1.- Chopper Module
| ECM control circuits for the operation of the Chopper Phase Module |
The Chopper Phase Module is a phase module that is the same as the other phase modules. The same hardware that is in the phase modules is in the Chopper Module.
The difference between the Chopper Module and the other phase modules is the way in which the chopper is used. The Chopper Module is not used for traction motor control.
The Motor 1 ECM will activate and control the Chopper Module for the following functions:
- Help the Drivetrain ECM to control and maintain the voltage of the DC Power Bus.
- Control the amount of dynamic retarding energy that is used to load the Generator and the Engine.
- Used to load the Generator and the Engine during the Engine Performance Test.
To accomplish these functions, the negative side transistor pair 2 is switched ON and OFF in order to connect (switch) the positive side DC bus through the chopper grid 1 load resistor elements to the negative DC Bus.
This shorts the positive DC bus to the negative DC bus, through the grid resistors, which will produce a "chopped" PWM signal. When the Motor 1 ECM switches the transistors ON, the voltage will be low. When the transistors are switched OFF, the voltage will be high.
The switching frequency is modulated to control the duration of the low to high voltage cycle. The longer that the transistors are turned ON (signal low) determines how much the voltage level of the DC bus will be pulled down.
Depending on the status of the DC Power bus voltage or depending on the dynamic retarding requirements, the Motor 1 ECM will switch and modulate the transistors at a frequency up to 150 hz. The control of the frequency and modulation will increase or decrease the current that is dissipated through the grid resistors.
The switching frequency duty cycle will determine the amount of electrical current that is dissipated through the resistors and the resulting amount of heat that is created.
When the Chopper Module is used for control of the DC bus voltage, the retarding contactors are not used. When the retarding contactors are not used, the Grid Blower Motor will not turn ON in order to cool the resistor elements. (The fan operation is covered in the following "Retarding Glower Blower Inverter" section.)
When the Chopper Module is activated without fan operation, the Motor 1 ECM will control and limit the duty cycle of the Chopper Module in order to avoid overheating the grid 1 resistor elements.
The Drivetrain ECM will try to maintain the voltage of the DC Power Bus in the range of 2700 VDC to 2800 VDC. If the voltage level increases beyond this range, the Drivetrain ECM will adjust the Generator output and command the Motor 1 ECM to switch the Chopper Module transistors ON and OFF at a rate that will aid in decreasing the voltage. If the voltage continues to increase, the ECM will accelerate the switching rate in order attempt to meet the commanded bus voltage.
When the Automatic Retarding Control (ARC) is activated, the Retarding Contactors are used to dissipate 50 percent of the retarding load back that is coming from the motors. The Chopper Module is used to control and increase the amount of retarding load between 50 percent to 100 percent.
When the Engine Performance Test / Grid Dry Test is active, a similar process is used to load the Engine. As the Drivetrain ECM commands a gradual increase in Generator output, the Retarding Contactors will close and supply the first 50 percent of the retarding load back to the Generator. The chopper module transistors will then be switched at a rate that will gradually increase the amount of current that is sent to the retarding resistor element. This switching sequence will gradually increase the Generator load and the load on the Engine until the rated Engine output is reached.
The fault condition logic that is used for the operation of the Chopper Module is:
- During the startup Motor 1 ECM transistor test or during Chopper Module operation, a faulty feedback signal or the loss of the feedback signal will result in the activation of a level 3, E1285 (Chopper Module Mismatch) by the ECM.
- The Motor 1 ECM continuously monitors the circuit current signal from the chopper grid current sensor (CMCT). Current in this circuit is enabled by the operation either the Chopper Module or the Crowbar. Both devices will not be activated at the same time.
- If the Chopper Module is in operation during retarding and Motor 1 ECM is detecting a chopper grid 1 circuit current that is less than what is expected, the ECM will activate a level 2 E907 Event (Low Chopper Module Output Current).
- If the Chopper Module or the Crowbar have not been activated and Motor 1 ECM is detecting a current that is greater than 100 amps in the circuit, the ECM will activate a level 3 E911 Event (Unexpected Chopper Module Output Current).
- If the chopper grid resistor elements should overheat during Chopper operation, the Motor 1 ECM will stop the Chopper Module operation in order to allow the grid elements to cool. The ECM will also activate an E1083 Event (High Contactor Retarding Grid Accumulated Thermal Energy).
2.- Retarding Contactor Assembly
| Retarding Contactor Assembly circuit connections |
| Retarding Contactors (58) Retarding Contactor 1 (59) Pilot Relay (60) Retarding Contactor 2 (61) Auxiliary contacts(62) Harness connector |
The Retarding Contactor Assembly consists of two identical high voltage magnetic contactors with auxiliary contacts and a pilot relay.
The Motor 1 ECM will use a sinking driver output to energize or de-energize the pilot relay. When the relay is energized, 24 VDC system voltage will energize the coils of the main high voltage contactors. A mechanical linkage that is connected to the auxiliary contacts for each contactor will cause the auxiliary contacts to close.
In order to prolong the life of the contactor tips that can occur if the DC bus voltage is too high, the Drivetrain ECM will reduce the output of the Generator and use the Chopper Module reduce the voltage of the DC Power bus to less than 1500 VDC before the retarding contactors are closed or opened.
When energized, the contacts close which will send electrical current from the positive DC Power Bus through the Retarding Grid 2 load resistor elements and back to the negative DC Power Bus.
During retarding, the closing of the contactors will provide the first 50 percent of the possible load on the traction motors. This load will cause a resistance to rotation of the motor.
At system shutdown, closing the contactors will discharge the voltage of the DC Power Bus.
When the pilot relay is energized, the auxiliary contacts for each main contactor will also be mechanically closed. This results in a two separate feedback circuits that are connected to the Motor 1 ECM being grounded. The two grounded circuits indicate to the ECM that the main contactors are closed.
Each of the retarding contactors is equipped with an electrical arc suppression device or arc chute on the top of the contactor. When the contacts are opened while conducting current, a high voltage electrical arc can occur. An uncontrolled arc can cause damage or premature wear to the contacts. When an arc occurs, magnets that are outside the chute pull the arc upward into the chute. As the arc is directed into the chute, the arc is elongated and cooled which extinguishes the arc.
The arc chute can be removed from the contactor housing. An interlock will prevent contactor operation when the arc chute is removed.
The main contacts in the retarding contactors can wear during use. The contacts are serviceable. A 500 hour service interval is recommended for checking the condition of the contacts.
Refer to the Disassembly and Assembly, KENR8715, "Retarding Contactor - Disassemble" manual for a procedure to service the contacts.
The Motor 1 ECM monitors the signal from the contactor grid current sensor (BMCT). If the contactors should be closed and the ECM is not detecting the expected current from the current sensor, the ECM will activate a level 2 E908 Event (Low Retarding Grid Contactor Output Current).
If the ECM does not expect the contactors to be closed and current is detected in the circuits, the ECM will activate a level 2 E912 Event (Unexpected Retarding Grid Contactor Output Current Detected).
The functions of the retarding contactors are:
- The primary function is to provide 50 percent of the available load to the traction motors when the Automatic Retarding Control (ARC), manual retarding or the blended braking function are activated.
- When the Engine Performance Test is active, the retarding contactors will close resulting in a 50 percent loading of the Generator.
- If a controlling ECM detects a system condition that is severe enough to cause the drive train to be disabled, the retarding contactors will close in order to aid in discharging the DC Power Bus voltage.
- When the machine is shut down, the retarding contactors will close in order to aid in discharging the DC Power Bus voltage.
3.- Crowbar
| Crowbar circuit connections |
| The Crowbar that is located in the crowbar compartment tray (63) Low voltage connector (fiber optic and copper circuits) (64) Crowbar thyristor (65) CHN bus bar connection(66) DCN bus bar connection (DC Power Bus negative) |
The Crowbar is a solid-state thyristor which is also referred to as a silicon controlled rectifier (SCR). When the thyristor is OFF (open), no current will flow through the device. When turned ON (closed), the thyristor will conduct current in only one direction.
In the electric drive train system, the Crowbar is used as an over voltage control device. When the Crowbar is activated, the positive (+) DC Power Bus is shorted to the negative (-) DC Power Bus through the Retarding Grid 1 resistor elements.
Either the Motor 1 ECM or the Motor 2 ECM can command Interface Module 2 to activate the Crowbar. To activate the Crowbar, an ECM will send a voltage pulse to Interface Module 2. Interface Module 2 will convert the voltage pulse to a single light pulse in a fiber optic driver circuit. The fiber optic circuit is connected to the Crowbar assembly. The optical pulse is converted back to a voltage pulse in the electronic crowbar gate driver circuit.
The fiber optic driver circuit that is connected between the interface module and the Crowbar assembly provides isolation between the low voltage control circuits and the high voltage circuits that are connected to the Crowbar. The fiber optic circuits also provide isolation from stray electrical fields that could cause accidental activation of the Crowbar.
When the Crowbar is turned ON, the thyristor will remain in the latched ON (closed) state. The battery disconnect switch must be turned OFF in order to unlatch (open) the thyristor.
Either motor control ECM can use a crowbar driver circuit to signal the interface module to activate the Crowbar.
The thyristor has an anode (A) connection that is connected to one side of the Retarding Grid 1 resistor elements. The other side of the resistor elements is connected to the positive (+) DC Power Bus. A cathode connection is connected to the negative (-) DC Power Bus.
When the gate of the thyristor is biased by the voltage pulse, the electrical current from the positive (+) DC bus is directed through the Retarding Grid 1 resistor elements and on to the negative (-) DC bus through the conducting thyristor. This results in an immediate discharge of the DC Power Bus voltage.
The control logic and the fault condition logic that is used for the operation of the Crowbar is:
- During machine operation, if one or more of the enable signals from the motor control ECM to either interface module is interrupted or lost, Interface Module 2 will activate the Crowbar.
- If the voltage level of the DC Power Bus reaches 3000 VDC, a level 2 - E655 Event (High DC Power Bus Voltage) will be activated by each motor control ECM. If the voltage level of the DC Power Bus reaches 3100 VDC, a level 3 - E655 Event will be activated by each motor control ECM. The Crowbar will be turned ON in order to discharge the DC Power Bus voltage immediately.
- If the Drivetrain ECM detects a current imbalance of greater than 20 percent between the Generator output phases, a level 3, E0978 (Generator Phase Current Imbalance) Event will be activated. The Crowbar will activate in order to discharge the DC Power Bus voltage immediately.
- The Motor 2 ECM continuously monitors the circuit current signal from the chopper grid current sensor (CMCT). Current in this circuit is enabled by the operation either the Crowbar or the Chopper Module. Both devices should not be activated at the same time.
- When the engine is turned OFF, the Motor 2 ECM will activate the Crowbar. This activation is done to assist in discharging the DC Power Bus and to check the operation of the Crowbar. If the Crowbar does not activate as expected, the ECM will activate the appropriate event.
- If the Crowbar has been activated and the expected current is not detected in the circuit, the Motor 2 ECM will activate a level 3 E757 Event (Crowbar Not Responding to Command).
- If the Crowbar or the Chopper Module have not been activated and Motor 2 ECM is detecting a current that is greater than 100 amps in the circuit, the ECM will activate a level 3 E911 Event (Unexpected Chopper Module Output Current Detected).
A Cat ET test is available that enables a technician to perform a key ON test that will turn ON the Crowbar driver circuits. When a circuit is turned ON, the interface module fiber optic driver circuit can be disconnected and the light pulses can be visually verified to be present. Refer to the Testing and Adjusting, "Crowbar - Test" section of this manual to learn more about this test.
4.- Traction Rectifiers
| Power rectifiers located in the rear Inverter Cabinet. Left - Traction Rectifier 2, Right - Traction Rectifier 1. |
| Circuit connections for the Traction Rectifier 1 and the Traction Rectifier 2 |
| Traction Rectifier 1 connections (right-hand rectifier) (67) DC Power bus positive (+) common bus bar connected to diode cathode connections (L-R) K1, K2, K3(68) Three phases of the Generator output voltage connected to the diode anode connections (L-R) A1, A2, A3 |
| Traction Rectifier 2 connections (left-hand rectifier) (69) DC Power bus negative common bus bar connected to diode anode connections (L-R) A1, A2, A3(70) Three phases of the Generator output voltage connected to the diode cathode connections (L-R) K1, K2, K3 |
Two identical rectifier assemblies are used to rectify the Generator three phase AC output voltages (A1, A2, A3) to the positive and negative DC Power Bus voltage in the Inverter Cabinet.
The anode ends of the Traction Rectifier 1 diodes are connected to the AC output voltage (A1, A2, A3) from the Generator. The diode cathode ends are all connected to the positive side of the DC Power bus.
The Traction Rectifier 2 diodes are connected in the opposite configuration. The cathode ends (K1, K2, K3) of the diodes are connected to the AC output voltage (A1, A2, A3) from the Generator. The diode anode ends are all connected to the negative side of the DC Power bus.
| Rectifier assembly orientation arrows properly matched when mounted |
Orientation arrows are present on the cabinet wall and on each of the traction rectifier assemblies. These arrows are provided in order to ensure that the orientation of the identical rectifier assemblies is correct for each mounting position. The arrows ensure proper connections of the bus bars to the assemblies. Ensure that the arrows are matched during any removal and replacement procedure.
When the assemblies are mounted in the cabinet, cooling fins on the rear of the assembly extend into the cabinets internal cooling duct. The fins dissipate the heat that is created by the diodes during machine operation.
A test procedure is available that allows the user to check the operation of the individual diodes in the assembly. The test can be performed when a low DC Power Bus voltage is indicated. The test can be performed anytime that a problem is suspected in the traction rectifier assemblies.
See You Soon!!!
MARYGAR
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