Traction Power Circuit ( WAG-9 & WAP-7)
Traction Power Circuit:
Power from the overhead Catenary is directed to the main transformer, mounted on the locomotive under frame, via the pantograph. The traction circuit is split into two separate circuits after the main transformer.
The traction converters can conduct current from the Catenary to the traction motors to provide propulsion, or can act as in the opposite manner conducting, and rectifying, current from the traction motors to the Catenary. This allows the converter to work in both traction and braking mode. During braking the traction motors act as generators feeding power back into the catenary. The traction converters then act to convert the three phases into single phase for the catenary.
The traction converters provide continuous and automatic control of both speed and torque of the traction motors according to the driver’s demand. The converters are controlled by the converter control electronics, and the locomotive central electronics.
Three, 3-phase asynchronous traction motors are connected in parallel to each traction converter.
Traction Converter: (SR)
Traction converter converts single-phase 25 KV AC supply into 3 phase AC, with Variable Voltage (max 2180 V) and frequency (from 0 to 130 Hz) while traction mode and fed it to traction motor group -1.
As such there are two traction converter i.e. Traction converter-1 for TM 1-2-3 and Traction converter-2 for TM 4-5-6 ( In case of WAP5,traction converter-1 for TM 1-2 and Traction converter-2 for TM-3-4) While electrical braking the traction motor works as a generator and fed generated 3-phase supply to Traction converter. This converter now act in reverse manner i.e. it converts 3 phase AC supply into single phase AC supply and fed it to Transformer. Further main transformer steps up this supply and fed back to OHE. In this way 3 phase loco works as a small powerhouse, which generate supply and share the load by feeding it back to OHE.
SR is cooled by two separate oil cooling unit.
traction converter has three main sub parts:
1) Line Converter
2) Intermediate DC link and
3) Drive converter.
One spy glass is provided on each SR to check the oil level.
Line Converter :(NSR)
The line converter converts the alternating current supplied from the main transformer into direct current (motoring) and forwards this direct current to the intermediate DC-Link. However, it is also able to convert direct current from the intermediate DC-Link into alternating current and to supply this alternating current in turn to the main transformer (braking). Both functions are activated by the traction converter control electronics.
DC Link:
The intermediate DC-Link performs two main tasks. Firstly, it smoothes the direct current that flows through. Secondly, it also performs the storage function, thus covering the peak current demand of the line converter or of the motor. It works as a electrical buffer between ASR and NSR
Drive Converter- (ASR):
The drive converter converts the direct current from the intermediate DC-Link into three-phase current for the drive motors (motoring). Conversely, it is also able to convert the three-phase current generated by the drive motors into direct current for braking. The construction of the motor inverter valve set is identical to that of the line converter. The complete assembly of line converter No.1, DC link and drive converter No.1 is termed as “TRACTION CONVERTER NO.1” which in turn converts 1-phase AC supply of main transformer into 3-phase AC supply with variable voltage and frequency and fed to the 3-phase traction motor.
Technical Data Of Traction Converter
Traction Motor: There are total 6 traction motors provided in WAG-9 / WAP-7 loco. TM 1-2-3 are mounted in bogie-1 and fed from traction converter -1 where as TM 4-5-6 are mounted in bogie -2 and fed from traction converter -2. In case of WAP-5 there are 4 traction motors in which, Traction converter-1 fed to TM-1-2 where as traction converter-2 fed to TM3-4.
Unlike conventional WAG-5/7 individual TM cannot be isolated in this loco only a group isolation is possible. For isolation of TM group one rotating switch No. 154 is provided in SB-1, its normal position is “ Norm”.
In WAP-7 & WAG-9, the traction motor is forced—air cooled and intended for transverse installation in a 3—motor bogie. The power transmission is effected via a spur—wheel gear. In WAP-5 the TM is fully suspended and connected with gear by hurth coupling by which power is transmitted.
Traction motor is suspended on axle, by axle cap at one end and on link at another end.
To check the oil in gear case one spy glass is provided on each gear case.
To monitor the temperature & speed, sensors are provided in the stator assembly.
Technical Data Of Traction Motor:
