speed sensor mounted on the Engine. Digital PID control is used to calculate desired fuel rack position dynamically, based on the selected notch on throttle handle and measured Engine RPM. A Stepper motor drive is used in the Actuator Unit to control the fuel rack of Diesel Engine. The Governor also controls load on the engine electrically, to limit horsepower at each notch to a pre-set level, through an electrical interface with the excitation system of Locomotive. Booster (Turbo) air pressure is measured through a pressure sensor mounted in the air manifold. Movement of fuel rack is limited as a function of this pressure to prevent incomplete combustion of fuel, black smoke, excessive engine temperature, fuel wastage etc caused by lack of air to burn the fuel. Lube oil pressure is continuously monitored and Engine is shutdown if the lube oil pressure is less than the specified pressure at each notch position. This protects the Engine from damage due to malfunction of lube oil pump etc.The system displays status of various engine parameters continuously on the Vacuum Fluorescent Display.  The  system  has  built  in  fault  diagnostic  facility.  In case  of  any  fault,  it  takes  appropriate action immediately, displays relevant fault message on the display for information to the driver, and also records the fault with date and time stamp, to help the maintenance crew later for analysing the root cause. The Governor has  number  of  user  programmable parameters,  which  permits the  system  to  be  used  on  various types of engines/locomotives. Configuration of the system through user settable parameters for fine tuning of operation and reading fault messages of Error Log can be done, on-line on the locomotive, using a laptop PC, even while the engine is running. The equipment is modular in construction and has functionally separated plug in modules for ease of repair and maintenance.More than 3500 units have been installed on Diesel Electric Locomotives of various designs on Indian Railways and other railways. Indian Railways currently fits Microcontroller based Governors on all new and retrofit Diesel Locomotives. Apart from new built Locomotives, Indian Railways have taken up a healthy retrofit program to upgrade more than 200 locomotives per year with Microcontroller based Governors. Medha is a market leader in these systems with over 99% market share. Medha's Governor can be installed in place of an existing Governor.

Medha supplies driver consoles in ready to install condition with TFT LCD displays, master controller, brake controller, electrical switches, gauges, lamp indications and other required components and sub-assemblies. Modular panels are used for easy changes/modifications including provisions for future additions.Depending on requirement, consoles are made from MS (mild steel), FRP (fibre reinforced plastic) or using polyester/phenolic resins to comply with fire standards for flammability, smoke and toxicity. Features Ergonomically optimized layout Improved functional segregation TFT LCD display Harmonized Driver Machine interface Standardized displays, independent of application Attractive exterior designs Standardized solutions Cost competitive Optimum utilization of cabin space Human safety and comfort considerations Scalable for installation of additional sub-systems in future for ‘New Driver Cabs’ or ‘Modernization of Old Vehicles’, driver consoles are designed to suit the vehicle design and to improve the driver's safety, comfort and effectiveness.  

Medha offers a wide range of auxiliary converters that are used for powering auxiliary loads in Diesel / Electric Locomotives, EMUs, DMUs and Metros. Typical loads involved are a combination of blowers, pumps, compressors, lighting, fans, air-conditioning (HVAC), battery charging and auxiliary power required by other sub-systems.Current product offering has a wide selection of input power type such as AC power from auxiliary winding of traction transformer, DC power from Alternators (rectified) / Traction Converter or battery banks. Offered converters are available for range of power rating from 2.5 kVA up to 300 kVA with combination of AC and DC outputs for different loads.Typically the input power is processed through a converter stage to provide a stable and controlled DC bus voltage. The output can be another DC stage (with or without galvanic isolation) or an AC inverter with regulated output to handle different AC loads with varying voltage, frequency and power.Auxiliary Converters also vary by type of cooling and mounting offered. From natural convection cooling to forced air cooling using extrusion heat sinks or heat pipe based sinks to water cooled heat sinks and from under-frame mounting to on-board systems. Type of cooling and mounting selection is based on customer preference, availability of space, auxiliary power and availability of filtered cooling air / water.Typically IGBT switching devices are used with Thyristors, power diodes and MOSFETs used in specific applications. Polypropylene capacitors are used for improved life and ripple handling capabilities. Magnetics (transformers and inductors) are used where required based on isolation and harmonic filtering requirements. Various sensors (voltage, current, temperature) are used for control, monitoring and protection purposes. Optic fiber communication is used where required for electrical noise immunity. Overall control is implemented using state of the art DSPs or microcontrollers. Complete Auxiliary Converter is typically type tested to latest IEC standards such as IEC-61287, IEC-60571, and IEC-61373.As an OEM experienced with design and supply of wide range of Auxiliary Converters, we can adopt existing designs or design new products to provide an optimized solution for varying applications. We believe in providing our customers with customized products that serve their objectives which are typically a combination of power rating, location, cooling method, input / output voltage, type of loads, harmonic distortion requirements, isolation and protection requirements.