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What are the auxiliary equipment used in an electric locomotive?
In addition to the main traction motors, the following additional equipment are required to be installed on an electric locomotive engine −
- Motor-Generator Set
- Pantograph Operating Equipment
- Air Compressor
- Traction Motor Blowers
- Heating Equipment
Let's check the functions of each of these equipment in detail.
The motor-generator set used in the electric locomotives is of the two bearing type and it consists of a series motor and a shunt generator. The speed of the series motor at light load is limited by the ventilating fan and the voltage of the generator is controlled by an automatic voltage regulator (AVR).
The generated voltage by the motor-generator set is used to supply lighting, control system and other power circuits at low voltage (from 30 volts to 100 volts) in the electric locomotive. The motor-generator set used in the electric trains must be of special design so that any fluctuations in the line voltage do not have any effect on the low-voltage supply.
In electric locomotives, the batteries are used as the source of energy required to raise the pantograph, to operate the air-blast circuit breaker, to run the auxiliary compressor, etc. The batteries used in the electric locomotives may be lead acid type or alkaline type.
The voltage of lead acid type battery is 2 volts per cell. The lead acid batteries require more attention and maintenance. These batteries cannot be left in discharged conditions, and cannot withstand high rate of charge and discharge without reducing their life.
The voltage of the alkaline battery is 1.2 volts per cell. The alkaline batteries can be left in discharged conditions and can withstand the short-circuit conditions even without effect on their life.
The battery used in the locomotive is charged either by a separate rectifier or from a DC generator. The capacity of the battery used depends on the locomotive and typically may be between 175 Ah to 375 Ah at 5 hours. Usually, the batteries are connected in parallel with the motor-generator set.
Pantograph Operating Equipment
The pantograph operating equipment is used for raising and lowering of pantograph and these two operations are usually carried out by compressed air. The mechanism has suitable switches for controlling the solenoid operated valves of the air supply required.
The air compressors are provided in the electric locomotives for supplying compressed air for operating brakes, pantograph operating equipment and electro-pneumatic control gear, etc. The air compressor used in the electric trains is usually of two-cylinder type and is directly connected to the motor.
To drive these compressors, a moderate speed motor is employed so that the weight is reduced and the compressor is driven through double-helical spur gearing. A pressure operated switch is used for automatic starting and stopping of the motor to maintain the air pressure within the desired limits. The moving contact of the pressure switch is actuated though a system of levers and a toggle mechanism by the air pressure on a spring loaded diaphragm.
At 1500 volts or below, the compressor motor can be supplied directly from the line. Otherwise, it is fed from the auxiliary generator.
Traction Motor Blowers
The traction motor blowers are required on locomotives when forced ventilated motors are used. In some cases, a single motor blower is used which delivers air at a low pressure into a central duct built into the frame of the locomotive body from which it is distributed to the motors. On the other hand, in case of large frame mounted motors, each motor is provided with a separate blower.
The heating equipment is required for heating the locomotive and train if desired. The heating equipment is supplied directly from the line up to 3000 volts.
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