Dissipation of the braking energy of electrically powered mining equipment by liquid-cooled braking resistors
Braking current generated by an electrical motor on mining equipment during a retard interval is switched through one or more grid resistors that are liquid cooled. Under low ambient temperatures, a heating current can be switched through the grid resistors when the electrical motor is not operating in a retard interval. An integrated cooling system can be used to cool grid resistors and power modules. Heat dissipated by the grid resistors and the power modules can be circulated through auxiliary heating loops to heat portions of the mining equipment under low ambient temperatures. Multiple liquid-cooled power modules, liquid-cooled grid resistors, auxiliary heating loops, control modules, radiators, and pumps can be coupled by a liquid distribution system with various combinations of parallel and serial branches. Temperature, pressure, and flow rate in each branch can be independently controlled. Operation of the integrated cooling system can be controlled by a computational system.
1. A heat distribution system for mining equipment, wherein the mining equipment comprises an electrical motor and the electrical motor is configured to operate in at least one propel interval and in at least one retard interval, the heat distribution system comprising:
a braking resistor;
a power module;
a control unit configured to:
determine whether the electrical motor is operating in a retard interval; and
upon determining that the electrical motor is operating in a retard interval: switch a braking current generated by the electrical motor through the braking resistor; and
a liquid distribution system configured to transfer heat from the braking resistor to a cooling liquid, the liquid distribution system being further configured to transfer heat generated by the power module to the cooling liquid.
2. The heat distribution system of claim 1 , further comprising:
a temperature measurement unit; and
a heating current source;
wherein the control unit is further configured to:
upon determining that the electrical motor is not operating in a retard interval:
receive a measured temperature from the temperature measurement unit;
compare the measured temperature to a predetermined temperature limit; and
upon determining that the measured temperature is less than the predetermined temperature limit:
switch a heating current from the heating current source through the braking resistor.
3. The heat distribution system of claim 2 , wherein:
the temperature measurement unit is configured to measure the ambient temperature; and
the predetermined temperature limit is about −40 deg C.
4. The heat distribution system of claim 1 , wherein the liquid distribution system comprises an auxiliary heating loop configured to transfer heat from the cooling liquid to a portion of the mining equipment.
5. The heat distribution system of claim 4 , wherein the mining equipment comprises a mining vehicle and the portion of the mining equipment comprises one of:
a body of the mining vehicle;
a chassis of the mining vehicle; or
an operator's cabin of the mining vehicle.
6. The heat distribution system of claim 1 , wherein the liquid distribution system comprises at least one pump configured to circulate the cooling liquid.
7. The heat distribution system of claim 1 , wherein the liquid distribution system comprises at least one of:
a temperature sensor configured to measure a temperature of the cooling liquid;
a flow sensor configured to measure a flow rate of the cooling liquid; or
a pressure sensor configured to measure a pressure of the cooling liquid.
8. The heat distribution system of claim 1 , wherein the cooling liquid comprises water.
9. The heat distribution system of claim 1 , wherein the liquid distribution system comprises a plurality of branches.
10. The heat distribution system of claim 1 , wherein the power module is configured to be powered by a direct current bus comprising a positive rail and a negative rail, wherein:
the magnitude of the voltage difference across the positive rail and the negative rail is about 1800 VDC to about 2000 VDC; and
the magnitude of the voltage between any point on the direct current bus with respect to ground is less than or equal to about 1000 VDC.
11. The heat distribution system of claim 1 , wherein the braking resistor is one of a plurality of braking resistors and the plurality of braking resistors is configured to dissipate at least about 4 megawatts.
12. The heat distribution system of claim 1 , wherein the braking resistor is configured to operate under an ambient temperature as low as about −40 deg C.
13. The heat distribution system of claim 1 , wherein the braking resistor is configured to operate under a continuous vibration of about 2 G over a spectrum of about 10 Hz to about 500 Hz.