Rheostatic brake for CME3 diesel locomotives
Operation of the electrical circuit, possible malfunctions
The article was published in the magazine "Locomotive" No. 7 (487) JULY 1997
OPERATION OF THE ELECTRIC BRAKE CIRCUIT
Power circuit. The power circuit and the excitation circuit of the main generator are shown in Fig. 1. In the electric braking mode, the armature windings of traction motors are connected in three groups of two electric motors in series and operate as generators with independent excitation. The load for each of the groups of electric motors is partitioned braking resistors Yat1 - Yatb, structurally assembled into a common unit. Groups of electric motors are connected to brake resistors using KT1 - KTZ contactors.
To expand the range of operation of the electric brake and increase its efficiency in the low-speed zone at the 3rd braking position, it is planned to bypass part of the brake resistors in each group of electric motors by means of contactors KT4 - KTb. At the same time, the value of the active resistance of the resistor per group of electric motors is halved, which ensures efficient operation of the brake to almost a speed of 1.5-2.5 km/h.
Shunting of a part of the braking resistors occurs automatically at the 3rd braking position at a speed of 7-10 km/h, when the excitation current of the traction motors increases to 250-300 A. For this purpose, a relay current indicator RIT3 is included in the excitation winding circuit of the first group of traction motors, which, through the BVT-U brake activation unit, gives the command to turn on the contactors KT4 - KT6.
The excitation circuit of the main generator. The braking characteristics of a diesel locomotive are formed by the excitation circuit of the main generator due to the combined action of independent and parallel excitation windings of the exciter. The independent excitation winding provides a stepwise change in the magnitude of the excitation current of the exciter when a part of the resistors R81 and R82 in its circuit is sequentially shunted by the closing contacts RT1 and RTZ, respectively, at the 1st and 2nd braking positions.
The parallel excitation winding in the braking mode through the limiting resistor of the AC and the closing contact PT11 is connected to a voltage drop across the braking resistor of the first group of electric motors and acts as a negative feedback on the braking current. The direction of current flow through the parallel winding in braking mode is opposite to the direction of current flow in the winding in traction mode.
For stable operation of the exciter in braking mode, an additional Id resistor is introduced into the circuit of the independent excitation winding of the main generator, which is shunted in traction mode by the KVV2 power contact of the KVV contactor. The differential winding of the exciter in braking mode is disconnected from the excitation circuit of the generator by contact KVB1 of the same contactor.
The control scheme. The locomotive is controlled in the electric braking mode through the driver's standard controller. A schematic diagram of the control is shown in Fig. 2. When the "Electric brake" toggle switch is turned on, power is supplied from the clamp 218 through the opening contact KP34 to the BVT-U brake activation unit via connector 11 of the plug connector of the unit. The electric brake circuit is assembled after pressing the "Electric brake" button. In this case, power is supplied to connectors 2 and 10 of the BVT-U unit, from which the coils of the RT1 and RT2 brake relays receive power through connectors 6 and 7 of the connector.
When the RT1 relay is triggered, its closing contact RT11 connects the parallel winding of the exciter to the brake resistors of the 1st group of traction motors, and the opening contact RT13 blocks the activation of the control relay PN5. In the circuit of the independent excitation winding of the exciter, a part of the resistor R81 is shunted by the closing contact RT18, and through the closing contact RT15, which shunts the auxiliary contacts KP11, KP21 and KP31 in braking mode, the power supply circuit of the KV contactor coil is prepared from the clamp 204.
After the RT2 relay is triggered, the closing contacts RT26, RT28 and RT23 prepare the power circuits of the coils of the RT4 relay, RTZ and contactors KVT1 -KVT3, and the opening contact RT21 blocks the activation of the KVV contactor in braking mode. Through the closing contacts of the RT22, the coils of contactors KT1 - KT3 receive power, connecting groups of traction motors to their braking resistors.
The closing contact PT25 provides power to the T1 terminal when the "Electric brake" button is released after the operator's controller handle is switched to the 1st position in braking mode. When the "Electric brake" button is turned on, the contactor coil KB receives power from the T1 clamp through the closing contacts PT25 and PT15. After the operator's controller handle is moved to the 1st position, the contactor coil is powered from the clamp 204 through the closing contact PT15.
When the contactors KT1 - KT3 turn on, the coils of the contactors KVT1 - KVT3 will receive power through their auxiliary contacts KT11 - KT31 and contacts RT23 and KVV3. With the help of the latter, the excitation windings of each of the traction motor groups are connected to the main generator with field bypass resistors RC1, RC3 and RC5 connected in series with them.
The opening auxiliary contact KVV3 of the KVV contactor in the power supply circuit of the coils of the KVT1 - KVT3 contactors serves to block their inclusion in thrust mode. The auxiliary contacts KW 12 -KVT32 block the power supply circuits of the coils of the standard control relays RU1 - RU4 from being switched on in braking mode.
The relay coil RT5 receives power through wire 601 from clamp T1 when the "Electric brake" button is pressed and, after actuation, the relay becomes self-powered through the closing contacts PT25 and PT51 or from clamp 222 when the operator's controller handle is set to the 1st position and the button is released. At the same time, the opening contacts RT53 and RT54 block the activation of the train contactors KP1 - KP3 in braking mode.
The presented circuit for switching on the RT5 relay prevents spontaneous assembly of the traction circuit after automatic disassembly of the brake circuit when any of the electric brake protections are activated when the driver's controller handle is in any position other than zero. In the specified sequence, the electric brake circuit is assembled and braking is performed according to the characteristics of the 1st braking position.
In case of short-term use of the electric brake in the braking mode of the train at the 1st braking position, the brake can be controlled with the "Electric brake" button. If it is necessary to use the electric brake for a longer period of time or work in the 2nd or 3rd brake positions, then after assembling the brake circuit, the driver's controller handle should be moved to the 1st position, and then the button can be released. In this case, the control circuit will be powered from the clamp 218 through the contact groups KM2 and KM7 of the driver's controller.
When the controller handle is moved to the 2nd position, the relay coil RT3 receives power through the closing contact RT28, which, with its closing contacts RT31, shunts part of the resistor R82 in the circuit of the independent excitation winding of the exciter. Braking will be performed according to the characteristics of the 2nd braking position. At the same time, through the closing contact PT34, a power supply circuit is prepared at the 3rd position from the clamp 223 to the connector 16 of the plug connector of the BVT-U brake actuation unit.
If the controller handle is placed in the 3rd position, the relay coil RT4 is powered through its contact group KM4, which ensures the reverse circuit transition from the 3rd to the 2nd braking position. And through the closing contact PT34, power is supplied from the clamp 223 to the connector 16 of the BVT-U unit.
As the speed of movement decreases and the excitation current of the traction motors increases to 250-300 A, the relay indicator of the current of the RITZ will turn on. From clamp 223, through connectors 16 and 5 of the BVT-U block and the closing contacts RT41 and RT42, the coils of contactors KT4 - KT6 will receive power, which will bypass parts of the brake resistors. Braking will be performed according to the characteristics of the 3rd braking position.
Switching of the circuit devices when the braking positions are reset by the driver's controller is carried out in reverse order. The electric brake can be deactivated in two ways: either by setting the driver's controller handle to the zero position, or automatically during stop braking.
In the first case, when the driver's controller handle is moved to the zero position, power is removed from the BVT-U unit (connectors 2 and 10), and the coils of the RT5 relay and the KV contactor are de-energized. In this case, the excitation circuit of the traction generator is broken. When the supply voltage is removed from the BVT-U unit, the RT1 relay is switched off and the RT2 relay is switched off with a time delay of 1.5-2 seconds. The coils of the contactors KT1 -KTZ are de-energized, and then KVT1 - KVTZ. Thus, the disassembly of the electric brake circuit occurs practically at low residual currents in the circuit's power circuit.
In the second case, if it is necessary to apply stop braking, the electric brake is turned off automatically, without moving the controller handle to the zero position. When the speed decreases to 1-1.5 km/h and the value of the braking current per group of traction motors decreases to 100 A, the minimum current relay RIT1 is switched off. At the same time, power is supplied through the connector 9 of the block to the coil of the electropneumatic brake replacement valve VZT and the air filling of the brake cylinders from the feed line through pressure reducer No. 348 begins.
